Measurement of turbulent flow in a narrow open channel
Directory of Open Access Journals (Sweden)
Sarkar Sankar
2016-09-01
Full Text Available The paper presents the experimental results of turbulent flow over hydraulically smooth and rough beds. Experiments were conducted in a rectangular flume under the aspect ratio b/h = 2 (b = width of the channel 0.5 m, and h = flow depth 0.25 m for both the bed conditions. For the hydraulically rough bed, the roughness was created by using 3/8″ commercially available angular crushed stone chips; whereas sand of a median diameter d50 = 1.9 mm was used as the bed material for hydraulically smooth bed. The three-dimensional velocity components were captured by using a Vectrino (an acoustic Doppler velocimeter. The study focuses mainly on the turbulent characteristics within the dip that were observed towards the sidewall (corner of the channel where the maximum velocity occurs below the free-surface. It was also observed that the nondimensional Reynolds shear stress changes its sign from positive to negative within the dip. The quadrant plots for the turbulent bursting shows that the signs of all the bursting events change within the dip. Below the dip, the probability of the occurrence of sweeps and ejections are more than that of inward and outward interactions. On the other hand, within the dip, the probability of the occurrence of the outward and inward interactions is more than that of sweeps and ejections.
Modelling of supercritical turbulent flow over transversal ribs in an open channel
Czech Academy of Sciences Publication Activity Database
Příhoda, Jaromír; Šulc, J.; Sedlář, M.; Zubík, P.
2009-01-01
Roč. 16, č. 1 (2009), s. 65-74 ISSN 1802-1484 R&D Projects: GA ČR GA103/06/0461 Institutional research plan: CEZ:AV0Z20760514 Keywords : turbulent flow in open channels * flow over obstacles Subject RIV: BK - Fluid Dynamics
A DNS Investigation of Non-Newtonian Turbulent Open Channel Flow
Guang, Raymond; Rudman, Murray; Chryss, Andrew; Slatter, Paul; Bhattacharya, Sati
2010-06-01
The flow of non-Newtonian fluids in open channels has great significance in many industrial settings from water treatment to mine waste disposal. The turbulent behaviour during transportation of these materials is of interest for many reasons, one of which is keeping settleable particles in suspension. The mechanism governing particle transport in turbulent flow has been studied in the past, but is not well understood. A better understanding of the mechanism operating in the turbulent flow of non-Newtonian suspensions in open channel would lead to improved design of many of the systems used in the mining and mineral processing industries. The objective of this paper is to introduce our work on the Direct Numerical Simulation of turbulent flow of non-Newtonian fluids in an open channel. The numerical method is based on spectral element/Fourier formulation. The flow simulation of a Herschel-Bulkley fluid agrees qualitatively with experimental results. The simulation results over-predict the flow velocity by approximately 15% for the cases considered, although the source of the discrepancy is difficult to ascertain. The effect of variation in yield stress and assumed flow depth are investigated and used to assess the sensitivity of the flow to these physical parameters. This methodology is seen to be useful in designing and optimising the transport of slurries in open channels.
Comparison of different turbulence models in open channels with smooth-rough bedforms
International Nuclear Information System (INIS)
Ghani, U.
2013-01-01
The turbulence models play an important role in all types of computational fluid dynamics based numerical modelling. There is no universal turbulence model which can be applied in all the scenarios. Therefore, if a suitable closure model is used in a simulation work, only then the successful numerical modelling will be achieved. This paper presents the evaluation of three turbulence models in numerical modelling of open channel flows having beds comprising of two parallel strips, one being smooth and the other one being rough. The roughness on the rough side of the channel was created with the help of gravels. The turbulence models tested for their suitability in this case were Reynolds stress model, k-model and RNG based k-model. A structured mesh was used in this simulation work. Grid independence test was also conducted in the simulation. The evaluation of the turbulence models was made through the primary velocity contours and secondary velocity vectors over the cross section of the channel. It was revealed that Reynolds stress model simulated the flow behaviour successfully and results obtained through this model matched very closely to that of the experimental data whereas k-model and RNG based k-model failed to reproduce the flow field successfully. These results will be helpful for CFD (Computational Fluid Dynamics) modellers in correct selection of the turbulence model in these types of channels. (author)
Turbulence characteristics of flow in an open channel with temporally varying mobile bedforms
Directory of Open Access Journals (Sweden)
Hanmaiahgari Prashanth Reddy
2017-03-01
Full Text Available Turbulence of flow over mobile bedforms in natural open channels is not yet clearly understood. An attempt is made in this paper to determine the effect of naturally formed mobile bedforms on velocities, turbulent intensities and turbulent stresses. Instantaneous velocities are measured using a two-dimensional particle image velocimetry (PIV to evaluate the turbulence structure of free surface flow over a fixed (immobile bed, a weakly mobile bed and a temporally varying mobile bed with different stages of bedform development. This paper documents the vertical distribution of velocity, turbulence intensities, Reynolds shear stress and higher-order moments including skewness and turbulent diffusion factors. Analysis of the velocity distributions shows a substantial decrease of velocity near the bed with increasing bedform mobility due to increased friction. A modified logarithmic law with a reduced von Kármán constant and increased velocity shift is proposed for the case of the mobile bedforms. A significant increase in the Reynolds shear stress is observed in the mobile bedforms experiments accompanied by changes over the entire flow depth compared to an immobile bed. The skewness factor distribution was found to be different in the case of the flow over the mobile bedforms. All higher-order turbulence descriptors are found to be significantly affected by the formation of temporally varying and non-equilibrium mobile bedforms. Quadrant analysis indicates that sweep and outward events are found to be dominant in strongly mobile bedforms and govern the bedform mobility.
Laboratorial studies on the seepage impact in open-channel flow turbulence
Energy Technology Data Exchange (ETDEWEB)
Herrera Granados, Oscar; Kostecki, Stanislaw, E-mail: Oscar.Herrera-Granados@pwr.wroc.pi [Institute of Geotechnics and Hydro-engineering (I-10), Wroclaw University of Technology. Plac Grunwaldzki 9 D-2 p.112. 50-377 Wroclaw (Poland)
2011-12-22
In natural streams, the interaction between water in motion and movable beds derives in transport of material. This is a fact that causes several problems for river regulation, above all in streams which were heavily modified by human interferences. Therefore, to find solutions or at least to alleviate the negative effects that sediment transport can bring with is a topic to be researched. The impact of seepage on river sedimentation processes and open-channel flow is important for environmental issues but it is commonly neglected by water specialists. The present contribution presents the output of a series of experimental works where the influence of seepage on the open channel turbulence is analyzed at the laboratory scale. Even though that the magnitude of the groundwater flow is significantly smaller than the magnitude of the open channel flow; the output of the experiments demonstrates that seepage not only modifies the water-sediment interaction as demonstrated Herrera Granados (2008; 2010); but also is affecting the velocity field and turbulence dynamics of the open-channel flow.
Laboratorial studies on the seepage impact in open-channel flow turbulence
International Nuclear Information System (INIS)
Herrera Granados, Oscar; Kostecki, Stanislaw
2011-01-01
In natural streams, the interaction between water in motion and movable beds derives in transport of material. This is a fact that causes several problems for river regulation, above all in streams which were heavily modified by human interferences. Therefore, to find solutions or at least to alleviate the negative effects that sediment transport can bring with is a topic to be researched. The impact of seepage on river sedimentation processes and open-channel flow is important for environmental issues but it is commonly neglected by water specialists. The present contribution presents the output of a series of experimental works where the influence of seepage on the open channel turbulence is analyzed at the laboratory scale. Even though that the magnitude of the groundwater flow is significantly smaller than the magnitude of the open channel flow; the output of the experiments demonstrates that seepage not only modifies the water-sediment interaction as demonstrated Herrera Granados (2008; 2010); but also is affecting the velocity field and turbulence dynamics of the open-channel flow.
Energy Technology Data Exchange (ETDEWEB)
Liu, Chun-Ho [The Hong Kong Polytechnic University, Kowloon (Hong Kong). Department of Building and Real Estate; Leung, Dennis Y.C. [The University of Hong Kong (Hong Kong). Department of Mechanical Engineering
2006-11-15
This study employs a direct numerical simulation (DNS) technique to study the flow, turbulence structure, and passive scalar plume transport behind line sources in an unstably stratified open channel flow. The scalar transport behaviors for five emission heights (z{sub s}=0, 0.25H, 0.5H, 0.75H, and H, where H is the channel height) at a Reynolds number of 3000, a Prandtl number and a Schmidt number of 0.72, and a Richardson number of -0.2 are investigated. The vertically meandering mean plume heights and dispersion coefficients calculated by the current DNS model agree well with laboratory results and field measurements in literature. It is found that the plume meandering is due to the movement of the positive and negative vertical turbulent scalar fluxes above and below the mean plume heights, respectively. These findings help explaining the plume meandering mechanism in the unstably stratified atmospheric boundary layer. (author)
Fractal-Markovian scaling of turbulent bursting process in open channel flow
International Nuclear Information System (INIS)
Keshavarzi, Ali Reza; Ziaei, Ali Naghi; Homayoun, Emdad; Shirvani, Amin
2005-01-01
The turbulent coherent structure of flow in open channel is a chaotic and stochastic process in nature. The coherence structure of the flow or bursting process consists of a series of eddies with a variety of different length scales and it is very important for the entrainment of sediment particles from the bed. In this study, a fractal-Markovian process is applied to the measured turbulent data in open channel. The turbulent data was measured in an experimental flume using three-dimensional acoustic Doppler velocity meter (ADV). A fractal interpolation function (FIF) algorithm was used to simulate more than 500,000 time series data of measured instantaneous velocity fluctuations and Reynolds shear stress. The fractal interpolation functions (FIF) enables to simulate and construct time series of u', v', and u'v' for any particular movement and state in the Markov process. The fractal dimension of the bursting events is calculated for 16 particular movements with the transition probability of the events based on 1st order Markov process. It was found that the average fractal dimensions of the streamwise flow velocity (u') are; 1.73, 1.74, 1.71 and 1.74 with the transition probability of 60.82%, 63.77%, 59.23% and 62.09% for the 1-1, 2-2, 3-3 and 4-4 movements, respectively. It was also found that the fractal dimensions of Reynold stress u'v' for quadrants 1, 2, 3 and 4 are 1.623, 1.623, 1.625 and 1.618, respectively
International Nuclear Information System (INIS)
Yamamoto, Yoshinobu; Kunugi, Tomoaki; Serizawa, Akimi
2002-01-01
In this study, investigation on effects of high frequency fluctuations on DNS of turbulent open-channel flows with high Pr passive scalar transport was conducted. As the results, although significant differences of energy spectra behaviors in temperature fields, are caused at high wave number region where insignificant area for velocity components, large difference dose not caused in mean and statistic behaviors in temperature component. But, if the buoyancy were considered, this temperature high-frequency fluctuations would be greatly changed mean and statistics behaviors from the difference of the accuracy and resolution at high wave number region. (author)
PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows
Nezu, Iehisa; Sanjou, Michio
2011-01-01
PIV is one of the most popular measurement techniques in hydraulic engineering as well as in fluid sciences. It has been applied to study various turbulent phenomena in laboratory experiments related to natural rivers, e.g., bursting phenomena near the bed, mixing layers observed at confluences, wake turbulence around dikes and piers, and so on. In these studies, PIV plays important roles in revealing the space-time structure of velocity fluctuations and coherent vortices. This review article...
Inlet effects on roll-wave development in shallow turbulent open-channel flows
Directory of Open Access Journals (Sweden)
Campomaggiore Francesca
2016-03-01
Full Text Available The present work investigates the effect of the flow profile induced by an inlet condition on the roll-wave evolution in turbulent clear-water flows. The study employs theoretical and numerical analyses. Firstly, the influence of the inlet condition on the spatial evolution of a single perturbation in a hypercritical flow is examined through the expansion near a wavefront analysis. The results show that an accelerated unperturbed profile reduces the disturbance spatial growth. A decelerated profile causes an increase. The effect of the flow profile on the spatial evolution of roll-wave trains is then numerically investigated solving the Saint Venant equations with a second-order Runge-Kutta Total Variation Diminishing (TVD Finite Volume scheme. The numerical simulations comply with the analytical results for the initial and transition phases of the roll-wave development. The unperturbed profile influences even the roll-waves statistical characteristics in the final stage, with a more evident effect in case of accelerated profiles. The influence of the flow profile should be therefore accounted for in the formulation of predictive criteria for roll-waves appearance based on the estimation of the disturbance spatial growth rate.
International Nuclear Information System (INIS)
Earl, T A; Thomas, L; David, L; Cochard, S; Tremblais, B
2015-01-01
The aim of this paper is to investigate and quantify the effect of vibration on experimental tomographic particle image velocimetry (TPIV) measurements. The experiment consisted of turbulence measurements in an open channel flow. Specifically, five trash rack assemblies, composed of regular grids, divided a 5 m long flume into four sequential, identical pools. This set-up established a globally stationary flow, with each pool generating a controlled amount of turbulence that is reset at every trash rack. TPIV measurements were taken in the central pool. To eliminate the vibration from the measurements, three vibration correction regimes are proposed and compared to a global volume self-calibration (Wieneke 2008 Exp. Fluids 45 549–56), a now standard calibration procedure in TPIV. As the amplitude of the vibrations was small, it was possible to extract acceptable reconstruction re-projection qualities (Q I > 75%) and velocity fields from the standard treatment. This paper investigates the effect of vibration on the cross-correlation signal and turbulence statistics, and shows the improvement to velocity field data by several correction schemes. A synthetic model was tested that simulated camera vibration to demonstrate its effects on key velocity parameters and to observe the effects on reconstruction and cross-correlation metrics. This work has implications for experimental measurements where vibrations are unavoidable and seemingly undetectable such as those in large open channel flows. (paper)
Czech Academy of Sciences Publication Activity Database
Příhoda, Jaromír; Zubík, P.; Šulc, J.; Sedlář, M.
2012-01-01
Roč. 14, 4a (2012), s. 6-12 ISSN 1335-4205 R&D Projects: GA ČR GA103/09/0977 Institutional support: RVO:61388998 Keywords : open channel flow * inclined backward-facing step Subject RIV: BK - Fluid Dynamics
Steady turbulent flow in curved rectangular channels
De Vriend, H.J.
1979-01-01
After the study of fully developed and developing steady laminar flow in curved channels of shallow rectangular wet cross-section (see earlier reports in this series), steady turbulent flow in such channels is investigated as a next step towards a mathematical model of the flow in shallow river
Dynamical eigenfunction decomposition of turbulent channel flow
Ball, K. S.; Sirovich, L.; Keefe, L. R.
1991-01-01
The results of an analysis of low-Reynolds-number turbulent channel flow based on the Karhunen-Loeve (K-L) expansion are presented. The turbulent flow field is generated by a direct numerical simulation of the Navier-Stokes equations at a Reynolds number Re(tau) = 80 (based on the wall shear velocity and channel half-width). The K-L procedure is then applied to determine the eigenvalues and eigenfunctions for this flow. The random coefficients of the K-L expansion are subsequently found by projecting the numerical flow field onto these eigenfunctions. The resulting expansion captures 90 percent of the turbulent energy with significantly fewer modes than the original trigonometric expansion. The eigenfunctions, which appear either as rolls or shearing motions, possess viscous boundary layers at the walls and are much richer in harmonics than the original basis functions.
Turbulent flow through channels in a viscously deforming matrix
Meyer, Colin; Hewitt, Ian; Neufeld, Jerome
2017-11-01
Channels of liquid melt form within a surrounding solid matrix in a variety of natural settings, for example, lava tubes and water flow through glaciers. Channels of water on the underside of glaciers, known as Rothlisberger (R-) channels, are essential components of subglacial hydrologic systems and can control the rate of glacier sliding. Water flow through these channels is turbulent, and dissipation melts open the channel while viscous creep of the surrounding closes the channel leading to the possibility of a steady state. Here we present an analogous laboratory experiment for R-channels. We pump warm water from the bottom into a tank of corn syrup and a channel forms. The pressure is lower in the water than in the corn syrup, therefore the syrup creeps inward. At the same time, the water ablates the corn syrup through dissolution and shear erosion, which we measure by determining the change in height of the syrup column over the course of the experiment. We find that the creep closure is much stronger than turbulent ablation which leads to traveling solitary waves along the water-syrup interface. These waves or `magmons' have been previously observed in experiments and theory for laminar magma melt conduits. We compliment our experiments with numerical simulations. David Crighton Fellowship.
Frank Huysmans; Jos de Haan
2010-01-01
Original title: Alle kanalen staan open. The rapid changes taking place in the media landscape in the Netherlands - characterised by digitisation and convergence of media technologies - raise the question of how the Dutch are dealing with the many new opportunities that have opened up. All
Mechanics of Bingham Flow in an Open Channel
荻原, 能男; 宮沢, 直季; 三浦, 美香
1988-01-01
In this paper, the velocity distribution on turbulent Bingham flow in an open channel is derived theoretically and the fitness of this distribution is examined by comparing with results of experiment using the fluid of water and bentonite mixture which shows the behavior of Bingham flow. The results show that the theoretical turbulent velocity distribution obtained here conforms to results of experiment in the region of lower bentonite concentration. By experiment, the empirical fomulae to es...
Turbulent shear layers in confining channels
Benham, Graham P.; Castrejon-Pita, Alfonso A.; Hewitt, Ian J.; Please, Colin P.; Style, Rob W.; Bird, Paul A. D.
2018-06-01
We present a simple model for the development of shear layers between parallel flows in confining channels. Such flows are important across a wide range of topics from diffusers, nozzles and ducts to urban air flow and geophysical fluid dynamics. The model approximates the flow in the shear layer as a linear profile separating uniform-velocity streams. Both the channel geometry and wall drag affect the development of the flow. The model shows good agreement with both particle image velocimetry experiments and computational turbulence modelling. The simplicity and low computational cost of the model allows it to be used for benchmark predictions and design purposes, which we demonstrate by investigating optimal pressure recovery in diffusers with non-uniform inflow.
Computer simulation of plasma turbulence in open systems
International Nuclear Information System (INIS)
Sigov, Yu.S.
1982-01-01
A short review of the results of kinetic simulation of collective phenomena in open plasma systems with the variable total energy and number of particles, i.e., the particle and energy fluxes on boundary surfaces and/or their internal sources and channels is given. Three specific problems are considered in different detail for such systems in one-dimensional geometry: the generation and evolution of double layers in a currently unstable plasma; the collisionless relaxation of strongly non-equilibrium electron distributions; the Langmuir collapse and strong electrostatic turbulence in systems with parametric excitation of a plasma by an external pumping wave and with cooling the fast non-Maxwell electrons. In all these cases the non-linearity and a collective character of processes give examples of new dissipative plasma structures that essentially widen our idea about the nature of the plasma turbulence in non-homogeneous open systems. (Auth.)
Plane waves and structures in turbulent channel flow
Sirovich, L.; Ball, K. S.; Keefe, L. R.
1990-01-01
A direct simulation of turbulent flow in a channel is analyzed by the method of empirical eigenfunctions (Karhunen-Loeve procedure, proper orthogonal decomposition). This analysis reveals the presence of propagating plane waves in the turbulent flow. The velocity of propagation is determined by the flow velocity at the location of maximal Reynolds stress. The analysis further suggests that the interaction of these waves appears to be essential to the local production of turbulence via bursting or sweeping events in the turbulent boundary layer, with the additional suggestion that the fast acting plane waves act as triggers.
Open channel steam generator feedwater system
International Nuclear Information System (INIS)
Kim, R.F.; Min-Hsiung Hu.
1985-01-01
A steam generator which utilizes a primary fluid to vaporize a secondary fluid is provided with an open flow channel and elevated discharge nozzle for the introduction of secondary fluid. The discharge nozzle is positioned above a portion of the inlet line such that the secondary fluid passes through a vertical section of inlet line prior to its discharge into the open channel. (author)
Evaporation of polydispersed droplets in a highly turbulent channel flow
Energy Technology Data Exchange (ETDEWEB)
Cochet, M.; Bazile, Rudy; Ferret, B.; Cazin, S. [INPT, UPS, IMFT (Institut de Mecanique des Fluides de Toulouse), Universite de Toulouse (France)
2009-09-15
A model experiment for the study of evaporating turbulent two-phase flows is presented here. The study focuses on a situation where pre-atomized and dispersed droplets vaporize and mix in a heated turbulent flow. The test bench consists in a channel flow with characteristics of homogeneous and isotropic turbulence where fluctuations levels reach very high values (25% in the established zone). An ultrasonic atomizer allows the injection of a mist of small droplets of acetone in the carrier flow. The large range diameters ensure that every kind of droplet behavior with regards to turbulence is possible. Instantaneous concentration fields of the vaporized phase are extracted from fluorescent images (PLIF) of the two phase flow. The evolution of the mixing of the acetone vapor is analyzed for two different liquid mass loadings. Despite the high turbulence levels, concentration fluctuations remain significant, indicating that air and acetone vapor are not fully mixed far from the injector. (orig.)
Three dimensional computation of turbulent flow in meandering channels
Energy Technology Data Exchange (ETDEWEB)
Van Thinh Nguyen
2000-07-01
In this study a finite element calculation procedure together with two-equation turbulent model k-{epsilon} and mixing length are applied to the problem of simulating 3D turbulent flow in closed and open meandering channels. Near the wall a special approach is applied in order to overcome the weakness of the standard k-{epsilon} in the viscous sub-layer. A specialized shape function is used in the special near wall elements to capture accurately the strong variations of the mean flow variables in the viscosity-affected near wall region. Based on the analogy of water and air flows, a few characteristics of hydraulic problems can be examined in aerodynamic models, respectively. To study the relationships between an aerodynamic and a hydraulic model many experiments have been carried out by Federal Waterway Engineering and Research Institute of Karlsruhe, Germany. In order to test and examine the results of these physical models, an appropriated numerical model is necessary. The numerical mean will capture the limitations of the experimental setup. The similarity and the difference between an aerodynamic and a hydraulic model will be found out by the results of numerical computations and will be depicted in this study. Despite the presence of similarities between the flow in closed channels and the flow in open channels, it should be stated that the presence of a free surface in the open channel introduces serious complications to three dimensional computation. A new unknown, which represents the position of nodes on this free surface, is introduced. A special approach is required for solving this unknown. A procedure surface tracking is applied to the free surface boundary like a moving boundary. Grid nodes on the free surface are free to move in such a way that they belong to the spines, which are the generator lines to define the allowed motion of the nodes on the free surface. (orig.) [German] Die numerische Simulation ist heute ein wichtiges Hilfsmittel fuer die
Scalar statistics in variable property turbulent channel flows
Patel, A.; Boersma, B.J.; Pecnik, R.
2017-01-01
Direct numerical simulation of fully developed, internally heated channel flows with isothermal walls is performed using the low-Mach-number approximation of Navier-Stokes equation to investigate the influence of temperature-dependent properties on turbulent scalar statistics. Different constitutive
Numerical simulation of particle-laden turbulent channel flow
Li, Y.; McLaughlin, J.B.; Kontomaris, K.; Portela, L.
2001-01-01
This paper presents results for the behavior of particle-laden gases in a small Reynolds number vertical channel down flow. Results will be presented for the effects of particle feedback on the gas-phase turbulence and for the concentration profile of the particles. The effects of density ratio,
Instability of shallow open channel flow with lateral velocity gradients
Energy Technology Data Exchange (ETDEWEB)
Lima, A C; Izumi, N, E-mail: adriano@eng.hokudai.ac.jp, E-mail: nizumi@eng.hokudai.ac.jp [River and Watershed Engineering Laboratory, Hokkaido University, Sapporo, 060-8628 (Japan)
2011-12-22
The turbulent flow in a wide rectangular open channel partially covered with vegetation is studied using linear stability analysis. In the base state normal flow condition, the water depth is constant and the transverse velocity vanishes, while there is a lateral gradient in the streamwise velocity with an inflexion point at the boundary between the vegetated zone and the main channel. The Reynolds stress is expressed by introducing the eddy viscosity, which is obtained from assuming a logarithmic distribution of the velocity near the bed. Perturbation expansions are introduced to the streamwise and transverse velocities, as well as to the water depth. The system of governing equations was solved in order to determine the maximum growth rate of the perturbations as a function of parameters which describe physical characteristics of the channel and the flow.
Semi-local scaling and turbulence modulation in variable property turbulent channel flows
Patel, A.; Peeters, J.W.R.; Boersma, B.J.; Pecnik, R.
2015-01-01
We theoretically and numerically investigate the effect of temperature dependent density and viscosity on turbulence in channel flows. First, a mathematical framework is developed to support the validity of the semi-local scaling as proposed based on heuristic arguments by Huang, Coleman, and
Direct numerical simulation of turbulent channel flow with deformed bubbles
International Nuclear Information System (INIS)
Yamamoto, Yoshinobu; Kunugi, Tomoaki
2010-01-01
In this study, the direct numerical simulation of a fully-developed turbulent channel flow with deformed bubbles were conducted by means of the refined MARS method, turbulent Reynolds number 150, and Bubble Reynolds number 120. As the results, large-scale wake motions were observed round the bubbles. At the bubble located region, mean velocity was degreased and turbulent intensities and Reynolds shear stress were increased by the effects of the large-scale wake motions round bubbles. On the other hands, near wall region, bubbles might effect on the flow laminarlize and drag reduction. Two types of drag coefficient of bubble were estimated from the accelerated velocity of bubble and correlation equation as a function of Particle Reynolds number. Empirical correlation equation might be overestimated the drag effects in this Particle Reynolds number range. (author)
Flow around turbulence promoters in parallel channel, 1
International Nuclear Information System (INIS)
Shiina, Yasuaki; Takizuka, Takakazu; Okamoto, Yoshizo
1982-01-01
Flow characteristics in relation to heat transfer characteristics in parallel channel with turbulence promoters were studied experimentally. Flow visualization experiments were made in paralle channel with one or two turbulence promoters for Reynolds number region of 100 lt = Resub(w) lt = 3,600. The vortex patterns behind one promoter were that a steady vortex was formed for low Reynolds number and vortex was shed for high Reynolds number,. For higher Reynolds number, it was observed that shedding vortex caused other vortices or disappeared itself randomly. The results indicate that the shedding vortices will augment heat transfer, whereas the steady vortex will give rise to deterioration in heat transfer. This inference agrees with the experimental results of Hishida et al. The results of two promoters experiment showed that the maximum performance of promoter would be attained at p/d -- 7. This agrees with the results formerly studied by other investigators. (author)
Effects of flow depth and wall roughness on turbulence in compound channels
International Nuclear Information System (INIS)
Prinos, P.; Townsend, R.; Tavoularis, S.
1985-01-01
Current methods for estimating discharge in compound channels often lead to large errors. The error is largely due to momentum transfer mechanism (MTM) generated in the junction regions of the flow field (between adjacent deep and shallow zones). The MTM adversely affects system conveyance, particularly when the velocity differential between the deep and shallow zones is large. Improved prediction methods, therefore, will necessarily reflect the MTM's presence and its effect on the compound flow field. The mechanism's influence on system hydraulics is best examined by analysing the related turbulence characteristics in the junction zones of the compound section. Townsend reported increased turbulence levels in the junction region between a main channel and its shallower flood plain zone and Elsawy, McKee and McKeogh found that observed normal turbulent stresses in a similar region were of the same order of magnitude as the apparent shear stress on the junction's vertical interface plane. The objective of the present study is to measure turbulent stresses in the junction region of a symmetrical compound open channel and examine their dependence on relative depth and relative boundary roughness. Further details of this phase of the larger study are presented elsewhere. (author)
Evaporative Lithography in Open Microfluidic Channel Networks
Lone, Saifullah
2017-02-24
We demonstrate a direct capillary-driven method based on wetting and evaporation of various suspensions to fabricate regular two-dimensional wires in an open microfluidic channel through continuous deposition of micro- or nanoparticles under evaporative lithography, akin to the coffee-ring effect. The suspension is gently placed in a loading reservoir connected to the main open microchannel groove on a PDMS substrate. Hydrophilic conditions ensure rapid spreading of the suspension from the loading reservoir to fill the entire channel length. Evaporation during the spreading and after the channel is full increases the particle concentration toward the end of the channel. This evaporation-induced convective transport brings particles from the loading reservoir toward the channel end where this flow deposits a continuous multilayered particle structure. The particle deposition front propagates backward over the entire channel length. The final dry deposit of the particles is thereby much thicker than the initial volume fraction of the suspension. The deposition depth is characterized using a 3D imaging profiler, whereas the deposition topography is revealed using a scanning electron microscope. The patterning technology described here is robust and passive and hence operates without an external field. This work may well become a launching pad to construct low-cost and large-scale thin optoelectronic films with variable thicknesses and interspacing distances.
Direct Numerical Simulations of Particle-Laden Turbulent Channel Flow
Jebakumar, Anand Samuel; Premnath, Kannan; Abraham, John
2017-11-01
In a recent experimental study, Lau and Nathan (2014) reported that the distribution of particles in a turbulent pipe flow is strongly influenced by the Stokes number (St). At St lower than 1, particles migrate toward the wall and at St greater than 10 they tend to migrate toward the axis. It was suggested that this preferential migration of particles is due to two forces, the Saffman lift force and the turbophoretic force. Saffman lift force represents a force acting on the particle as a result of a velocity gradient across the particle when it leads or lags the fluid flow. Turbophoretic force is induced by turbulence which tends to move the particle in the direction of decreasing turbulent kinetic energy. In this study, the Lattice Boltzmann Method (LBM) is employed to simulate a particle-laden turbulent channel flow through Direct Numerical Simulations (DNS). We find that the preferential migration is a function of particle size in addition to the St. We explain the effect of the particle size and St on the Saffman lift force and turbophoresis and present how this affects particle concentration at different conditions.
Inception of supraglacial channelization under turbulent flow conditions
Mantelli, E.; Camporeale, C.; Ridolfi, L.
2013-12-01
Glacier surfaces exhibit an amazing variety of meltwater-induced morphologies, ranging from small scale ripples and dunes on the bed of supraglacial channels to meandering patterns, till to large scale drainage networks. Even though the structure and geometry of these morphologies play a key role in the glacier melting processes, the physical-based modeling of such spatial patterns have attracted less attention than englacial and subglacial channels. In order to partially fill this gap, our work concerns the large scale channelization occurring on the ice slopes and focuses on the role of turbulence on the wavelength selection processes during the channelization inception. In a recent study[1], two of us showed that the morphological instability induced by a laminar film flowing over an ice bed is characterized by transversal length scales of order of centimeters. Being these scales much smaller than the spacing observed in the channelization of supraglacial drainage networks (that are of order of meters) and considering that the water films flowing on glaciers can exhibit Reynolds numbers larger than 104, we investigated the role of turbulence in the inception of channelization. The flow-field is modeled by means of two-dimensional shallow water equations, where Reynolds stresses are also considered. In the depth-averaged heat balance equation an incoming heat flux from air is assumed and forced convection heat exchange with the wall is taken into account, in addition to convection and diffusion in the liquid. The temperature profile in the ice is finally coupled to the liquid through Stefan equation. We then perform a linear stability analysis and, under the assumption of small Stefan number, we solve the differential eigenvalue problem analytically. As main outcome of such an analysis, the morphological instability of the ice-water interface is detected and investigated in a wide range of the independent parameters: longitudinal and transversal wavenumbers
Bailly, Christophe
2015-01-01
This book covers the major problems of turbulence and turbulent processes, including physical phenomena, their modeling and their simulation. After a general introduction in Chapter 1 illustrating many aspects dealing with turbulent flows, averaged equations and kinetic energy budgets are provided in Chapter 2. The concept of turbulent viscosity as a closure of the Reynolds stress is also introduced. Wall-bounded flows are presented in Chapter 3, and aspects specific to boundary layers and channel or pipe flows are also pointed out. Free shear flows, namely free jets and wakes, are considered in Chapter 4. Chapter 5 deals with vortex dynamics. Homogeneous turbulence, isotropy, and dynamics of isotropic turbulence are presented in Chapters 6 and 7. Turbulence is then described both in the physical space and in the wave number space. Time dependent numerical simulations are presented in Chapter 8, where an introduction to large eddy simulation is offered. The last three chapters of the book summarize remarka...
LDPC coded OFDM over the atmospheric turbulence channel.
Djordjevic, Ivan B; Vasic, Bane; Neifeld, Mark A
2007-05-14
Low-density parity-check (LDPC) coded optical orthogonal frequency division multiplexing (OFDM) is shown to significantly outperform LDPC coded on-off keying (OOK) over the atmospheric turbulence channel in terms of both coding gain and spectral efficiency. In the regime of strong turbulence at a bit-error rate of 10(-5), the coding gain improvement of the LDPC coded single-side band unclipped-OFDM system with 64 sub-carriers is larger than the coding gain of the LDPC coded OOK system by 20.2 dB for quadrature-phase-shift keying (QPSK) and by 23.4 dB for binary-phase-shift keying (BPSK).
Design of open rectangular and trapezoidal channels
González, C. P.; Vera, P. E.; Carrillo, G.; García, S.
2018-04-01
In this work, the results of designing open channels in rectangular and trapezoidal form are presented. For the development of the same important aspects were taken as determination of flows by means of formula of the rational method, area of the surface for its implementation, optimal form of the flow to meet the needs of that environment. In the design the parameter of the hydraulic radius expressed in terms of the hydraulic area and wet perimeter was determined, considering that the surface on which the fluid flows is the product of the perimeter of the section and the length of the channel and where shear is generated by the condition of no slippage.
Ejection mechanisms in the sublayer of a turbulent channel
Jimenez, Javier; Moin, P.; Moser, R.; Keefe, L.
1988-01-01
The structure of the vorticity field in the viscous wall layer of a turbulent channel is studied by examining the results of a fully resolved direct numerical simulation. It is shown that this region is dominated by intense three-dimensional shear layers in which the dominant vorticity component is spanwise. The advection and reproduction processes of these structures are examined and shown to be consistent with the classical generation mechanism for two-dimensional Tollmien-Schlichting waves. This process is fundamentally different from the usually accepted mechanism involving hairpin vortices.
Oubei, Hassan M.; Zedini, Emna; Elafandy, Rami T.; Kammoun, Abla; Ng, Tien Khee; Alouini, Mohamed-Slim; Ooi, Boon S.
2017-01-01
Recent advances in underwater wireless optical communications necessitate a better understanding of the underwater channel. We propose the Weibull model to characterize the fading of salinity induced turbulent underwater wireless optical channels
Turbulent subcooled boiling flow visualization experiments through a rectangular channel
International Nuclear Information System (INIS)
Estrada-Perez, Carlos E.; Dominguez-Ontiveros, Elvis E.; Hassan, Yassin A.
2008-01-01
Full text of publication follows: Proper characterization of subcooled boiling flow is of importance in many applications. It is of exceptional significance in the development of empirical models for the design of nuclear reactors, steam generators, and refrigeration systems. Most of these models are based on experimental studies that share the characteristics of utilizing point measurement probes with high temporal resolution, e.g. Hot Film Anemometry (HFA), Laser Doppler Velocimetry (LDV), and Fiber Optic Probes (FOP). However there appears to be a scarcity of experimental studies that can capture instantaneous whole-field measurements with a fast time response. Particle Tracking Velocimetry (PTV) may be used to overcome the limitations associated with point measurement techniques. PTV is a whole-flow-field technique providing instantaneous velocity vectors capable of high spatial and temporal resolution. PTV is also an exceptional tool for the analysis of boiling flow due to its ability to differentiate between the gas and liquid phases and subsequently deliver independent velocity fields associated with each phase. In this work, using PTV, liquid velocity fields of a turbulent subcooled boiling flow in a rectangular channel were successfully obtained. The present results agree with similar studies that used point measurement probes. However, the present study provides additional information; not only averaged profiles of the velocity components were obtained, instantaneous 2-D velocity fields were also readily available with a high temporal and spatial resolution. Analysis of fluctuating velocities, Reynolds stresses, and higher order statistics of the flow are presented. This work is an attempt to enrich the database already collected on turbulent subcooled boiling flow, with the hope that it will be useful in turbulence modeling efforts. (authors)
Dynamic evolution process of turbulent channel flow after opposition control
Energy Technology Data Exchange (ETDEWEB)
Ge, Mingwei; Tian, De; Yongqian, Liu, E-mail: gmwncepu@163.com [State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources (North China Electric Power University), Beijing102206 (China)
2017-02-15
Dynamic evolution of turbulent channel flow after application of opposition control (OC), together with the mechanism of drag reduction, is studied through direct numerical simulation (DNS). In the simulation, the pressure gradient is kept constant, and the flow rate increases due to drag reduction. In the transport of mean kinetic energy (MKE), one part of the energy from the external pressure is dissipated by the mean shear, and the other part is transported to the turbulent kinetic energy (TKE) through a TKE production term (TKP). It is found that the increase of MKE is mainly induced by the reduction of TKP that is directly affected by OC. Further analysis shows that the suppression of the redistribution term of TKE in the wall normal direction plays a key role in drag reduction, which represses the wall normal velocity fluctuation and then reduces TKP through the attenuation of its main production term. When OC is suddenly applied, an acute imbalance of energy in space is induced by the wall blowing and suction. Both the skin-friction and TKP terms exhibit a transient growth in the initial phase of OC, which can be attributed to the local effect of 〈 v ′ v ′〉 and 〈− u ′ v ′〉 in the viscous sublayer. (paper)
Simulation of a 3D Turbulent Wavy Channel based on the High-order WENO Scheme
Tsai, Bor-Jang; Chou, Chung-Chyi; Tsai, Yeong-Pei; Chuang, Ying Hung
2018-02-01
Passive interest turbulent drag reduction, effective means to improve air vehicle fuel consumption costs. Most turbulent problems happening to the nature and engineering applications were exactly the turbulence problem frequently caused by one or more turbulent shear flows. This study was operated with incompressible 3-D channels with cyclic wavy boundary to explore the physical properties of turbulence flow. This research measures the distribution of average velocity, instant flowing field shapes, turbulence and pressure distribution, etc. Furthermore, the systematic computation and analysis for the 3-D flow field was also implemented. It was aimed to clearly understand the turbulence fields formed by wavy boundary of tube flow. The purpose of this research is to obtain systematic structural information about the turbulent flow field and features of the turbulence structure are discussed.
Compressible turbulent channel flow with impedance boundary conditions
Scalo, Carlo; Bodart, Julien; Lele, Sanjiva K.
2015-03-01
We have performed large-eddy simulations of isothermal-wall compressible turbulent channel flow with linear acoustic impedance boundary conditions (IBCs) for the wall-normal velocity component and no-slip conditions for the tangential velocity components. Three bulk Mach numbers, Mb = 0.05, 0.2, 0.5, with a fixed bulk Reynolds number, Reb = 6900, have been investigated. For each Mb, nine different combinations of IBC settings were tested, in addition to a reference case with impermeable walls, resulting in a total of 30 simulations. The adopted numerical coupling strategy allows for a spatially and temporally consistent imposition of physically realizable IBCs in a fully explicit compressible Navier-Stokes solver. The IBCs are formulated in the time domain according to Fung and Ju ["Time-domain impedance boundary conditions for computational acoustics and aeroacoustics," Int. J. Comput. Fluid Dyn. 18(6), 503-511 (2004)]. The impedance adopted is a three-parameter damped Helmholtz oscillator with resonant angular frequency, ωr, tuned to the characteristic time scale of the large energy-containing eddies. The tuning condition, which reads ωr = 2πMb (normalized with the speed of sound and channel half-width), reduces the IBCs' free parameters to two: the damping ratio, ζ, and the resistance, R, which have been varied independently with values, ζ = 0.5, 0.7, 0.9, and R = 0.01, 0.10, 1.00, for each Mb. The application of the tuned IBCs results in a drag increase up to 300% for Mb = 0.5 and R = 0.01. It is shown that for tuned IBCs, the resistance, R, acts as the inverse of the wall-permeability and that varying the damping ratio, ζ, has a secondary effect on the flow response. Typical buffer-layer turbulent structures are completely suppressed by the application of tuned IBCs. A new resonance buffer layer is established characterized by large spanwise-coherent Kelvin-Helmholtz rollers, with a well-defined streamwise wavelength λx, traveling downstream with
Computation of a turbulent channel flow using PDF method
International Nuclear Information System (INIS)
Minier, J.P.; Pozorski, J.
1997-05-01
The purpose of the present paper is to present an analysis of a PDF model (Probability Density Function) and an illustration of the possibilities offered by such a method for a high-Reynolds turbulent channel flow. The first part presents the principles of the PDF approach and the introduction of stochastic processes along with a Lagrangian point of view. The model retained is the one put forward by Pope (1991) and includes evolution equations for location, velocity and dissipation of a large number of particles. Wall boundary conditions are then developed for particles. These conditions allow statistical results of the logarithmic region to be correctly reproduced. Simulation of non-homogeneous flows require a pressure-gradient algorithm which is briefly described. Developments are validated by analysing numerical predictions with respect to Comte Bellot experimental data (1965) on a channel flow. This example illustrates the ability of the approach to simulate wall-bounded flows and to provide detailed information such as skewness and flatness factors. (author)
Energy Technology Data Exchange (ETDEWEB)
Futtersack, R., E-mail: romain.futtersack@cea.fr [CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Universite Paul Sabatier Toulouse, LAPLACE, 118 Route de Narbonne, F-31062 Toulouse Cedex 9 (France); Tamain, P. [CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Hagelaar, G. [Universite Paul Sabatier Toulouse, LAPLACE, 118 Route de Narbonne, F-31062 Toulouse Cedex 9 (France); Ghendrih, Ph.; Simonin, A. [CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France)
2013-07-15
We investigate the impact of both parallel and transverse boundary conditions on the current and charge transport in open field line systems using the TOKAM2D code, which solves a minimal model for interchange turbulence. Various limit test cases are discussed and analyzed. In the parallel direction, the sheath conductivity is found to play an essential role in the stabilization of large-scale potential structures, leading to the formation of transport channel or transport barrier respectively for an insulating end wall or a wall with an enhanced sheath conductivity. On another hand, the addition of transverse boundary conditions intrinsically changes the transport characteristics, influencing both radial profiles and probability density functions. It underlines that in some cases a detailed description of the plasma-wall interaction process is required to get a proper description of the current loop pattern that determines electrostatic turbulent transport.
universal specific energy curve for para- bolic open channels
African Journals Online (AJOL)
DEPT OF AGRICULTURAL ENGINEERING
UNIVERSAL SPECIFIC ENERGY CURVE FOR PARA-. BOLIC OPEN CHANNELS. K.O. Aiyesimoju. Department of Civil Engineering. University of Lagos. Lagos, Nigeria. ABSTRACT. From the general relationship between specific energy and flow depth for all open channels, the specific relationship for parabolic open ...
Oubei, Hassan M.
2017-12-13
Recent advances in underwater wireless optical communications necessitate a better understanding of the underwater channel. We propose the Weibull model to characterize the fading of salinity induced turbulent underwater wireless optical channels. The model shows an excellent agreement with the measured data under all channel conditions.
Establishment of DNS database in a turbulent channel flow by large-scale simulations
Abe, Hiroyuki; Kawamura, Hiroshi; 阿部 浩幸; 河村 洋
2008-01-01
In the present study, we establish statistical DNS (Direct Numerical Simulation) database in a turbulent channel flow with passive scalar transport at high Reynolds numbers and make the data available at our web site (http://murasun.me.noda.tus.ac.jp/turbulence/). The established database is reported together with the implementation of large-scale simulations, representative DNS results and results on turbulence model testing using the DNS data.
Modeling water droplet condensation and evaporation in DNS of turbulent channel flow
Russo, E.; Kuerten, J.G.M.; Geld, van der C.W.M.; Geurts, B.J.
2011-01-01
In this paper a point particle model for two-way coupling in water droplet-laden incompressible turbulent flow of air is proposed. The model is based on conservation laws and semi-empirical correlations. It has been implemented and tested in a DNS code based for turbulent channel flow with an
Modeling water droplet condensation and evaporation in DNS of turbulent channel flow
Russo, E; Kuerten, Johannes G.M.; van der Geld, C.W.M.; Geurts, Bernardus J.
In this paper a point particle model for two-way coupling in water droplet-laden incompressible turbulent flow of air is proposed. The model is based on conservation laws and semi-empirical correlations. It has been implemented and tested in a DNS code based for turbulent channel flow with an
Experimental and Computational Studies of Turbulent Mass Transfer in a Mixing Channel
DEFF Research Database (Denmark)
Hjertager, Lene Kristin; Hjertager, Bjørn H.; Solberg, Tron
2008-01-01
. Three different flow cases are studied. The 2D numerical predictions of the mixing channel show that none of the k- ε turbulence models tested is suitable for the flow cases studied here. The turbulent Schmidt number is reduced to obtain a better agreement between measured and predicted mean...
Water circulation in non-isothermal droplet-laden turbulent channel flow
Russo, E; Kuerten, Johannes G.M.; van der Geld, C.W.M.; Geurts, Bernardus J.; Simos, T.; Psihoyios, G.; Tsitouras, Ch.
2013-01-01
We propose a point-particle model for two-way coupling of water droplets dispersed in turbulent flow of a carrier gas consisting of air and water vapor. An incompressible flow formulation is applied for direct numerical simulation (DNS) of turbulent channel flow with a warm and a cold wall. Compared
Numerical Simulations of Competitive-Consecutive Reactions in Turbulent Channel Flow
Vrieling, A.J.
2003-01-01
This thesis deals with mixing of passive scalars in a turbulent flow. The passive scalars are released in a turbulent plane channel flow and interpreted as either non-reactive components or reactive components that are involved in a competitive-consecutive reaction system. The evolution of these
DNS of Turbulent Flow and Heat Transfer in a Channel with Surface Mounted Cubes
Verstappen, R.W.C.P.; Velde, R.M. van der; Veldman, A.E.P.
2000-01-01
The turbulent flow and heat transfer in a channel with surface mounted cubical obstacles forms a generic example of a problem that occurs in many engineering applications, for instance in the design of cooling devices. We have performed a numerical simulation of it without using any turbulence
DNS of turbulent flow and heat transfer in a channel with surface mounted cubes
Verstappen, R.W.C.P.; Velde, R.M. van der; Veldman, A.E.P.
2000-01-01
The turbulent flow and heat transfer in a channel with surface mounted cubical obstacles forms a generic example of a problem that occurs in many engineering applications, for instance in the design of cooling devices. We have performed a numerical simulation of it without using any turbulence
Transport coefficients for laminar and turbulent flow through a four-cusp channel
International Nuclear Information System (INIS)
Souza Dutra, A. de; Parise, J.A.R.; Souza Mendes, P.R. de.
1986-01-01
The heat transfer coefficients for laminar and turbulent flow in a four-cusp channel were determined. A numerical solution was developed for laminar flow an and experimental study for turbulent flow was carried out. Systematic variations of the Reynolds number were done in the range 900-30000. The results show that the heat transfer coefficients for the four-cusp channel are much lower than the coefficients for the circular tube. (author) [pt
Characteristics of flow past a slender, emergent cylinder in shallow open channels
Heidari, Mehdi; Balachandar, Ram; Roussinova, Vesselina; Barron, Ronald M.
2017-06-01
The complex wake created by an emergent cylinder with a large aspect ratio in a shallow open channel flow is studied experimentally using particle image velocimetry. The unique characteristics of the bed-mounted slender cylinder wake are analysed. Velocity fields, turbulence parameters, and wake development in shallow open channel flow are studied at two different Reynolds numbers and subcritical Froude numbers by carrying out measurements in different horizontal and vertical planes. In the mid-depth plane, velocity and turbulence statistics are independent of Reynolds number, while higher turbulence intensities and Reynolds shear stresses were observed in the near-bed plane for the low Reynolds number case. The narrower wake is observed in the near-bed plane due to the effect of the bed. Combined with stronger vertical velocity and turbulence intensities noted near the bed in the vertical midplane, this suggests increased activity of the vortex structures in the low Reynolds number case. Under shallow conditions, stronger disturbances of the free surface are observed for the case of high Reynolds and Froude numbers. The study also revisits the definition of the wake stability parameter and proposes a new definition which incorporates not only the bed friction but also the drag experienced by the cylinder.
Experiments and CFD Modelling of Turbulent Mass Transfer in a Mixing Channel
DEFF Research Database (Denmark)
Hjertager Osenbroch, Lene Kristin; Hjertager, Bjørn H.; Solberg, Tron
2006-01-01
. Three different flow cases are studied. The 2D numerical predictions of the mixing channel show that none of the k-ε turbulence models tested is suitable for the flow cases studied here. The turbulent Schmidt number is reduced to obtain a better agreement between measured and predicted mean......Experiments are carried out for passive mixing in order to obtain local mean and turbulent velocities and concentrations. The mixing takes place in a square channel with two inlets separated by a block. A combined PIV/PLIF technique is used to obtain instantaneous velocity and concentration fields...... and fluctuating concentrations. The multi-peak presumed PDF mixing model is tested....
Mechanics of dense suspensions in turbulent channel flows
Picano, F.; Costa, P.; Breugem, W.P.; Brandt, L.
2015-01-01
Dense suspensions are usually investigated in the laminar limit where inertial effects are insignificant. When the flow rate is high enough, i.e. at high Reynolds number, the flow may become turbulent and the interaction between solid and liquid phases modifies the turbulence we know in single-phase
Energy Technology Data Exchange (ETDEWEB)
Khazaee, I. [Department of Mechanical Engineering, Torbat-e-jam branch, Islamic Azad University, Torbat-e-jam (Iran, Islamic Republic of); Mohammadiun, M. [Department of Mechanical Engineering, Shahrood branch, Islamic Azad University, Shahrood (Iran, Islamic Republic of)
2012-07-01
In this paper a complete three-dimensional and two phase CFD model for flow distribution in an open channel investigated. The finite volume method (FVM) with a dynamic Sub grid-scale was carried out for seven cases of different aspect ratios, different inclination angles or slopes and convergence-divergence condition. The volume of fluid (VOF) method was used to allow the free-surface to deform freely with the underlying turbulence. The discharge through open channel flow is often evaluated by velocity-area integration method from the measurement of velocity at discrete locations in the measuring section. The variation of velocity along horizontal and vertical directions is thus very important to decide the location of the sensors. The aspect ratio of the channel, slope of the channel and divergence- convergence of the channel have investigated and the results show that the depth of water at the end of the channel is higher at AR=0.8 against the AR=0.4 and AR=1.2. Also it is clear that by increasing the inclination angle or slope of the channel in case1, case4 and case5 the depth of the water increases. Also it is clear that the outlet mass flow rate is at a minimum value at a range of inclination angle of the channel.
Characteristics of turbulent velocity and temperature in a wall channel of a heated rod bundle
Energy Technology Data Exchange (ETDEWEB)
Krauss, T.; Meyer, L. [Forschungszentrum Karlsruhe (Germany)
1995-09-01
Turbulent air flow in a wall sub-channel of a heated 37-rod bundle (P/D = 1.12, W/D = 1.06) was investigated. measurements were performed with hot-wire probe with X-wires and a temperature wire. The mean velocity, the mean fluid temperature, the wall shear stress and wall temperature, the turbulent quantities such as the turbulent kinetic energy, the Reynolds-stresses and the turbulent heat fluxes were measured and are discussed with respect to data from isothermal flow in a wall channel and heated flow in a central channel of the same rod bundle. Also, data on the power spectral densities of the velocity and temperature fluctuations are presented. These data show the existence of large scale periodic fluctuations are responsible for the high intersubchannel heat and momentum exchange.
Multi-scale viscosity model of turbulence for fully-developed channel flows
International Nuclear Information System (INIS)
Kriventsev, V.; Yamaguchi, A.; Ninokata, H.
2001-01-01
The full text follows. Multi-Scale Viscosity (MSV) model is proposed for estimation of the Reynolds stresses in turbulent fully-developed flow in a straight channel of an arbitrary shape. We assume that flow in an ''ideal'' channel is always stable, i.e. laminar, but turbulence is developing process of external perturbations cased by wall roughness and other factors. We also assume that real flows are always affected by perturbations of every scale lower than the size of the channel. And the turbulence is generated in form of internal, or ''turbulent'' viscosity increase to preserve stability of ''disturbed'' flow. The main idea of MSV can be expressed in the following phenomenological rule: A local deformation of axial velocity can generate the turbulence with the intensity that keeps the value of local turbulent Reynolds number below some critical value. Here, the local turbulent Reynolds number is defined as a product of value of axial velocity deformation for a given scale and generic length of this scale divided by accumulated value of laminar and turbulent viscosity of lower scales. In MSV, the only empirical parameter is the critical Reynolds number that is estimated to be around 100. It corresponds for the largest scale which is hydraulic diameter of the channel and, therefore represents the regular Reynolds number. Thus, the value Re=100 corresponds to conditions when turbulent flow can appear in case of ''significant'' (comparable with size of channel) velocity disturbance in boundary and/or initial conditions for velocity. Of course, most of real flows in channels with relatively smooth walls remain laminar for this small Reynolds number because of absence of such ''significant'' perturbations. MSV model has been applied to the fully-developed turbulent flows in straight channels such as a circular tube and annular channel. Friction factor and velocity profiles predicted with MSV are in a very good agreement with numerous experimental data. Position of
Drifting plasmons in open two-dimensional channels: modal analysis
International Nuclear Information System (INIS)
Sydoruk, O
2013-01-01
Understanding the properties of plasmons in two-dimensional channels is important for developing methods of terahertz generation. This paper presents a modal analysis of plasmonic reflection in open channels supporting dc currents. As it shows, the plasmons can be amplified upon reflection if a dc current flows away from a conducting boundary; de-amplification occurs for the opposite current direction. The problem is solved analytically, based on a perturbation calculation, and numerically, and agreement between the methods is demonstrated. The power radiated by a channel is found to be negligible, and plasmon reflection in open channels is shown to be similar to that in closed channels. Based on this similarity, the oscillator designs developed earlier for closed channels could be applicable also for open ones. The results develop the modal-decomposition technique further as an instrument for the design of terahertz plasmonic sources. (paper)
The stress generated by non-Brownian fibers in turbulent channel flow simulations
Gillissen, J.J.J.; Boersma, B.J.; Mortensen, P.H.; Andersson, H.I.
2007-01-01
Turbulent fiber suspension channel flow is studied using direct numerical simulation. The effect of the fibers on the fluid mechanics is governed by a stress tensor, involving the distribution of fiber position and orientation. Properties of this function in channel flow are studied by computing the
Large-eddy simulation of open channel flow with surface cooling
International Nuclear Information System (INIS)
Walker, R.; Tejada-Martínez, A.E.; Martinat, G.; Grosch, C.E.
2014-01-01
Highlights: • Open channel flow comparable to a shallow tidal ocean flow is simulated using LES. • Unstable stratification is imposed by a constant surface cooling flux. • Full-depth, convection-driven, rotating supercells develop when cooling is applied. • Strengthening of cells occurs corresponding to an increasing of the Rayleigh number. - Abstract: Results are presented from large-eddy simulations of an unstably stratified open channel flow, driven by a uniform pressure gradient and with zero surface shear stress and a no-slip lower boundary. The unstable stratification is applied by a constant cooling flux at the surface and an adiabatic bottom wall, with a constant source term present to ensure the temperature reaches a statistically steady state. The structure of the turbulence and the turbulence statistics are analyzed with respect to the Rayleigh number (Ra τ ) representative of the surface buoyancy relative to shear. The impact of the surface cooling-induced buoyancy on mean and root mean square of velocity and temperature, budgets of turbulent kinetic energy (and components), Reynolds shear stress and vertical turbulent heat flux will be investigated. Additionally, colormaps of velocity fluctuations will aid the visualization of turbulent structures on both vertical and horizontal planes in the flow. Under neutrally stratified conditions the flow is characterized by weak, full-depth, streamwise cells similar to but less coherent than Couette cells in plane Couette flow. Increased Ra τ and thus increased buoyancy effects due to surface cooling lead to full-depth convection cells of significantly greater spanwise size and coherence, thus termed convective supercells. Full-depth convective cell structures of this magnitude are seen for the first time in this open channel domain, and may have important implications for turbulence analysis in a comparable tidally-driven ocean boundary layer. As such, these results motivate further study of the
Heat transfer and friction characteristics in steam cooled rectangular channels with rib turbulators
Energy Technology Data Exchange (ETDEWEB)
Gong, Jianying; Gao, Tieyu; Li, Guojun [Xi' an Jiaotong University, Xi' an (China)
2014-01-15
We studied the heat transfer and friction characteristics in steam-cooled rectangular channels with rib turbulators on W side or H side walls in the Reynolds number (Re) range of 10000-80000. Each of the test channels was welded by four stainless steel plates to simulate the actual geometry and heat transfer structure of blade/vane internal cooling passage. The length of the channel L was 1000 mm, the cross section of the channel was 40 mm X 80 mm, and the pitch-to-rib height ratio p/e was kept at 10. The channel blockage ratio (W/H) was 0.047. Results showed that the Nusselt number (Nu) distributions displayed different trends at the entrance region with the increase of Re for the rib turbulators on the W side walls. The heat transfer performance of the rib turbulators on the H side walls was about 24- 27% higher than that on the W side walls at the same pumping power. In addition, semi-empirical correlations for the two cases, rib turbulators on W side walls and rib turbulators on H side walls, were developed based on the heat transfer results, which could be used in the design of the internal cooling passage of new generation steam-cooled gas turbine blade/vane.
Oubei, Hassan M.
2017-06-16
In this Letter, we use laser beam intensity fluctuation measurements to model and describe the statistical properties of weak temperature-induced turbulence in underwater wireless optical communication (UWOC) channels. UWOC channels with temperature gradients are modeled by the generalized gamma distribution (GGD) with an excellent goodness of fit to the measured data under all channel conditions. Meanwhile, thermally uniform channels are perfectly described by the simple gamma distribution which is a special case of GGD. To the best of our knowledge, this is the first model that comprehensively describes both thermally uniform and gradient-based UWOC channels.
LightNVM: The Linux Open-Channel SSD Subsystem
DEFF Research Database (Denmark)
Bjørling, Matias; Gonzalez, Javier; Bonnet, Philippe
2017-01-01
resource utilization. We propose that SSD management trade-offs should be handled through Open-Channel SSDs, a new class of SSDs, that give hosts control over their internals. We present our experience building LightNVM, the Linux Open-Channel SSD subsystem. We introduce a new Physical Page Ad- dress I...... to limit read latency variability and that it can be customized to achieve predictable I/O latencies....
Computation of gradually varied flow in compound open channel ...
Indian Academy of Sciences (India)
The flow of water in an open channel can be treated as steady, gradually varied flow for ... channel between two nodes is treated as a single reach to calculate the loss ... dition at control points and (iii) critical depth is also required to verify the ...
DNS of turbulent channel flow at ReΤ=395, 590 AND Pr=0.01
Energy Technology Data Exchange (ETDEWEB)
Tiselj, I. [Jozef Stefan Inst., Ljubljana (Slovenia)
2011-07-01
The paper presents results of the Direct Numerical Simulation of turbulent channel flow at friction Reynolds numbers 395 and 590 with passive scalar at Prandtl number 0.01, which corresponds to the Prandtl number of liquid sodium. Fluctuating and non-fluctuating temperature boundary conditions are analyzed and compared. Results clearly describe the minor role of the turbulent Prandtl number in the integral wall-to-fluid heat transfer. (author)
Bakosi, J.; Franzese, P.; Boybeyi, Z.
2010-01-01
Dispersion of a passive scalar from concentrated sources in fully developed turbulent channel flow is studied with the probability density function (PDF) method. The joint PDF of velocity, turbulent frequency and scalar concentration is represented by a large number of Lagrangian particles. A stochastic near-wall PDF model combines the generalized Langevin model of Haworth & Pope with Durbin's method of elliptic relaxation to provide a mathematically exact treatment of convective and viscous ...
Energy Technology Data Exchange (ETDEWEB)
Mantzaras, I; Benz, P; Schaeren, R; Bombach, R [Paul Scherrer Inst. (PSI), Villigen (Switzerland)
1999-08-01
The catalytically stabilised thermal combustion (CST) of lean hydrogen-air mixtures was investigated numerically in a turbulent channel flow configuration using a two-dimensional elliptic model with detailed heterogeneous and homogeneous chemical reactions. Comparison between turbulent and laminar cases having the same incoming mean properties shows that turbulence inhibits homogeneous ignition due to increased heat transport away from the near-wall layer. The peak root-mean-square temperature and species fluctuations are always located outside the extent of the homogeneous reaction zone indicating that thermochemical fluctuations have no significant influence on gaseous combustion. (author) 4 figs., 6 refs.
International Nuclear Information System (INIS)
Matsuda, Y.; Kato, K.; Yabusaki, N.; Hirano, M.; Nakanishi, R.; Sakai, M.
1997-01-01
Open-channel effects on charmonium (S- and D-waves) and bottomonium (S-wave) J P = 1 - spectra are investigated within a one-open-channel approximation. Mass shifts and decay widths of these states just above the threshold are obtained by taking into account a coupling between confined quarkonium states and decaying states of the open channel. The final-state interaction (FSI) between the decaying meson and antimeson plays a very important role in producing a reasonable magnitude of coupling; the FSI provides the open-channel poles (R 1 , R 2 ) at the appropriate positions on the complex energy plane. The result is found to be independent of the detailed form of the transition potential and the final-state interaction. (author)
Water droplet condensation and evaporation in turbulent channel flow
Russo, E; Kuerten, Johannes G.M.; van der Geld, C.W.M.; Geurts, Bernardus J.
We propose a point-particle model for two-way coupling of water droplets dispersed in the turbulent flow of a carrier gas consisting of air and water vapour. We adopt an Euler–Lagrangian formulation based on conservation laws for the mass, momentum and energy of the continuous phase and on empirical
Symmetry-preserving discretization of turbulent channel flow
Verstappen, RWCP; Veldman, AEP; Breuer, M; Durst, F; Zenger, C
2002-01-01
We propose to perform turbulent flow simulations in such manner that the difference operators do have the same symmetry properties as the underlying differential operators, i.e. the convective operator is represented by a skew-symmetric matrix and the diffusive operator is approximated by a
Numerical simulation of turbulent buoyant flows in horizontal channels
International Nuclear Information System (INIS)
Seiter, C.
1995-09-01
A numerical method is presented, to calculate the three-dimensional, time-dependent large scale structure of turbulent buoyant flows. The subject of the study is the Rayleigh-Benard-convection with air (Pr=0.71, Ra=2.5 10 6 , 10 7 ) and sodium (Pr=0.006, Ra=8.4 10 4 , 2.5 10 5 , 10 6 , 10 7 ) and a fluid layer with water and an internal heat source (Pr=7.0, Ra I =1.5 10 10 ) at moderate and high Rayleigh-numbers. The goal of the work is both, the analysis of structures of instantaneous as well as the statistical analysis of spatially and/or time averaged data, to give a contribution to the investigation of the characteristics of turbulent natural convection mainly in fluids with small Prandtl-numbers. The large eddy simulation of natural convection requires the development of appropriate momentum and heat subgrid scale models and the formulation of new boundary conditions. The used energy-length-models in the computer code TURBIT are extended methodically by modification of the characteristic length scales of the sub scale turbulence. The reduction or the increase of the sub scale turbulence correlations, caused by the influence of solid boundaries or the stratification, is considered. In the same way the new boundary conditions for the diffusive terms of the conservation equations are seen to be necessary, when the thermal or in the case of liquid metals the more critical hydrodynamic boundary layer is resolved insufficiently or not at all. The extended and new methods, models and boundary conditions, which enabled the realization of the planned simulations, are presented. (orig.)
Low SNR Capacity of FSO Links over Gamma-Gamma Atmospheric Turbulence Channels
Benkhelifa, Fatma; Alouini, Mohamed-Slim; Rezki, Zouheir
2013-01-01
free space optical communication systems over Gamma-Gamma atmospheric turbulence fading channels with perfect channel state information at both the transmitter and the receiver. In our framework, we mainly focus on the low signal-to-noise ratio range and show that the ergodic capacity scales proportionally to SNR log^4(1/SNR). We show also that one-bit CSI feedback at the transmitter is enough to achieve this capacity using an on-o ff power control scheme.
Comparison of superhydrophobic drag reduction between turbulent pipe and channel flows
Im, Hyung Jae; Lee, Jae Hwa
2017-09-01
It has been known over several decades that canonical wall-bounded internal flows of a pipe and channel share flow similarities, in particular, close to the wall due to the negligible curvature effect. In the present study, direct numerical simulations of fully developed turbulent pipe and channel flows are performed to investigate the influence of the superhydrophobic surfaces (SHSs) on the turbulence dynamics and the resultant drag reduction (DR) of the flows under similar conditions. SHSs at the wall are modeled in spanwise-alternating longitudinal regions with a boundary with no-slip and shear-free conditions, and the two parameters of the spanwise periodicity (P/δ) and SHS fraction (GF) within a pitch are considered. It is shown, in agreement with previous investigations in channels, that the turbulent drag for the pipe and channel flows over SHSs is continuously decreased with increases in P/δ and GF. However, the DR rate in the pipe flows is greater than that in the channel flows with an accompanying reduction of the Reynolds stress. The enhanced performance of the DR for the pipe flow is attributed to the increased streamwise slip and weakened Reynolds shear stress contributions. In addition, a mathematical analysis of the spanwise mean vorticity equation suggests that the presence of a strong secondary flow due to the increased spanwise slip of the pipe flows makes a greater negative contribution of advective vorticity transport than the channel flows, resulting in a higher DR value. Finally, an inspection of the origin of the mean secondary flow in turbulent flows over SHSs based on the spatial gradients of the turbulent kinetic energy demonstrates that the secondary flow is both driven and sustained by spatial gradients in the Reynolds stress components, i.e., Prandtl's secondary flow of the second kind.
Turbulent mixed convection in asymmetrically heated vertical channel
Directory of Open Access Journals (Sweden)
Mokni Ameni
2012-01-01
Full Text Available In this paper an investigation of mixed convection from vertical heated channel is undertaken. The aim is to explore the heat transfer obtained by adding a forced flow, issued from a flat nozzle located in the entry section of a channel, to the up-going fluid along its walls. Forced and free convection are combined studied in order to increase the cooling requirements. The study deals with both symmetrically and asymmetrically heated channel. The Reynolds number based on the nozzle width and the jet velocity is assumed to be 3 103 and 2.104; whereas, the Rayleigh number based on the channel length and the wall temperature difference varies from 2.57 1010 to 5.15 1012. The heating asymmetry effect on the flow development including the mean velocity and temperature the local Nusselt number, the mass flow rate and heat transfer are examined.
Self-channeling of high-power laser pulses through strong atmospheric turbulence
Peñano, J.; Palastro, J. P.; Hafizi, B.; Helle, M. H.; DiComo, G. P.
2017-07-01
We present an unusual example of truly long-range propagation of high-power laser pulses through strong atmospheric turbulence. A form of nonlinear self-channeling is achieved when the laser power is close to the self-focusing power of air and the transverse dimensions of the pulse are smaller than the coherence diameter of turbulence. In this mode, nonlinear self-focusing counteracts diffraction, and turbulence-induced spreading is greatly reduced. Furthermore, the laser intensity is below the ionization threshold so that multiphoton absorption and plasma defocusing are avoided. Simulations show that the pulse can propagate many Rayleigh lengths (several kilometers) while maintaining a high intensity. In the presence of aerosols, or other extinction mechanisms that deplete laser energy, the pulse can be chirped to maintain the channeling.
Direct numerical simulation of the passive scalar field in a two-dimensional turbulent channel flow
International Nuclear Information System (INIS)
Kasagi, N.; Tomita, Y.; Kuroda, A.
1991-01-01
This paper reports on a direct numerical simulation (DNS) of the fully developed thermal field in a two-dimensional turbulent channel flow of air that was carried out. The iso-flux condition is imposed on the walls so that the local mean temperature linearly increases in the streamwise direction. The computation was executed on 1,589,248 grid points by using a spectral method. The statistics obtained include rms velocity and temperature fluctuations, Reynolds stresses, turbulent heat fluxes and other higher order correlations. They are compared mainly with the DNS data obtained by Kim and Moin (1987) and Kim (1987) in a higher Reynolds number flow with isothermal walls. Agreement between these two results is generally good. Each term in the budget equations of temperature variance, its dissipation rate and turbulent heat fluxes is also calculated in order to establish a data base of convective heat transfer for thermal turbulence modeling
Comparison of direct numerical simulation databases of turbulent channel flow at $Re_{\\tau}$ = 180
Vreman, A.W.; Kuerten, Johannes G.M.
2014-01-01
Direct numerical simulation (DNS) databases are compared to assess the accuracy and reproducibility of standard and non-standard turbulence statistics of incompressible plane channel flow at $Re_{\\tau}$ = 180. Two fundamentally different DNS codes are shown to produce maximum relative deviations
Comparison of direct numerical simulation databases of turbulent channel flow at Re = 180
Vreman, A.W.; Kuerten, J.G.M.
2014-01-01
Direct numerical simulation (DNS) databases are compared to assess the accuracy and reproducibility of standard and non-standard turbulence statistics of incompressible plane channel flow at Re t = 180. Two fundamentally different DNS codes are shown to produce maximum relative deviations below 0.2%
Numerical simulation of secondary flow in bubbly turbulent flow in sub-channel
International Nuclear Information System (INIS)
Ikeno, Tsutomu; Kataoka, Isao
2009-01-01
Secondary flow in bubbly turbulent flow in sub-channel was simulated by using an algebraic turbulence stress model. The mass, momentum, turbulence energy and bubble diffusion equations were used as fundamental equation. The basis for these equations was the two-fluid model: the equation of liquid phase was picked up from the equation system theoretically derived for the gas-liquid two-fluid turbulent flow. The fundamental equation was transformed onto a generalized coordinate system fitted to the computational domain in sub-channel. It was discretized for the SIMPLE algorism using the finite-volume method. The shape of sub-channel causes a distortion of the computational mesh, and orthogonal nature of the mesh is sometimes broken. An iterative method to satisfy a requirement for the contra-variant velocity was introduced to represent accurate symmetric boundary condition. Two-phase flow at a steady state was simulated for different magnitude of secondary flow and void fraction. The secondary flow enhanced the momentum transport in sub-channel and accelerated the liquid phase in the rod gap. This effect was slightly mitigated when the void fraction increased. The acceleration can contribute to effective cooling in the rod gap. The numerical result implied a phenomenon of industrial interest. This suggested that experimental approach is necessary to validate the numerical model and to identify the phenomenon. (author)
Ryzhenkov, V.; Ivashchenko, V.; Vinuesa, R.; Mullyadzhanov, R.
2016-10-01
We use the open-source code nek5000 to assess the accuracy of high-order spectral element large-eddy simulations (LES) of a turbulent channel flow depending on the spatial resolution compared to the direct numerical simulation (DNS). The Reynolds number Re = 6800 is considered based on the bulk velocity and half-width of the channel. The filtered governing equations are closed with the dynamic Smagorinsky model for subgrid stresses and heat flux. The results show very good agreement between LES and DNS for time-averaged velocity and temperature profiles and their fluctuations. Even the coarse LES grid which contains around 30 times less points than the DNS one provided predictions of the friction velocity within 2.0% accuracy interval.
Transient behavior of superfluid turbulence in a large channel
International Nuclear Information System (INIS)
Schwarz, K.W.; Rozen, J.R.
1991-01-01
The transient behavior of superfluid turbulence is studied theoretically and experimentally with the aim of understanding the disagreement between vortex-tangle theory and past measurements of free vortex-tangle decay in superfluid 4 He. Scaling theory is extended and large-scale simulations based on the reconnecting-vortex model are carried out. These imply that the Vinen equation should be a reasonable approximation even for rather large transients, and predict definite values for the Vinen parameters. Direct measurements of the vortex-tangle response to a sudden change in the driving velocity are seen to be in reasonable agreement with these predictions. It is found, however, that when the vortex tangle is allowed to decay farther toward zero, it eventually crosses over into a state of anomalously slow decay, which appears to be that observed in previous experiments. We argue that this regime should be interpreted in terms of a coupled-turbulence state in which random superfluid and normal-fluid motion interacts with the vortex tangle, the whole system decaying self-consistently at a rate controlled by the normal-fluid viscosity. Several additional qualitative observations which may be relevant to the question of how the vortex tangle is initiated are also reported
Heat Transport Enhancement of Turbulent Thermal Convection by Inserted Channels
Xia, Ke-Qing; Zhang, Lu
2017-11-01
We report an experimental study on the heat transport properties of turbulent Rayleigh Benard Convection (RBC) in a rectangular cell with two types of 3D-printed structures inserted inside. The first one splits the original rectangular cell into 60 identical sub cells whose aspect ratio is 1:1:10 (length, width, height). The second one splits the cell into 30 sub cells, each with a 1:2:10 aspect ratio and a baffle in the center. We find that for large Rayleigh numbers (Ra), the Nusselt numbers (Nu) of both structures increase compared with that of the empty rectangular cell. An enhancement in Nu as much as 20% is found for the second type of insertion at Rayleigh number 2 ×109 . Moreover, the Nu-Ra scaling shows a transition with both geometries. The particle image velocimetry (PIV) measurement within a single sub unit indicates that the transition may be related to the laminar to turbulent transition in flow field. Direct numerical simulations (DNS) confirm the experimental results. Our results demonstrate the potential in using insertions to enhance passive heat transfer. This work was supported by the Research Grants Council (RGC) of HKSAR (Nos. CUHK404513 and CUHK14301115).
Characterization of dual-polarization LTE radio over a free-space optical turbulence channel.
Bohata, J; Zvanovec, S; Korinek, T; Mansour Abadi, M; Ghassemlooy, Z
2015-08-10
A dual polarization (DP) radio over a free-space optical (FSO) communication link using a long-term evolution (LTE) radio signal is proposed and analyzed under different turbulence channel conditions. Radio signal transmission over the DP FSO channel is experimentally verified by means of error vector magnitude (EVM) statistics. We demonstrate that such a system, employing a 64 quadrature amplitude modulation at the frequency bands of 800 MHz and 2.6 GHz, evinces reliability with LTE signal over the FSO channel is a potential solution for last-mile access or backbone networks, when using multiple-input multiple-output based DP signals.
Flow around turbulence promoters in parallel channel, (2)
International Nuclear Information System (INIS)
Shiina, Yasuaki
1983-01-01
Effects of walls on shedding vortex in developed channel flow were investigated putting a cylinder at the center of channels or on a wall for the value of w/d from 2 to 4. Results were compared with the uniform flow result. When a cylinder was put at the center of the channels, non-dimensional frequency plotted against Reynolds number agreed with the uniform flow result at low Reynolds number. However, it increased rapidly with Reynolds number, then it lay considerably above the uniform flow results at high Reynolds number. When a cylinder was put on a wall, non-dimensional frequency was considerably lower than the uniform flow result in the cases of w/d = 3 and 4. In the case of w/d = 2, however, frequency was higher than the uniform flow result at high Reynolds number. In all cases in the present study, the transition Reynolds number increased with decrease in the value of w/d. These results indicate that the increase in shedding frequency was due to the shift in velocity distribution from Poiseuille parabora in the wake region, which obviously increased with Reynolds number and with decrease in channel width. (author)
Modeling water droplet condensation and evaporation in DNS of turbulent channel flow
Energy Technology Data Exchange (ETDEWEB)
Russo, E; Kuerten, J G M; Geld, C W M van der [Department of Mechanical Engineering, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Geurts, B J, E-mail: e.russo@tue.nl [Faculty EEMCS, University of Twente, PO Box 217, 7500 AE Enschede (Netherlands)
2011-12-22
In this paper a point particle model for two-way coupling in water droplet-laden incompressible turbulent flow of air is proposed. The model is based on conservation laws and semi-empirical correlations. It has been implemented and tested in a DNS code based for turbulent channel flow with an Eulerian-Lagrangian approach. The two-way coupling is investigated in terms of the effects of mass and heat transfer on the droplets distributions along the channel wall-normal direction and by comparison of the droplet temperature statistics with respect to the case without evaporation and condensation. A remarkable conclusion is that the presence of evaporating and condensing droplets results in an increase in the non-dimensional heat transfer coefficient of the channel flow represented by the Nusselt number.
Drag reduction in a turbulent channel flow using a passivity-based approach
Heins, Peter; Jones, Bryn; Sharma, Atul
2013-11-01
A new active feedback control strategy for attenuating perturbation energy in a turbulent channel flow is presented. Using a passivity-based approach, a controller synthesis procedure has been devised which is capable of making the linear dynamics of a channel flow as close to passive as is possible given the limitations on sensing and actuation. A controller that is capable of making the linearized flow passive is guaranteed to globally stabilize the true flow. The resulting controller is capable of greatly restricting the amount of turbulent energy that the nonlinearity can feed back into the flow. DNS testing of a controller using wall-sensing of streamwise and spanwise shear stress and actuation via wall transpiration acting upon channel flows with Reτ = 100 - 250 showed significant reductions in skin-friction drag.
Yang, Liang
2014-04-01
Free-space optical (FSO) communication has become a cost-effective method to provide high data rates. However, the turbulence-induced fading limits its application to short-range applications. To address this, we propose a multiuser diversity (MD) FSO scheme in which the Nth best user is selected and the channel fluctuations can be effectively exploited to produce a selection diversity gain. More specifically, we first present the statistics analysis for the considered system over both weak and strong atmospheric turbulence channels. Based on these statistics, the outage probability, bit-error rate performance, average capacity, diversity order, and coverage are analyzed. Results show that the diversity order for the gamma-gamma fading is N min{α, β}/2, where N is the number of users, and α and β are the channel fading parameters related to the effective atmospheric conditions of the link.
Canuto, V. M.; Hartke, G. J.; Battaglia, A.; Chasnov, J.; Albrecht, G. F.
1990-01-01
In this paper, we apply two theoretical turbulence models, DIA and the recent GISS model, to study properties of a turbulent channel flow. Both models provide a turbulent kinetic energy spectral function E(k) as the solution of a non-linear equation; the two models employ the same source function but different closures. The source function is characterized by a rate n sub s (k) which is derived from the complex eigenvalues of the Orr-Sommerfeld (OS) equation in which the basic flow is taken to be of a Poiseuille type. The O-S equation is solved for a variety of Reynolds numbers corresponding to available experimental data. A physical argument is presented whereby the central line velocity characterizing the basic flow, U0 sup L, is not to be identified with the U0 appearing in the experimental Reynolds number. The theoretical results are compared with two types of experimental data: (1) turbulence bulk properties, and (2) properties that depend strongly on the structure of the turbulence spectrum at low wave numbers. The only existing analytical expression for Pi (k) cannot be used in the present case because it applies to the case of a flat plate, not a finite channel.
Numerical study of elastic turbulence in a 3D curvilinear micro-channel
Zhang, Hongna; Kunugi, Tomoaki; Li, Fengchen
2012-11-01
Elastic turbulence is an intriguing phenomenon of viscoelastic fluid flow, and dominated by the strong nonlinear elasticity due to the existence of flexible microstructures. It implies the possibility to generate a turbulent state (so-called an elastic turbulence) in the micro-scale devices by introducing the viscoelastic fluids, which could significantly enhance the mixing efficiency therein. Several experiments have been carried out to study its characteristics and underlying physics. However, the difficulty in measuring the flow information and behaviors of the microstructures, especially in the cross section normal to the mean flow direction, limits our current understanding and controlling. In the present study, the nondimensionalization method in which the characteristic velocity is defined as the ratio of the solution viscosity to the width of the channel was adopted to simulate the elastic turbulence in the micro-scale devices. And the elastic turbulent flow was obtained numerically in the 3D curvilinear micro-channel. Therein, the characteristics of the velocity field and polymer's behavior are discussed. Moreover, the energy transfer between the kinetic energy and the polymer's elastic energy is also investigated to understand its physical mechanism. Supported by the Japan Society for the Promotion of Science research fellowship and the Ministry of Education, Culture, Sports, Science and Technology via `Energy Science in the Age of Global Warming' of Global Center of Excellence (G-COE) program (J-051).
Directory of Open Access Journals (Sweden)
M. R. Rastan
2018-03-01
Full Text Available In the first part of the present study, a two dimensional half-corrugated channel flow is simulated at Reynolds number of 104, in no-slip condition (hydrophilic surfaces( using various low Reynolds turbulence models as well as standard k-ε model; and an appropriate turbulence model (k-ω 1998 model( is proposed. Then, in order to evaluate the proposed solution method in simulation of flow adjacent to hydrophobic surfaces, turbulent flow is simulated in simple channel and the results are compared with the literature. Finally, two dimensional half-corrugated channel flow at Reynolds number of 104 is simulated again in vicinity of hydrophobic surfaces for varoius slip lengths. The results show that this method is capable of drag reduction in such a way that an increase of 200 μm in slip length leads to a massive drag reduction up to 38%. In addition, to access a significant drag reduction in turbulent flows, the non-dimensionalized slip length should be larger than the minimum.
DNS of turbulent channel flow with conjugate heat transfer at Prandtl number 0.01
Energy Technology Data Exchange (ETDEWEB)
Tiselj, Iztok, E-mail: iztok.tiselj@ijs.si [' Jozef Stefan' Institute, Jamova 39, SI-1000 Ljubljana (Slovenia); Cizelj, Leon, E-mail: leon.cizelj@ijs.si [' Jozef Stefan' Institute, Jamova 39, SI-1000 Ljubljana (Slovenia)
2012-12-15
Highlights: Black-Right-Pointing-Pointer DNS database for turbulent channel flow at Prandtl number 0.01 and various Re{sub {tau}}. Black-Right-Pointing-Pointer Two ideal boundary condition analyzed: non-fluctuating and fluctuating temperature. Black-Right-Pointing-Pointer DNS database with conjugate heat transfer for liquid sodium-steel contact. Black-Right-Pointing-Pointer Penetration of the turbulent temperature fluctuations into the solid wall analyzed. - Abstract: Direct Numerical Simulation (DNS) of the fully developed velocity and temperature fields in a turbulent channel flow coupled with the unsteady conduction in the heated walls was carried out. Simulations were performed with passive scalar approximation at Prandtl number 0.01, which roughly corresponds to the Prandtl number of liquid sodium. DNSs were performed at friction Reynolds numbers 180, 395 and 590. The obtained statistical quantities like mean temperatures, profiles of the root-mean-square (RMS) temperature fluctuations for various thermal properties of wall and fluid, and various wall thicknesses were obtained from a pseudo-spectral channel-flow code. Even for the highest implemented Reynolds number the temperature profile in the fluid does not exhibit log-law region and the near-wall RMS temperature fluctuations show Reynolds number dependence. Conjugate heat transfer simulations of liquid sodium-steel system point to a relatively intensive penetration of turbulent temperature fluctuations into the heated wall. Database containing the results is available in a digital form.
DNS of turbulent channel flow with conjugate heat transfer at Prandtl number 0.01
International Nuclear Information System (INIS)
Tiselj, Iztok; Cizelj, Leon
2012-01-01
Highlights: ► DNS database for turbulent channel flow at Prandtl number 0.01 and various Re τ . ► Two ideal boundary condition analyzed: non-fluctuating and fluctuating temperature. ► DNS database with conjugate heat transfer for liquid sodium–steel contact. ► Penetration of the turbulent temperature fluctuations into the solid wall analyzed. - Abstract: Direct Numerical Simulation (DNS) of the fully developed velocity and temperature fields in a turbulent channel flow coupled with the unsteady conduction in the heated walls was carried out. Simulations were performed with passive scalar approximation at Prandtl number 0.01, which roughly corresponds to the Prandtl number of liquid sodium. DNSs were performed at friction Reynolds numbers 180, 395 and 590. The obtained statistical quantities like mean temperatures, profiles of the root-mean-square (RMS) temperature fluctuations for various thermal properties of wall and fluid, and various wall thicknesses were obtained from a pseudo-spectral channel-flow code. Even for the highest implemented Reynolds number the temperature profile in the fluid does not exhibit log-law region and the near-wall RMS temperature fluctuations show Reynolds number dependence. Conjugate heat transfer simulations of liquid sodium–steel system point to a relatively intensive penetration of turbulent temperature fluctuations into the heated wall. Database containing the results is available in a digital form.
Structural organization of the quiescent core region in a turbulent channel flow
International Nuclear Information System (INIS)
Yang, Jongmin; Hwang, Jinyul; Sung, Hyung Jin
2016-01-01
Highlights: • The structural organization of the quiescent core region in a turbulent channel flow is explored. • The quiescent core region is the uniform momentum zone located at the center of the channel. • The boundary of the quiescent core region can be identified from the probability density function of the streamwise modal velocity. • The prograde and retrograde vortices form a counter-rotating vortex pair at the boundary of the core region. - Abstract: The structural organization of the quiescent core region in a turbulent channel flow was explored using direct numerical simulation data at Re_τ = 930. The quiescent core region is the uniform momentum zone located at the center of the channel, and contains the highest momentum with a low level of turbulence. The boundary of the quiescent core region can be identified from the probability density function of the streamwise modal velocity. The streamwise velocity changes abruptly near the boundary of the core region. The abrupt jump leads the increase of the velocity gradient, which is similar to the vorticity thickness of the laminar superlayer at the turbulent/non-turbulent interface. The strong shear induced from the abrupt change is originated from the vortical structure lying on the boundary of the core region. The spanwise population densities of the prograde and retrograde vortices have a local maximum near the boundary of the core region. The prograde vortex dominantly contributes to the total mean shear near the core boundary and the contribution to the total mean shear rapidly decreases within the core region. The prograde and retrograde vortices form a counter-rotating vortex pair at the boundary of the core region associated with the nibbling mechanism. The boundary of the core region contains large-scale concave and convex features. The concave (convex) core interface is organized by the negative-u (positive-u) regions which induce the ejections (sweeps) around the core boundary.
Statistical properties of chaotic scattering with one open channel
International Nuclear Information System (INIS)
Izrajlev, F.M.; Saher, D.; Sokolov, V.V.
1993-01-01
The correspondence between statistical properties of decaying states and fluctuations in resonance scattering is studied in a statistical model with one open channel. The model is described by an ensemble of random nonhermitian matrices. The dependence of the correlation length on the coupling parameter both for the S-matrix and the cross-section is studied numerically. 37 refs., 7 figs
Secondary flow in sharp open-channel bends
Blanckaert, K.; De Vriend, H.J.
2004-01-01
Secondary currents are a characteristic feature of flow in open-channel bends. Besides the classical helical motion (centre-region cell), a weaker and smaller counter-rotating circulation cell (outer-bank cell) is often observed near the outer bank, which is believed to play an important role in
Entrainment at a sediment concentration interface in turbulent channel flow
Salinas, Jorge; Shringarpure, Mrugesh; Cantero, Mariano; Balachandar, S.
2016-11-01
In this work we address the role of turbulence on entrainment at a sediment concentration interface. This process can be conceived as the entrainment of sediment-free fluid into the bottom sediment-laden flow, or alternatively, as the entrainment of sediment into the top sediment-free flow. We have performed direct numerical simulations for fixed Reynolds and Schmidt numbers while varying the values of Richardson number and particle settling velocity. The analysis performed shows that the ability of the flow to pick up a given sediment size decreases with the distance from the bottom, and thus only fine enough sediment particles are entrained across the sediment concentration interface. For these cases, the concentration profiles evolve to a final steady state in good agreement with the well-known Rouse profile. The approach towards the Rouse profile happens through a transient self-similar state. Detailed analysis of the three dimensional structure of the sediment concentration interface shows the mechanisms by which sediment particles are lifted up by tongues of sediment-laden fluid with positive correlation between vertical velocity and sediment concentration. Finally, the mixing ability of the flow is addressed by monitoring the center of mass of the sediment-laden layer. With the support of ExxonMobil, NSF, ANPCyT, CONICET.
Intense structures of different momentum fluxes in turbulent channels
Osawa, Kosuke; Jiménez, Javier
2018-04-01
The effect of different definitions of the momentum flux on the properties of the coherent structures of the logarithmic region of wall-bounded turbulence is investigated by comparing the structures of intense tangential Reynolds stress with those of the alternative flux proposed in [Jimenez (2016) J. Fluid Mech. 809:585]. Despite the fairly different statistical properties of the two flux definitions, it is found that their intense structures show many similarities, such as the dominance of ‘wall-attached’ objects, and geometric self-similarity. However, the new structures are wider, although not taller, than the classical ones, and include both high- and low-momentum regions within the same object. It is concluded that they represent the same phenomenon as the classical group of a sweep, an ejection, and a roller, which should thus be considered as the fundamental coherent structure of the momentum flux. The present results suggest that the properties of these momentum structures are robust with respect to the definition of the fluxes.
Jiang, Zhou; Xia, Zhenhua; Shi, Yipeng; Chen, Shiyi
2018-04-01
A fully developed spanwise rotating turbulent channel flow has been numerically investigated utilizing large-eddy simulation. Our focus is to assess the performances of the dynamic variants of eddy viscosity models, including dynamic Vreman's model (DVM), dynamic wall adapting local eddy viscosity (DWALE) model, dynamic σ (Dσ ) model, and the dynamic volumetric strain-stretching (DVSS) model, in this canonical flow. The results with dynamic Smagorinsky model (DSM) and direct numerical simulations (DNS) are used as references. Our results show that the DVM has a wrong asymptotic behavior in the near wall region, while the other three models can correctly predict it. In the high rotation case, the DWALE can get reliable mean velocity profile, but the turbulence intensities in the wall-normal and spanwise directions show clear deviations from DNS data. DVSS exhibits poor predictions on both the mean velocity profile and turbulence intensities. In all three cases, Dσ performs the best.
Scaling of normalized mean energy and scalar dissipation rates in a turbulent channel flow
Abe, Hiroyuki; Antonia, Robert Anthony
2011-05-01
Non-dimensional parameters for the mean energy and scalar dissipation rates Cɛ and Cɛθ are examined using direct numerical simulation (DNS) data obtained in a fully developed turbulent channel flow with a passive scalar (Pr = 0.71) at several values of the Kármán (Reynolds) number h+. It is shown that Cɛ and Cɛθ are approximately equal in the near-equilibrium region (viz., y+ = 100 to y/h = 0.7) where the production and dissipation rates of either the turbulent kinetic energy or scalar variance are approximately equal and the magnitudes of the diffusion terms are negligibly small. The magnitudes of Cɛ and Cɛθ are about 2 and 1 in the logarithmic and outer regions, respectively, when h+ is sufficiently large. The former value is about the same for the channel, pipe, and turbulent boundary layer, reflecting the similarity between the mean velocity and temperature distributions among these three canonical flows. The latter value is, on the other hand, about twice as large as in homogeneous isotropic turbulence due to the existence of the large-scale u structures in the channel. The behaviour of Cɛ and Cɛθ impacts on turbulence modeling. In particular, the similarity between Cɛ and Cɛθ leads to a simple relation for the scalar variance to turbulent kinetic energy time-scale ratio, an important ingredient in the eddy diffusivity model. This similarity also yields a relation between the Taylor and Corrsin microscales and analogous relations, in terms of h+, for the Taylor microscale Reynolds number and Corrsin microscale Peclet number. This dependence is reasonably well supported by both the DNS data at small to moderate h+ and the experimental data of Comte-Bellot [Ph. D. thesis (University of Grenoble, 1963)] at larger h+. It does not however apply to a turbulent boundary layer where the mean energy dissipation rate, normalized on either wall or outer variables, is about 30% larger than for the channel flow.
Microfluidic mixing in a Y-junction open channel
Directory of Open Access Journals (Sweden)
Jue Nee Tan
2012-09-01
Full Text Available In the laminar regimes typical of microfluidic systems’, mixing is governed by molecular diffusion; however this process is slow in nature. Consequently, passive or active methods are usually sought for effective mixing. In this work, open fluidic channels will be investigated; these channels are bounded on all but one face by an air/fluid interface. Firstly, it will be shown that flow in open channels can merge at a Y-junction in a stable manner; hence two fluids can be brought into contact with each other. Secondly, the mixing of these two fluids will be studied. At high flow rates (>300 μl/min mixing occurs at the junction without need for additional intervention, this mixing is far swifter than can be expected from molecular diffusion. At lower flow rates, intervention is required. A major motivation for open fluidic channels is the ability to interact with the surrounding air environment; this feature is used to effect the desired mixing. It is shown that by blowing an air jet across the junction, shear stresses at the air/fluid interface causes a flow profile within the fluid inductive to rapid mixing of the fluids.
Modification of Turbulence Structures in a Channel Flow by Uniform Magnetic Fluxes
Lee, D.; Choi, H.; Kim, J.
1997-11-01
Effects of electromagnetic forcing on the near-wall turbulence are investigated by applying a uniform magnetic flux in a turbulent channel flow in the streamwise and spanwise directions, respectively. The base flow is a fully developed turbulent channel flow and the direct numerical simulation technique is used. The electromagnetic force induced from the magnetic fluxes reduces the intensity of the wall-layer structures and thus drag is significantly reduced. The wall-normal and spanwise velocity fluctuations and the Reynolds shear stress decrease with the increased magnetic flux in both directions. The streamwise velocity fluctuations increase with the streamwise magnetic flux, whereas they decrease with the spanwise magnetic flux. It is also shown that the spanwise magnetic flux is much more effective than the streamwise magnetic flux in reducing the skin-friction drag. Instantaneous Lorentz force vectors show that the flow motions by the near-wall vortices are directly inhibited by the spanwise magnetic flux, while they are less effectively inhibited by the streamwise magnetic flux. Other turbulence statistics that reveal the effects of the applied magnetic forcing will be presented. ^* Supported by KOSEF Contract No. 965-1008-003-2 and ONR Grant No. N00014-95-1-0352.
International Nuclear Information System (INIS)
Dey, Prasanta K.; Zikanov, Oleg
2012-01-01
Highlights: ► Turbulent passive scalar transport in an MHD flow in a channel is studied using DNS. ► Magnetic fields of wall-normal, spanwise, and streamwise orientations are considered. ► Magnetic fields suppress turbulent transport and modifies scalar distribution. ► The effect is particularly strong at wall-normal and spanwise magnetic fields. ► Decrease of Nusselt number is approximated by a linear function of magnetic interaction parameter. - Abstract: DNS of turbulent flow and passive scalar transport in a channel are conducted for the situation when the fluid is electrically conducting (for example, a liquid metal) and the flow is affected by an imposed magnetic field. The cases of wall-normal, spanwise, and streamwise orientation of the magnetic field are considered. As main results, we find that the magnetic fields, especially those in the wall-normal and spanwise directions, significantly reduce the turbulent scalar transport and modify the properties of the scalar distribution.
Effects of elevated line sources on turbulent mixing in channel flow
Nguyen, Quoc; Papavassiliou, Dimitrios
2016-11-01
Fluids mixing in turbulent flows has been studied extensively, due to the importance of this phenomena in nature and engineering. Convection effects along with motion of three-dimensional coherent structures in turbulent flow disperse a substance more efficiently than molecular diffusion does on its own. We present here, however, a study that explores the conditions under which turbulent mixing does not happen, when different substances are released into the flow field from different vertical locations. The study uses a method which combines Direct Numerical Simulation (DNS) with Lagrangian Scalar Tracking (LST) to simulate a turbulent channel flow and track the motion of passive scalars with different Schmidt numbers (Sc). The particles are released from several instantaneous line sources, ranging from the wall to the center region of the channel. The combined effects of mean velocity difference, molecular diffusion and near-wall coherent structures lead to the observation of different concentrations of particles downstream from the source. We then explore in details the conditions under which particles mixing would not happen. Results from numerical simulation at friction Reynolds number of 300 and 600 will be discussed and for Sc ranging from 0.1 to 2,400.
Heat transfer in initial region of a plane channel at different turbulence levels of inlet flow
International Nuclear Information System (INIS)
Sukomel, A.S.; Gutsev, D.F.; Velichko, V.I.
1976-01-01
Local heat transfer has been experimentally studied on the initial portion of the flat channel in the turbulent air flow. The channel measures 37.5 mm in height and 212.5 mm in width. The heat transfer measurements have been taken at inlet flow turbulence of epsilon 0 =0.7-0.8%. The charts are plotted showing variation of trannser with inlet and additional agitation of the flow. Critical values are found of the Reynolds number which are characteristic of the zones with various types of flow (laminar, transient and turbulent) at epsilon 0 =0.7-0.8%: Resub(crit 1) = 9.3x10sup(4), Resub(crit 2) = 2.9x10sup(5). With the increase of epsilon 0 up to 5% and above, the flow in the boundary layer becomes turbulent practically from the very beginning of the experimental portion. Considerable increase has been revealed of the heat transfer in this group of the experiments. At epsilon (>=) 5% the heat transfer grows up regularly
A model for the two-point velocity correlation function in turbulent channel flow
International Nuclear Information System (INIS)
Sahay, A.; Sreenivasan, K.R.
1996-01-01
A relatively simple analytical expression is presented to approximate the equal-time, two-point, double-velocity correlation function in turbulent channel flow. To assess the accuracy of the model, we perform the spectral decomposition of the integral operator having the model correlation function as its kernel. Comparisons of the empirical eigenvalues and eigenfunctions with those constructed from direct numerical simulations data show good agreement. copyright 1996 American Institute of Physics
Modified distribution parameter for churn-turbulent flows in large diameter channels
International Nuclear Information System (INIS)
Schlegel, J.P.; Macke, C.J.; Hibiki, T.; Ishii, M.
2013-01-01
Highlights: • Void fraction data collected in pipe sizes up to 0.304 m using impedance void meters. • Flow conditions extend to transition between churn-turbulent and annular flow. • Flow regime identification results agree with previous studies. • A new model for the distribution parameter in churn-turbulent flow is proposed. -- Abstract: Two phase flows in large diameter channels are important in a wide range of industrial applications, but especially in analysis of nuclear reactor safety for the prediction of BWR behavior and safety analysis in PWRs. To remedy an inability of current drift-flux models to accurately predict the void fraction in churn-turbulent flows in large diameter pipes, extensive experiments have been performed in pipes with diameters of 0.152 m, 0.203 m and 0.304 m to collect area-averaged void fraction data using electrical impedance void meters. The standard deviation and skewness of the impedance meter signal have been used to characterize the flow regime and confirm previous flow regime transition results. By treating churn-turbulent flow as a transition between cap-bubbly dispersed flow and annular separated flow and using a linear ramp, the distribution parameter has been modified for churn-turbulent flow. The modified distribution parameter has been evaluated through comparison of the void fraction predicted by the drift-flux model and the measured void fraction
Subgrid-scale models for large-eddy simulation of rotating turbulent channel flows
Silvis, Maurits H.; Bae, Hyunji Jane; Trias, F. Xavier; Abkar, Mahdi; Moin, Parviz; Verstappen, Roel
2017-11-01
We aim to design subgrid-scale models for large-eddy simulation of rotating turbulent flows. Rotating turbulent flows form a challenging test case for large-eddy simulation due to the presence of the Coriolis force. The Coriolis force conserves the total kinetic energy while transporting it from small to large scales of motion, leading to the formation of large-scale anisotropic flow structures. The Coriolis force may also cause partial flow laminarization and the occurrence of turbulent bursts. Many subgrid-scale models for large-eddy simulation are, however, primarily designed to parametrize the dissipative nature of turbulent flows, ignoring the specific characteristics of transport processes. We, therefore, propose a new subgrid-scale model that, in addition to the usual dissipative eddy viscosity term, contains a nondissipative nonlinear model term designed to capture transport processes, such as those due to rotation. We show that the addition of this nonlinear model term leads to improved predictions of the energy spectra of rotating homogeneous isotropic turbulence as well as of the Reynolds stress anisotropy in spanwise-rotating plane-channel flows. This work is financed by the Netherlands Organisation for Scientific Research (NWO) under Project Number 613.001.212.
Modified distribution parameter for churn-turbulent flows in large diameter channels
Energy Technology Data Exchange (ETDEWEB)
Schlegel, J.P., E-mail: jschlege@purdue.edu; Macke, C.J.; Hibiki, T.; Ishii, M.
2013-10-15
Highlights: • Void fraction data collected in pipe sizes up to 0.304 m using impedance void meters. • Flow conditions extend to transition between churn-turbulent and annular flow. • Flow regime identification results agree with previous studies. • A new model for the distribution parameter in churn-turbulent flow is proposed. -- Abstract: Two phase flows in large diameter channels are important in a wide range of industrial applications, but especially in analysis of nuclear reactor safety for the prediction of BWR behavior and safety analysis in PWRs. To remedy an inability of current drift-flux models to accurately predict the void fraction in churn-turbulent flows in large diameter pipes, extensive experiments have been performed in pipes with diameters of 0.152 m, 0.203 m and 0.304 m to collect area-averaged void fraction data using electrical impedance void meters. The standard deviation and skewness of the impedance meter signal have been used to characterize the flow regime and confirm previous flow regime transition results. By treating churn-turbulent flow as a transition between cap-bubbly dispersed flow and annular separated flow and using a linear ramp, the distribution parameter has been modified for churn-turbulent flow. The modified distribution parameter has been evaluated through comparison of the void fraction predicted by the drift-flux model and the measured void fraction.
Performance of BICM-based QAM-SIM OWC over gamma-gamma turbulence channels
Malik, Muhammad Talha
2015-05-01
We derive a series expression for the pair-wise error probability (PEP) of bit interleaved coded modulation (BICM)-based subcarrier intensity modulation (SIM) optical wireless communication (OWC) system employing M^{2}-ary quadrature amplitude modulation ( M^{2} -QAM) over the Gamma-Gamma turbulence channels. Using this expression, we develop an upper bound (UB) to predict the bit-error rate performance of such system. Simulation results are presented to verify the analytical results. We also develop an asymptotic UB which reveals that the diversity order depends on the smaller channel parameter and the free distance of the convolutional code. © 1997-2012 IEEE.
Low SNR Capacity of FSO Links over Gamma-Gamma Atmospheric Turbulence Channels
Benkhelifa, Fatma
2013-01-27
In this paper, we study the ergodic capacity of free space optical communication systems over Gamma-Gamma atmospheric turbulence fading channels with perfect channel state information at both the transmitter and the receiver. In our framework, we mainly focus on the low signal-to-noise ratio range and show that the ergodic capacity scales proportionally to SNR log^4(1/SNR). We show also that one-bit CSI feedback at the transmitter is enough to achieve this capacity using an on-o ff power control scheme.
Low SNR Capacity of FSO Links over Gamma-Gamma Atmospheric Turbulence Channels
Benkhelifa, Fatma
2013-02-23
In this paper, we study the ergodic capacity of free space optical communication systems over Gamma-Gamma atmospheric turbulence fading channels with perfect channel state information at both the transmitter and the receiver. In our framework, we mainly focus on the low signal-to-noise ratio range and show that the ergodic capacity scales proportionally to SNR log^4(1/SNR). We show also that one-bit CSI feedback at the transmitter is enough to achieve this capacity using an on-off power control scheme.
Low SNR Capacity of FSO Links over Gamma-Gamma Atmospheric Turbulence Channels
Benkhelifa, Fatma; Alouini, Mohamed-Slim; Rezki, Zouheir
2013-01-01
In this paper, we study the ergodic capacity of free space optical communication systems over Gamma-Gamma atmospheric turbulence fading channels with perfect channel state information at both the transmitter and the receiver. In our framework, we mainly focus on the low signal-to-noise ratio range and show that the ergodic capacity scales proportionally to SNR log^4(1/SNR). We show also that one-bit CSI feedback at the transmitter is enough to achieve this capacity using an on-off power control scheme.
International Nuclear Information System (INIS)
Goetzbach, G.
1977-10-01
For the simulation of non stationary, three-dimensional, turbulent flow- and temperature-fields in channel flows with constant properties a method is presented which is based on a finite difference scheme of the complete conservation equations for mass, momentum and enthalpie. The fluxes of momentum and heat within the grid cells are described by sub-grid scale models. The sub-grid scale model for momentum introduced here is for the first time applicable to small Reynolds-numbers, rather coarse grids, and channels with space dependent roughness distributions. (orig.) [de
Experimental investigation of turbulent flow in a channel with the backward-facing inclined step
Directory of Open Access Journals (Sweden)
Uruba Václav
2012-04-01
Full Text Available The work deals with the experimental investigation of turbulent flow in a closed channel with the backward-facing inclined step. Experiments were carried by means of the PIV optical measuring method in the channel of the rectangular cross-section in the inlet part and with inclined steps of the constant height H mm and various inclination angles for a wide range of the Reynolds number. The attention was paid especially to the separation region behind the step and to the relaxation of the shear layer after the reattachment in the outlet part of the channel. The dependence of the length of the separation region on the Reynolds number was obtained for various step angles. Optical measurements were completed by the measurement of static pressure distribution in the inlet and outlet part of the channel to estimate energy losses.
Alheadary, Wael Ghazy; Park, Kihong; Alouini, Mohamed-Slim
2016-01-01
In this paper, we derive the performances of optical wireless communication system utilizing adaptive subcarrier intensity modulation over the Malaga turbulent channel. More specifically, analytical closed-form solutions and asymptotic results
Alpha Channeling in Open-System Magnetic Devices
International Nuclear Information System (INIS)
Fisch, Nathaniel
2016-01-01
The Grant DE-SC0000736, Alpha Channeling in Open-System Magnetic Devices, is a continuation of the Grant DE-FG02-06ER54851, Alpha Channeling in Mirror Machines. In publications funded by DE-SC0000736, the grant DE-FG02-06ER54851 was actually credited. The key results obtained under Grant DE-SC0000736, Alpha Channeling in Open-System Magnetic Devices, appear in a series of publications. The earlier effort under DE-FG02- 06ER54851 was the subject of a previous Final Report. The theme of this later effort has been unusual confinement effects, or de-confinement effects, in open-field magnetic confinement devices. First, the possibilities in losing axisymmetry were explored. Then a number of issues in rotating plasma were addressed. Most importantly, a spinoff application to plasma separations was recognized, which also resulted in a provisional patent application. (That provisional patent application, however, was not pursued further.) Alpha channeling entails injecting waves into magnetically confined plasma to release energy from one particular ion while ejecting that ion. The ejection of the ion is actually a concomitant effect in releasing energy from the ion to the wave. In rotating plasma, there is the opportunity to store the energy in a radial electric field rather than in waves. In other words, the ejected alpha particle loses its energy to the radial potential, which in turn produces plasma rotation. This is a very useful effect, since producing radial electric fields by other means are technologically more difficult. In fact, one can heat ions, and then eject them, to produce the desired radial field. In each case, there is a separation effect of different ions, which generalizes the original alpha-channeling concept of separating alpha ash from hydrogen. In a further generalization of the separation concept, a double-well filter represents a new way to produce high-throughput separations of ions, potentially useful for nuclear waste remediation.
Opening of K+ channels by capacitive stimulation from silicon chip
Ulbrich, M. H.; Fromherz, P.
2005-10-01
The development of stable neuroelectronic systems requires a stimulation of nerve cells from semiconductor devices without electrochemical effects at the electrolyte/solid interface and without damage of the cell membrane. The interaction must rely on a reversible opening of voltage-gated ion channels by capacitive coupling. In a proof-of-principle experiment, we demonstrate that Kv1.3 potassium channels expressed in HEK293 cells can be opened from an electrolyte/oxide/silicon (EOS) capacitor. A sufficient strength of electrical coupling is achieved by insulating silicon with a thin film of TiO2 to achieve a high capacitance and by removing NaCl from the electrolyte to enhance the resistance of the cell-chip contact. When a decaying voltage ramp is applied to the EOS capacitor, an outward current through the attached cell membrane is observed that is specific for Kv1.3 channels. An open probability up to fifty percent is estimated by comparison with a numerical simulation of the cell-chip contact.
RANS Modeling of Stably Stratified Turbulent Boundary Layer Flows in OpenFOAM®
Directory of Open Access Journals (Sweden)
Wilson Jordan M.
2015-01-01
Full Text Available Quantifying mixing processes relating to the transport of heat, momentum, and scalar quantities of stably stratified turbulent geophysical flows remains a substantial task. In a stably stratified flow, such as the stable atmospheric boundary layer (SABL, buoyancy forces have a significant impact on the flow characteristics. This study investigates constant and stability-dependent turbulent Prandtl number (Prt formulations linking the turbulent viscosity (νt and diffusivity (κt for modeling applications of boundary layer flows. Numerical simulations of plane Couette flow and pressure-driven channel flow are performed using the Reynolds-averaged Navier-Stokes (RANS framework with the standard k-ε turbulence model. Results are compared with DNS data to evaluate model efficacy for predicting mean velocity and density fields. In channel flow simulations, a Prandtl number formulation for wall-bounded flows is introduced to alleviate overmixing of the mean density field. This research reveals that appropriate specification of Prt can improve predictions of stably stratified turbulent boundary layer flows.
Flow model for open-channel reach or network
Schaffranek, R.W.
1987-01-01
Formulation of a one-dimensional model for simulating unsteady flow in a single open-channel reach or in a network of interconnected channels is presented. The model is both general and flexible in that it can be used to simulate a wide range of flow conditions for various channel configurations. It is based on a four-point (box), implicit, finite-difference approximation of the governing nonlinear flow equations with user-definable weighting coefficients to permit varying the solution scheme from box-centered to fully forward. Unique transformation equations are formulated that permit correlation of the unknowns at the extremities of the channels, thereby reducing coefficient matrix and execution time requirements. Discharges and water-surface elevations computed at intermediate locations within a channel are determined following solution of the transformation equations. The matrix of transformation and boundary-condition equations is solved by Gauss elimination using maximum pivot strategy. Two diverse applications of the model are presented to illustrate its broad utility. (USGS)
Direct numerical simulation of turbulent channel flow over a liquid-infused micro-grooved surface
Chang, Jaehee; Jung, Taeyong; Choi, Haecheon; Kim, John
2016-11-01
Recently a superhydrophobic surface has drawn much attention as a passive device to achieve high drag reduction. Despite the high performance promised at ideal conditions, maintaining the interface in real flow conditions is an intractable problem. A non-wetting surface, known as the slippery liquid-infused porous surface (SLIPS) or the lubricant-impregnated surface (LIS), has shown a potential for drag reduction, as the working fluid slips at the interface but cannot penetrate into the lubricant layer. In the present study, we perform direct numerical simulation of turbulent channel flow over a liquid-infused micro-grooved surface to investigate the effects of this surface on the interfacial slip and drag reduction. The flow rate of water is maintained constant corresponding to Reτ 180 in a fully developed turbulent channel flow, and the lubricant layer is shear-driven by the turbulent water flow. The lubricant layer is also simulated with the assumption that the interface is flat (i.e. the surface tension effect is neglected). The solid substrate in which the lubricant is infused is modelled as straight ridges using an immersed boundary method. DNS results show that drag reduction by the liquid-infused surface is highly dependent on the viscosity of the lubricant.
Bakosi, J.; Franzese, P.; Boybeyi, Z.
2007-11-01
Dispersion of a passive scalar from concentrated sources in fully developed turbulent channel flow is studied with the probability density function (PDF) method. The joint PDF of velocity, turbulent frequency and scalar concentration is represented by a large number of Lagrangian particles. A stochastic near-wall PDF model combines the generalized Langevin model of Haworth and Pope [Phys. Fluids 29, 387 (1986)] with Durbin's [J. Fluid Mech. 249, 465 (1993)] method of elliptic relaxation to provide a mathematically exact treatment of convective and viscous transport with a nonlocal representation of the near-wall Reynolds stress anisotropy. The presence of walls is incorporated through the imposition of no-slip and impermeability conditions on particles without the use of damping or wall-functions. Information on the turbulent time scale is supplied by the gamma-distribution model of van Slooten et al. [Phys. Fluids 10, 246 (1998)]. Two different micromixing models are compared that incorporate the effect of small scale mixing on the transported scalar: the widely used interaction by exchange with the mean and the interaction by exchange with the conditional mean model. Single-point velocity and concentration statistics are compared to direct numerical simulation and experimental data at Reτ=1080 based on the friction velocity and the channel half width. The joint model accurately reproduces a wide variety of conditional and unconditional statistics in both physical and composition space.
On the Capacity of FSO Links over Gamma-Gamma Atmospheric Turbulence Channels Using OOK Signaling
Directory of Open Access Journals (Sweden)
Antonio García-Zambrana
2010-01-01
Full Text Available A new upper bound on the capacity of power- and bandwidth-constrained optical wireless links over gamma-gamma atmospheric turbulence channels with intensity modulation and direct detection is derived when on-off keying (OOK formats are used. In this free-space optical (FSO scenario, unlike previous capacity bounds derived from the classic capacity of the well-known additive white Gaussian noise (AWGN channel with uniform input distribution, a new closed-form upper bound on the capacity is found by bounding the mutual information subject to an average optical power constraint and not only to an average electrical power constraint, showing the fact that the input distribution that maximizes the mutual information varies with the turbulence strength and the signal-to-noise ratio (SNR. Additionally, it is shown that an increase of the peak-to-average optical power ratio (PAOPR provides higher capacity values. Simulation results for the mutual information are further demonstrated to confirm the analytical results under several turbulence conditions.
Experimental study of transition from laminar to turbulent flow in vertical narrow channel
International Nuclear Information System (INIS)
Wang Chang; Gao Puzhen; Wang Zhanwei; Tan Sichao
2012-01-01
Highlights: ► The effect of wall heating on the laminar to turbulent transition is experimentally studied. ► The flow characteristic demonstrates that heating leads to the delay of transition from laminar to turbulent regimes. ► The heat transfer characteristics also indicates that heating leads to the delay of flow regime transition. - Abstract: Experimental investigation of flow and heat transfer characteristics of a vertical narrow channel with uniform heat flux condition are conducted to analysis the effect of wall heating on the laminar to turbulent transition. The friction factor in the heating condition is compared with that in the adiabatic condition and the results show that wall heating leads to the delay of laminar to turbulent transition. In addition, the heat transfer characteristic indicates that the critical Reynolds number at the point of laminar flow breakdown increases with the increase of fluid temperature difference, and the local Nusselt number at the point of laminar breakdown increases with the increase of the inlet Reynolds number. The analyses of the flow and heat transfer characteristics both indicate that the heating has a stabilizing effect on the water flow at present experimental scale.
International Nuclear Information System (INIS)
Joong Hun Bae; Jung Yul Yoo; Haecheon Choi
2005-01-01
Full text of publication follows: The influence of variable fluid property on turbulent convective heat transfer is investigated using direct numerical simulations. We consider thermally-developing flows of air and supercritical-pressure CO 2 in a vertical annular channel where the inner wall is heated with a constant heat flux and the outer wall is insulated. Turbulence statistics show that the heat and momentum transport characteristics of variable-property flows are significantly different from those of constant-property flows. The difference is mainly caused by the spatial and temporal variations of fluid density. The non-uniform density distribution causes fluid particles to be accelerated either by expansion or buoyancy force, while the temporal density fluctuations change the heat and momentum transfer via transport of turbulent mass flux, ρ'u' i . Both effects of the spatial and temporal variations of density are shown to be important in the analysis of turbulent convective heat transfer for supercritical-pressure fluids. For variable-property heated air flows, however, the effect of temporal density fluctuations can be neglected at low Mach number, which is in good accordance with the Morkovin's hypothesis. (authors)
Kang, Seokkoo; Yang, Xiaolei; Sotiropoulos, Fotis
2012-11-01
While a considerable amount of work has focused on studying the effects and performance of wind farms, very little is known about the performance of hydrokinetic turbine arrays in open channels. Unlike large wind farms, where the vertical fluxes of momentum and energy from the atmospheric boundary layer comprise the main transport mechanisms, the presence of free surface in hydrokinetic turbine arrays inhibits vertical transport. To explore this fundamental difference between wind and hydrokinetic turbine arrays, we carry out LES with the actuator disk model to systematically investigate various layouts of hydrokinetic turbine arrays mounted on the bed of a straight open channel with fully-developed turbulent flow fed at the channel inlet. Mean flow quantities and turbulence statistics within and downstream of the arrays will be analyzed and the effect of the turbine arrays as means for increasing the effective roughness of the channel bed will be extensively discussed. This work was supported by Initiative for Renewable Energy & the Environment (IREE) (Grant No. RO-0004-12), and computational resources were provided by Minnesota Supercomputing Institute.
Outer region scaling using the freestream velocity for nonuniform open channel flow over gravel
Stewart, Robert L.; Fox, James F.
2017-06-01
The theoretical basis for outer region scaling using the freestream velocity for nonuniform open channel flows over gravel is derived and tested for the first time. Owing to the gradual expansion of the flow within the nonuniform case presented, it is hypothesized that the flow can be defined as an equilibrium turbulent boundary layer using the asymptotic invariance principle. The hypothesis is supported using similarity analysis to derive a solution, followed by further testing with experimental datasets. For the latter, 38 newly collected experimental velocity profiles across three nonuniform flows over gravel in a hydraulic flume are tested as are 43 velocity profiles previously published in seven peer-reviewed journal papers that focused on fluid mechanics of nonuniform open channel over gravel. The findings support the nonuniform flows as equilibrium defined by the asymptotic invariance principle, which is reflective of the consistency of the turbulent structure's form and function within the expanding flow. However, roughness impacts the flow structure when comparing across the published experimental datasets. As a secondary objective, we show how previously published mixed scales can be used to assist with freestream velocity scaling of the velocity deficit and thus empirically account for the roughness effects that extend into the outer region of the flow. One broader finding of this study is providing the theoretical context to relax the use of the elusive friction velocity when scaling nonuniform flows in gravel bed rivers; and instead to apply the freestream velocity. A second broader finding highlighted by our results is that scaling of nonuniform flow in gravel bed rivers is still not fully resolved theoretically since mixed scaling relies to some degree on empiricism. As researchers resolve the form and function of macroturbulence in the outer region, we hope to see the closing of this research gap.
Implementation of k-kL-omega turbulence model for compressible flow into OpenFOAM
Czech Academy of Sciences Publication Activity Database
Kožíšek, Martin; Fürst, J.; Příhoda, Jaromír; Doerffer, P.
2016-01-01
Roč. 821, Januar (2016), s. 63-69 ISSN 1662-7482 R&D Projects: GA ČR GAP101/12/1271; GA TA ČR(CZ) TA03020277 Institutional support: RVO:61388998 Keywords : CFD * openFOAM * RANS * transition * turbulence Subject RIV: BK - Fluid Dynamics
Directory of Open Access Journals (Sweden)
Xuan Wu
2013-01-01
Full Text Available Direct numerical simulation has been performed to study a polymer drag-reducing channel flow by using a discrete-element model. And then, wavelet analyses are employed to investigate the multiresolution characteristics of velocity components based on DNS data. Wavelet decomposition is applied to decompose velocity fluctuation time series into ten different frequency components including approximate component and detailed components, which show more regular intermittency and burst events in drag-reducing flow. The energy contribution, intermittent factor, and intermittent energy are calculated to investigate characteristics of different frequency components. The results indicate that energy contributions of different frequency components are redistributed by polymer additives. The energy contribution of streamwise approximate component in drag-reducing flow is up to 82%, much more than 25% in the Newtonian flow. Feature of turbulent multiscale structures is shown intuitively by continuous wavelet transform, verifying that turbulent structures become much more regular in drag-reducing flow.
Generalisation of two-layer turbulent model for passive cooling in a channel
International Nuclear Information System (INIS)
Bennacer, R.; Hammami, T.; Mohamad, A.A.; Beji, H.
2003-01-01
Turbulent natural convection still under improvement and no perfect compromise exist. The near wall region modelisation poses numerical difficulties and current modeling are either expensive or lack universality. Uncertainness in evaluating the good heat transfer rate can be catastrophically in causing local overheat and materials destruction which can be of heavy consequence as cooling nuclear component (rodes). Using the recent DNS done on natural convection flow in an infinite channel differentially heated for (10 4 6 ) a scaling analysis is developed and a one-equation near-wall turbulence model is deduced (inner layer). The inner model is coupled with a Low Reynolds Model (LRM) in the outer region (second layer) and applied to calculate natural flow for different Ra numbers. It yields good performance, computation time reduction and much better heat transfer prediction compared to the diffusive Jones Launder LRM. The efficiency is tested in one-dimensional and two-dimensional case. (author)
Three-dimensional numerical simulations of turbulent cavitating flow in a rectangular channel
Iben, Uwe; Makhnov, Andrei; Schmidt, Alexander
2018-05-01
Cavitation is a phenomenon of formation of bubbles (cavities) in liquid as a result of pressure drop. Cavitation plays an important role in a wide range of applications. For example, cavitation is one of the key problems of design and manufacturing of pumps, hydraulic turbines, ship's propellers, etc. Special attention is paid to cavitation erosion and to performance degradation of hydraulic devices (noise, fluctuations of the mass flow rate, etc.) caused by the formation of a two-phase system with an increased compressibility. Therefore, development of a model to predict cavitation inception and collapse of cavities in high-speed turbulent flows is an important fundamental and applied task. To test the algorithm three-dimensional simulations of turbulent flow of a cavitating liquid in a rectangular channel have been conducted. The obtained results demonstrate the efficiency and robustness of the formulated model and the algorithm.
Temperature fluctuations in fully-developed turbulent channel flow with heated upper wall
Bahri, Carla; Mueller, Michael; Hultmark, Marcus
2013-11-01
The interactions and scaling differences between the velocity field and temperature field in a wall-bounded turbulent flow are investigated. In particular, a fully developed turbulent channel flow perturbed by a step change in the wall temperature is considered with a focus on the details of the developing thermal boundary layer. For this specific study, temperature acts as a passive scalar, having no dynamical effect on the flow. A combination of experimental investigation and direct numerical simulation (DNS) is presented. Velocity and temperature data are acquired with high accuracy where, the flow is allowed to reach a fully-developed state before encountering a heated upper wall at constant temperature. The experimental data is compared with DNS data where simulations of the same configuration are conducted.
Guo, Ying; Xie, Cailang; Liao, Qin; Zhao, Wei; Zeng, Guihua; Huang, Duan
2017-08-01
The survival of Gaussian quantum states in a turbulent atmospheric channel is of crucial importance in free-space continuous-variable (CV) quantum key distribution (QKD), in which the transmission coefficient will fluctuate in time, thus resulting in non-Gaussian quantum states. Different from quantum hacking of the imperfections of practical devices, here we propose a different type of attack by exploiting the security loopholes that occur in a real lossy channel. Under a turbulent atmospheric environment, the Gaussian states are inevitably afflicted by decoherence, which would cause a degradation of the transmitted entanglement. Therefore, an eavesdropper can perform an intercept-resend attack by applying an entanglement-distillation operation on the transmitted non-Gaussian mixed states, which allows the eavesdropper to bias the estimation of the parameters and renders the final keys shared between the legitimate parties insecure. Our proposal highlights the practical CV QKD vulnerabilities with free-space quantum channels, including the satellite-to-earth links, ground-to-ground links, and a link from moving objects to ground stations.
Flow topology of rare back flow events and critical points in turbulent channels and toroidal pipes
Chin, C.; Vinuesa, R.; Örlü, R.; Cardesa, J. I.; Noorani, A.; Schlatter, P.; Chong, M. S.
2018-04-01
A study of the back flow events and critical points in the flow through a toroidal pipe at friction Reynolds number Re τ ≈ 650 is performed and compared with the results in a turbulent channel flow at Re τ ≈ 934. The statistics and topological properties of the back flow events are analysed and discussed. Conditionally-averaged flow fields in the vicinity of the back flow event are obtained, and the results for the torus show a similar streamwise wall-shear stress topology which varies considerably for the spanwise wall-shear stress when compared to the channel flow. The comparison between the toroidal pipe and channel flows also shows fewer back flow events and critical points in the torus. This cannot be solely attributed to differences in Reynolds number, but is a clear effect of the secondary flow present in the toroidal pipe. A possible mechanism is the effect of the secondary flow present in the torus, which convects momentum from the inner to the outer bend through the core of the pipe, and back from the outer to the inner bend through the pipe walls. In the region around the critical points, the skin-friction streamlines and vorticity lines exhibit similar flow characteristics with a node and saddle pair for both flows. These results indicate that back flow events and critical points are genuine features of wall-bounded turbulence, and are not artifacts of specific boundary or inflow conditions in simulations and/or measurement uncertainties in experiments.
Energy Technology Data Exchange (ETDEWEB)
Wu Hong [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, Beihang University, Beijing 100191 (China); Wang Jiao, E-mail: wangjiao@sjp.buaa.edu.cn [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, Beihang University, Beijing 100191 (China); Tao Zhi [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, Beihang University, Beijing 100191 (China)
2011-12-15
Highlights: Black-Right-Pointing-Pointer A double MRT-LBM is used to study heat transfer in turbulent channel flow. Black-Right-Pointing-Pointer Turbulent Pr is modeled by dynamic subgrid scale model. Black-Right-Pointing-Pointer Temperature gradients are calculated by the non-equilibrium temperature distribution moments. - Abstract: In this paper, a large eddy simulation based on the lattice Boltzmann framework is carried out to simulate the heat transfer in a turbulent channel flow, in which the temperature can be regarded as a passive scalar. A double multiple relaxation time (DMRT) thermal lattice Boltzmann model is employed. While applying DMRT, a multiple relaxation time D3Q19 model is used to simulate the flow field, and a multiple relaxation time D3Q7 model is used to simulate the temperature field. The dynamic subgrid stress model, in which the turbulent eddy viscosity and the turbulent Prandtl number are dynamically computed, is integrated to describe the subgrid effect. Not only the strain rate but also the temperature gradient is calculated locally by the non-equilibrium moments. The Reynolds number based on the shear velocity and channel half height is 180. The molecular Prandtl numbers are set to be 0.025 and 0.71. Statistical quantities, such as the average velocity, average temperature, Reynolds stress, root mean square (RMS) velocity fluctuations, RMS temperature and turbulent heat flux are obtained and compared with the available data. The results demonstrate great reliability of DMRT-LES in studying turbulence.
On the low SNR capacity of log-normal turbulence channels with full CSI
Benkhelifa, Fatma; Tall, Abdoulaye; Rezki, Zouheir; Alouini, Mohamed-Slim
2014-01-01
In this paper, we characterize the low signal-To-noise ratio (SNR) capacity of wireless links undergoing the log-normal turbulence when the channel state information (CSI) is perfectly known at both the transmitter and the receiver. We derive a closed form asymptotic expression of the capacity and we show that it scales essentially as λ SNR where λ is the water-filling level satisfying the power constraint. An asymptotically closed-form expression of λ is also provided. Using this framework, we also propose an on-off power control scheme which is capacity-achieving in the low SNR regime.
On the low SNR capacity of log-normal turbulence channels with full CSI
Benkhelifa, Fatma
2014-09-01
In this paper, we characterize the low signal-To-noise ratio (SNR) capacity of wireless links undergoing the log-normal turbulence when the channel state information (CSI) is perfectly known at both the transmitter and the receiver. We derive a closed form asymptotic expression of the capacity and we show that it scales essentially as λ SNR where λ is the water-filling level satisfying the power constraint. An asymptotically closed-form expression of λ is also provided. Using this framework, we also propose an on-off power control scheme which is capacity-achieving in the low SNR regime.
Skin-friction drag reduction in turbulent channel flow based on streamwise shear control
International Nuclear Information System (INIS)
Kim, Jung Hoon; Lee, Jae Hwa
2017-01-01
Highlights: • We perform DNSs of fully developed turbulent channel flows to explore an active flow control concept using streamwise velocity shear control at the wall. • The structural spacing and wall amplitude parameters are systematically changed to achieve a high-efficient drag reduction rate for longitudinal control surface. • Significant drag reduction is observed with an increase in the two parameters with an accompanying reduction of the Reynolds stresses and vorticity fluctuations. • The generation and evolution of the turbulent vortices in the absence of velocity shear and how they contribute to DR have been examined. - Abstract: It is known that stretching and intensification of a hairpin vortex by mean shear play an important role to create a hairpin vortex packet, which generates the large Reynolds shear stress associated with skin-friction drag in wall-bounded turbulent flows. In order to suppress the mean shear at the wall for high efficient drag reduction (DR), in the present study, we explore an active flow control concept using streamwise shear control (SSC) at the wall. The longitudinal control surface is periodically spanwise-arranged with no-control surface while varying the structural spacing, and an amplitude parameter for imposing the strength of the actuating streamwise velocity at the wall is introduced to further enhance the skin-friction DR. Significant DR is observed with an increase in the two parameters with an accompanying reduction of the Reynolds stresses and vorticity fluctuations, although a further increase in the parameters amplifies the turbulence activity in the near-wall region. In order to study the direct relationship between turbulent vortical structures and DR under the SSC, temporal evolution with initial eddies extracted by conditional averages for Reynolds-stress-maximizing Q2 events are examined. It is shown that the generation of new vortices is dramatically inhibited with an increase in the parameters
A Numerical Study of Non-hydrostatic Shallow Flows in Open Channels
Zerihun, Yebegaeshet T.
2017-06-01
The flow field of many practical open channel flow problems, e.g. flow over natural bed forms or hydraulic structures, is characterised by curved streamlines that result in a non-hydrostatic pressure distribution. The essential vertical details of such a flow field need to be accounted for, so as to be able to treat the complex transition between hydrostatic and non-hydrostatic flow regimes. Apparently, the shallow-water equations, which assume a mild longitudinal slope and negligible vertical acceleration, are inappropriate to analyse these types of problems. Besides, most of the current Boussinesq-type models do not consider the effects of turbulence. A novel approach, stemming from the vertical integration of the Reynolds-averaged Navier-Stokes equations, is applied herein to develop a non-hydrostatic model which includes terms accounting for the effective stresses arising from the turbulent characteristics of the flow. The feasibility of the proposed model is examined by simulating flow situations that involve non-hydrostatic pressure and/or nonuniform velocity distributions. The computational results for free-surface and bed pressure profiles exhibit good correlations with experimental data, demonstrating that the present model is capable of simulating the salient features of free-surface flows over sharply-curved overflow structures and rigid-bed dunes.
Effect of aspect ratio on the laminar-to-turbulent transition in rectangular channel
International Nuclear Information System (INIS)
Wang Chang; Gao Puzhen; Tan Sichao; Xu Chao
2012-01-01
Highlights: ► Effect of aspect ratio on the transition Reynolds number in rectangular channel is studied. ► Prediction correlation for transition Reynolds number is proposed. ► The initiation location of flow transition is studied. - Abstract: The critical Reynolds number of the laminar-to-turbulent transition in the rectangular channel is investigated based on the energy gradient method. The results show that the critical Reynolds number decreases with the increasing aspect ratio. However, the relative location of laminar breakdown does not migrate significantly with the variation of the aspect ratio. In addition, a theoretical correlation as a function of the aspect ratio is proposed to calculate the transition Reynolds number, and the predicted values are in good agreement with the experimental data obtained in the published literatures.
On the implicit density based OpenFOAM solver for turbulent compressible flows
Fürst, Jiří
The contribution deals with the development of coupled implicit density based solver for compressible flows in the framework of open source package OpenFOAM. However the standard distribution of OpenFOAM contains several ready-made segregated solvers for compressible flows, the performance of those solvers is rather week in the case of transonic flows. Therefore we extend the work of Shen [15] and we develop an implicit semi-coupled solver. The main flow field variables are updated using lower-upper symmetric Gauss-Seidel method (LU-SGS) whereas the turbulence model variables are updated using implicit Euler method.
Low-Rynolds number k-ε turbulence model for calculation of fast-reactor-channel flows
International Nuclear Information System (INIS)
Mikhin, V.I.
2000-01-01
For calculating the turbulent flows in the complex geometry channels typical for the nuclear reactor installation elements the low-Reynolds-number k-ε turbulence model with the model functions not containing the spatial coordinate like y + is proposed. Such spatial coordinate is usually used for modeling the turbulence near the wall correctly. The model completed on the developed flow of the non-viscous incompressible liquid in the plane channel correctly describes the transition from the laminar regime to the turbulent one. The calculated skin friction coefficients obey the well-known Dean and Zarbi - Reynolds laws. The mean velocity distributions are close to that obtained from the empirical three-layer Karman model. (author)
Aarthi, G.; Ramachandra Reddy, G.
2018-03-01
In our paper, the impact of adaptive transmission schemes: (i) optimal rate adaptation (ORA) and (ii) channel inversion with fixed rate (CIFR) on the average spectral efficiency (ASE) are explored for free-space optical (FSO) communications with On-Off Keying (OOK), Polarization shift keying (POLSK), and Coherent optical wireless communication (Coherent OWC) systems under different turbulence regimes. Further to enhance the ASE we have incorporated aperture averaging effects along with the above adaptive schemes. The results indicate that ORA adaptation scheme has the advantage of improving the ASE performance compared with CIFR under moderate and strong turbulence regime. The coherent OWC system with ORA excels the other modulation schemes and could achieve ASE performance of 49.8 bits/s/Hz at the average transmitted optical power of 6 dBm under strong turbulence. By adding aperture averaging effect we could achieve an ASE of 50.5 bits/s/Hz under the same conditions. This makes ORA with Coherent OWC modulation as a favorable candidate for improving the ASE of the FSO communication system.
Aghaei Jouybari, Mostafa; Yuan, Junlin
2017-11-01
Direct numerical simulations of turbulent channel flows are carried out over two surfaces: a synthesized sand-grain surface and a realistic turbine roughness that is characterized by more prominent large-scale surface features. To separate the effects of wall-normal variation of the roughness area fraction from the (true) variation of flow statistics, the governing equations are area-averaged using intrinsic averaging, contrary to the usually practice based on the total area (i.e., superficial averaging). Additional terms appear in the mean-momentum equation resulted from the wall-normal variation of the solid fraction and play a role in the near-wall balance. Results from surfaces with a step solidity function (e.g., cubes) will also be discussed. Compared to the sand grains, the turbine surface generates stronger form-induced fluctuations, despite weaker dispersive shear stress. This is associated with more significant form-induced productions (comparable to shear production) in Reynolds stress budgets, weaker pressure work, and, consequently, more anisotropic redistribution of turbulent kinetic energy in the roughness sublayer, which potentially leads to different turbulent responses between the two surfaces in non-equilibrium flows.
Turbulence Measurements from a Moored Platform at Mid-Depth in a Swift Tidal Channel
Hay, Alex; Lueck, Rolf; Wolk, Fabian; McMillan, Justine
2014-05-01
Results are presented from a turbulence experiment with a 3-m long streamlined floatation body, instrumented with velocity shear probes, fast-response thermistors, a 1 MHz Acoustic Doppler Current Profiler (AD2CP), and an Acoustic Doppler Velocimeter (ADV). The system was deployed over seven tidal cycles at mid-depth in a 30-m deep tidal channel in the lower Bay of Fundy, Canada. Peak flow speeds exceeded 2 m s-1, and while 10-min time scale average speeds were similar between ebb and flood, the variances were markedly higher during flood. Turbulent kinetic energy (TKE) dissipation rates measured with the shear probes exhibit a pronounced flood/ebb contrast: O(10-4) W kg-1 peak values during flood, but lower by an order of magnitude during ebb. Dissipation rates follow u3 scaling over a wide range of flow speeds between 0.5 and 2.5 m s-1. Below 0.5 m s-1 an asymmetry in the mounting arrangement caused the floatation body to pitch upward, biasing the measured dissipation values high. The ADV on the platform registered mean speed - used to implement Taylor's hypothesis - which was corroborated with the platform-mounted ADCP. Additional ADCPs were also deployed on a nearby bottom pod, sampling at turbulence resolving rates - up to 8 Hz. Comparisons between the shear probe and acoustic estimates of the TKE spectrum and dissipation rate - at comparable depths - are presented.
Visualization of an air-water interface on superhydrophobic surfaces in turbulent channel flows
Kim, Hyunseok; Park, Hyungmin
2017-11-01
In the present study, three-dimensional deformation of air-water interface on superhydrophobic surfaces in turbulent channel flows at the Reynolds numbers of Re = 3000 and 10000 is measured with RICM (Reflection Interference Contrast Microscopy) technique. Two different types of roughness feature of circular hole and rectangular grate are considered, whose depth is 20 μm and diameter (or width) is varied between 20-200 μm. Since the air-water interface is always at de-pinned state at the considered condition, air-water interface shape and its sagging velocity is maintained to be almost constant as time goes one. In comparison with the previous results under the laminar flow, due to turbulent characteristics of the flow, sagging velocity is much faster. Based on the measured sagging profiles, a modified model to describe the air-water interface dynamics under turbulent flows is suggested. Supported by City of Seoul through Seoul Urban Data Science Laboratory Project (Grant No 0660-20170004) administered by SNU Big Data Institute.
Probability density function of a puff dispersing from the wall of a turbulent channel
Nguyen, Quoc; Papavassiliou, Dimitrios
2015-11-01
Study of dispersion of passive contaminants in turbulence has proved to be helpful in understanding fundamental heat and mass transfer phenomena. Many simulation and experimental works have been carried out to locate and track motions of scalar markers in a flow. One method is to combine Direct Numerical Simulation (DNS) and Lagrangian Scalar Tracking (LST) to record locations of markers. While this has proved to be useful, high computational cost remains a concern. In this study, we develop a model that could reproduce results obtained by DNS and LST for turbulent flow. Puffs of markers with different Schmidt numbers were released into a flow field at a frictional Reynolds number of 150. The point of release was at the channel wall, so that both diffusion and convection contribute to the puff dispersion pattern, defining different stages of dispersion. Based on outputs from DNS and LST, we seek the most suitable and feasible probability density function (PDF) that represents distribution of markers in the flow field. The PDF would play a significant role in predicting heat and mass transfer in wall turbulence, and would prove to be helpful where DNS and LST are not always available.
International Nuclear Information System (INIS)
De Marchis, M.; Napoli, E.
2012-01-01
Highlights: ► 3D irregular rough surfaces produce higher effects than those observed over 2D. ► Effective slope is a geometrical parameter representative of the roughness effects. ► 3D rough surfaces enhance the turbulence isotropization. ► 2D and 3D irregular roughness partially support the wall similarity. ► Irregular rough surfaces shear some features with regular rough walls. - Abstract: Wall-resolved Large Eddy Simulation of fully developed turbulent channel flows over two different rough surfaces is performed to investigate on the effects of irregular 2D and 3D roughness on the turbulence. The two geometries are obtained through the superimposition of sinusoidal functions having random amplitudes and different wave lengths. In the 2D configuration the irregular shape in the longitudinal direction is replicated in the transverse one, while in the 3D case the sinusoidal functions are generated both in streamwise and spanwise directions. Both channel walls are roughened in such a way as to obtain surfaces with statistically equivalent roughness height, but different shapes. In order to compare the turbulence properties over the two rough walls and to analyse the differences with a smooth wall, the simulations are performed at the same Reynolds number Re τ = 395. The same mean roughness height h = 0.05δ (δ the half channel height) is used for the rough walls. The roughness function obtained with the 3D roughness is larger than in the 2D case, although the two walls share the same mean height. Thus, the considered irregular 3D roughness is more effective in reducing the flow velocity with respect to the 2D roughness, coherently with the literature results that identified a clear dependence of the roughness function on the effective slope (see ), higher in the generated 3D rough wall. The analysis of higher-order statistics shows that the effects of the roughness, independently on its two- or three-dimensional shape, are mainly confined in the inner
DNS of passive scalar transport in turbulent channel flow at high Schmidt numbers
International Nuclear Information System (INIS)
Schwertfirm, Florian; Manhart, Michael
2007-01-01
We perform DNS of passive scalar transport in low Reynolds number turbulent channel flow at Schmidt numbers up to Sc = 49. The high resolutions required to resolve the scalar concentration fields at such Schmidt numbers are achieved by a hierarchical algorithm in which only the scalar fields are solved on the grid dictated by the Batchelor scale. The velocity fields are solved on coarser grids and prolonged by a conservative interpolation to the fine-grid. The trends observed so far at lower Schmidt numbers Sc ≤ 10 are confirmed, i.e. the mean scalar gradient steepens at the wall with increasing Schmidt number, the peaks of turbulent quantities increase and move towards the wall. The instantaneous scalar fields show a dramatic change. Observable structures get longer and thinner which is connected with the occurrence of steeper gradients, but the wall concentrations penetrate less deeply into the plateau in the core of the channel. Our data shows that the thickness of the conductive sublayer, as defined by the intersection point of the linear with the logarithmic asymptote scales with Sc -0.29 . With this information it is possible to derive an expression for the dimensionless transfer coefficient K + which is only dependent on Sc and Re τ . This expression is in full accordance to previous results which demonstrates that the thickness of the conductive sublayer is the dominating quantity for the mean scalar profile
DNS of passive scalar transport in turbulent channel flow at high Schmidt numbers
Energy Technology Data Exchange (ETDEWEB)
Schwertfirm, Florian [Fachgebiet Hydromechanik, Technische Universitaet Muenchen, Arcisstr. 21, 80337 Muenchen (Germany); Manhart, Michael [Fachgebiet Hydromechanik, Technische Universitaet Muenchen, Arcisstr. 21, 80337 Muenchen (Germany)], E-mail: m.manhart@bv.tum.de
2007-12-15
We perform DNS of passive scalar transport in low Reynolds number turbulent channel flow at Schmidt numbers up to Sc = 49. The high resolutions required to resolve the scalar concentration fields at such Schmidt numbers are achieved by a hierarchical algorithm in which only the scalar fields are solved on the grid dictated by the Batchelor scale. The velocity fields are solved on coarser grids and prolonged by a conservative interpolation to the fine-grid. The trends observed so far at lower Schmidt numbers Sc {<=} 10 are confirmed, i.e. the mean scalar gradient steepens at the wall with increasing Schmidt number, the peaks of turbulent quantities increase and move towards the wall. The instantaneous scalar fields show a dramatic change. Observable structures get longer and thinner which is connected with the occurrence of steeper gradients, but the wall concentrations penetrate less deeply into the plateau in the core of the channel. Our data shows that the thickness of the conductive sublayer, as defined by the intersection point of the linear with the logarithmic asymptote scales with Sc{sup -0.29}. With this information it is possible to derive an expression for the dimensionless transfer coefficient K{sup +} which is only dependent on Sc and Re{sub {tau}}. This expression is in full accordance to previous results which demonstrates that the thickness of the conductive sublayer is the dominating quantity for the mean scalar profile.
Numerical simulation of turbulent liquid metal flows in plane channels and annuli
International Nuclear Information System (INIS)
Groetzbach, G.
1980-06-01
The method of direct numerical simulation is used to study heat transfer and statistical data for fully developed turbulent liquid metal flows in plane channels and annuli. Subgrid scale models using one transport equation account for the high wave-number turbulence not resolved by the finite difference grid. A special subgrid-scale heat flux model is deduced together with an approximative theory to calculate all model coefficients. This model can be applied on the total Peclet number range of technical liquid metal flows. Especially it can be used for very small Peclet numbers, where the results are independent on model parameters. A verification of the numerical results for liquid sodium and mercury flows is undertaken by the Nusselt number in plane channels and radial temperature and eddy conductivity profiles for annuli. The numerically determined Nusselt numbers for annuli indicate that many empirical correlations overestimate the influence of the ratio of radii. The numerical results for the eddy conductivity profiles may be used to remove these problems. The statistical properties of the simulated temperature fluctuations are within the wide scatter-band of experimental data. The numerical results give reasonable heat flux correlation coefficients which depend only weakly on the problem marking parameters. (orig.) [de
Djordjevic, Ivan B
2007-08-06
We describe a coded power-efficient transmission scheme based on repetition MIMO principle suitable for communication over the atmospheric turbulence channel, and determine its channel capacity. The proposed scheme employs the Q-ary pulse-position modulation. We further study how to approach the channel capacity limits using low-density parity-check (LDPC) codes. Component LDPC codes are designed using the concept of pairwise-balanced designs. Contrary to the several recent publications, bit-error rates and channel capacities are reported assuming non-ideal photodetection. The atmospheric turbulence channel is modeled using the Gamma-Gamma distribution function due to Al-Habash et al. Excellent bit-error rate performance improvement, over uncoded case, is found.
Energy Technology Data Exchange (ETDEWEB)
Lefeuvre, N; Djenidi, L [University of Newcastle, NSW Australia (Australia); Tardu, S, E-mail: nathan.lefeuvre@uon.edu.au [Laboratoire des Ecoulements Geophysiques et Industriels (LEGI), Grenoble (France)
2011-12-22
A numerical simulation is undertaken to investigate the transport of momentum and a passive scalar in a localised turbulence in a channel with a contraction. The simulation is carried out using a hybrid method which combines the lattice Boltzmann method (LBM, for the velocity field) and the energy equation (for the temperature field). The localised turbulence is generated through pulsed jets issued in the Poiseuille flow developing in the channel at a Reynolds number of about 1000. The aim of the study is twofold : i) determine effect of the contraction on the localised turbulence, and ii) study how the passive scalar behaves in such contracted localised turbulence. The contraction increase the averaged vorticity in the channel flow, which is accompanied by an increase in the averaged kinetic energy. The contraction also tends to reduce the Reynolds stresses. These results are similar those obtained in turbulent pipe flow with an axisymmetric contraction and in a turbulent boundary layer subjected to a favourable pressure gradient. However, it is found that the heat transport in the normal to the wall direction is more dramatically affected (reduced) than that in the direction of the flow.
Influence of a k-type Roughness on the Behaviour of Turbulence in an Unsteady Channel Flow
International Nuclear Information System (INIS)
Seddighi, Mehdi; He Shuisheng; Vardy, Alan E; Orlandi, Paolo
2011-01-01
Direct Numerical Simulations (DNS) have been carried out for a spatially fully developed turbulent channel flow with one smooth wall and one k-type rough-wall surface to study the influence of a square bar roughness on the behaviour of unsteady turbulent flow. The flow state under investigation is a uniform acceleration from an initially steady turbulent flow. Results are compared with simulations of flows in a smooth wall channel undergoing a similar acceleration, and with quasi-steady behaviour obtained using steady flow simulations. The turbulence in the wall region and the buffer layer of an accelerating flow with a rough wall shows strikingly different behaviour from that of corresponding flows with smooth walls. The characteristic long delays in the response of the streamwise turbulent velocity and the different behaviours of the three turbulent velocity components that are exhibited in smooth wall flows are not seen in the rough wall flow. This is attributed to different turbulent production mechanisms in the two types of flows. Important differences are also seen in the wall shear stress responses one wall is rough and when both walls are smooth.
Management of a Complex Open Channel Network During Flood Events
Franchini, M.; Valiani, A.; Schippa, L.; Mascellani, G.
2003-04-01
Most part of the area around Ferrara (Italy) is below the mean sea level and an extensive drainage system combined with several pump stations allows the use of this area for both urban development and industrial and agricultural activities. The three main channels of this hydraulic system constitute the Ferrara Inland Waterway (total length approximately 70 km), which connects the Po river near Ferrara to the sea. Because of the level difference between the upstream and dowstream ends of the waterway, three locks are located along it, each of them combined with a set of gates to control the water levels. During rainfall events, most of the water of the basin flows into the waterway and heavy precipitations sometimes cause flooding in several areas. This is due to the insufficiency of the channel network dimensions and an inadequate manual operation of the gates. This study presents a hydrological-hydraulic model for the entire Ferrara basin and a system of rules in order to operate the gates. In particular, their opening is designed to be regulated in real time by monitoring the water level in several sections along the channels. Besides flood peak attenuation, this operation strategy contributes also to the maintenance of a constant water level for irrigation and fluvial navigation during the dry periods. With reference to the flood event of May 1996, it is shown that this floodgate operation policy, unlike that which was actually adopted during that event, would lead to a significant flood peak attenuation, avoiding flooding in the area upstream of Ferrara.
Probability distribution functions of turbulence in seepage-affected alluvial channel
Energy Technology Data Exchange (ETDEWEB)
Sharma, Anurag; Kumar, Bimlesh, E-mail: anurag.sharma@iitg.ac.in, E-mail: bimk@iitg.ac.in [Department of Civil Engineering, Indian Institute of Technology Guwahati, 781039 (India)
2017-02-15
The present experimental study is carried out on the probability distribution functions (PDFs) of turbulent flow characteristics within near-bed-surface and away-from-bed surfaces for both no seepage and seepage flow. Laboratory experiments were conducted in the plane sand bed for no seepage (NS), 10% seepage (10%S) and 15% seepage (15%) cases. The experimental calculation of the PDFs of turbulent parameters such as Reynolds shear stress, velocity fluctuations, and bursting events is compared with theoretical expression obtained by Gram–Charlier (GC)-based exponential distribution. Experimental observations follow the computed PDF distributions for both no seepage and seepage cases. Jensen-Shannon divergence (JSD) method is used to measure the similarity between theoretical and experimental PDFs. The value of JSD for PDFs of velocity fluctuation lies between 0.0005 to 0.003 while the JSD value for PDFs of Reynolds shear stress varies between 0.001 to 0.006. Even with the application of seepage, the PDF distribution of bursting events, sweeps and ejections are well characterized by the exponential distribution of the GC series, except that a slight deflection of inward and outward interactions is observed which may be due to weaker events. The value of JSD for outward and inward interactions ranges from 0.0013 to 0.032, while the JSD value for sweep and ejection events varies between 0.0001 to 0.0025. The theoretical expression for the PDF of turbulent intensity is developed in the present study, which agrees well with the experimental observations and JSD lies between 0.007 and 0.015. The work presented is potentially applicable to the probability distribution of mobile-bed sediments in seepage-affected alluvial channels typically characterized by the various turbulent parameters. The purpose of PDF estimation from experimental data is that it provides a complete numerical description in the areas of turbulent flow either at a single or finite number of points
Bukhvostova, A.; Kuerten, J.G.M.; Geurts, B.J.; Grigoriadis, D.G.E.; Geurts, B.J.; Kuerten, H.; Fröhlich, J.; Armenio, V.
2018-01-01
In the field of multiphase systems droplet-laden channel flow presents a challenging topic not only because of how turbulent flow influences the mass and heat transfer properties of droplets but also how droplets modulate the flow. In this contribution we focus on droplet-laden turbulent channel
Sahu, M. K.; Pandey, K. M.; Chatterjee, S.
2018-05-01
In this two dimensional numerical investigation, small rectangular channel with right angled triangular protrusions in the bottom wall of test section is considered. A slot nozzle is placed at the middle of top wall of channel which impinges air normal to the protruded surface. A duct flow and nozzle flow combined to form cross flow which is investigated for heat transfer enhancement of protruded channel. The governing equations for continuity, momentum, energy along with SST k-ω turbulence model are solved with finite volume based Computational fluid dynamics code ANSYS FLUENT 14.0. The range of duct Reynolds number considered for this analysis is 8357 to 51760. The ratios of pitch of protrusion to height of duct considered are 0.5, 0.64 and 0.82. The ratios of height of protrusion to height of duct considered are 0.14, 0.23 and 0.29. The effect of duct Reynolds number, pitch and height of protrusion on thermal-hydraulic performance is studied under cross flow condition. It is found that heat transfer rate is more at relatively larger pitch and small pressure drop is found in case of low height of protrusion.
International Nuclear Information System (INIS)
Ishitsuka, Shota; Motozawa, Masaaki; Kawaguchi, Yasuo; Iwamoto, Kaoru; Ando, Hirotomo; Senda, Tetsuya
2011-01-01
Coherent vortex structure in turbulent drag-reducing channel flow with blown polymer solution from the wall was investigated. As a statistical analysis, we carried out Galilean decomposition, swirling strength and linear stochastic estimation of the PIV data obtained by the PIV measurement in x – y plane. Reynolds number based on bulk velocity and channel height was set to 40000. As a result, the angle of shear layer that cleared up by using Galilean decomposition becomes small in the drag-reducing flow. Q3 events were observed near the shear layer. In addition, as a result of linear stochastic estimation (LSE) based on swirling strength, we confirmed that the velocity under the vortex core is strong in the water flow. This result shows Q2 (ejection) are dominant in the water flow. However, in the drag-reducing flow with blown polymer solution, the velocity above the vortex core become strong, that is, Q4 (sweep) events are relatively strong around the vortex core. This is the result of Q4 events to come from the channel center region because the polymer solution does not exist in this region. The typical structure like this was observed in the drag -reducing flow with blown polymer solution from the wall.
Energy Technology Data Exchange (ETDEWEB)
Schumann, U
1973-10-01
Thesis. Submitted to Technische Hochschule, Karlsruhe (West Germany). A numerical difference scheme is described to simulate threedimensional, time- dependent, turbulent flows of incompressible fluids at high Reynolds numbers in a plane channel and in concertric annuli. Starting from the results of Deardorff, the NavierStokes equations, averaged over grid volumes, are integrated. For description of the subgrid scale motion a novel model has been developed which takes into account strongly inhomogeneous turbulence and grid volumes of unequal side lengths. The premises used in the model are described and discussed. Stability criteria are established for this method and for similar difference schemes. For computation of the pressure field the appropriate Poisson's equation is solved accurately, except for rounding errors, by Fast Fourier Transform. The procedure implemented in the TURBIT-1 program is used to simulate turbulent flows in a plane channel and an annulus of 5: 1 ratio of radii. For both types of flow, different cases are realized with a maximum number of grid volumes of 65536. For rather small grid volume numbers the numerical results are in good agreement with experimental values. Especially the velocity profile and the mean velocity fluctuations are computed with significantly better accuracy than in earlier, direct simulations. The energy --length-scale model and the pressurestrain correlation are used as examples to show that the method may be used successfully to evaluate the parameters of turbulence models. Earlier results are reviewed and proposals for future research are made. (auth)
International Nuclear Information System (INIS)
Ribeiro, T.; Scott, B.
2007-01-01
The field line connection of a tokamak sheared magnetic field has an important impact on turbulence, by ensuring a finite parallel dynamical response for every degree of freedom available in the system. This constitutes the main property which distinguishes closed from open flux surfaces in such a device. In the latter case, the poloidal periodicity of the magnetic field is replaced by a Debye sheath arising where the field lines strike the limiter/divertor plates. This is enough to break the field line connection constraint and allow the existence of convective cell modes, leading to a change in the character of the turbulence from drift wave- (closed flux surfaces) to interchange-type (open flux surfaces), and hence increasing the turbulent transport observed. Here we study the effect of changing the poloidal position of the limiter/divertor plates, using the three-dimensional electromagnetic gyrofluid turbulence code GEM, which has time dependently self consistent field aligned flux tube coordinates. For the closed flux surfaces, the globally consistent periodic boundary conditions are invoked, and for open flux surfaces a standard Debye sheath is used at the striking points. In particular, the use of two limiter positions simultaneously, top and bottom, is in order, such to allow a separation between the inboard and outboard sides of the tokamak. This highlights the differences between those two regions of the tokamak, where the curvature is either favourable (former) or unfavourable (latter), and further makes room for future experimental qualitative comparisons, for instance, on double null configurations of the tokamak ASDEX Upgrade. (author)
TIME-DEPENDENT TURBULENT HEATING OF OPEN FLUX TUBES IN THE CHROMOSPHERE, CORONA, AND SOLAR WIND
Energy Technology Data Exchange (ETDEWEB)
Woolsey, L. N.; Cranmer, S. R., E-mail: lwoolsey@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)
2015-10-01
We investigate several key questions of plasma heating in open-field regions of the corona that connect to the solar wind. We present results for a model of Alfvén-wave-driven turbulence for three typical open magnetic field structures: a polar coronal hole, an open flux tube neighboring an equatorial streamer, and an open flux tube near a strong-field active region. We compare time-steady, one-dimensional turbulent heating models against fully time-dependent three-dimensional reduced-magnetohydrodynamic modeling of BRAID. We find that the time-steady results agree well with time-averaged results from BRAID. The time dependence allows us to investigate the variability of the magnetic fluctuations and of the heating in the corona. The high-frequency tail of the power spectrum of fluctuations forms a power law whose exponent varies with height, and we discuss the possible physical explanation for this behavior. The variability in the heating rate is bursty and nanoflare-like in nature, and we analyze the amount of energy lost via dissipative heating in transient events throughout the simulation. The average energy in these events is 10{sup 21.91} erg, within the “picoflare” range, and many events reach classical “nanoflare” energies. We also estimated the multithermal distribution of temperatures that would result from the heating-rate variability, and found good agreement with observed widths of coronal differential emission measure distributions. The results of the modeling presented in this paper provide compelling evidence that turbulent heating in the solar atmosphere by Alfvén waves accelerates the solar wind in open flux tubes.
Statistical properties of wall shear stress fluctuations in turbulent channel flows
International Nuclear Information System (INIS)
Keirsbulck, L.; Labraga, L.; Gad-el-Hak, M.
2012-01-01
Highlights: ► Accurate measurements of instantaneous wall shear stress are conducted. ► LDA is used to measure near-wall streamwise velocity. ► Electrochemical probe is used to measure wall shear stress. ► Frequency response and non-uniform correction methods were used to provide an accurate, well-resolved wall-statistics database. ► Reynolds number dependency of the statistical wall quantities is investigated. - Abstract: Instantaneous velocity and wall shear stress measurements are conducted in a turbulent channel flow in the Kármán number range of Re τ = 74–400. A one-dimensional LDA system is used to measure the streamwise velocity fluctuations, and an electrochemical technique is utilized to measure the instantaneous wall shear stress. For the latter, frequency response and nonuniform correction methods are used to provide an accurate, well-resolved wall statistics database. The Reynolds number dependency of the statistical wall quantities is carefully investigated. The corrected relative wall shear stress fluctuations fit well with the best DNS data available and meet the need for clarification of the small discrepancy observed in the literature between the experimental and numerical results of such quantities. Higher-order statistics of the wall shear stress, spectra, and the turbulence kinetic energy budget at the wall are also investigated. The present paper shows that the electrochemical technique is a powerful experimental method for hydrodynamic studies involving highly unsteady flows. The study brings with it important consequences, especially in the context of the current debate regarding the appropriate scaling as well as the validation of new predictive models of near-wall turbulence.
Croze, Ottavio A; Sardina, Gaetano; Ahmed, Mansoor; Bees, Martin A; Brandt, Luca
2013-04-06
Shear flow significantly affects the transport of swimming algae in suspension. For example, viscous and gravitational torques bias bottom-heavy cells to swim towards regions of downwelling fluid (gyrotaxis). It is necessary to understand how such biases affect algal dispersion in natural and industrial flows, especially in view of growing interest in algal photobioreactors. Motivated by this, we here study the dispersion of gyrotactic algae in laminar and turbulent channel flows using direct numerical simulation (DNS) and a previously published analytical swimming dispersion theory. Time-resolved dispersion measures are evaluated as functions of the Péclet and Reynolds numbers in upwelling and downwelling flows. For laminar flows, DNS results are compared with theory using competing descriptions of biased swimming cells in shear flow. Excellent agreement is found for predictions that employ generalized Taylor dispersion. The results highlight peculiarities of gyrotactic swimmer dispersion relative to passive tracers. In laminar downwelling flow the cell distribution drifts in excess of the mean flow, increasing in magnitude with Péclet number. The cell effective axial diffusivity increases and decreases with Péclet number (for tracers it merely increases). In turbulent flows, gyrotactic effects are weaker, but discernable and manifested as non-zero drift. These results should have a significant impact on photobioreactor design.
Dynamics of Small Inertia-Free Spheroidal Particles in a Turbulent Channel Flow
Challabotla, Niranjan Reddy; Zhao, Lihao; Andersson, Helge I.; Department of Energy; Process Engineering Team
2015-11-01
The study of small non-spherical particles suspended in turbulent fluid flows is of interest in view of the potential applications in industry and the environment. In the present work, we investigated the dynamics of inertia-free spheroidal particles suspended in fully-developed turbulent channel flow at Re τ = 180 by using the direct numerical simulations (DNS) for the Eulerian fluid phase coupled with the Lagrangian point-particle tracking. We considered inertia-free spheroidal particles with a wide range of aspect ratios from 0.01 to 50, i.e. from flat disks to long rods. Although the spheroids passively translate along with the fluid, the particle orientation and rotation strongly depend on the particle shape. The flattest disks were preferentially aligned with their symmetry axis normal to the wall, whereas the longest rods aligned parallel to the wall. Strong mean rotational spin was observed for spherical particles and this has been damped with increasing asphericity both for rod-like and disk-like spheroids. The anisotropic mean and fluctuating fluid vorticity resulted in particle spin anisotropies which exhibited a complex dependence on the particle asphericty. The Research Council of Norway, Notur and COST Action FP1005 are gratefully acknowledged.
Drag-reducing performance of obliquely aligned superhydrophobic surface in turbulent channel flow
Energy Technology Data Exchange (ETDEWEB)
Watanabe, Sho; Fukagata, Koji [Department of Mechanical Engineering, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522 (Japan); Mamori, Hiroya, E-mail: fukagata@mech.keio.ac.jp [Department of Mechanical Engineering, Tokyo University of Science, Niijuku 6-3-1, Katsushika-ku, Tokyo 125-8585 (Japan)
2017-04-15
Friction drag reduction effect by superhydrophobic surfaces in a turbulent channel flow is investigated by means of direct numerical simulation. The simulations are performed under a constant pressure gradient at the friction Reynolds number of 180. A special focus is laid upon the influence of the angle of microridge structure to flow direction, while the gas area fraction on the surface is kept at 50% and the groove width is kept constant at 33.75 wall units. Larger drag reduction effect is observed for a smaller angle: the bulk-mean velocity is increased about 15% when the microridge is parallel to the flow. The drag reduction effect is found to deteriorate rapidly with the microridge angle due to a decrease in the slip velocity. The Reynolds stress budgets show that the modification in each physical effect is qualitatively similar but more pronounced when the microridge is aligned with the stream. (paper)
LES of Supersonic Turbulent Channel Flow at Mach Numbers 1.5 and 3
Raghunath, Sriram; Brereton, Giles
2009-11-01
LES of compressible, turbulent, body-force driven, isothermal-wall channel flows at Reτ of 190 and 395 at moderate supersonic speeds (Mach 1.5 and 3) are presented. Simulations are fully resolved in the wall-normal direction without the need for wall-layer models. SGS models for incompressible flows, with appropriate extensions for compressibility, are tested a priori/ with DNS results and used in LES. Convergence of the simulations is found to be sensitive to the initial conditions and to the choice of model (wall-normal damping) in the laminar sublayer. The Nicoud--Ducros wall adapting SGS model, coupled with a standard SGS heat flux model, is found to yield results in good agreement with DNS.
Numerical simulations of turbulent heat transfer in a channel at Prandtl numbers higher than 100
International Nuclear Information System (INIS)
Bergant, R.; Tiselj, I.
2005-01-01
During the last years, many attempts have been made to extend turbulent heat transfer at low Prandtl numbers to high Prandtl numbers in the channel based on a very accurate pseudo-spectral code of direct numerical simulation (DNS). DNS describes all the length and time scales for velocity and temperature fields, which are different when Prandtl number is not equal to 1. DNS can be used at low Reynolds (Re τ =150. Very similar approach as for Pr=5.4 was done for numerical simulations at Pr=100 and Pr=200. Comparison was made with results of temperature fields performed on 9-times finer numerical grid, however without damping of the highest Fourier coefficients. The results of mean temperature profiles show no differences larger than statistical uncertainties (∼1%), while slightly larger differences are seen for temperature fluctuations. (author)
On the Lamb vector divergence as a momentum field diagnostic employed in turbulent channel flow
Hamman, Curtis W.; Kirby, Robert M.; Klewicki, Joseph C.
2006-11-01
Vorticity, enstrophy, helicity, and other derived field variables provide invaluable information about the kinematics and dynamics of fluids. However, whether or not derived field variables exist that intrinsically identify spatially localized motions having a distinct capacity to affect a time rate of change of linear momentum is seldom addressed in the literature. The purpose of the present study is to illustrate the unique attributes of the divergence of the Lamb vector in order to qualify its potential for characterizing such spatially localized motions. Toward this aim, we describe the mathematical properties, near-wall behavior, and scaling characteristics of the divergence of the Lamb vector for turbulent channel flow. When scaled by inner variables, the mean divergence of the Lamb vector merges to a single curve in the inner layer, and the fluctuating quantities exhibit a strong correlation with the Bernoulli function throughout much of the inner layer.
Kramer, W.; Clercx, H.J.H.; van Heijst, G.J.F.
2008-01-01
This paper reports on a numerical study of forced two-dimensional turbulence in a periodic channel with flat no-slip walls. Since corners or curved domain boundaries, which are met in the standard rectangular, square, or circular geometries, are absent in this geometry, the (statistical) analysis of
Kramer, W.; Clercx, H.J.H.; Heijst, van G.J.F.
2008-01-01
This paper reports on a numerical study of forced two-dimensional turbulence in a periodic channel with flat no-slip walls. Since corners or curved domain boundaries, met in the standard rectangular, square or circular geometries, are absent in this geometry, the (statistical) analysis of the flow
International Nuclear Information System (INIS)
Capecelatro, Jesse; Desjardins, Olivier; Fox, Rodney O.
2016-01-01
Simulations of strongly coupled (i.e., high-mass-loading) fluid-particle flows in vertical channels are performed with the purpose of understanding the fundamental physics of wall-bounded multiphase turbulence. The exact Reynolds-averaged (RA) equations for high-mass-loading suspensions are presented, and the unclosed terms that are retained in the context of fully developed channel flow are evaluated in an Eulerian–Lagrangian (EL) framework for the first time. A key distinction between the RA formulation presented in the current work and previous derivations of multiphase turbulence models is the partitioning of the particle velocity fluctuations into spatially correlated and uncorrelated components, used to define the components of the particle-phase turbulent kinetic energy (TKE) and granular temperature, respectively. The adaptive spatial filtering technique developed in our previous work for homogeneous flows [J. Capecelatro, O. Desjardins, and R. O. Fox, “Numerical study of collisional particle dynamics in cluster-induced turbulence,” J. Fluid Mech. 747, R2 (2014)] is shown to accurately partition the particle velocity fluctuations at all distances from the wall. Strong segregation in the components of granular energy is observed, with the largest values of particle-phase TKE associated with clusters falling near the channel wall, while maximum granular temperature is observed at the center of the channel. The anisotropy of the Reynolds stresses both near the wall and far away is found to be a crucial component for understanding the distribution of the particle-phase volume fraction. In Part II of this paper, results from the EL simulations are used to validate a multiphase Reynolds-stress turbulence model that correctly predicts the wall-normal distribution of the two-phase turbulence statistics.
Capecelatro, Jesse; Desjardins, Olivier; Fox, Rodney O.
2016-03-01
Simulations of strongly coupled (i.e., high-mass-loading) fluid-particle flows in vertical channels are performed with the purpose of understanding the fundamental physics of wall-bounded multiphase turbulence. The exact Reynolds-averaged (RA) equations for high-mass-loading suspensions are presented, and the unclosed terms that are retained in the context of fully developed channel flow are evaluated in an Eulerian-Lagrangian (EL) framework for the first time. A key distinction between the RA formulation presented in the current work and previous derivations of multiphase turbulence models is the partitioning of the particle velocity fluctuations into spatially correlated and uncorrelated components, used to define the components of the particle-phase turbulent kinetic energy (TKE) and granular temperature, respectively. The adaptive spatial filtering technique developed in our previous work for homogeneous flows [J. Capecelatro, O. Desjardins, and R. O. Fox, "Numerical study of collisional particle dynamics in cluster-induced turbulence," J. Fluid Mech. 747, R2 (2014)] is shown to accurately partition the particle velocity fluctuations at all distances from the wall. Strong segregation in the components of granular energy is observed, with the largest values of particle-phase TKE associated with clusters falling near the channel wall, while maximum granular temperature is observed at the center of the channel. The anisotropy of the Reynolds stresses both near the wall and far away is found to be a crucial component for understanding the distribution of the particle-phase volume fraction. In Part II of this paper, results from the EL simulations are used to validate a multiphase Reynolds-stress turbulence model that correctly predicts the wall-normal distribution of the two-phase turbulence statistics.
ISS modeling strategy for the numerical simulation of turbulent sub-channel liquid-vapor flows
International Nuclear Information System (INIS)
Olivier Lebaigue; Benoit Mathieu; Didier Jamet
2005-01-01
Full text of publication follows: The general objective is to perform numerical simulation of the liquid-vapor turbulent two-phase flows that occur in sub-channels of a nuclear plant assembly under nominal or incidental situations. Additional features concern nucleate boiling at the surface of fuel rods and the sliding of vapor bubbles on this surface with possible dynamic contact lines. The Interfaces and Sub-grid Scales (ISS) modeling strategy for numerical simulations is one of the possible two-phase equivalents for the one-phase LES concept. It consists in solving the two-phase flows features at the scales that are resolved by the grid of the numerical method, and to take into account the unresolved scales with sub-grid models. Interfaces are tracked in a DNS-like approach while specific features of the behavior of interfaces such as contact line physics, coalescence and fragmentation, and the smallest scales of turbulence within each phase have an unresolved scale part that is modeled. The problem of the modeling of the smallest scales of turbulence is rather simple even if the classical situation is altered by the presence of the interfaces. In a typical sub-channel situation (e.g., 15 MPa and 3.5 m.s -1 water flow in a PWR sub-channel), the Kolmogorov scale is ca. 1 μm whereas typical bubble size are supposed to be close to 150 μm. Therefore, the use of a simple sub-grid model between, e.g., 1 and 20 μm allows a drastic reduction of the number of nodes in the space discretization while it remains possible to validate by comparison to true DNS results. Other sub-grid models have been considered to recover physical phenomena that cannot be captured with a realistic discretization: they rely on physical scales from molecular size to 1 μm. In these cases, the use of sub-grid model is no longer a matter of CPU-time and memory saving only, but also a corner stone to recover physical behavior. From this point of view at least we are no longer performing true
Correlations of Surface Deformation and 3D Flow Field in a Compliant Wall Turbulent Channel Flow.
Wang, Jin; Zhang, Cao; Katz, Joseph
2015-11-01
This study focuses on the correlations between surface deformation and flow features, including velocity, vorticity and pressure, in a turbulent channel flow over a flat, compliant Polydimethylsiloxane (PDMS) wall. The channel centerline velocity is 2.5 m/s, and the friction Reynolds number is 2.3x103. Analysis is based on simultaneous measurements of the time resolved 3D velocity and surface deformation using tomographic PIV and Mach-Zehnder Interferometry. The volumetric pressure distribution is calculated plane by plane by spatially integrating the material acceleration using virtual boundary, omni-directional method. Conditional sampling based on local high/low pressure and deformation events reveals the primary flow structures causing the deformation. High pressure peaks appear at the interface between sweep and ejection, whereas the negative deformations peaks (dent) appear upstream, under the sweeps. The persistent phase lag between flow and deformations are presumably caused by internal damping within the PDMS. Some of the low pressure peaks and strong ejections are located under the head of hairpin vortices, and accordingly, are associated with positive deformation (bump). Others bumps and dents are correlated with some spanwise offset large inclined quasi-streamwise vortices that are not necessarily associated with hairpins. Sponsored by ONR.
Time Resolved Tomographic PIV Measurements of Rough-Wall Turbulent Channel Flow
Miorini, Rinaldo; Zhang, Cao; Katz, Joseph
2013-11-01
Time resolved tomographic PIV is used to study flow structures in the outer region of a rough-wall turbulent boundary layer, focusing on imprints of the roughness on the outer layer. Measurements are performed in a transparent channel installed in the JHU optically index matched facility. The roughness consists of pyramids with height, k = 0.46 mm, and wavelength, λ = 3.2 mm, satisfying h/k = 55 (h = 25.4 mm is the channel half-height), k + = 64 and Re = 40000. The TPIV setup consists of four high-speed cameras operating at 3 kHz, which view the sample volume through acrylic prisms. The flow field is illuminated by an Nd:YLF laser. Following enhancement, calibration, and reconstruction, 643 voxels interrogation volumes with 0.75 overlap provide 3D velocity fields with spacing of 0.5883 mm3. Formation and transport of near-wall 3D U-shaped vortex structures, with base in front of the pyramids, and quasi-streamwise legs extending between pyramid crest lines are evident from the data. Extended streamwise regions of high wall-normal vorticity appear ``latched'' to the roughness elements close to the wall, but are transported downstream at higher elevations. Also evident are traveling streamwise low velocity streaks, which cover many roughness elements. Sponsored by NSF CBET and ONR.
Ni, Weidan; Lu, Lipeng; Fang, Jian; Moulinec, Charles; Yao, Yufeng
2018-05-01
The effect of spanwise alternatively distributed strips (SADS) control on turbulent flow in a plane channel has been studied by direct numerical simulations to investigate the characteristics of large-scale streamwise vortices (LSSVs) induced by small-scale active wall actuation, and their potential in suppressing flow separation. SADS control is realized by alternatively arranging out-of-phase control (OPC) and in-phase control (IPC) wall actuations on the lower channel wall surface, in the spanwise direction. It is found that the coherent structures are suppressed or enhanced alternatively by OPC or IPC, respectively, leading to the formation of a vertical shear layer, which is responsible for the LSSVs’ presence. Large-scale low-speed region can also be observed above the OPC strips, which resemble large-scale low-speed streaks. LSSVs are found to be in a statistically-converged steady state and their cores are located between two neighboring OPC and IPC strips. Their motions contribute significantly to the momentum transport in the wall-normal and spanwise directions, demonstrating their potential ability to suppress flow separation.
Turbulent flow and heat transfer in channels with combined rough and smooth surfaces
International Nuclear Information System (INIS)
Aytekin, A.
1978-01-01
A two-part experimental investigation is reported on the effects of transverse square rib roughening on fluid flow and heat transfer in channels with uniform and non-uniform boundary conditions. The first part of the experimental programme consisted of providing detailed measurements of mean and basic turbulent characteristics of fully developed flow in two rectangular ducts of aspect ratios 1.63 and 3.0. In each duct only one wall was roughened. In channels having low aspect ratios secondary flows play an important part in momentum transfer, and an interpretation of their effect on the measured Reynolds shear stress distribution has been attempted. In the second part of the experimental programme mean velocity and temperature profiles, friction factors and Stanton numbers were measured in an internally roughened pipe and annuli composed of a rough inner rod and either a smooth or a rough outer pipe. Heating was always applied on the outer surface. In all the geometries the mean velocities near the rough walls were found to be represented by logarithmic straight lines. The gradients of these lines were independent of Reynolds number but differed for various geometries. The mean temperature profiles, measured in the rough pipe and the fully rough annulus, showed that these could also be represented by logarithmic straight lines, but the slopes of these profiles were markedly different from those of the velocity profiles. (author)
Fully-resolved prolate spheroids in turbulent channel flows: A lattice Boltzmann study
Eshghinejadfard, Amir; Hosseini, Seyed Ali; Thévenin, Dominique
2017-09-01
Particles are present in many natural and industrial multiphase flows. In most practical cases, particle shape is not spherical, leading to additional difficulties for numerical studies. In this paper, DNS of turbulent channel flows with finite-size prolate spheroids is performed. The geometry includes a straight wall-bounded channel at a frictional Reynolds number of 180 seeded with particles. Three different particle shapes are considered, either spheroidal (aspect ratio λ =2 or 4) or spherical (λ =1 ). Solid-phase volume fraction has been varied between 0.75% and 1.5%. Lattice Boltzmann method (LBM) is used to model the fluid flow. The influence of the particles on the flow field is simulated by immersed boundary method (IBM). In this Eulerian-Lagrangian framework, the trajectory of each particle is computed individually. All particle-particle and particle-fluid interactions are considered (four-way coupling). Results show that, in the range of examined volume fractions, mean fluid velocity is reduced by addition of particles. However, velocity reduction by spheroids is much lower than that by spheres; 2% and 1.6%, compared to 4.6%. Maximum streamwise velocity fluctuations are reduced by addition of particle. By comparing particle and fluid velocities, it is seen that spheroids move faster than the fluid before reaching the same speed in the channel center. Spheres, on the other hand, move slower than the fluid in the buffer layer. Close to the wall, all particle types move faster than the fluid. Moreover, prolate spheroids show a preferential orientation in the streamwise direction, which is stronger close to the wall. Far from the wall, the orientation of spheroidal particles tends to isotropy.
Fully-resolved prolate spheroids in turbulent channel flows: A lattice Boltzmann study
Directory of Open Access Journals (Sweden)
Amir Eshghinejadfard
2017-09-01
Full Text Available Particles are present in many natural and industrial multiphase flows. In most practical cases, particle shape is not spherical, leading to additional difficulties for numerical studies. In this paper, DNS of turbulent channel flows with finite-size prolate spheroids is performed. The geometry includes a straight wall-bounded channel at a frictional Reynolds number of 180 seeded with particles. Three different particle shapes are considered, either spheroidal (aspect ratio λ=2 or 4 or spherical (λ=1. Solid-phase volume fraction has been varied between 0.75% and 1.5%. Lattice Boltzmann method (LBM is used to model the fluid flow. The influence of the particles on the flow field is simulated by immersed boundary method (IBM. In this Eulerian-Lagrangian framework, the trajectory of each particle is computed individually. All particle-particle and particle-fluid interactions are considered (four-way coupling. Results show that, in the range of examined volume fractions, mean fluid velocity is reduced by addition of particles. However, velocity reduction by spheroids is much lower than that by spheres; 2% and 1.6%, compared to 4.6%. Maximum streamwise velocity fluctuations are reduced by addition of particle. By comparing particle and fluid velocities, it is seen that spheroids move faster than the fluid before reaching the same speed in the channel center. Spheres, on the other hand, move slower than the fluid in the buffer layer. Close to the wall, all particle types move faster than the fluid. Moreover, prolate spheroids show a preferential orientation in the streamwise direction, which is stronger close to the wall. Far from the wall, the orientation of spheroidal particles tends to isotropy.
Kim, Kyoungyoun; Sureshkumar, Radhakrishna
2018-03-01
The effects of polymer stresses on the analogy between momentum and heat transfer are examined by using a direct numerical simulation (DNS) of viscoelastic turbulent channel flows using a constant heat flux boundary condition. The Reynolds number based on the friction velocity and channel half height is 125, and the Prandtl number is 5. The polymer stress is modeled using the finitely extensible nonlinear elastic-Peterlin constitutive model, and low (15%), intermediate (34%), and high drag reduction (DR) (52%) cases are examined. The Colburn analogy is found to be inapplicable for viscoelastic turbulent flows, suggesting dissimilarity between the momentum and heat transfer at the macroscopic coefficient level. The mean temperature profile also shows behaviour different from the mean velocity profile in drag-reduced flows. In contrast to the dissimilarity in the mean profiles, the turbulent Prandtl number Prt predicted by the DNS is near unity. This implies that turbulent heat transfer is still analogous to turbulent momentum transfer in drag-reduced flows, as in Newtonian flow. An increase in DR is accompanied by an increase in the correlation coefficient ρuθ between the instantaneous fluctuations in the streamwise velocity u and temperature θ. The correlation coefficient between u' and wall-normal velocity fluctuations v', ρ-u v, exhibits a profile similar to that of ρ-θ v in drag-reduced and Newtonian flows. Finally, the budget analysis of the transport equations of turbulent heat flux shows a strong similarity between the turbulent momentum and heat transfer, which is consistent with the predictions of Prt near unity.
Flow in a triangular open channel with hydraulic jump | Eyo | Journal ...
African Journals Online (AJOL)
Mathematical model for dredging a triangular open channel with hydraulic jump is developed using the method of successive approximation. Applying the model to a numerical example new parameters of the new (excavated) channel are determined and compared with those of the original channel. Another feature of the ...
Sesti, Federico; Rajan, Sindhu; Gonzalez-Colaso, Rosana; Nikolaeva, Natalia; Goldstein, Steve A N
2003-04-01
MVP, a Methanococcus jannaschii voltage-gated potassium channel, was cloned and shown to operate in eukaryotic and prokaryotic cells. Like pacemaker channels, MVP opens on hyperpolarization using S4 voltage sensors like those in classical channels activated by depolarization. The MVP S4 span resembles classical sensors in sequence, charge, topology and movement, traveling inward on hyperpolarization and outward on depolarization (via canaliculi in the protein that bring the extracellular and internal solutions into proximity across a short barrier). Thus, MVP opens with sensors inward indicating a reversal of S4 position and pore state compared to classical channels. Homologous channels in mammals and plants are expected to function similarly.
Radiative effects on turbulent buoyancy-driven air flow in open square cavities
International Nuclear Information System (INIS)
Zamora, B.; Kaiser, A.S.
2016-01-01
The effects of the radiative effects and the air variable properties (density, viscosity and thermal conductivity) on the buoyancy-driven flows established in open square cavities are investigated. Two-dimensional, laminar, transitional and turbulent simulations are obtained, considering both uniform wall temperature and uniform heat flux heating conditions. In transitional and turbulent cases, the low- Reynolds k-ω turbulence model is employed. The average Nusselt number and the dimensionless mass-flow rate have been obtained for a wide range of the Rayleigh number varying from 10 3 to 10 16 . The results obtained taking into account the variable thermophysical properties of air are compared to those calculated assuming constant properties and the Boussinesq approximation. In addition, the influence of considering surface radiative effects on the differences reached for the Nusselt number and the mass flow rate obtained with several intensities of heating is studied; specifically, the effects of thermal radiation on the appearance of the burnout phenomenon is analyzed. The changes produced in the flow patterns into the cavity when the radiative heat transfer and the effects of variation of properties are relevant, are also shown. (authors)
Hakim, Ammar; Shi, Eric; Juno, James; Bernard, Tess; Hammett, Greg
2017-10-01
For weakly collisional (or collisionless) plasmas, kinetic effects are required to capture the physics of micro-turbulence. We have implemented solvers for kinetic and gyrokinetic equations in the computational plasma physics framework, Gkeyll. We use a version of discontinuous Galerkin scheme that conserves energy exactly. Plasma sheaths are modeled with novel boundary conditions. Positivity of distribution functions is maintained via a reconstruction method, allowing robust simulations that continue to conserve energy even with positivity limiters. We have performed a large number of benchmarks, verifying the accuracy and robustness of our code. We demonstrate the application of our algorithm to two classes of problems (a) Vlasov-Maxwell simulations of turbulence in a magnetized plasma, applicable to space plasmas; (b) Gyrokinetic simulations of turbulence in open-field-line geometries, applicable to laboratory plasmas. Supported by the Max-Planck/Princeton Center for Plasma Physics, the SciDAC Center for the Study of Plasma Microturbulence, and DOE Contract DE-AC02-09CH11466.
Minoxidil opens mitochondrial KATP channels and confers cardioprotection
Sato, Toshiaki; Li, Yulong; Saito, Tomoaki; Nakaya, Haruaki
2003-01-01
ATP-sensitive potassium channel in the mitochondrial inner membrane (mitoKATP channel) rather than in the sarcolemma (sarcKATP channel) appears to play an important role in cardioprotection. We examined the effect of minoxidil, a potent antihypertensive agent and hair growth stimulator, on sarcKATP and mitoKATP channels in guinea-pig ventricular myocytes. Minoxidil activated a glybenclamide-sensitive sarcKATP channel current in the whole-cell recording mode with an EC50 of 182.6 μM. Minoxidil reversibly increased the flavoprotein oxidation, an index of mitoKATP channel activity, in a concentration-dependent manner. The EC50 for mitoKATP channel activation was estimated to be 7.3 μM; this value was notably ≈25-fold lower than that for sarcKATP channel activation. Minoxidil (10 μM) significantly attenuated the ouabain-induced increase of mitochondrial Ca2+ concentration, which was measured by loading cells with rhod-2 fluorescence. Furthermore, pretreatment with minoxidil (10 μM) before 20-min no-flow ischaemia significantly improved the recovery of developed tension measured after 60 min of reperfusion in coronary perfused guinea-pig ventricular muscles. These cardioprotective effects of minoxidil were completely abolished by the mitoKATP channel blocker 5-hydroxydecanoate (500 μM). Our results indicate that minoxidil exerts a direct cardioprotective effect on heart muscle cells, an effect mediated by the selective activation of mitoKATP channels. PMID:14691056
Low-order dynamical system model of a fully developed turbulent channel flow
Hamilton, Nicholas; Tutkun, Murat; Cal, Raúl Bayoán
2017-06-01
A reduced order model of a turbulent channel flow is composed from a direct numerical simulation database hosted at the Johns Hopkins University. Snapshot proper orthogonal decomposition (POD) is used to identify the Hilbert space from which the reduced order model is obtained, as the POD basis is defined to capture the optimal energy content by mode. The reduced order model is defined by coupling the evolution of the dynamic POD mode coefficients through their respective time derivative with a least-squares polynomial fit of terms up to third order. Parameters coupling the dynamics of the POD basis are defined in analog to those produced in the classical Galerkin projection. The resulting low-order dynamical system is tested for a range of basis modes demonstrating that the non-linear mode interactions do not lead to a monotonic decrease in error propagation. A basis of five POD modes accounts for 50% of the integrated turbulence kinetic energy but captures only the largest features of the turbulence in the channel flow and is not able to reflect the anticipated flow dynamics. Using five modes, the low-order model is unable to accurately reproduce Reynolds stresses, and the root-mean-square error of the predicted stresses is as great as 30%. Increasing the basis to 28 modes accounts for 90% of the kinetic energy and adds intermediate scales to the dynamical system. The difference between the time derivatives of the random coefficients associated with individual modes and their least-squares fit is amplified in the numerical integration leading to unstable long-time solutions. Periodic recalibration of the dynamical system is undertaken by limiting the integration time to the range of the sampled data and offering the dynamical system new initial conditions. Renewed initial conditions are found by pushing the mode coefficients in the end of the integration time toward a known point along the original trajectories identified through a least-squares projection. Under
Ferreras Fernández, Tránsito; García-Peñalvo, Francisco José; Merlo Vega, José Antonio
2015-01-01
This is the presentation of the paper entitled “Open access repositories as channel of publication scientific grey literature” in the TEEM 2015 International Conference held in Porto (Portugal) in October 7-9, 2015. In this paper we describe how the open access repositories are valid channels for the publication of scientific grey literature. Technological development facilitates the communication of scientific knowledge, allowing expand distribution channels and significantly reducing tra...
Estimation of Outage Capacity for Free Space Optical Links Over I-K and K Turbulent Channels
Directory of Open Access Journals (Sweden)
D. Marinos
2011-06-01
Full Text Available The free space optical communication systems are attracting great research and commercial interest due to their capability of transferring data, over short distances, with high rate and security, low cost demands and without licensing fees. However, their performance depends strongly on the atmospheric conditions in the link’s area. In this work, we investigate the influence of the turbulence on the outage capacity of such a system for weak to strong turbulence channels modeled by the I-K and the K-distribution and we derive closed-form expressions for its estimation. Finally, using these expressions we present numerical results for various link cases with different turbulence conditions.
Turbulence and finestructure in a deep ocean channel with sill overflow on the mid-Atlantic ridge
Tippenhauer, Sandra; Dengler, Marcus; Fischer, Tim; Kanzow, Torsten
2015-05-01
Diapycnal mixing in the deep ocean is known to be much stronger in the vicinity of rough topography of mid-ocean ridges than above abyssal plains. In this study a horizontally profiling microstructure probe attached to an autonomous underwater vehicle (AUV) is used to infer the spatial distribution of the dissipation rate of turbulent kinetic energy (ε) in the central valley of the Mid-Atlantic Ridge. To the authors' knowledge, this is the first successful realization of a horizontal, deep-ocean microstructure survey. More than 22 h of horizontal, near-bottom microstructure data from the Lucky Strike segment (37°N) are presented. The study focuses on a channel with unidirectional sill overflow. Density was found to decrease along the channel following the mean northward flow of 3 to 8 cm/s. The magnitude of the rate of turbulent kinetic energy dissipation was distributed asymmetrically relative to the position of the sill. Elevated dissipation rates were present in a segment 1-4 km downstream (north) of the sill with peak values of 1 ×10-7 W/kg. Large flow speeds and elevated density finestructure were observed within this segment. Lowered hydrographic measurements indicated unstable stratification in the same region. The data indicate that hydraulic control was established at least temporarily. Inside the channel at wavelengths between 1 m and 250 m the slopes of AUV-inferred horizontal temperature gradient spectra were found to be consistent with turbulence in the inertial-convective subrange. Integrated temperature gradient variance in this wavelength interval was consistent with an ε2/3 dependence. The results illustrate that deep-reaching AUVs are a useful tool to study deep ocean turbulence over complex terrain where free-falling and lowered turbulence measurements are inefficient and time-consuming.
Studying the formation of non-linear bursts in fully turbulent channel flows
Encinar, Miguel P.; Jimenez, Javier
2017-11-01
Linear transient growth has been suggested as a possible explanation for the intermittent behaviour, or `bursting', in shear flows with a stable mean velocity profile. Analysing fully non-linear DNS databases yields a similar Orr+lift-up mechanism, but acting on spatially localised wave packets rather than on monochromatic infinite wavetrains. The Orr mechanism requires the presence of backwards-leaning wall-normal velocity perturbations as initial condition, but the linear theory fails to clarify how these perturbations are formed. We investigate the latter in a time-resolved wavelet-filtered turbulent channel database, which allows us to assign an amplitude and an inclination angle to a flow region of selected size. This yields regions that match the dynamics of linear Orr for short times. We find that a short streamwise velocity (u) perturbation (i.e. a streak meander) consistently appears before the burst, but disappears before the burst reaches its maximum amplitude. Lift-up then generates a longer streamwise velocity perturbation. The initial streamwise velocity is also found to be backwards-leaning, contrary to the averaged energy-containing scales, which are known to be tilted forward. Funded by the ERC COTURB project.
Localised burst reconstruction from space-time PODs in a turbulent channel
Garcia-Gutierrez, Adrian; Jimenez, Javier
2017-11-01
The traditional proper orthogonal decomposition of the turbulent velocity fluctuations in a channel is extended to time under the assumption that the attractor is statistically stationary and can be treated as periodic for long-enough times. The objective is to extract space- and time-localised eddies that optimally represent the kinetic energy (and two-event correlation) of the flow. Using time-resolved data of a small-box simulation at Reτ = 1880 , minimal for y / h 0.25 , PODs are computed from the two-point spectral-density tensor Φ(kx ,kz , y ,y' , ω) . They are Fourier components in x, z and time, and depend on y and on the temporal frequency ω, or, equivalently, on the convection velocity c = ω /kx . Although the latter depends on y, a spatially and temporally localised `burst' can be synthesised by adding a range of PODs with specific phases. The results are localised bursts that are amplified and tilted, in a time-periodic version of Orr-like behaviour. Funded by the ERC COTURB project.
"Hypothetical" Heavy Particles Dynamics in LES of Turbulent Dispersed Two-Phase Channel Flow
Gorokhovski, M.; Chtab, A.
2003-01-01
The extensive experimental study of dispersed two-phase turbulent flow in a vertical channel has been performed in Eaton's research group in the Mechanical Engineering Department at Stanford University. In Wang & Squires (1996), this study motivated the validation of LES approach with Lagrangian tracking of round particles governed by drag forces. While the computed velocity of the flow have been predicted relatively well, the computed particle velocity differed strongly from the measured one. Using Monte Carlo simulation of inter-particle collisions, the computation of Yamamoto et al. (2001) was specifically performed to model Eaton's experiment. The results of Yamamoto et al. (2001) improved the particle velocity distribution. At the same time, Vance & Squires (2002) mentioned that the stochastic simualtion of inter-particle collisions is too expensive, requiring significantly more CPU resources than one needs for the gas flow computation. Therefore, the need comes to account for the inter-particle collisions in a simpler and still effective way. To present such a model in the framework of LES/Lagrangian particle approach, and to compare the calculated results with Eaton's measurement and modeling of Yamamoto is the main objective of the present paper.
Turbulent mixed convection in vertical and inclined flat channels with aiding flows
Energy Technology Data Exchange (ETDEWEB)
Poskas, P.; Vilemas, J.; Adomaitis, J.E.; Bartkus, G.
1995-09-01
This paper presents an experimental study of turbulent mixed convection heat transfer for aiding flows in a vertical ({phi}=90{degrees}), inclined ({phi}=60{degrees},30{degrees}), and horizontal ({phi}=0{degrees}) flat channels with symmetrical heating and a ratio of height h to width b of about 1:10 and with length about 4 m (x/2h about 44). The study covered Re from 4x10{sup 3} to 5x10{sup 4} and Gr{sub q} from 5x10{sup 7}to 3x10{sup 10}. For the upper wall, a region of impaired heat transfer was found for all angular positions (from vertical to horizontal) and for bottom wall the augmentation of heat transfer in comparison to forced convection was revealed in the region of {phi}=0{degrees}-60{degrees}. Different characteristic buoyancy parameters were found for regions of impaired and enhanced heat transfer. General relations are suggested to predict the heat transfer for fully-developed-flow conditions and different angular positions.
``Large''- vs Small-scale friction control in turbulent channel flow
Canton, Jacopo; Örlü, Ramis; Chin, Cheng; Schlatter, Philipp
2017-11-01
We reconsider the ``large-scale'' control scheme proposed by Hussain and co-workers (Phys. Fluids 10, 1049-1051 1998 and Phys. Rev. Fluids, 2, 62601 2017), using new direct numerical simulations (DNS). The DNS are performed in a turbulent channel at friction Reynolds number Reτ of up to 550 in order to eliminate low-Reynolds-number effects. The purpose of the present contribution is to re-assess this control method in the light of more modern developments in the field, in particular also related to the discovery of (very) large-scale motions. The goals of the paper are as follows: First, we want to better characterise the physics of the control, and assess what external contribution (vortices, forcing, wall motion) are actually needed. Then, we investigate the optimal parameters and, finally, determine which aspects of this control technique actually scale in outer units and can therefore be of use in practical applications. In addition to discussing the mentioned drag-reduction effects, the present contribution will also address the potential effect of the naturally occurring large-scale motions on frictional drag, and give indications on the physical processes for potential drag reduction possible at all Reynolds numbers.
Ma, Jing; Fu, Yulong; Tan, Liying; Yu, Siyuan; Xie, Xiaolong
2018-05-01
Spatial diversity as an effective technique to mitigate the turbulence fading has been widely utilized in free space optical (FSO) communication systems. The received signals, however, will suffer from channel correlation due to insufficient spacing between component antennas. In this paper, the new expressions of the channel correlation coefficient and specifically its components (the large- and small-scale channel correlation coefficients) for a plane wave with aperture effects are derived for horizontal link in moderate-to-strong turbulence, using a non-Kolmogorov spectrum that has a generalized power law in the range of 3-4 instead of the fixed classical Kolmogorov power law of 11/3. And then the influence of power law variations on the channel correlation coefficient and its components are analysed. The numerical results indicated that various value of the power law lead to varying effects on the channel correlation coefficient and its components. This work will help with the further investigation on the fading correlation in spatial diversity systems.
Viumdal, Håkon; Mylvaganam, Saba
2017-01-01
In oil and gas and geothermal installations, open channels followed by sieves for removal of drill cuttings, are used to monitor the quality and quantity of the drilling fluids. Drilling fluid flow rate is difficult to measure due to the varying flow conditions (e.g., wavy, turbulent and irregular) and the presence of drilling cuttings and gas bubbles. Inclusion of a Venturi section in the open channel and an array of ultrasonic level sensors above it at locations in the vicinity of and above the Venturi constriction gives the varying levels of the drilling fluid in the channel. The time series of the levels from this array of ultrasonic level sensors are used to estimate the drilling fluid flow rate, which is compared with Coriolis meter measurements. Fuzzy logic, neural networks and support vector regression algorithms applied to the data from temporal and spatial ultrasonic level measurements of the drilling fluid in the open channel give estimates of its flow rate with sufficient reliability, repeatability and uncertainty, providing a novel soft sensing of an important process variable. Simulations, cross-validations and experimental results show that feedforward neural networks with the Bayesian regularization learning algorithm provide the best flow rate estimates. Finally, the benefits of using this soft sensing technique combined with Venturi constriction in open channels are discussed. PMID:29072595
Tanner, Geoffrey R; Lutas, Andrew; Martínez-François, Juan Ramón; Yellen, Gary
2011-06-08
ATP-sensitive potassium channels (K(ATP) channels) are important sensors of cellular metabolic state that link metabolism and excitability in neuroendocrine cells, but their role in nonglucosensing central neurons is less well understood. To examine a possible role for K(ATP) channels in modulating excitability in hippocampal circuits, we recorded the activity of single K(ATP) channels in cell-attached patches of granule cells in the mouse dentate gyrus during bursts of action potentials generated by antidromic stimulation of the mossy fibers. Ensemble averages of the open probability (p(open)) of single K(ATP) channels over repeated trials of stimulated spike activity showed a transient increase in p(open) in response to action potential firing. Channel currents were identified as K(ATP) channels through blockade with glibenclamide and by comparison with recordings from Kir6.2 knock-out mice. The transient elevation in K(ATP) p(open) may arise from submembrane ATP depletion by the Na(+)-K(+) ATPase, as the pump blocker strophanthidin reduced the magnitude of the elevation. Both the steady-state and stimulus-elevated p(open) of the recorded channels were higher in the presence of the ketone body R-β-hydroxybutyrate, consistent with earlier findings that ketone bodies can affect K(ATP) activity. Using perforated-patch recording, we also found that K(ATP) channels contribute to the slow afterhyperpolarization following an evoked burst of action potentials. We propose that activity-dependent opening of K(ATP) channels may help granule cells act as a seizure gate in the hippocampus and that ketone-body-mediated augmentation of the activity-dependent opening could in part explain the effect of the ketogenic diet in reducing epileptic seizures.
Evanescent-Wave Visualizations of the Viscous Sublayer in Turbulent Channel Flow
2015-09-02
SECURITY CLASSIFICATION OF: The study of wall turbulence dates back more than a century. Recently, however, a number of studies suggest that the flow...in the inner region (i.e., the viscous sublayer and buffer layer) is not “universal”—and actually depends upon the specific type of wall turbulence ...Many of these new insights on wall turbulence are recent because we have only recently developed the experimental techniques, such as volumetric
Open channels in fractures maintained by deposition and erosion of colloids
International Nuclear Information System (INIS)
Kessler, J.H.; Hunt, J.R.
1993-01-01
Material in the colloidal size range is present in many natural groundwater systems at existing or proposed radioactive waste storage locations. Colloids initially suspended in the water in fractures can deposit onto the fracture surfaces, and will partially or fully clog the fracture. The amount of clogging will depend on whether the deposited colloidal material can erode from the fracture surfaces. If the fracture remains only partially clogged the unclogged regions take the form of open channels. The purpose of this paper is to assess under what conditions these open channels form. An analytical model of a steady state, average open channel width is presented which is a function of the fluid flow rate and viscosity, fracture aperture, and the permeability and shear strength of the deposited colloidal material. The implications of the presence of open channels for colloidal transport is also discussed. However, for most repository conditions the fractures are expected to fully clog with colloids
Directory of Open Access Journals (Sweden)
Adel Asnaashari
2016-01-01
Full Text Available Transitions are structures that can change geometry and flow velocity through varying the cross-sections of their channels. Under subcritical flow and steady flow conditions, it is necessary to reduce the flow velocity gradually due to increasing water pressure and adverse pressure gradients. Due to the separation of flow and subsequent eddy formation, a significant energy loss is incurred along the transition. This study presents the results of experimental investigations of the subcritical flow along the expansive transition of rectangular to trapezoidal channels. A numerical simulation was developed using a finite volume of fluid (VOF method with a Reynolds stress turbulence model. Water surface profiles and velocity distributions of flow through the transition were measured experimentally and compared with the numerical results. A good agreement between the experimental and numerical model results showed that the Reynolds model and VOF method are capable of simulating the hydraulic flow in open channel transitions. Also, the efficiency of the transition and coefficient of energy head loss were calculated. The results show that with an increasing upstream Froude number, the efficiency of the transition and coefficient of energy head loss decrease and increase, respectively. The results also show the ability of numerical simulation to simulate the flow separation zones and secondary current along the transition for different inlet discharges.
Hydralazine-induced vasodilation involves opening of high conductance Ca2+-activated K+ channels
DEFF Research Database (Denmark)
Bang, Lone; Nielsen-Kudsk, J E; Gruhn, N
1998-01-01
The purpose of this study was to investigate whether high conductance Ca2+-activated K+ channels (BK(Ca)) are mediating the vasodilator action of hydralazine. In isolated porcine coronary arteries, hydralazine (1-300 microM), like the K+ channel opener levcromakalim, preferentially relaxed......M) suppressed this response by 82% (P opening of BK(Ca) takes part in the mechanism whereby...
International Nuclear Information System (INIS)
Takase, Kazuyuki
1996-01-01
The square-ribbed fuel rod for high temperature gas-cooled reactors was developed in order to enhance the turbulent heat transfer in comparison with the standard fuel rod. To evaluate the heat transfer performance of the square-ribbed fuel rod, the turbulent heat transfer coefficients in an annular fuel channel with repeated two-dimensional square ribs were analyzed numerically on a fully developed incompressible flow using the k - ε turbulence model and the two-dimensional axisymmetrical coordinate system. Numerical analyses were carried out for a range of Reynolds numbers from 3000 to 20000 and ratios of square-rib pitch to height of 10, 20 and 40, respectively. The predicted values of the heat transfer coefficients agreed within an error of 10% for the square-rib pitch to height ratio of 10, 20% for 20 and 25% for 40, respectively, with the heat transfer empirical correlations obtained from the experimental data. It was concluded by the present study that the effect of the heat transfer augmentation by square ribs could be predicted sufficiently by the present numerical simulations and also a part of its mechanism could be explained by means of the change in the turbulence kinematic energy distribution along the flow direction. (author)
International Nuclear Information System (INIS)
Takase, K.
1996-01-01
The square-ribbed fuel rod for high temperature gas-cooled reactors was designed and developed so as to enhance the turbulent heat transfer in comparison with the previous standard fuel rod. The turbulent heat transfer characteristics in an annular fuel channel with repeated two-dimensional square ribs were analysed numerically on a fully developed incompressible flow using the k-ε turbulence model and the two-dimensional axisymmetrical coordinate system. Numerical analyses were carried out under the conditions of Reynolds numbers from 3000 to 20000 and ratios of square-rib pitch to height of 10, 20 and 40 respectively. The predictions of the heat transfer coefficients agreed well within an error of 10% for the square-rib pitch to height ratio of 10, 20% for 20 and 25% for 40 respectively, with the heat transfer empirical correlations obtained from the experimental data due to the simulated square-ribbed fuel rods. Therefore it was found that the effect of heat transfer augmentation due to the square ribs could be predicted by the present numerical simulations and the mechanism could be explained by the change in the turbulence kinematic energy distribution along the flow direction. (orig.)
International Nuclear Information System (INIS)
Yamamoto, Yoshinobu; Kunugi, Tomoaki
2015-01-01
Graphical abstract: - Highlights: • For the first time, the MHD heat transfer DNS database corresponding to the typical nondimensional parameters of the fusion blanket design using molten salt, were established. • MHD heat transfer correlation was proposed and about 20% of the heat transfer degradation was evaluated under the design conditions. • The contribution of the turbulent diffusion to heat transfer is increased drastically with increasing Hartmann number. - Abstract: The high-Prandtl number passive scalar transport of the turbulent channel flow imposed a wall-normal magnetic field is investigated through the large-scale direct numerical simulation (DNS). All essential turbulence scales of velocities and temperature are resolved by using 2048 × 870 × 1024 computational grid points in stream, vertical, and spanwise directions. The heat transfer phenomena for a Prandtl number of 25 were observed under the following flow conditions: the bulk Reynolds number of 14,000 and Hartman number of up to 28. These values were equivalent to the typical nondimensional parameters of the fusion blanket design proposed by Wong et al. As a result, a high-accuracy DNS database for the verification of magnetohydrodynamic turbulent heat transfer models was established for the first time, and it was confirmed that the heat transfer correlation for a Prandtl number of 5.25 proposed by Yamamoto and Kunugi was applicable to the Prandtl number of 25 used in this study
Energy Technology Data Exchange (ETDEWEB)
Yamamoto, Yoshinobu, E-mail: yamamotoy@yamanashi.ac.jp [Department of Mechanical Systems Engineering, University of Yamanashi, 4-3-11 Takeda, Kofu 400-8511 (Japan); Kunugi, Tomoaki [Department of Nuclear Engineering, Kyoto University Yoshida, Sakyo, Kyoto 606-8501 (Japan)
2015-01-15
Graphical abstract: - Highlights: • For the first time, the MHD heat transfer DNS database corresponding to the typical nondimensional parameters of the fusion blanket design using molten salt, were established. • MHD heat transfer correlation was proposed and about 20% of the heat transfer degradation was evaluated under the design conditions. • The contribution of the turbulent diffusion to heat transfer is increased drastically with increasing Hartmann number. - Abstract: The high-Prandtl number passive scalar transport of the turbulent channel flow imposed a wall-normal magnetic field is investigated through the large-scale direct numerical simulation (DNS). All essential turbulence scales of velocities and temperature are resolved by using 2048 × 870 × 1024 computational grid points in stream, vertical, and spanwise directions. The heat transfer phenomena for a Prandtl number of 25 were observed under the following flow conditions: the bulk Reynolds number of 14,000 and Hartman number of up to 28. These values were equivalent to the typical nondimensional parameters of the fusion blanket design proposed by Wong et al. As a result, a high-accuracy DNS database for the verification of magnetohydrodynamic turbulent heat transfer models was established for the first time, and it was confirmed that the heat transfer correlation for a Prandtl number of 5.25 proposed by Yamamoto and Kunugi was applicable to the Prandtl number of 25 used in this study.
Raddatz, Natalia; Castillo, Juan P.; Gonzalez, Carlos; Alvarez, Osvaldo; Latorre, Ramon
2014-01-01
Expressed in somatosensory neurons of the dorsal root and trigeminal ganglion, the transient receptor potential melastatin 8 (TRPM8) channel is a Ca2+-permeable cation channel activated by cold, voltage, phosphatidylinositol 4,5-bisphosphate, and menthol. Although TRPM8 channel gating has been characterized at the single channel and macroscopic current levels, there is currently no consensus regarding the extent to which temperature and voltage sensors couple to the conduction gate. In this study, we extended the range of voltages where TRPM8-induced ionic currents were measured and made careful measurements of the maximum open probability the channel can attain at different temperatures by means of fluctuation analysis. The first direct measurements of TRPM8 channel temperature-driven conformational rearrangements provided here suggest that temperature alone is able to open the channel and that the opening reaction is voltage-independent. Voltage is a partial activator of TRPM8 channels, because absolute open probability values measured with fully activated voltage sensors are less than 1, and they decrease as temperature rises. By unveiling the fast temperature-dependent deactivation process, we show that TRPM8 channel deactivation is well described by a double exponential time course. The fast and slow deactivation processes are temperature-dependent with enthalpy changes of 27.2 and 30.8 kcal mol−1. The overall Q10 for the closing reaction is about 33. A three-tiered allosteric model containing four voltage sensors and four temperature sensors can account for the complex deactivation kinetics and coupling between voltage and temperature sensor activation and channel opening. PMID:25352597
Sun, Xiaole; Djordjevic, Ivan B.; Neifeld, Mark A.
2016-03-01
Free-space optical (FSO) channels can be characterized by random power fluctuations due to atmospheric turbulence, which is known as scintillation. Weak coherent source based FSO quantum key distribution (QKD) systems suffer from the scintillation effect because during the deep channel fading the expected detection rate drops, which then gives an eavesdropper opportunity to get additional information about protocol by performing photon number splitting (PNS) attack and blocking single-photon pulses without changing QBER. To overcome this problem, in this paper, we study a large-alphabet QKD protocol, which is achieved by using pulse-position modulation (PPM)-like approach that utilizes the time-frequency uncertainty relation of the weak coherent photon state, called here TF-PPM-QKD protocol. We first complete finite size analysis for TF-PPM-QKD protocol to give practical bounds against non-negligible statistical fluctuation due to finite resources in practical implementations. The impact of scintillation under strong atmospheric turbulence regime is studied then. To overcome the secure key rate performance degradation of TF-PPM-QKD caused by scintillation, we propose an adaptation method for compensating the scintillation impact. By changing source intensity according to the channel state information (CSI), obtained by classical channel, the adaptation method improves the performance of QKD system with respect to the secret key rate. The CSI of a time-varying channel can be predicted using stochastic models, such as autoregressive (AR) models. Based on the channel state predictions, we change the source intensity to the optimal value to achieve a higher secret key rate. We demonstrate that the improvement of the adaptation method is dependent on the prediction accuracy.
Directory of Open Access Journals (Sweden)
Da Liu
2017-09-01
Full Text Available Riverbank vegetation is of high importance both for preserving the form (morphology and function (ecology of natural river systems. Revegetation of riverbanks is commonly used as a means of stream rehabilitation and management of bank instability and erosion. In this experimental study, the effect of different riverbank vegetation densities on flow hydrodynamics across the channel, including the riparian zone, are reported and discussed. The configuration of vegetation elements follows either linear or staggered arrangements as vegetation density is progressively increased, within a representative range of vegetation densities found in nature. Hydrodynamic measurements including mean streamwise velocity and turbulent intensity flow profiles are recorded via acoustic Doppler velocimetry (ADV—both at the main channel and within the riverbank. These results show that for the main channel and the toe of riverbank, turbulence intensity for the low densities (λ ≈ 0 to 0.12 m−1 can increase up to 40% compared the case of high densities (λ = 0.94 to 1.9 m−1. Further analysis of these data allowed the estimation of bed-shear stresses, demonstrating 86% and 71% increase at the main channel and near the toe region, for increasing densities (λ = 0 to 1.9 m−1. Quantifying these hydrodynamic effects is important for assessing the contribution of physically representative ranges of riparian vegetation densities on hydrogeomorphologic feedback.
International Nuclear Information System (INIS)
Amaya, J.; Cabrit, O.; Poitou, D.; Cuenot, B.; El Hafi, M.
2010-01-01
Direct numerical simulations (DNS) of an anisothermal reacting turbulent channel flow with and without radiative source terms have been performed to study the influence of the radiative heat transfer on the optically non-homogeneous boundary layer structure. A methodology for the study of the emitting/absorbing turbulent boundary layer (TBL) is presented. Details on the coupling strategy and the parallelization techniques are exposed. An analysis of the first order statistics is then carried out. It is shown that, in the studied configuration, the global structure of the thermal boundary layer is not significantly modified by radiation. However, the radiative transfer mechanism is not negligible and contributes to the heat losses at the walls. The classical law-of-the-wall for temperature can thus be improved for RANS/LES simulations taking into account the radiative contribution.
DEFF Research Database (Denmark)
Liin, Sara I; Karlsson, Urban; Bentzen, Bo Hjorth
2016-01-01
the threshold current to evoke action potentials in dorsal root ganglion neurons. The polyunsaturated fatty acids docosahexaenoic acid, α-linolenic acid, and eicosapentaenoic acid facilitated opening of the human M-channel, comprised of the heteromeric human KV 7.2/3 channel expressed in Xenopus oocytes......, by shifting the conductance-versus-voltage curve towards more negative voltages (by -7.4 to -11.3 mV by 70 μM). Uncharged docosahexaenoic acid methyl ester and monounsaturated oleic acid did not facilitate opening of the human KV 7.2/3 channel. CONCLUSIONS: These findings suggest that circulating...... polyunsaturated fatty acids, with a minimum requirement of multiple double bonds and a charged carboxyl group, dampen excitability by opening neuronal M-channels. Collectively, our data bring light to the molecular targets of polyunsaturated fatty acids and thus a possible mechanism by which polyunsaturated fatty...
Schäfer, L.; Dierksheide, U.; Klaas, M.; Schröder, W.
2011-03-01
A new method to describe statistical information from passive scalar fields has been proposed by Wang and Peters ["The length-scale distribution function of the distance between extremal points in passive scalar turbulence," J. Fluid Mech. 554, 457 (2006)]. They used direct numerical simulations (DNS) of homogeneous shear flow to introduce the innovative concept. This novel method determines the local minimum and maximum points of the fluctuating scalar field via gradient trajectories, starting from every grid point in the direction of the steepest ascending and descending scalar gradients. Relying on gradient trajectories, a dissipation element is defined as the region of all the grid points, the trajectories of which share the same pair of maximum and minimum points. The procedure has also been successfully applied to various DNS fields of homogeneous shear turbulence using the three velocity components and the kinetic energy as scalar fields [L. Wang and N. Peters, "Length-scale distribution functions and conditional means for various fields in turbulence," J. Fluid Mech. 608, 113 (2008)]. In this spirit, dissipation elements are, for the first time, determined from experimental data of a fully developed turbulent channel flow. The dissipation elements are deduced from the gradients of the instantaneous fluctuation of the three velocity components u', v', and w' and the instantaneous kinetic energy k', respectively. The measurements are conducted at a Reynolds number of 1.7×104 based on the channel half-height δ and the bulk velocity U. The required three-dimensional velocity data are obtained investigating a 17.75×17.75×6 mm3 (0.355δ×0.355δ×0.12δ) test volume using tomographic particle-image velocimetry. Detection and analysis of dissipation elements from the experimental velocity data are discussed in detail. The statistical results are compared to the DNS data from Wang and Peters ["The length-scale distribution function of the distance between
Directory of Open Access Journals (Sweden)
Sigrid Marie Blom
Full Text Available The voltage-gated potassium channels of the KV7 family (KV7.1-5 play important roles in controlling neuronal excitability and are therefore attractive targets for treatment of CNS disorders linked to hyperexcitability. One of the main challenges in developing KV7 channel active drugs has been to identify compounds capable of discriminating between the neuronally expressed subtypes (KV7.2-5, aiding the identification of the subunit composition of KV7 currents in various tissues, and possessing better therapeutic potential for particular indications. By taking advantage of the structure-activity relationship of acrylamide KV7 channel openers and the effects of these compounds on mutant KV7 channels, we have designed and synthesized a novel KV7 channel modulator with a unique profile. The compound, named SMB-1, is an inhibitor of KV7.2 and an activator of KV7.4. SMB-1 inhibits KV7.2 by reducing the current amplitude and increasing the time constant for the slow component of the activation kinetics. The activation of KV7.4 is seen as an increase in the current amplitude and a slowing of the deactivation kinetics. Experiments studying mutant channels with a compromised binding site for the KV7.2-5 opener retigabine indicate that SMB-1 binds within the same pocket as retigabine for both inhibition of KV7.2 and activation of KV7.4. SMB-1 may serve as a valuable tool for KV7 channel research and may be used as a template for further design of better subtype selective KV7 channel modulators. A compound with this profile could hold novel therapeutic potential such as the treatment of both positive and cognitive symptoms in schizophrenia.
Numerical study on turbulent flow inside a channel with an extended chamber
International Nuclear Information System (INIS)
Lee, Young Tae; Lim, Hee Chang
2009-01-01
The paper presents a LES numerical simulation of turbulent flow around an extended chamber. The simulations are carried out on a series of 3-dimensional cavities placed in a turbulent boundary layer at a Reynolds number of 1.0x10 5 based on U and h, which are the velocity at the upper top of the cavity and the depth height, respectively. In order to get an appropriate solution in the Filtered Navier-Stokes equation for the incompressible flow, the computational mesh is densely attracted to the cavity surface and coarsely far-field, as this aids saving the computation cost and rapid convergence. The Boussinesq hypothesis is employed in the subgrid-scale turbulence model. In order to obtain the subgrid-scale turbulent viscosity, the Smagorinsky-Lilly SGS model is applied and the CFL number for time marching is 1.0. The results include the flow variations inside a cavity with the different sizes and shapes.
Numerical Study on Turbulent Flow Inside a Channel with an Extended Chamber
International Nuclear Information System (INIS)
Lee, Young Tae; Lim, Hee Chang
2010-01-01
The paper describes a Large Eddy Simulation (LES) study of turbulent flow around a cavity. A series of three-dimensional cavities placed in a turbulent boundary layer are simulated at a Reynolds number of 1.0 x 10 5 by considering U and h, which represent the velocity at the top and the depth of the cavity, respectively. In order to obtain the appropriate solution for the filtered Navier-Stokes equation for incompressible flow, the computational mesh forms dense close to the wall of the cavity but relatively coarse away from the wall; this helps reduce computation cost and ensure rapid convergence. The Boussinesq hypothesis is employed in the subgrid-scale turbulence model. In order to determine the subgrid-scale turbulent viscosity, the Smagorinsky-Lilly SGS model is applied and the CFL number for time marching is set as 1.0. The results show the flow variations inside cavities of different sizes and shapes
Zhu, Lu; Xi, Li
2018-04-01
Drag reduction induced by polymer additives in wall-bounded turbulence has been studied for decades. A small dosage of polymer additives can drastically reduce the energy dissipation in turbulent flows and alter the flow structures at the same time. As the polymer-induced fluid elasticity increases, drag reduction goes through several stages of transition with drastically different flow statistics. While much attention in the area of polymer-turbulence interactions has been focused on the onset and the asymptotic stage of maximum drag reduction, the transition between the two intermediate stages – low-extent drag reduction (LDR) and high-extent drag reduction (HDR) – likely reflects a qualitative change in the underlying vortex dynamics according to our recent study [1]. In particular, we proposed that polymers start to suppress the lift-up and bursting of vortices at HDR, leading to the localization of turbulent structures. To test our hypothesis, a statistically robust conditional sampling algorithm, based on Jenong and Hussain [2]’s work, was adopted in this study. The comparison of conditional eddies between the Newtonian and the highly elastic turbulence shows that (i) the lifting “strength” of vortices is suppressed by polymers as reflected by the decreasing lifting angle of the conditional eddy and (ii) the curvature of vortices is also eliminated as the orientation of the head of the conditional eddy changes. In summary, the results of conditional sampling support our hypothesis of polymer-turbulence interactions during the LDR-HDR transition.
International Nuclear Information System (INIS)
Takase, Kazuyuki; Akino, Norio
1996-06-01
Thermal-hydraulic characteristics of an annular fuel channel with spacer ribs for high temperature gas-cooled reactors were analyzed numerically by three-dimensional heat transfer computations under a fully developed turbulent flow. The two-equations κ-ε turbulence model was applied to the present turbulent analysis. In particular, the κ-ε turbulence model constants and the turbulent Prandtl number were improved from the previous standard values proposed by Jones and Launder in order to obtain heat transfer predictions with higher accuracy. Consequently, heat transfer coefficients and friction factors in the spacer-ribbed fuel channel were predicted with sufficient accuracy in the range of Reynolds number exceeding 3000. It was clarified quantitatively from the present study that main mechanism for the heat transfer augmentation in the spacer-ribbed fuel channel was combined effects of the turbulence promoter effect by the spacer ribs and the velocity acceleration effect by a reduction in the channel cross-section. (author)
Alheadary, Wael Ghazy
2017-07-20
This work investigates the end-to-end performance of a free space optical amplify-and-forward (AF) fixed-gain relaying system using heterodyne detection over misaligned general Malaga turbulence channels. More specifically, we present exact closed-form expressions for average bit-error rate achievable spectral efficiency non-adaptive/adaptive modulation schemes by employing generalized power series identity of Meijer\\'s G-function. Moreover, asymptotic closed-form expressions are derived to validate our results at high signal-to-noise ratio. In addition, the analytical results have been presented with compare to range of numerical values.
Alheadary, Wael Ghazy
2016-12-24
In this work, we present a bit error rate (BER) and achievable spectral efficiency (ASE) performance of a freespace optical (FSO) link with pointing errors based on intensity modulation/direct detection (IM/DD) and heterodyne detection over general Malaga turbulence channel. More specifically, we present exact closed-form expressions for adaptive and non-adaptive transmission. The closed form expressions are presented in terms of generalized power series of the Meijer\\'s G-function. Moreover, asymptotic closed form expressions are provided to validate our work. In addition, all the presented analytical results are illustrated using a selected set of numerical results.
International Nuclear Information System (INIS)
Huggins, E.R.
1994-01-01
Expressing hydrodynamics in terms of the flow of vorticity, using the vortex current tensor, helps unify the picture of turbulent channel flow for viscous fluids and for superfluids. In both, eddy viscosity plays a major role in energy dissipation, and in both there is a similar cross stream flow of vorticity, which in the case of superfluids leads to the Josephson frequency. The vortex current tensor, which was introduced in an earlier paper to derive an exact three dimensional Magnus effect formula, turns out to be the classical hydrodynamic limit of the vortex current that is the source for a classical Goldstone-boson field
Alheadary, Wael Ghazy; Park, Kihong; Alouini, Mohamed-Slim
2017-01-01
This work investigates the end-to-end performance of a free space optical amplify-and-forward (AF) fixed-gain relaying system using heterodyne detection over misaligned general Malaga turbulence channels. More specifically, we present exact closed-form expressions for average bit-error rate achievable spectral efficiency non-adaptive/adaptive modulation schemes by employing generalized power series identity of Meijer's G-function. Moreover, asymptotic closed-form expressions are derived to validate our results at high signal-to-noise ratio. In addition, the analytical results have been presented with compare to range of numerical values.
Flow of two stratified fluids in an open channel with addition of fluids along the channel length
International Nuclear Information System (INIS)
Gardner, G.C.
1980-01-01
It is shown that two stably stratified fluids flowing in an open channel have two critical flow conditions. The one at higher flowrates is equivalent to the choked flow condition of a single fluid over a broad-crested weir, when the Froude number is unity. The lower critical condition imposes restrictions, which define the system if fluids are added progressively along the channel length and the flowrates increase from low to high values. However, if the flowrate does not become sufficiently large to pass through the lower critical condition, this condition will then define a form of choking, which again determines the system. It is shown that an important special case, with the proportional flowrates of the two fluids kept constant, has an analytical solution in which the relative depths of the fluids is a constant along the channel. Other systems must be solved numerically. (orig.)
Gupta, Rajeev
2017-09-02
The drift kinetic energy of ionic flow through single ion channels cause vibrations of the pore walls which are observed as open-state current fluctuations (open-channel noise) during single-channel recordings. Vibration of the pore wall leads to transitions among different conformational sub-states of the channel protein in the open-state. Open-channel noise analysis can provide important information about the different conformational sub-state transitions and how biochemical modifications of ion channels would affect their transport properties. It has been shown that c-Jun N-terminal kinase-3 (JNK3) becomes activated by phosphorylation in various neurodegenerative diseases and phosphorylates outer mitochondrion associated proteins leading to neuronal apoptosis. In our earlier work, JNK3 has been reported to phosphorylate purified rat brain mitochondrial voltage-dependent anion channel (VDAC) in vitro and modify its conductance and opening probability. In this article we have compared the open-state noise profile of the native and the JNK3 phosphorylated VDAC using Power Spectral Density vs frequency plots. Power spectral density analysis of open-state noise indicated power law with average slope value α ≈1 for native VDAC at both positive and negative voltage whereas average α value open-state noise arises due to coupling of ionic transport and conformational sub-states transitions in open-state and this coupling is perturbed as a result of channel phosphorylation. Copyright © 2017 Elsevier Inc. All rights reserved.
Yang, Liang
2014-12-01
In this study, we consider a relay-assisted free-space optical communication scheme over strong atmospheric turbulence channels with misalignment-induced pointing errors. The links from the source to the destination are assumed to be all-optical links. Assuming a variable gain relay with amplify-and-forward protocol, the electrical signal at the source is forwarded to the destination with the help of this relay through all-optical links. More specifically, we first present a cumulative density function (CDF) analysis for the end-to-end signal-to-noise ratio. Based on this CDF, the outage probability, bit-error rate, and average capacity of our proposed system are derived. Results show that the system diversity order is related to the minimum value of the channel parameters.
Alheadary, Wael G.
2016-10-13
In this paper, we derive the performances of optical wireless communication system utilizing adaptive subcarrier intensity modulation over the Malaga turbulent channel. More specifically, analytical closed-form solutions and asymptotic results are derived for average bit error rate, achievable spectral efficiency, outage probability, and ergodic capacity by utilizing series expansion identity of modified Bessel function. Our asymptotic and analytical results based on series solutions with finite numbers highly matched to the numerical results. By exploiting the inherent nature of fading channel, the proposed adaptive scheme enhances the spectral efficiency without additional transmit power while satisfying the required bit error rate criterion. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
Alheadary, Wael Ghazy
2017-11-16
This work investigates the end-to-end performance of a free space optical amplify-and-forward relaying system using heterodyne detection over Malaga turbulence channels at the presence of pointing error. In order to overcome the analytical difficulties of the proposed composite channel model, we employed the mixture Gamma (MG) distribution. The proposed model shows a high accurate and tractable approximation just by adjusting some parameters. More specifically, we derived new closed-form expression for average bit error rate employing rectangular quadrature amplitude modulation in term of MG distribution and generalized power series of the Meijer\\'s G- function. The closed-form has been validated numerically and asymptotically at high signal to noise ratio.
Alheadary, Wael Ghazy
2017-09-21
This work investigates the end-to-end performance of a free space optical amplify-and-forward (AF) channel-state-information (CSI)-assisted relaying system using heterodyne detection over Malaga turbulence channels at the presence of pointing error employing rectangular quadrature amplitude modulation (R-QAM). More specifically, we present exact closed-form expressions for average bit-error rate for adaptive/non-adaptive modulation, achievable spectral efficiency, and ergodic capacity by utilizing generalized power series of Meijer\\'s G-function. Moreover, asymptotic closed form expressions are provided to validate our work at high power regime. In addition, all the presented analytical results are illustrated using a selected set of numerical results. Moreover, we applied the bisection method to find the optimum beam width for the proposed FSO system.
Turbulence from a microorganism's perspective: Does the open ocean feel different than a coral reef?
Pepper, Rachel; Variano, Evan; Koehl, M. A. R.
2012-11-01
Microorganisms in the ocean live in turbulent flows. Swimming microorganisms navigate through the water (e.g. larvae land on suitable substrata, predators find patches of prey), but the mechanisms by which they do so in turbulent flow are poorly understood as are the roles of passive transport versus active behaviors. Because microorganisms are smaller than the Kolmagorov length (the smallest scale of eddies in turbulent flow), they experience turbulence as a series of linear gradients in the velocity that vary in time. While the average strength of these gradients and a timescale can be computed from some typical characteristics of the flow, such as the turbulent kinetic energy or the dissipation rate, there are indications that organisms are disproportionally affected by rare, extreme events. Understanding the frequency of such events in different environments will be critical to understanding how microorganisms respond to and navigate in turbulence. To understand the hydrodynamic cues that microorganisms experience in the ocean we must measure velocity gradients in realistic turbulent flow on the spatial and temporal scales encountered by microorganisms. We have been exploring the effect of the spatial resolution of PIV and DNS of turbulent flow on the presence of velocity gradients of different magnitudes at the scale of microorganisms. Here we present some results of PIV taken at different resolutions in turbulent flow over rough biological substrata to illustrate the challenges of quantifying the fluctuations in velocity gradients encountered by aquatic microorganisms.
Upadhya, Abhijeet; Dwivedi, Vivek K.; Singh, G.
2018-06-01
In this paper, we have analyzed the performance of dual hop radio frequency (RF)/free-space optical (FSO) fixed gain relay environment confined by atmospheric turbulence induced fading channel over FSO link and modeled using α - μ distribution. The RF hop of the amplify-and-forward scheme undergoes the Rayleigh fading and the proposed system model also considers the pointing error effect on the FSO link. A novel and accurate mathematical expression of the probability density function for a FSO link experiencing α - μ distributed atmospheric turbulence in the presence of pointing error is derived. Further, we have presented analytical expressions of outage probability and bit error rate in terms of Meijer-G function. In addition to this, a useful and mathematically tractable closed-form expression for the end-to-end ergodic capacity of the dual hop scheme in terms of bivariate Fox's H function is derived. The atmospheric turbulence, misalignment errors and various binary modulation schemes for intensity modulation on optical wireless link are considered to yield the results. Finally, we have analyzed each of the three performance metrics for high SNR in order to represent them in terms of elementary functions and the achieved analytical results are supported by computer-based simulations.
Mitochondrial BK Channel Openers CGS7181 and CGS7184 Exhibit Cytotoxic Properties
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Bartłomiej Augustynek
2018-01-01
Full Text Available Potassium channel openers (KCOs have been shown to play a role in cytoprotection through the activation of mitochondrial potassium channels. Recently, in several reports, a number of data has been described as off-target actions for KCOs. In the present study, we investigated the effects of BKCa channel openers CGS7181, CGS7184, NS1619, and NS004 in neuronal cells. For the purpose of this research, we used a rat brain, the mouse hippocampal HT22 cells, and the human astrocytoma U-87 MG cell line. We showed that CGS7184 activated the mitochondrial BKCa (mitoBKCa channel in single-channel recordings performed on astrocytoma mitoplasts. Moreover, when applied to the rat brain homogenate or isolated rat brain mitochondria, CGS7184 increased the oxygen consumption rate, and can thus be considered a potentially cytoprotective agent. However, experiments on intact neuronal HT22 cells revealed that both CGS7181 and CGS7184 induced HT22 cell death in a concentration- and time-dependent manner. By contrast, we did not observe cell death when NS1619 or NS004 was applied. CGS7184 toxicity was not abolished by BKCa channel inhibitors, suggesting that the observed effects were independent of a BKCa-type channel activity. CGS7184 treatment resulted in an increase of cytoplasmic Ca2+ concentration that likely involved efflux from internal calcium stores and the activation of calpains (calcium-dependent proteases. The cytotoxic effect of the channel opener was partially reversed by a calpain inhibitor. Our data show that KCOs under study not only activate mitoBKCa channels from brain tissue, but also induce cell death when used in cellular models.
Nicorandil directly and cyclic GMP-dependently opens K+ channels in human bypass grafts
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Marija Marinko
2015-06-01
Full Text Available As we previously demonstrated the role of different K+ channels in the action of nicorandil on human saphenous vein (HSV and human internal mammary artery (HIMA, this study aimed to analyse the contribution of the cGMP pathway in nicorandil-induced vasorelaxation and to determine the involvement of cGMP in the K+ channel-activating effect of nicorandil. An inhibitor of soluble guanylate cyclase (GC, ODQ, significantly inhibited nicorandil-induced relaxation, while ODQ plus glibenclamide, a selective ATP-sensitive K+ (KATP channel inhibitor, produced a further inhibition of both vessels. In HSV, ODQ in combination with 4-aminopyridine, a blocker of voltage-gated K+ (KV channels, did not modify the concentration-response to nicorandil compared with ODQ, whereas in HIMA, ODQ plus iberiotoxin, a selective blocker of large-conductance Ca2+-activated K+ (BKCa channels, produced greater inhibition than ODQ alone. We showed that the cGMP pathway plays a significant role in the vasorelaxant effect of nicorandil on HSV and HIMA. It seems that nicorandil directly opens KATP channels in both vessels and BKCa channels in HIMA, although it is possible that stimulation of GC contributes to KATP channels activation in HIMA. Contrary, the activation of KV channels in HSV is probably due to GC activation and increased levels of cGMP.
Grid-generated He II turbulence in a finite channel - experiment
International Nuclear Information System (INIS)
Niemela, J.J.; Skrbek, L.; Stalp, S.R.
2001-01-01
We present experimental data on decaying turbulence, generated by towing a grid through a stationary sample of He II. We describe in detail the experimental apparatus and physical principles that allow observation of up to six orders of magnitude of decaying vortex line density over three orders of magnitude in time using the second sound attenuation technique. (orig.)
Yang, Liang; Gao, Xiqi; Alouini, Mohamed-Slim
2014-01-01
Free-space optical (FSO) communication has become a cost-effective method to provide high data rates. However, the turbulence-induced fading limits its application to short-range applications. To address this, we propose a multiuser diversity (MD
Varotsos, G. K.; Nistazakis, H. E.; Petkovic, M. I.; Djordjevic, G. T.; Tombras, G. S.
2017-11-01
Over the last years terrestrial free-space optical (FSO) communication systems have demonstrated an increasing scientific and commercial interest in response to the growing demands for ultra high bandwidth, cost-effective and secure wireless data transmissions. However, due the signal propagation through the atmosphere, the performance of such links depends strongly on the atmospheric conditions such as weather phenomena and turbulence effect. Additionally, their operation is affected significantly by the pointing errors effect which is caused by the misalignment of the optical beam between the transmitter and the receiver. In order to address this significant performance degradation, several statistical models have been proposed, while particular attention has been also given to diversity methods. Here, the turbulence-induced fading of the received optical signal irradiance is studied through the M (alaga) distribution, which is an accurate model suitable for weak to strong turbulence conditions and unifies most of the well-known, previously emerged models. Thus, taking into account the atmospheric turbulence conditions along with the pointing errors effect with nonzero boresight and the modulation technique that is used, we derive mathematical expressions for the estimation of the average bit error rate performance for SIMO FSO links. Finally, proper numerical results are given to verify our derived expressions and Monte Carlo simulations are also provided to further validate the accuracy of the analysis proposed and the obtained mathematical expressions.
Universal model of finite Reynolds number turbulent flow in channels and pipes
L'vov, V.S.; Procaccia, I.; Rudenko, O.
2008-01-01
In this Letter, we suggest a simple and physically transparent analytical model of pressure driven turbulent wall-bounded flows at high but finite Reynolds numbers Re. The model provides an accurate quantitative description of the profiles of the mean-velocity and Reynolds stresses (second order
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Su Xue-Feng
2010-05-01
Full Text Available Abstract Background Lung epithelial Na+ channels (ENaC are regulated by cell Ca2+ signal, which may contribute to calcium antagonist-induced noncardiogenic lung edema. Although K+ channel modulators regulate ENaC activity in normal lungs, the therapeutical relevance and the underlying mechanisms have not been completely explored. We hypothesized that K+ channel openers may restore calcium channel blocker-inhibited alveolar fluid clearance (AFC by up-regulating both apical and basolateral ion transport. Methods Verapamil-induced depression of heterologously expressed human αβγ ENaC in Xenopus oocytes, apical and basolateral ion transport in monolayers of human lung epithelial cells (H441, and in vivo alveolar fluid clearance were measured, respectively, using the two-electrode voltage clamp, Ussing chamber, and BSA protein assays. Ca2+ signal in H441 cells was analyzed using Fluo 4AM. Results The rate of in vivo AFC was reduced significantly (40.6 ± 6.3% of control, P Ca3.1 (1-EBIO and KATP (minoxidil channel openers significantly recovered AFC. In addition to short-circuit current (Isc in intact H441 monolayers, both apical and basolateral Isc levels were reduced by verapamil in permeabilized monolayers. Moreover, verapamil significantly altered Ca2+ signal evoked by ionomycin in H441 cells. Depletion of cytosolic Ca2+ in αβγ ENaC-expressing oocytes completely abolished verapamil-induced inhibition. Intriguingly, KV (pyrithione-Na, K Ca3.1 (1-EBIO, and KATP (minoxidil channel openers almost completely restored the verapamil-induced decrease in Isc levels by diversely up-regulating apical and basolateral Na+ and K+ transport pathways. Conclusions Our observations demonstrate that K+ channel openers are capable of rescuing reduced vectorial Na+ transport across lung epithelial cells with impaired Ca2+ signal.
Kv7.1 ion channels require a lipid to couple voltage sensing to pore opening.
Zaydman, Mark A; Silva, Jonathan R; Delaloye, Kelli; Li, Yang; Liang, Hongwu; Larsson, H Peter; Shi, Jingyi; Cui, Jianmin
2013-08-06
Voltage-gated ion channels generate dynamic ionic currents that are vital to the physiological functions of many tissues. These proteins contain separate voltage-sensing domains, which detect changes in transmembrane voltage, and pore domains, which conduct ions. Coupling of voltage sensing and pore opening is critical to the channel function and has been modeled as a protein-protein interaction between the two domains. Here, we show that coupling in Kv7.1 channels requires the lipid phosphatidylinositol 4,5-bisphosphate (PIP2). We found that voltage-sensing domain activation failed to open the pore in the absence of PIP2. This result is due to loss of coupling because PIP2 was also required for pore opening to affect voltage-sensing domain activation. We identified a critical site for PIP2-dependent coupling at the interface between the voltage-sensing domain and the pore domain. This site is actually a conserved lipid-binding site among different K(+) channels, suggesting that lipids play an important role in coupling in many ion channels.
PIV Measurements of Turbulent Flow in a Channel with Solid or Perforated Ribs
DEFF Research Database (Denmark)
Wang, Lei; Salewski, Mirko; Sundén, Bengt
2011-01-01
Particle image velocimetry measurements are performed in a channel with periodic ribs on one wall. We investigate the flow around two different rib configurations: solid and perforated ribs with a slit. The ribs obstruct the channel by 20% of its height and are arranged 10 rib heights apart. For ...
The regulation of mitochondrial respiration by opening of mKCa channels is age-dependent
Heinen, André; Winning, Adrian; Schlack, Wolfgang; Hollmann, Markus W.; Preckel, Benedikt; Frässdorf, Jan; Weber, Nina C.
2008-01-01
The protective potency of ischemic preconditioning decreases with increasing age. A key step in ischemic preconditioning is the opening of mitochondrial Ca(2+) sensitive K(+) (mK(Ca)) channels, which causes mild uncoupling of mitochondrial respiration. We hypothesized that aging reduces the effects
Study of the interference of plumes released from two near-ground point sources in an open channel
International Nuclear Information System (INIS)
Oskouie, Shahin N.; Wang, Bing-Chen; Yee, Eugene
2015-01-01
Highlights: • DNS study of turbulent dispersion and mixing of passive scalars. • Interference of two passive plumes in a boundary layer flow. • Cross correlation, co-spectra and coherency spectra of two plumes. - Abstract: The dispersion and mixing of passive scalars released from two near-ground point sources into an open-channel flow are studied using direct numerical simulation. A comparative study based on eight test cases has been conducted to investigate the effects of Reynolds number and source separation distance on the dispersion and interference of the two plumes. In order to determine the nonlinear relationship between the variance of concentration fluctuations of the total plume and those produced by each of the two plumes, the covariance of the two concentration fields is studied in both physical and spectral spaces. The results show that at the source height, the streamwise evolution of the cross correlation between the fluctuating components of the two concentration fields can be classified into four stages, which feature zero, destructive and constructive interferences and a complete mixing state. The characteristics of these four stages of plume mixing are further confirmed through an analysis of the pre-multiplied co-spectra and coherency spectra. From the coherency spectrum, it is observed that there exists a range of ‘leading scales’, which are several times larger than the Kolmogorov scale but are smaller than or comparable to the scale of the most energetic eddies of turbulence. At the leading scales, the mixing between the two interfering plumes is the fastest and the coherency spectrum associated with these scales can quickly approach its asymptotic value of unity.
Turbulent heat transfer in a coolant channel of a pressurized water reactor (PWR) core
International Nuclear Information System (INIS)
Kumar, Sanjeev; Saha, Arun K.; Munshi, Prabhat
2016-01-01
Exact predictions in nuclear reactors are more crucial, because of the safety aspects. It necessitates the appropriate modeling of heat transfer phenomena in the reactors core. A two-dimensional thermal-hydraulics model is used to study the detailed analysis of the coolant region of a fuel pin. Governing equations are solved using Marker and Cell (MAC) method. Standard wall functions k-ε turbulence model is incorporated to consider the turbulent behaviour of the flow field. Validation of the code and a few results for a typical PWR running at normal operating conditions reported earlier. There were some discrepancies in the old calculations. These discrepancies have been resolved and updated results are presented in this work. 2D thermal-hydraulics model results have been compared with the 1D thermal-hydraulics model results and conclusions have been drawn. (author)
Mechanism of transition to turbulence in a circular cylinder wake in a channel
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Molochnikov Valery
2017-01-01
Full Text Available Transition to turbulence in the circular cylinder wake has been studied experimentally and numerically at growing Reynolds number. Good agreement of calculation results with the flow visualization and measurements of instantaneous vector fields of velocity and vorticity has been demonstrated. The growing Reynolds number is shown to make large-scale vortex generation onset move upstream. It also triggers the transition to 3D flow pattern in the cylinder wake. This process is accompanied by non-monotonous behavior of the profiles of velocity and its turbulent fluctuations at equal distances from the cylinder. Non-monotonous behavior of the cylinder drag has been revealed for the Reynolds numbers ranging from 120 to 300.
Inhomogeneous vortex tangles in counterflow superfluid turbulence: flow in convergent channels
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Saluto Lidia
2016-06-01
Full Text Available We investigate the evolution equation for the average vortex length per unit volume L of superfluid turbulence in inhomogeneous flows. Inhomogeneities in line density L andincounterflowvelocity V may contribute to vortex diffusion, vortex formation and vortex destruction. We explore two different families of contributions: those arising from asecondorder expansionofthe Vinenequationitself, andthose whichare notrelated to the original Vinen equation but must be stated by adding to it second-order terms obtained from dimensional analysis or other physical arguments.
The influence of the Reynolds number on the passive scalar field in a turbulent channel flow
International Nuclear Information System (INIS)
Bergant, R.; Tiselj, I.
2006-01-01
Many different turbulent heat transfer calculations based on a very accurate pseudo-spectral code have been performed in the last 5 years. The main effort was to investigate temperature fields at different Prandtl numbers, ranging from Pr=0.7 to Pr=200. For the treatment of the turbulent heat transfer at low Reynolds and high Prandtl numbers, a Direct Numerical Simulation (DNS) was used for structures of the turbulent motions. DNS describes all the length and time scales for velocity and temperature fields. When Prandtl number is higher than 1, the smallest temperature scales are approximately inversely proportional to the square root of Prandtl number. For the smallest temperature scales, not resolved in the high Prandtl number simulation, a spectral turbulent diffusivity model was used in the pseudo-spectral computer code for DNS. A comparison of our temperature profiles obtained at friction Reynolds number Reτ=150 and Pr=100 and Pr=200 to the mean profiles of Calmet and Magnaudet, Wang and Lu and Kader's correlation that was built as a best fit of various experimental data at higher Reynolds numbers, revealed the discrepancies up to 10%. The most important reason for the differences was in different Reynolds numbers, which were much lower in our simulations than in the above mentioned LES simulations and experiments. The similar phenomenon as in our case can be found when DNS of Kawamura and Kader's results at Reτ=180 and Pr=0.71 were compared. On the other hand, the comparisons to the Kader's correlation at higher Reynolds numbers (i.e. DNS of Kawamura at Reτ=640 and DNS of Tiselj at Reτ=424) show that the differences are within statistical uncertainties. It follows that the heat transfer depends much more on Reynolds number in the range of low Reynolds numbers than in the range of high Reynolds numbers. (author)
Characterization of Unruh channel in the context of open quantum systems
International Nuclear Information System (INIS)
Banerjee, Subhashish; Alok, Ashutosh Kumar; Omkar, S.; Srikanth, R.
2017-01-01
In this work, we study an important facet of field theories in curved spacetime, viz. the Unruh effect, by making use of ideas of statistical mechanics and quantum foundations. Aspects of decoherence and dissipation, natural artifacts of open quantum systems, along with foundational issues such as the trade-off between coherence and mixing as well as various aspects of quantum correlations are investigated in detail for the Unruh effect. We show how the Unruh effect can be quantified mathematically by the Choi matrix approach. We study how environmentally induced decoherence modifies the effect of the Unruh channel. The differing effects of a dissipative or non-dissipative environment are noted. Further, useful parameters characterizing channel performance such as gate and channel fidelity are applied here to the Unruh channel, both with and without external influences. Squeezing, which is known to play an important role in the context of particle creation, is shown to be a useful resource in a number of scenarios.
Heat mass transfer in turbulent flow of dissociating N2O4 in a channel of complex geometry
International Nuclear Information System (INIS)
Nesterenko, V.B.; Tverkovkin, B.E.; Yakushev, A.P.; Mikryukova, T.I.
1976-01-01
The processes of heat and mass transfer at turbulent flow of the N 2 O 4 -dissociating gas along the bundles of fuel elements are investigated. A numerical solution has been obtained by the method of variable directions with the second-order boundary conditions in the following range of parameters: Reinolds number, Re=(0.12-1.73)x10 5 ; pressure, p=45-170 bar; a relative spacing between rods, t=1.05; 1.1; and the gsub(e)rsub(0)/Λsub(f)=(0.2-1.44)x10 5 , where qsub(e) is a specific thermal flux on the rod surface; rsub(0) - a rod radius; Λsub(f)-thermal conductivity of the coolant. The coolant temperature at channel inlet is 450 deg K. Temperature and concentration fields of the O 2 -component are obtained. The effect of pressure on the distribution of temperatures and concentrations of the O 2 -component and their non-uniformity over a perimeter are investigated. The distributions average Nusselt numbers over the channel length versus the pressure of a gaseous mixture are obtained. A significant effect of chemical reactions on heat transfer in the channel of a complicated form is shown
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Suranga Dharmarathne
2018-02-01
Full Text Available Direct numerical simulations of a turbulent channel flow with a passive scalar at R e τ = 394 with blowing perturbations is carried out. The blowing is imposed through five spanwise jets located near the upstream end of the channel. Behind the blowing jets (about 1 D , where D is the jet diameter, we observe regions of reversed flow responsible for the high temperature region at the wall: hot spots that contribute to further heating of the wall. In between the jets, low pressure regions accelerate the flow, creating long, thin, streaky structures. These structures contribute to the high temperature region near the wall. At the far downstream of the jet (about 3 D , flow instabilities (high shear created by the blowing generate coherent vortical structures. These structures move hot fluid near the wall to the outer region of the channel; thereby, these are responsible for cooling of the wall. Thus, for engineering applications where cooling of the wall is necessary, it is critical to promote the generation of coherent structures near the wall.
Heat and mass transfer for turbulent flow of chemically reacting gas in eccentric annular channels
International Nuclear Information System (INIS)
Besedina, T.V.; Tverkovkin, B.E.; Udot, A.V.; Yakushev, A.P.
1988-01-01
Because of the possibility of using dissociating gases as coolants and working bodies of nuclear power plants, it is necessary to develop computational algorithms for calculating heat and mass transfer processes under conditions of nonequilibrium flow of chemically reacting gases not only in axisymmetric channels, but also in channels with a complex transverse cross section (including also in eccentric annular channels). An algorithm is proposed for calculating the velocity, temperature, and concentration fields under conditions of cooling of a cylindrical heat-releasing rod, placed off-center in a circular casing pipe, by a longitudinal flow of chemically reacting gas [N 2 O 4
In Vitro Contractile Response of Rabbit Myometrium to BKCa and KATP Potassium Channel Openers
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Soňa Fraňová
2009-01-01
Full Text Available The aim of the study was to evaluate the participation of ligand-sensitive potassium large conductance calcium-activated channels (BKCa and ATP-sensitive potassium channels in uterine smooth muscle reactivity during different stages of the experimentally induced proliferatory and secretory phase in the sexual cycle in ovariectomised rabbits in vitro. The myometrial reactivity to oxytocin (10-6 mol l-1 was investigated by an in vitro method in female rabbits 14 days after ovariectomy treated with 17β-estradiol - 1 mg/kg/day i.m. for 7 days, or with a combination of progesterone 2 mg/kg/day s.c. for 7 days and 17β-estradiol - 0.2 mg/ kg/day (day 3–7. The strips of myometrial smooth muscle were incubated with a specific opener (NS 1619 and an antagonist (TEA of potassium large conductance calcium-activated channel, or with a specific opener (pinacidil and an antagonist (glybenclamide of ATP-sensitive potassium channels before the administration of oxytocin. NS1619 produced more potent inhibition of the oxytocin-induced contraction during the gestagen dominance (experimental secretory phase than the one observed during the oestrogen dominance (experimental proliferatory phase. TEA antagonized the NS1619 induced inhibition of the myometrial contraction. In the matter of KATP potassium channels, after the administration of pinacidil we observed a similar situation in the changes of myometrial contractility. Pinacidil produced more pronounced inhibition of oxytocin-induced contraction during the secretory phase, and its effect was abolished by the selective inhibitor glybenclamide. Our experimental results indicate that both potassium large conductance calcium-activated channels and ATP-sensitive potassium channels significantly participate in the regulation of myometrial oxytocin-induced contractions and the activity of these channels is probably influenced by the levels of oestrogens and gestagens.
Experimental study of the critical density of heat flux in open channels cooled with helium - II
International Nuclear Information System (INIS)
Pron'ko, V.G.; Gorokhov, V.V.; Saverin, V.N.
1981-01-01
Experimental values of the critical density of a heat flux qsub(cr) in uniformly heated open channels cooled with helium-2 are reported for the first time. The experimental test bench and experimental element are described. Experimental data are obtained in cylindrical channels of 12Kh18N1OT steel with inner diameter d=0.8, 1.8; 2.8 mm and ratio l/d=20.8, 44, 85. The channel orientation has varied from vertical to horizontal position, the immersion depth - from 100, to 600 mm. It has been found that the heat transfer crisis propagation over the whole length of the channel with He-2 occurs practically instantaneously. The qsub(cr) value depends essentially on the bath liquid temperature, angle of inclivnation and relative length (l/d) of the channel with qsub(cr) approximately (l/d)sup(-1.5) being independent of the depth of channel immersion. The obtained values of critical density of a heat flux in channels are papproximately by an order less than those found for a great bulk of He-2. The results presented may be used for designing various types of devices cooled with He-2 and development of heat exchange theory in it [ru
Zamora, Blas; Kaiser, Antonio S.
2012-01-01
The effects of the air variable properties (density, viscosity and thermal conductivity) on the buoyancy-driven flows established in open square cavities are investigated, as well as the influence of the stated boundary conditions at open edges and the employed differencing scheme. Two-dimensional, laminar, transitional and turbulent simulations are obtained, considering both uniform wall temperature and uniform heat flux heating conditions. In transitional and turbulent cases, the low-Reynolds k - ω turbulence model is employed. The average Nusselt number and the dimensionless mass-flow rate have been obtained for a wide and not yet covered range of the Rayleigh number varying from 103 to 1016. The results obtained taking into account variable properties effects are compared with those calculated assuming constant properties and the Boussinesq approximation. For uniform heat flux heating, a correlation for the critical heating parameter above which the burnout phenomenon can be obtained is presented, not reported in previous works. The effects of variable properties on the flow patterns are analyzed.
Bargiello, Thaddeus A; Oh, Seunghoon; Tang, Qingxiu; Bargiello, Nicholas K; Dowd, Terry L; Kwon, Taekyung
2018-01-01
Voltage is an important physiologic regulator of channels formed by the connexin gene family. Connexins are unique among ion channels in that both plasma membrane inserted hemichannels (undocked hemichannels) and intercellular channels (aggregates of which form gap junctions) have important physiological roles. The hemichannel is the fundamental unit of gap junction voltage-gating. Each hemichannel displays two distinct voltage-gating mechanisms that are primarily sensitive to a voltage gradient formed along the length of the channel pore (the transjunctional voltage) rather than sensitivity to the absolute membrane potential (V m or V i-o ). These transjunctional voltage dependent processes have been termed V j - or fast-gating and loop- or slow-gating. Understanding the mechanism of voltage-gating, defined as the sequence of voltage-driven transitions that connect open and closed states, first and foremost requires atomic resolution models of the end states. Although ion channels formed by connexins were among the first to be characterized structurally by electron microscopy and x-ray diffraction in the early 1980's, subsequent progress has been slow. Much of the current understanding of the structure-function relations of connexin channels is based on two crystal structures of Cx26 gap junction channels. Refinement of crystal structure by all-atom molecular dynamics and incorporation of charge changing protein modifications has resulted in an atomic model of the open state that arguably corresponds to the physiologic open state. Obtaining validated atomic models of voltage-dependent closed states is more challenging, as there are currently no methods to solve protein structure while a stable voltage gradient is applied across the length of an oriented channel. It is widely believed that the best approach to solve the atomic structure of a voltage-gated closed ion channel is to apply different but complementary experimental and computational methods and to use
International Nuclear Information System (INIS)
Dashti, Mohsen; Rasouli, Saifollah
2012-01-01
Recently, an adjustable, high-sensitivity, wide dynamic range, two-channel wavefront sensor based on moiré deflectometry was proposed by Rasouli et al (2010 Opt. Express 18 23906). In this work we have used this sensor on a telescope for measuring turbulence-induced wavefront distortions. A slightly divergent laser beam passes through turbulent ground level atmosphere and enters the telescope’s aperture. The laser beam is collimated behind the telescope’s focal point by means of a collimator and the beam enters the wavefront sensor. First, from deviations in the moiré fringes we calculate the two orthogonal components of the angle of arrival at each location across the wavefront. The deviations have been deduced in successive frames which allows evolution of the wavefront shape and Fried’s seeing parameter r 0 to be determined. Mainly, statistical analysis of the reconstructed wavefront distortions are presented. The achieved accuracy in the measurements and comparison between the measurements and the theoretical models are presented. Owing to the use of the sensor on a telescope, and using sub-pixel accuracy for the measurement of the moiré fringe displacements, the sensitivity of the measurements is improved by more than one order of magnitude. In this work we have achieved a minimum measurable angle of arrival fluctuations equal to 3.7 × 10 −7 rad or 0.07 arc s. Besides, because of the large area of the telescope’s aperture, a high spatial resolution is achieved in detecting the spatial perturbations of the atmospheric turbulence. (paper)
Numerical study of an impinging jet to a turbulent channel flow in a T-Junction configuration
Georgiou, Michail; Papalexandris, Miltiadis
2016-11-01
In this talk we report on Large Eddy Simulations of an impinging planar jet to a turbulent channel flow in a T-Junction configuration. Due to its capacity for mixing and heat transfer enhancement, this type of flow is encountered in various industrial applications. In particular, our work is related to the emergency cooling systems of pressurized water reactors. As is well known, this type of flow is dominated by a large separation bubble downstream the jet impingement location. Secondary regions of flow separation are predicted both upstream and downstream the impinging jet. We describe how these separation regions interact with the shear layer that is formed by the injection of the jet to the crossflow, and how they affect the mixing process. In our talk we further examine the influence of the jet's velocity to characteristic quantities of the jet, such as penetration length and expansion angle, as well as to the first and second-order statistics of the flow.
Gritti, Fabrice; Fogwill, Michael
2017-06-09
The potential advantage of turbulent supercritical fluid chromatography (TSFC) in open tubular columns (OTC) was evaluated on both theoretical and practical viewpoints. First, the dispersion model derived by Golay in 1958 and recently extended from laminar to turbulent flow regime is used for the predictions of the speed-resolution performance in TSFC. The average dispersion coefficient of matter in the turbulent flow regime was taken from the available experimental data over a range of Reynolds number from 2000 to 6000. Kinetic plots are built at constant pressure drop (ΔP=4500psi) and Schmidt number (Sc=15) for four inner diameters (10, 30, 100, and 300μm) of the OTC and for three retention factors (0, 1, and 10). Accordingly, in turbulent flow regime, for a Reynolds number of 4000 and a retention factor of 1 (the stationary film thickness is assumed to be negligible with respect to the OTC diameter), the theory projects that a 300μm i.d. OTC has the same speed-resolution power (200,000 theoretical plates; 2.4min hold-up time) as that of a 10μm i.d. OTC operated in laminar flow regime. Secondly, the experimental plate heights of n-butylbenzene are measured in laminar and turbulent flow regimes for a 180μm×4.8m fused silica capillary column using pure carbon dioxide as the mobile phase. The back pressure regulator was set at 1500psi, the temperature was uniform at 297K, and the flow rate was increased step-wise from 0.50 to 3.60mL/min so that the experimental Reynolds number increases from 700 to 5400. The experiments are in good agreement with the plate heights projected in TSFC at high flow rates and with those expected at low flow rates in a laminar flow regime. Copyright © 2017 Elsevier B.V. All rights reserved.
A KCNQ channel opener for experimental neonatal seizures and status epilepticus
Raol, YogendraSinh H.; Lapides, David A.; Keating, Jeffery; Brooks-Kayal, Amy R.; Cooper, Edward C.
2009-01-01
Objective Neonatal seizures occur frequently, are often refractory to anticonvulsants, and are associated with considerable morbidity and mortality. Genetic and electrophysiological evidence indicates that KCNQ voltage-gated potassium channels are critical regulators of neonatal brain excitability. This study tests the hypothesis that selective openers of KCNQ channels may be effective for treatment of neonatal seizures. Methods We induced seizures in postnatal day 10 rats with either kainic acid or flurothyl. We measured seizure activity using quantified behavioral rating and electrocorticography. We compared the efficacy of flupirtine, a selective KCNQ channel opener, with phenobarbital and diazepam, two drugs in current use for neonatal seizures. Results Unlike phenobarbital or diazepam, flupirtine prevented animals from developing status epilepticus (SE) when administered prior to kainate. In the flurothyl model, phenobarbital and diazepam increased latency to seizure onset, but flupirtine completely prevented seizures throughout the experiment. Flupirtine was also effective in arresting electrographic and behavioral seizures when administered after animals had developed continuous kainate-induced SE. Flupirtine caused dose-related sedation and suppressed EEG activity, but did not result in respiratory suppression or result in any mortality. Interpretation Flupirtine appears more effective than either of two commonly used anti-epileptic drugs, phenobarbital and diazepam, in preventing and suppressing seizures in both the kainic acid and flurothyl models of symptomatic neonatal seizures. KCNQ channel openers merit further study as potential treatments for seizures in infants and children. PMID:19334075
Numerical study on flow rate limitation of open capillary channel flow through a wedge
Directory of Open Access Journals (Sweden)
Ting-Ting Zhang
2016-04-01
Full Text Available The flow characteristics of slender-column flow in wedge-shaped channel under microgravity condition are investigated in this work. The one-dimensional theoretical model is applied to predict the critical flow rate and surface contour of stable flow. However, the one-dimensional model overestimates the critical flow rate for not considering the extra pressure loss. Then, we develop a three-dimensional simulation method with OpenFOAM, a computational fluid dynamics tool, to simulate various phenomena in wedge channels with different lengths. The numerical results are verified with the capillary channel flow experimental data on the International Space Station. We find that the three-dimensional simulation perfectly predicts the critical flow rates and surface contours under various flow conditions. Meanwhile, the general behaviors in subcritical, critical, and supercritical flow are studied in three-dimensional simulation considering variations of flow rate and open channel length. The numerical techniques for three-dimensional simulation is validated for a wide range of configurations and is hopeful to provide valuable guidance for capillary channel flow experiment and efficient liquid management in space.
Nakashima, K.; Watanabe, S.; Matsushita, D.; Tsuda, S.; Furukawa, A.
2016-11-01
Small hydropower is one of the renewable energies and is expected to be effectively used for local supply of electricity. We have developed Darrieus-type hydro-turbine systems, and among them, the Darrieus-turbine with a weir and a nozzle installed upstream of turbine is, so far, in success to obtain more output power by gathering all water into the turbine. However, there can several cases exist, in which installing the weir covering all the flow channel width is unrealistic, and in such cases, the turbine should be put alone in open channels without upstream weir. Since the output power is very small in such a utilization of small hydropower, it is important to derive more power for the cost reduction. In the present study, we parametrically investigate the preferable shape of the inlet nozzle for the Darrieus-type hydroturbine operated in an open flow channel. Experimental investigation is carried out in the open channel in our lab. Tested inlet nozzles are composed of two flat plates with the various nozzle converging angles and nozzle outlet (runner inlet) widths with the nozzle inlet width kept constant. As a result, the turbine with the nozzles having large converging angle and wide outlet width generates higher power. Two-dimensional unsteady numerical simulation is also carried out to qualitatively understand the flow mechanism leading to the better performance of turbine. Since the depth, the width and the flow rate in the real open flow channels are different from place to place and, in some cases from time to time, it is also important to predict the onsite performance of the hydroturbine from the lab experiment at planning stage. One-dimensional stream-tube model is developed for this purpose, in which the Darrieus-type hydroturbine with the inlet nozzle is considered as an actuator-disk modelled based on our experimental and numerical results.
Directory of Open Access Journals (Sweden)
Jiandong Yang
2015-10-01
Full Text Available On the basis of the state–space method (SSM, a novel linear mathematical model of the unsteady flow for the tailrace system with an open channel is proposed. This novel model is an elastic linearized model of water hammer. The validity of the model has been verified by several examples of numerical simulation, which are based on a finite difference technique. Then, the complete mathematical model for the hydro-turbine governing system of hydropower station with an open tailrace channel, which is used for simulating the transient process of the hydro-turbine governing system under load disturbance, is established by combining the models of hydro-turbine, generator, governor and open tailrace channel. Finally, according to the complete model, the regulation quality for hydro-turbine governing system with an open tailrace channel under load disturbance is studied, and the effects of open tailrace channel and tailrace surge tank on regulation quality are analyzed. The results indicate that: The open tailrace channel has a strong influence on the regulation quality by observing the water level fluctuations in tailrace surge tank. The surge shows a piecewise periodical change along with the variation in the length of an open channel. The open tailrace channel can be used to improve the regulation quality of hydro-turbine governing system.
uFLIP-OC: Understanding Flash I/O Patterns on Open-Channel Solid State Drives
DEFF Research Database (Denmark)
Picoli, Ivan Luiz; Villegas Pasco, Carla Ysabela; Jónsson, Björn Thór
2017-01-01
on a clean break from the block device abstraction. Open-channel SSDs embed a minimal flash translation layer (FTL) and expose their internals to the host. The Linux open-channel SSD subsystem, LightNVM, lets kernel modules as well as user-space applications control data placement and I/O scheduling...
Oliveira, Bruna Gonçalves; Carvalho, João Luís Nunes; Chagas, Mateus Ferreira; Cerri, Carlos Eduardo Pellegrino; Cerri, Carlos Clemente; Feigl, Brigitte Josefine
2017-06-01
Over the last few years the brazilian sugarcane sector has produced an average of 23.5 million liters of ethanol annually. This scale of production generates large amounts of vinasse, which depending on the manner that is disposed, can result significant greenhouse gas emissions. This study aimed to quantify the methane (CH4) emissions associated with the two most widespread systems of vinasse storage and transportation used in Brazil; open channel and those comprising of tanks and pipes. Additionally, a laboratory incubation study was performed with the aim of isolating the effects of vinasse, sediment and the interaction between these factors on CH4 emissions. We observed significant differences in CH4 emissions between the sampling points along the channels during both years of evaluation (2012-2013). In the channel system, around 80% of CH4 emissions were recorded from uncoated sections. Overall, the average CH4 emission intensity was 1.36 kg CO2eq m-3 of vinasse transported in open channels, which was 620 times higher than vinasse transported through a system of tanks and closed pipes. The laboratory incubation corroborated field results, suggesting that vinasse alone does not contribute significant emissions of CH4. Higher CH4 emissions were observed when vinasse and sediment were incubated together. In summary, our findings demonstrate that CH4 emissions originate through the anaerobic decomposition of organic material deposited on the bottom of channels and tanks. The adoption of coated channels as a substitute to uncoated channels offers the potential for an effective and affordable means of reducing CH4 emissions. Ultimately, the modernization of vinasse storage and transportation systems through the adoption of tank and closed pipe systems will provide an effective strategy for mitigating CH4 emissions generated during the disposal phase of the sugarcane ethanol production process.
Sukhodolov, Alexander N.; Krick, Julian; Sukhodolova, Tatiana A.; Cheng, Zhengyang; Rhoads, Bruce L.; Constantinescu, George S.
2017-06-01
Only a handful of field studies have examined turbulent flow structure at discordant confluences; the dynamics of flow at such confluences have mainly been examined in the laboratory. This paper reports results of a field-based investigation of turbulent flow structure at a discordant river confluence. These results support the hypothesis that flow at a discordant alluvial confluence with a velocity ratio greater than 2 exhibits jet-like characteristics. Scaling analysis shows that the dynamics of the jet core are quite similar to those of free jets but that the complex structure of flow at the confluence imposes strong effects that can locally suppress or enhance the spreading rate of the jet. This jet-like behavior of the flow has important implications for morphodynamic processes at these types of confluences. The highly energetic core of the jet at this discordant confluence is displaced away from the riverbed, thereby inhibiting scour; however, helical motion develops adjacent to the jet, particularly at high flows, which may promote scour. Numerical experiments demonstrate that the presence or absence of a depositional wedge at the mouth of the tributary can strongly influence detachment of the jet from the bed and the angle of the jet within the confluence.
A Fast, Open EEG Classification Framework Based on Feature Compression and Channel Ranking
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Jiuqi Han
2018-04-01
Full Text Available Superior feature extraction, channel selection and classification methods are essential for designing electroencephalography (EEG classification frameworks. However, the performance of most frameworks is limited by their improper channel selection methods and too specifical design, leading to high computational complexity, non-convergent procedure and narrow expansibility. In this paper, to remedy these drawbacks, we propose a fast, open EEG classification framework centralized by EEG feature compression, low-dimensional representation, and convergent iterative channel ranking. First, to reduce the complexity, we use data clustering to compress the EEG features channel-wise, packing the high-dimensional EEG signal, and endowing them with numerical signatures. Second, to provide easy access to alternative superior methods, we structurally represent each EEG trial in a feature vector with its corresponding numerical signature. Thus, the recorded signals of many trials shrink to a low-dimensional structural matrix compatible with most pattern recognition methods. Third, a series of effective iterative feature selection approaches with theoretical convergence is introduced to rank the EEG channels and remove redundant ones, further accelerating the EEG classification process and ensuring its stability. Finally, a classical linear discriminant analysis (LDA model is employed to classify a single EEG trial with selected channels. Experimental results on two real world brain-computer interface (BCI competition datasets demonstrate the promising performance of the proposed framework over state-of-the-art methods.
Large Eddy Simulation of turbulent flows in compound channels with a finite element code
International Nuclear Information System (INIS)
Xavier, C.M.; Petry, A.P.; Moeller, S.V.
2011-01-01
This paper presents the numerical investigation of the developing flow in a compound channel formed by a rectangular main channel and a gap in one of the sidewalls. A three dimensional Large Eddy Simulation computational code with the classic Smagorinsky model is introduced, where the transient flow is modeled through the conservation equations of mass and momentum of a quasi-incompressible, isothermal continuous medium. Finite Element Method, Taylor-Galerkin scheme and linear hexahedrical elements are applied. Numerical results of velocity profile show the development of a shear layer in agreement with experimental results obtained with Pitot tube and hot wires. (author)
Moreno, P. A.; Bombardelli, F. A.
2012-12-01
Particles laying motionless at the bed of rivers, lakes and estuaries can be put into motion when the shear stress exerted by the flow on the particles exceeds the critical shear stress. When these particles start their motion they can either remain suspended by long periods of time (suspended load) or move close to the bed (bed load). Particles are transported as bed load in three different modes: Sliding, rolling and saltation. Saltation is usually described as the bouncing motion of sediment particles in a layer a few particle diameters thick. The amount of particles and the bed-load mode in which they move depend on the particle size and density, and the flow intensity, usually quantified by the shear velocity. The bottom shear stress in natural streams will most likely be large enough to set saltation as the most important bed-load transport mechanism among all three modes. Thus, studying the saltation process is crucial for the overall understanding of bed-load transport. Particularly, numerical simulations of this process have been providing important insight regarding the relative importance of the physical mechanisms involved in it. Several processes occur when particles are saltating near the bed: i) Particles collide with the bed, ii) they "fly" between collisions with the bed, as a result of their interaction with the fluid flow, iii) and they collide among themselves. These processes can be simulated using a three-dimensional Eulerian-Lagrangian model. In order to mimic these processes we have experimented with an averaged turbulent flow field represented by the logarithmic law of the wall, and with a more involved approach in which a computed turbulent velocity field for a flat plate was used as a surrogate of the three-dimensional turbulent conditions present close to stream beds. Since flat-plate and open-channel boundary layers are essentially different, a dynamic similarity analysis was performed showing that the highly-resolved three
Wang, Zhan-zhi; Xiong, Ying
2013-04-01
A growing interest has been devoted to the contra-rotating propellers (CRPs) due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibration. Compared with the single-screw system, it is more difficult for the open water performance prediction because forward and aft propellers interact with each other and generate a more complicated flow field around the CRPs system. The current work focuses on the open water performance prediction of contra-rotating propellers by RANS and sliding mesh method considering the effect of computational time step size and turbulence model. The validation study has been performed on two sets of contra-rotating propellers developed by David W Taylor Naval Ship R & D center. Compared with the experimental data, it shows that RANS with sliding mesh method and SST k-ω turbulence model has a good precision in the open water performance prediction of contra-rotating propellers, and small time step size can improve the level of accuracy for CRPs with the same blade number of forward and aft propellers, while a relatively large time step size is a better choice for CRPs with different blade numbers.
Turbulent oscillating channel flow subjected to a free-surface stress.
Kramer, W.; Clercx, H.J.H.; Armenio, V.
2010-01-01
The channel flow subjected to a wind stress at the free surface and an oscillating pressure gradient is investigated using large-eddy simulations. The orientation of the surface stress is parallel with the oscillating pressure gradient and a purely pulsating mean flow develops. The Reynolds number
Determination of Flow Resistance Coefficient for Vegetation in Open Channel: Laboratory study
Aliza Ahmad, Noor; Ali, ZarinaMd; Arish, Nur Aini Mohd; Munirah Mat Daud, Azra; Fatin Amirah Alias, Nur
2018-04-01
This study focused on determination of flow resistances coefficient for grass in an open channel. Laboratory works were conducted to examine the effects of varying of roughness elements on the flume to determine flow resistance coefficient and also to determine the optimum flow resistance with five different flow rate, Q. Laboratory study with two type of vegetation which are Cow Grass and Pearl Grass were implementing to the bed of a flume. The roughness coefficient, n value is determine using Manning’s equation while Soil Conservation Services (SCS) method was used to determine the surface resistance. From the experiment, the flow resistance coefficient for Cow Grass in range 0.0008 - 0.0039 while Pearl Grass value for the flow resistance coefficient are in between 0.0013 - 0.0054. As a conclusion the vegetation roughness value in open channel are depends on density, distribution type of vegetation used and physical characteristic of the vegetation itself
Robust boundary treatment for open-channel flows in divergence-free incompressible SPH
Pahar, Gourabananda; Dhar, Anirban
2017-03-01
A robust Incompressible Smoothed Particle Hydrodynamics (ISPH) framework is developed to simulate specified inflow and outflow boundary conditions for open-channel flow. Being purely divergence-free, the framework offers smoothed and structured pressure distribution. An implicit treatment of Pressure Poison Equation and Dirichlet boundary condition is applied on free-surface to minimize error in velocity-divergence. Beyond inflow and outflow threshold, multiple layers of dummy particles are created according to specified boundary condition. Inflow boundary acts as a soluble wave-maker. Fluid particles beyond outflow threshold are removed and replaced with dummy particles with specified boundary velocity. The framework is validated against different cases of open channel flow with different boundary conditions. The model can efficiently capture flow evolution and vortex generation for random geometry and variable boundary conditions.
International Nuclear Information System (INIS)
Yasuda, K; Sogo, M; Iwamoto, Y
2013-01-01
The present note describes a method for use in conjunction with a scanning electron microscope (SEM) that has been developed to visualize a liquid flow under a high-level vacuum and to measure a velocity field in a small-scale flow through an open channel. In general, liquid cannot be observed via a SEM, because liquid evaporates under the high-vacuum environment of the SEM. As such, ionic liquid and room temperature molten salt having a vapor pressure of nearly zero is used in the present study. We use ionic liquid containing Au-coated tracer particles to visualize a small-scale flow under a SEM. Furthermore, the velocity distribution in the open channel is obtained by particle tracking velocimetry measurement and a parabolic profile is confirmed. (technical design note)
Directory of Open Access Journals (Sweden)
Yu Han
2017-01-01
Full Text Available We report the development of a new analytical model similar to the Reynolds-averaged Navier-Stokes equations to determine the distribution of streamwise velocity by considering the bursting phenomenon. It is found that, in two-dimensional (2D flows, the underlying mechanism of the wake law in 2D uniform flow is actually a result of up/down events. A special experiment was conducted to examine the newly derived analytical model, and good agreement is achieved between the experimental data in the inner region and the model’s prediction. The obtained experimental data were also used to examine the DML-Law (dip-modified-log-law, MLW-Law (modified-log-wake law, and CML-Law (Cole’s wake law, and the agreement is not very satisfactory in the outer region.
Turbulent flow in a ribbed channel: Flow structures in the vicinity of a rib
DEFF Research Database (Denmark)
Wang, Lei; Salewski, Mirko; Sundén, Bengt
2010-01-01
PIV measurements are performed in a channel with periodic ribs on one wall. The emphasis of this study is to investigate the flow structures in the vicinity of a rib in terms of mean velocities, Reynolds stresses, probability density functions (PDF), and two-point correlations. The PDF distribution......-based visualization is applied to the separation bubble upstream of the rib. Salient critical points and limit cycles are extracted, which gives clues to the physical processes occurring in the flow....
The smallest thermal scales in a turbulent channel flow at Prandtl number
International Nuclear Information System (INIS)
Bergant, R.; Tiselj, I.
2004-01-01
For describing the turbulent heat transfer from a wall to a fluid at low Reynolds (Re < 10000) and low Prandtl numbers (Pr < 20) a direct numerical simulation (DNS) can be used, which describes all the length and time scales of the phenomenon. The object of this paper is to find out the influence of the smallest temperature scales on the largest ones, which are responsible for the macro behavior of the near-wall heat transfer. Simulation, performed at Re = 2650 and Pr = 1, was calculated for velocity field with the DNS accuracy and for three different temperature fields. First temperature field, calculated with the DNS accuracy, was used as a reference to the second and third temperature fields where the highest Fourier coefficients in streamwise and spanwise directions were filtered and damped. It means, that the smallest temperature scales were not described with DNS accuracy anymore. New approach shows that results, for at least first and second order statistics, are comparable to the DNS ones without filtering and damping. (author)
Parashar, T.; Yang, Y.; Chasapis, A.; Matthaeus, W. H.
2017-12-01
High resolution Magnetospheric Multiscale (MMS) plasma and magnetic field data obtained in the inhomogeneous turbulent magnetosheath directly reveals the exchanges of energy between electromagnetic, flow and random kinetic energy. The parameters that quantify these exchanges are based on standard manipulations of the collisionless Vlasov model of plasma dynamics [1], without appeal to viscous or other closures. No analysis of heat transport or heat conduction is carried out. Several intervals of burst mode data in the magnetosheath are considered. Time series of the work done by the electromagnetic field, and the pressure-stress interaction enable description of the pathways to dissipation in this low collisionality plasma. Using these examples we demonstrate that the pressure-stress interaction provides important information not readily revealed in other diagnostics concerning the physical processes that are observed. This method does not require any specific mechanism for its application such as reconnection or a selected mode, although with increased experience it will be useful in distinguishing among proposed possibilities. [1] Y. Yang et al, Phys. Plasmas 24, 072306 (2017); doi: 10.1063/1.4990421.
On the relative rotational motion between rigid fibers and fluid in turbulent channel flow
Energy Technology Data Exchange (ETDEWEB)
Marchioli, C. [Department of Electrical, Management and Mechanical Engineering, University of Udine, 33100 Udine (Italy); Zhao, L., E-mail: lihao.zhao@ntnu.no [Department of Energy and Process Engineering, Norwegian University of Science and Technology, 7491 Trondheim (Norway); Andersson, H. I. [Department of Electrical, Management and Mechanical Engineering, University of Udine, 33100 Udine (Italy); Department of Energy and Process Engineering, Norwegian University of Science and Technology, 7491 Trondheim (Norway)
2016-01-15
In this study, the rotation of small rigid fibers relative to the surrounding fluid in wall-bounded turbulence is examined by means of direct numerical simulations coupled with Lagrangian tracking. Statistics of the relative (fiber-to-fluid) angular velocity, referred to as slip spin in the present study, are evaluated by modelling fibers as prolate spheroidal particles with Stokes number, St, ranging from 1 to 100 and aspect ratio, λ, ranging from 3 to 50. Results are compared one-to-one with those obtained for spherical particles (λ = 1) to highlight effects due to fiber length. The statistical moments of the slip spin show that differences in the rotation rate of fibers and fluid are influenced by inertia, but depend strongly also on fiber length: Departures from the spherical shape, even when small, are associated with an increase of rotational inertia and prevent fibers from passively following the surrounding fluid. An increase of fiber length, in addition, decouples the rotational dynamics of a fiber from its translational dynamics suggesting that the two motions can be modelled independently only for long enough fibers (e.g., for aspect ratios of order ten or higher in the present simulations)
Islam, Md Moshiul; Ye, Wenxiu; Matsushima, Daiki; Khokon, Md Atiqur Rahman; Munemasa, Shintaro; Nakamura, Yoshimasa; Murata, Yoshiyuki
2015-01-01
Acrolein is a reactive α,β-unsaturated aldehyde derived from lipid peroxides, which are produced in plants under a variety of stress. We investigated effects of acrolein on light-induced stomatal opening using Arabidopsis thaliana. Acrolein inhibited light-induced stomatal opening in a dose-dependent manner. Acrolein at 100 μM inhibited plasma membrane inward-rectifying potassium (Kin) channels in guard cells. Acrolein at 100 μM inhibited Kin channel KAT1 expressed in a heterologous system using Xenopus leaves oocytes. These results suggest that acrolein inhibits light-induced stomatal opening through inhibition of Kin channels in guard cells.
International Nuclear Information System (INIS)
Abdeen, Mostafa A. M.
2008-01-01
Most of the open water irrigation channels in Egypt suffer from the infestation of aquatic weeds, especially the submerged ones that cause numerous hydraulic problems for the open channels themselves and their water distributaries such as increasing water losses, obstructing water flow, and reducing channels' water distribution efficiencies. Accurate simulation and prediction of flow behavior in such channels is very essential for water distribution decision makers. Artificial neural networks (ANN) have proven to be very successful in the simulation of several physical phenomena, in general, and in the water research field in particular. Therefore, the current study aims towards introducing the utilization of ANN in simulating the impact of vegetation in main open channel, which supplies water to different distributaries, on the water surface profile in this main channel. Specifically, the study, presented in the current paper utilizes ANN technique for the development of various models to simulate the impact of different submerged weeds' densities, different flow discharges, and different distributaries operation scheduling on the water surface profile in an experimental main open channel that supplies water to different distributaries. In the investigated experiment, the submerged weeds were simulated as branched flexible elements. The investigated experiment was considered as an example for implementing the same methodology and technique in a real open channel system. The results showed that the ANN technique is very successful in simulating the flow behavior of the pre-mentioned open channel experiment with the existence of the submerged weeds. In addition, the developed ANN models were capable of predicting the open channel flow behavior in all the submerged weeds' cases that were considered in the ANN development process
Liu, Chengfang; Liu, Enli; Luo, Tiane; Zhang, Weifang; He, Rongli
2016-08-01
Activation of the inward rectifier potassium current (IK1) channel has been reported to be associated with suppression of ventricular arrhythmias. In this study, we tested the hypothesis that opening of the IK1 channel with zacopride (ZAC) was involved in the modulation of tissue repair after myocardial infarction. Sprague-Dawley rats were subject to coronary artery ligation and ZAC was administered intraperitoneally (15 µg/kg/day) for 28 days. Compared with the ischemia group, treatment with ZAC significantly reduced the ratio of heart/body weight and the cross-sectional area of cardiomyocytes, suggesting less cardiac hypertrophy. ZAC reduced the accumulation of collagen types I and III, accompanied with decrease of collagen area, which were associated with a reduction of collagen deposition in the fibrotic myocardium. Echocardiography showed improved cardiac function, evidenced by the reduced left ventricular end-diastolic dimension and left ventricular end-systolic dimension, and the increased ejection fraction and fractional shortening in ZAC-treated animals (all P < 0.05 vs. ischemia group). In coincidence with these changes, ZAC up-regulated the protein level of the IK1 channel and down-regulated the phosphorylation of mammalian target of rapamycin (mTOR) and 70-kDa ribosomal protein S6 (p70S6) kinase. Administration of chloroquine alone, an IK1 channel antagonist, had no effect on all the parameters measured, but significantly blocked the beneficial effects of ZAC on cardiac repair. In conclusion, opening of the IK1 channel with ZAC inhibits maladaptive tissue repair and improves cardiac function, potentially mediated by the inhibition of ischemia-activated mTOR-p70S6 signaling pathway via the IK1 channel. So the development of pharmacological agents specifically targeting the activation of the IK1 channel may protect the heart against myocardial ischemia-induced cardiac dysfunction. © The Author 2016. Published by Oxford University Press on behalf of
Kumar, Sourabh; Amano, R. S.; Lucci, Jose Martinez
2013-08-01
The blade tip region in gas turbine encounters high thermal loads due to temperature difference and hence efforts for high durability and safe operations are essential. Improved and robust methods of cooling are required to downgrade heat transfer rate to turbine blades. The blade tip regions, which are exposed to high gas flow, suffers high local thermal load which are due to external tip leakage. Jet impingement, pin cooling etc. are techniques used for cooling blades. A more usual way is to use serpentine passage with 180-degree turn. In this study, numerical simulation of heat transfer distribution of a two-pass square channel with rib turbulators and bleed holes were done. Periodical rib turbulators and bleed holes were used in the channel. The ribs arrangement were 60 degree V rib, 60 degree inverted V ribs, combination of 60 degree V rib at inlet and 60 inverted V rib at outlet section and combination of Inverted V at inlet and V rib at the outlet. The results were numerically computed using Fluent with Reynolds number of 12,500 and 28,500. Turbulence models used for computations were k-ω-SST and RSM. Temperature based and shear stress based techniques were used for heat transfer distribution prediction. The results for 60 degree V rib, 60 degree inverted V ribs were compared with the experimental results for validation of the results obtained. Detailed distribution shows distinctive peaks in heat transfer around bleed holes and rib turbulator. Comparisons of the overall performance of the models with different orientation of rib turbulator are presented. It is found that due to the combination of 60 degree inverted V rib in inlet and 60 V rib in outlet with bleed holes provides better heat treatment. It is suggested that the use of rib turbulator with bleed holes provides suitable for augmenting blade cooling to achieve an optimal balance between thermal and mechanical design requirements.
Transient mixed convection in a channel with an open cavity filled with porous media
International Nuclear Information System (INIS)
Buonomo, B; Cresci, G; Manca, O; Mesolella, P; Nardini, S
2012-01-01
In this work transient mixed convection in a porous medium in a horizontal channel with a open cavity below is studied numerically. The cavity presents a heated wall at uniform heat flux and the other walls of the cavity and the channel are assumed adiabatic. Air flows through the horizontal channel. The heated wall of the cavity experiences a uniform heat flux in such a way that the forced flow is perpendicular to the motion due to natural convection. The study is carried out employing Brinkman-Forchheimer-extended Darcy model and two energy equations due to the local thermal non-equilibrium assumption. The flow in the channel is assumed to be two-dimensional, laminar, incompressible. Boussinesq approximation is considered. The thermophysical properties of the fluid are evaluated at the ambient temperature. The results for stream function and temperature distribution given at different times are obtained. Wall temperature value are given and also, the velocity and temperature profiles in several sections of the cavity are presented. In addition, the Nusselt number, both local and average, is presented along with the temporal variations of the average Nusselt number.
Battisti, L; Baggio, P
2001-05-01
In gas turbine cooling design, techniques for heat extraction from the surfaces exposed to the hot stream are based on the increase of the inner heat transfer areas and on the promotion of the turbulence of the cooling flow. This is currently obtained by casting periodic ribs on one or more sides of the serpentine passages into the core of the blade. Fluid dynamic and thermal behaviour of the cooling flow have been extensively investigated by means of experimental facilities and many papers dealing with this subject have appeared in the latest years. The evaluation of the average value of the heat transfer coefficient most of the time is inferred from local measurements obtained by various experimental techniques. Moreover the great majority of these studies are not concerned with the overall average heat transfer coefficient for the combined ribs and region between them, but do focus just on one of them. This paper presents an attempt to collect information about the average Nusselt number inside a straight ribbed duct. Series of measurements have been performed in steady state eliminating the error sources inherently connected with transient methods. A low speed wind tunnel, operating in steady state flow, has been built to simulate the actual flow condition occurring in a rectilinear blade cooling channel. A straight square channel with 20 transverse ribs on two sides has been tested for Re of about 3 x 10(4), 4.5 x 10(4) and 6 x 10(4). The ribbed wall test section is electrically heated and the heat removed by a stationary flow of known thermal and fluid dynamic characteristics.
Lim, Wansu; Cho, Tae-Sik; Yun, Changho; Kim, Kiseon
2009-11-09
In this paper, we derive the average bit error rate (BER) of subcarrier multiplexing (SCM)-based free space optics (FSO) systems using a dual-drive Mach-Zehnder modulator (DD-MZM) for optical single-sideband (OSSB) signals under atmospheric turbulence channels. In particular, we consider the third-order intermodulation (IM3), a significant performance degradation factor, in the case of high input signal power systems. The derived average BER, as a function of the input signal power and the scintillation index, is employed to determine the optimum number of SCM users upon the designing FSO systems. For instance, when the user number doubles, the input signal power decreases by almost 2 dBm under the log-normal and exponential turbulence channels at a given average BER.
Features of reducing the turbulent friction of a liquid on the channel wall by gas-saturation
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Evseev Aleksei
2017-01-01
Full Text Available The report presents the results of an experimental study of the efficiency of reducing the local friction at gas saturation of the turbulent boundary layer (TBL in the input section of the channel at different gravitational orientation of the wall, and its dependence on the structure of gas-liquid flow. Profiles of gas concentration have a peak near the wall, which increases with the gas flow increase. The growth of concentration in the near-wall zone leads to rapid coalescence of bubbles, as a result of which the flow in TBL transits to the film-bubble regime with increasing the buoyancy effect of the gas phase, especially at low flow rates. It is shown that the key parameter of friction reduction by gas saturation is the gas phase concentration in the inner region of the boundary layer, whose magnitude is determined by the gas flow rate, the flow velocity, the distance downstream behind the gas generator, and the gravitational orientation of the wall.
International Nuclear Information System (INIS)
Tongmin Liou; Jennjiang Hwang; Shihhui Chen
1993-01-01
This paper performs a numerical and experimental analysis to investigate the heat transfer and fluid flow behaviour in a rectangular channel flow with streamwise-periodic ribs mounted on one of the principal walls. The k --A PDM turbulence model together with a smoothed hybrid central/skew upstream difference scheme (SCSUDS) and the PISO pressure-velocity coupling algorithm was applied to solving the accelerated, separated and recirculating flows. The real-time holographic interferometry technique was adopted to measure the time-dependent temperature field in the ribbed duct. The predicted fluid flow and temperature field were tested by previous laser-Doppler velocimetry measurements and present holographic interferometry data, and reasonable agreement was achieved. By the examination of the local wall temperature distribution for the uniform wall heat flux (UHF) boundary condition the regions susceptible to the hot spots are identified. Moreover, the study provided the numerical solution to investigate the effect of geometry and flow parameters on the local as well as average heat transfer coefficients. The compact correlation of the average heat transfer coefficient was further developed and accounted for the rib height, rib spacing, and Reynolds number. (Author)
International Nuclear Information System (INIS)
Patterson, G.K.; Zakin, J.L.
1983-01-01
Investigations related to the study of boundary layers are discussed, taking into account the simulation of turbulent shear flows, turbulent shear flows behind two-dimensional obstacles placed on a plane boundary, the development of turbulent boundary layers in open channel flows, the turbulent kinetic energy balance in a conical diffuser, strong adverse pressure gradient effects on supersonic turbulent boundary layers, the effects of upstream boundary layer thickness upon flow past a backward-facing step, and a turbulent wall jet issued from a Coanda nozzle. Other topics considered are concerned with scalar transport and combustion, particulate flows, experimental techniques and signal processing, thermal anemometry, complient surface and polymer effects, the coherent structure of turbulence, laser Doppler anemometry, and the transition to turbulence. Attention is given to a pattern recognition study of coherent motion in a transpired turbulent boundary layer, investigations of flow visualization techniques for detecting turbulent bursts, and the frequency response of cold wires
Directory of Open Access Journals (Sweden)
Mauricio Antonio Retamal
2014-06-01
Full Text Available Satellite glial cells (SGCs are the main glia in sensory ganglia. They surround neuronal bodies and form a cap that prevents the formation of chemical or electrical synapses between neighboring neurons. SGCs have been suggested to establish bidirectional paracrine communication with sensory neurons. However, the molecular mechanism involved in this cellular communication is unknown. In the central nervous system, astrocytes present connexin43 (Cx43 hemichannels and pannexin1 (Panx1 channels, and their opening allows the release of signal molecules, such as ATP and glutamate. We propose that these channels could play a role in the glia-neuron communication in sensory ganglia. Therefore, we studied the expression and function of Cx43 and Panx1 in rat and mouse nodose-petrosal-jugular complex (NPJc by confocal immunofluorescence, molecular and electrophysiological techniques. Cx43 and Panx1 were detected in SGCs and sensory neurons, respectively. In the rat and mouse, the electrical activity of vagal nerve increased significantly after nodose neurons were exposed to Ca2+/ Mg2+-free solution, a condition that increases the open probability of Cx hemichannels. This response was partially mimicked by a cell-permeable peptide corresponding to the last 10 amino acids of Cx43 (TAT-Cx43CT. Enhanced neuronal activity was reduced by Cx hemichannel, Panx1 channel and P2X7 receptor blockers. Moreover, the role of Panx1 was confirmed in NPJc, because Panx1 knockout mouse showed a reduced increase of neuronal activity induced by Ca2+/Mg2+-free extracellular conditions. Data suggest that Cx hemichannels and Panx channels serve as paracrine communication pathways between SGCs and neurons by modulating the excitability of sensory neurons.
Energy Technology Data Exchange (ETDEWEB)
Dritselis, Chris D, E-mail: dritseli@mie.uth.gr [Mechanical Engineering Department, University of Thessaly, Pedion Areos, 38334 Volos (Greece)
2017-04-15
In the first part of this study (Dritselis 2016 Fluid Dyn. Res. 48 015507), the Reynolds stress budgets were evaluated through point-particle direct numerical simulations (pp-DNSs) for the particle-laden turbulent flow in a vertical channel with two- and four-way coupling effects. Here several turbulence models are assessed by direct comparison of the particle contribution terms to the budgets, the dissipation rate, the pressure-strain rate, and the transport rate with the model expressions using the pp-DNS data. It is found that the models of the particle sources to the equations of fluid turbulent kinetic energy and dissipation rate cannot represent correctly the physics of the complex interaction between turbulence and particles. A relatively poor performance of the pressure-strain term models is revealed in the particulate flows, while the algebraic models for the dissipation rate of the fluid turbulence kinetic energy and the transport rate terms can adequately reproduce the main trends due to the presence of particles. Further work is generally needed to improve the models in order to account properly for the momentum exchange between the two phases and the effects of particle inertia, gravity and inter-particle collisions. (paper)
International Nuclear Information System (INIS)
Dritselis, Chris D
2017-01-01
In the first part of this study (Dritselis 2016 Fluid Dyn. Res. 48 015507), the Reynolds stress budgets were evaluated through point-particle direct numerical simulations (pp-DNSs) for the particle-laden turbulent flow in a vertical channel with two- and four-way coupling effects. Here several turbulence models are assessed by direct comparison of the particle contribution terms to the budgets, the dissipation rate, the pressure-strain rate, and the transport rate with the model expressions using the pp-DNS data. It is found that the models of the particle sources to the equations of fluid turbulent kinetic energy and dissipation rate cannot represent correctly the physics of the complex interaction between turbulence and particles. A relatively poor performance of the pressure-strain term models is revealed in the particulate flows, while the algebraic models for the dissipation rate of the fluid turbulence kinetic energy and the transport rate terms can adequately reproduce the main trends due to the presence of particles. Further work is generally needed to improve the models in order to account properly for the momentum exchange between the two phases and the effects of particle inertia, gravity and inter-particle collisions. (paper)
Jiandong Yang; Mingjiang Wang; Chao Wang; Wencheng Guo
2015-01-01
On the basis of the state–space method (SSM), a novel linear mathematical model of the unsteady flow for the tailrace system with an open channel is proposed. This novel model is an elastic linearized model of water hammer. The validity of the model has been verified by several examples of numerical simulation, which are based on a finite difference technique. Then, the complete mathematical model for the hydro-turbine governing system of hydropower station with an open tailrace channel, whi...
Analysis of radiometric signal in sedimentating suspension flow in open channel
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Zych Marcin
2015-01-01
Full Text Available The article discusses issues related to the estimation of the sedimentating solid particles average flow velocity in an open channel using radiometric methods. Due to the composition of the compound, which formed water and diatomite, received data have a very weak signal to noise ratio. In the process analysis the known determining of the solid phase transportation time delay the classical cross-correlation function is the most reliable method. The use of advanced frequency analysis based on mutual spectral density function and wavelet transform of recorded signals allows a reduction of the noise contribution.
Lyapin Anton; Lyapin Valery
2018-01-01
The influence of non-uniformity on mass transfer processes in open channels have been investigated under the action of urbanization factors. The study is related to the urgent problem of environmental degradation of water objects in urbanized areas. It is known that the water quality in the water objects depends on the manner in which the contaminants spread how they mix with the river water and diluted by it. The main results of the study consist of recommendations to incorporate non-uniform...
Ansari, Imran Shafique
2015-03-01
Generalized fading has been an imminent part and parcel of wireless communications. It not only characterizes the wireless channel appropriately but also allows its utilization for further performance analysis of various types of wireless communication systems. Under the umbrella of generalized fading channels, a unified performance analysis of a free-space optical (FSO) link over the Malaga (M) atmospheric turbulence channel that accounts for pointing errors and both types of detection techniques (i.e. indirect modulation/direct detection (IM/DD) as well as heterodyne detection) is presented. Specifically, unified exact closed-form expressions for the probability density function (PDF), the cumulative distribution function (CDF), the moment generating function (MGF), and the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system are presented, all in terms of the Meijer\\'s G function except for the moments that is in terms of simple elementary functions. Then capitalizing on these unified results, unified exact closed-form expressions for various performance metrics of FSO link transmission systems are offered, such as, the outage probability (OP), the higher-order amount of fading (AF), the average error rate for binary and M-ary modulation schemes, and the ergodic capacity (except for IM/DD technique, where closed-form lower bound results are presented), all in terms of Meijer\\'s G functions except for the higher-order AF that is in terms of simple elementary functions. Additionally, the asymptotic results are derived for all the expressions derived earlier in terms of the Meijer\\'s G function in the high SNR regime in terms of simple elementary functions via an asymptotic expansion of the Meijer\\'s G function. Furthermore, new asymptotic expressions for the ergodic capacity in the low as well as high SNR regimes are derived in terms of simple elementary functions via utilizing moments. All the presented results are
Tiselj, Iztok
2014-12-01
Channel flow DNS (Direct Numerical Simulation) at friction Reynolds number 180 and with passive scalars of Prandtl numbers 1 and 0.01 was performed in various computational domains. The "normal" size domain was ˜2300 wall units long and ˜750 wall units wide; size taken from the similar DNS of Moser et al. The "large" computational domain, which is supposed to be sufficient to describe the largest structures of the turbulent flows was 3 times longer and 3 times wider than the "normal" domain. The "very large" domain was 6 times longer and 6 times wider than the "normal" domain. All simulations were performed with the same spatial and temporal resolution. Comparison of the standard and large computational domains shows the velocity field statistics (mean velocity, root-mean-square (RMS) fluctuations, and turbulent Reynolds stresses) that are within 1%-2%. Similar agreement is observed for Pr = 1 temperature fields and can be observed also for the mean temperature profiles at Pr = 0.01. These differences can be attributed to the statistical uncertainties of the DNS. However, second-order moments, i.e., RMS temperature fluctuations of standard and large computational domains at Pr = 0.01 show significant differences of up to 20%. Stronger temperature fluctuations in the "large" and "very large" domains confirm the existence of the large-scale structures. Their influence is more or less invisible in the main velocity field statistics or in the statistics of the temperature fields at Prandtl numbers around 1. However, these structures play visible role in the temperature fluctuations at low Prandtl number, where high temperature diffusivity effectively smears the small-scale structures in the thermal field and enhances the relative contribution of large-scales. These large thermal structures represent some kind of an echo of the large scale velocity structures: the highest temperature-velocity correlations are not observed between the instantaneous temperatures and
2D Numerical Investigation of the Laminar and Turbulent Flow Over Different Airfoils Using OpenFOAM
International Nuclear Information System (INIS)
Rahimi, H; Stoevesandt, B; Peinke, J; Medjroubi, W
2014-01-01
The aim of this work is to assess the prediction capabilities of the turbulence models and the transition model kkl-ω available in OpenFOAM and to achieve a database of airfoil aerodynamical characteristics. The airfoils chosen for the simulations are FX 79-W- 15A and NACA 63-430, which are widely used in wind turbines. The numerically obtained lift and drag coefficients are compared with available experimental results. A quantitative and qualitative study is conducted to determine the influence of meshing strategies, computational time step together with interpolation and temporal schemes. Two Reynolds Averaged Navier- Stokes models (RANS models) are used, which are the k-ω SST model by Menter and the kkl-ω model (which involves transition modeling) by Walters and Davor
Flow Patterns in an Open Channel Confluence with Increasingly Dominant Tributary Inflow
Directory of Open Access Journals (Sweden)
Laurent Schindfessel
2015-08-01
Full Text Available Despite the ratio of incoming discharges being recognized as a key parameter in open-channel confluence hydrodynamics, little is known about the flow patterns when the tributary provides more than 90% of the total discharge. This paper offers a systematic study of flow features when the tributary becomes increasingly dominant in a 90° confluence with a fixed concordant bed. Large-eddy simulations are used to investigate the three-dimensional complex flow patterns for three different discharge ratios. It is found that the tributary flow impinges on the opposing bank when the tributary flow becomes sufficiently dominant, causing a recirculating eddy in the upstream channel of the confluence, which induces significant changes in the incoming velocity distribution. Moreover, it results in stronger helicoidal cells in the downstream channel, along with zones of upwelling flow. In turn, the changed flow patterns also influence the mixing layer and the flow recovery. Finally, intermittent events of stronger upwelling flow are discerned. Improved understanding of flow patterns at confluences where the tributary is dominant is applicable to both engineering and earth sciences.
Rizalihadi, M.; Ziana; Shaskia, Nina; Asharly, H.
2018-05-01
One of the important factors in channel dimension is the Manning’s coefficient ( n ). This coefficient is influenced not only by the channel roughness but also by the presence of plants in the channel. The aim of the study is to see the effect of the ratio between the height of the rigid plant and water depth on the Manning’s coefficient (n) in open channel. The study was conducted in open channel with 15.5 m long, 0.5 m wide and 1.0 m high, in which at the center of the channel is planted with the rigid plants with a density of 42 plants/m2. The flow was run with a discharge of 0.013 m3/s at 6 ratios of Hplants/Hwater, namely: 0; 0.2; 0.6; 0.8; 1,0 and 1,2, to obtain the velocity and water profiles. Then the value of n is analyzed using Manning’s equation. The results showed that the mean velocity becomes decrease 17.81-34.01% as increase the ratio of Hplants/Hwater. This results in increasing n value to become 1.22-1.52 times compared to the unplanted channel ( no =0.038). So, it can be concluded that the ratio between the rigid plant’s height and water depth in the open channel can affect the value of Manning coefficient.
Role of mixed boundaries on flow in open capillary channels with curved air-water interfaces.
Zheng, Wenjuan; Wang, Lian-Ping; Or, Dani; Lazouskaya, Volha; Jin, Yan
2012-09-04
Flow in unsaturated porous media or in engineered microfluidic systems is dominated by capillary and viscous forces. Consequently, flow regimes may differ markedly from conventional flows, reflecting strong interfacial influences on small bodies of flowing liquids. In this work, we visualized liquid transport patterns in open capillary channels with a range of opening sizes from 0.6 to 5.0 mm using laser scanning confocal microscopy combined with fluorescent latex particles (1.0 μm) as tracers at a mean velocity of ∼0.50 mm s(-1). The observed velocity profiles indicate limited mobility at the air-water interface. The application of the Stokes equation with mixed boundary conditions (i.e., no slip on the channel walls and partial slip or shear stress at the air-water interface) clearly illustrates the increasing importance of interfacial shear stress with decreasing channel size. Interfacial shear stress emerges from the velocity gradient from the adjoining no-slip walls to the center where flow is trapped in a region in which capillary forces dominate. In addition, the increased contribution of capillary forces (relative to viscous forces) to flow on the microscale leads to increased interfacial curvature, which, together with interfacial shear stress, affects the velocity distribution and flow pattern (e.g., reverse flow in the contact line region). We found that partial slip, rather than the commonly used stress-free condition, provided a more accurate description of the boundary condition at the confined air-water interface, reflecting the key role that surface/interface effects play in controlling flow behavior on the nanoscale and microscale.
Directory of Open Access Journals (Sweden)
Naveed Anjum
2018-01-01
Full Text Available In the present study, the flow structure of discontinuous double-layered vegetation patches was investigated using a 3D Reynolds stress turbulence model (RSM. The channel domain was built using GAMBIT (Geometry and Mesh Building Intelligent Toolkit. For the simulation and postprocessing, FLUENT (ANSYS was used to analyze the distribution of the mean velocity, Reynolds stresses, and other flow properties against two different flow conditions. The results captured by the turbulence model at specific locations and the cross section are presented in the form of various velocity profiles and contour plots. In the gap portion, the velocity was visibly lower than that in the vegetation areas, while the influence of patch distribution was not visible in the overlying flow layer. The velocity profiles at critical locations were categorized by numerous modulation points and velocity projections close to the bed, principally for positions straight after the vegetation structures. A distinction in the velocity at the topmost of the smaller vegetation structure was prominent. Reynolds stresses, turbulent kinetic energy, and turbulence intensity exhibited large fluctuations inside the vegetation regions and just behind the vegetation structures compared with in the gap regions.
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Fan Bai
2015-10-01
Full Text Available This paper presents a novel model of heterodyne-detected optical code-division multiple-access (OCDMA systems employing polarization shift keying (PolSK modulation over a free-space optical (FSO turbulence channel. In this article, a new transceiver configuration and detailed analytical model for the proposed system are provided and discussed, taking into consideration the potential of heterodyne detection on mitigating the impact of turbulence-induced irradiance fluctuation on the performance of the proposed system under the gamma-gamma turbulence channel. Furthermore, we derived the closed-form expressions for the system error probability and outage probability, respectively. We determine the advantages of the proposed modeling by performing a comparison with a direct detection scheme obtained from an evaluation of link performance under the same environment conditions. The presented work also shows the most significant impact factor that degrades the performance of the proposed system and indicates that the proposed approach offers an optimum link performance compared to conventional cases.
Deviations of Atmospheric Coastal Flow from the Open-channel Hydraulics Analogy
Rahn, D. A.; Parish, T. R.; Juliano, T. W.
2017-12-01
Low-level atmospheric flow along the coast of California bears resemblance to open-channel engineering applications referred to as hydraulic flow. During the warm season, strong equatorward wind is common near the surface. A marked temperature inversion separates the cool, moist marine air and the warm, dry free troposphere aloft. The low-level flow is bounded laterally by the coastal topography. Given the high wind speed in the shallow marine layer, the flow is often supercritical (Fr > 1). Features resembling oblique compression jumps and expansion fans occur near concave and convex bends in the coastline and impact wind energy production, wind stress on the ocean surface, and propagation of electromagnetic waves by modifying the vertical refractivity gradient. An aircraft collected fine-scale measurements offshore of southern California to test how well the observed features conform to the single-layer hydraulic approximation. Although the open-channel framework captures major features of the flow as indicated by prior work, the detailed measurements reveal when the analogy breaks down. The assumption of a passive upper layer can be violated due to mesoscale pressure gradients aloft and lee troughing associated with offshore flow, which can enhance the thinning of the marine layer associated with the expansion fan. The sharp interface between layers can be eroded when Ri becomes low, Kelvin-Helmholtz instability develops, and the structure of the lower atmosphere is drastically altered. This is poorly simulated in operational weather forecast models due to their relatively coarse grid spacing. The layer associated with the expansion fan rarely keeps its identity into the Santa Barbara Channel. An increase of surface heat flux and vertical mixing as the flow moves over warmer sea surface temperatures in the channel rapidly erodes the layer. Only one flight captured a hydraulic jump between the supercritical flow in the expansion fan and the subcritical flow
Fancello, A.; Bastiaans, R.J.M.; Goey, de L.P.H.
2013-01-01
This work proposes an application of the Flamelet-Generated Manifolds (FGM) technique in the OpenFOAM environment. FGM is a chemical reduced method for combustion modeling. This technique treats the combustion process as the solution of a small amount of controlling variables. Regarding laminar
International Nuclear Information System (INIS)
Kun, S.Yu.
1985-01-01
On the basis of the symmetrized Simonius representation of the S matrix statistical properties of its fluctuating component in the presence of direct reactions are investigated. The case is considered where the resonance levels are strongly overlapping and there is a lot of open channels, assuming that compound-nucleus cross sections which couple different channels are equal. It is shown that using the averaged unitarity condition on the real energy axis one can eliminate both resonance-resonance and channel-channel correlations from partial r transition amplitudes. As a result, we derive the basic points of the Epicson fluctuation theory of nuclear cross sections, independently of the relation between the resonance overlapping and the number of open channels, and the validity of the Hauser-Feshbach model is established. If the number of open channels is large, the time of uniform population of compound-nucleus configurations, for an open excited nuclear system, is much smaller than the Poincare time. The life time of compound nucleus is discussed
Influence of turbulence on bed load sediment transport
DEFF Research Database (Denmark)
Sumer, B. Mutlu; Chua, L.; Cheng, N. S.
2003-01-01
This paper summarizes the results of an experimental study on the influence of an external turbulence field on the bedload sediment transport in an open channel. The external turbulence was generated by: (1) with a horizontal pipe placed halfway through the depth, h; (2) with a series of grids......-bed experiments and the ripple-covered-bed experiments. In the former case, the flow in the presence of the turbulence generator was adjusted so that the mean bed shear stress was the same as in the case without the turbulence generator in order to single out the effect of the external turbulence on the sediment...... correlated with the sediment transport rate. The sediment transport increases markedly with increasing turbulence level....
International Nuclear Information System (INIS)
Shinji Ebara; Takehiko Yokomine; Akihiko Shimizu
2006-01-01
During irradiation test periods in the International Fusion Material Irradiation Facility (IFMIF), irradiated materials must be maintained at constant temperatures because irradiation characteristics of materials have a large dependency on temperature. In the high flux test module of the IFMIF, required performances for temperature control using gas-cooling and heater-heating are especially stringent because available space for temperature control is remarkably restricted due to very small irradiation volume of about 0.5 l. We proposed an alternative design of the test module with advantages of temperature monitoring and temperature uniformity in specimens. This design employs a rectangular duct as the vessel to pack capsules housing specimens compactly into the small irradiation volume. In the vessel the coolant flows between the capsules and vessel wall. In the basic design, both thickness of a vessel wall and a width of cooling channel are considered as 1.0 mm. Since inside the vessel gaseous helium of several atmospheric pressure flows as a coolant and a low vacuum environment is kept outside the vessel for safety requirements and thermal stress is foreseen to appear due to nuclear heating of the vessel itself, the vessel wall is considered to deform readily and this leads expansion of the cooling channels. It is also considered that a slight expansion of the vessel can have severe influence on the cooling performance due to the initial narrow channel width of 1.0 mm. Therefore, it is necessary to estimate cooling performances for the coolant flowing in the deformed channel. We conduct a finite element analysis of turbulent heat transfer in a mildly expanded channel using large-eddy simulation in this study. In a numerical system, fluid is enclosed by three-dimensionally expanded vessel wall and flat capsule wall, and flows into the system with a fully developed velocity profile. In this study, we focus not only on the cooling performances but also on change in
Identification of BKCa channel openers by molecular field alignment and patent data-driven analysis
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Yaseen Gigani
2016-01-01
Full Text Available In this work, we present the first comprehensive molecular field analysis of patent structures on how the chemical structure of drugs impacts the biological binding. This task was formulated as searching for drug structures to reveal shared effects of substitutions across a common scaffold and the chemical features that may be responsible. We used the SureChEMBL patent database, which provides search of the patent literature using keyword-based functionality, as a query engine. The extraction of data of the BKCa channel openers and aligning them for molecular field similarity with newly designed structures did provide a probable validation method with accurate values. Therefore, in an attempt to increase the true positives, we report a procedure that functions on a multiple analyses modeled on molecular field similarity and common sub-structural search with consensus scoring and high confidence values to obtain greater accuracy during conventional virtual screening.
Directory of Open Access Journals (Sweden)
Lyapin Anton
2018-01-01
Full Text Available The influence of non-uniformity on mass transfer processes in open channels have been investigated under the action of urbanization factors. The study is related to the urgent problem of environmental degradation of water objects in urbanized areas. It is known that the water quality in the water objects depends on the manner in which the contaminants spread how they mix with the river water and diluted by it. The main results of the study consist of recommendations to incorporate non-uniformity factor to the calculation of diffusion dilution of wastewater and prediction of river processes. So the effect of the flow non-uniformity on the diffusion model of pollutants dilution and diffusion coefficient have been investigated. Formulas for the concentration profiles calculating and the average concentration of fine particulate matter in nonuniform gradually varied flow were presented. The deposition length of suspended contaminants were received, based on the hydraulic resistance laws of nonuniform gradually varied flow.
Dynamics of the di-nucleus binary decay: role of the number of open channels
International Nuclear Information System (INIS)
Beck, C.; Abe, Y.; Aissaoui, N.; Djerroud, B.; Haas, F.
1995-01-01
The coexistence of quasi-molecular resonances, orbiting mechanisms and the fusion-fission (FF) process for medium light di-nuclear systems is examined in terms of the Number of Open Channels (NOC). The calculated NOC, based on a statistical model approach, shows a characteristic dependence which reflects the surface transparency needed to observe both resonant structure and orbiting phenomena. For more absorbing reactions FF has been found experimentally to compete with the fusion-evaporation (FE) process in agreement with larger predicted NOC values. Finally it is shown that the coexistence of the statistical fission from the 48 Cr compound nucleus (CN) and the resonances arising from very deformed configurations of this di-nucleus are well explained in the framework of the present simple model. ((orig.))
International Nuclear Information System (INIS)
Abreu Zamora, Maria A.; Gonzalez Lopez, Dagoberto E.; Robaina Leon, Yalaina; Dominguez Catasus, Judith; Borroto Portela, Jorge I.; Jauregui Haza, Ulises J.
2015-01-01
The conventional wastewater treatment plants do not guarantee the degradation of Persistent Organic Pollutants (POPs). Advanced oxidation processes, like photodegradation that use artificial ultraviolet and solar radiation, are proposed as an alternative for the treatment of contaminated water with POPs. In the present work, the hydrodynamic characterization and evaluation of an open channel reactor for the degradation of paracetamol are presented. The hydrodynamic characterization was performed through the analysis of the residence time distribution using a radioisotope 99m Tc. This process was done in two steps. First, the open channel reactor was evaluated in continuous mode operation. To study the influence of the fluid volume in the reactor and the diameter of the flow distributor's orifices on the flow pattern, an experimental 3 2 design with two replicas in the center was used. The dependent variables were the number of perfectly mixed tanks (J), the mean residence time of the model (τ) and the experimental mean residence time (Trm). The model of perfectly mixed tanks in series exchanging with stagnant zones was assumed as the best model. In a second moment, the mixing time of the system operating in close loop mode was determined. Finally, the degradation of paracetamol in aqueous dissolution trough photolysis, photolysis intensified with H 2 O 2 , photo-Fenton with artificial ultraviolet radiation and photo-Fenton with solar radiation was evaluated. The results show that the photo-Fenton processes employing artificial ultraviolet and solar radiation warranty the total degradation of the pharmaceutical after 15 minutes of reaction. (Author)
Role of protein sulfation in vasodilation induced by minoxidil sulfate, a K+ channel opener
International Nuclear Information System (INIS)
Meisheri, K.D.; Oleynek, J.J.; Puddington, L.
1991-01-01
Evidence from contractile, radioisotope ion flux and electrophysiological studies suggest that minoxidil sulfate (MNXS) acts as a K+ channel opener in vascular smooth muscle. This study was designed to examine possible biochemical mechanisms by which MNXS exerts such an effect. Experiments performed in the isolated rabbit mesenteric artery (RMA) showed that MNXS, 5 microM, but not the parent compound minoxidil, was a potent vasodilator. Whereas the relaxant effects of an another K+ channel opener vasodilator, BRL-34915 (cromakalim), were removed by washing with physiological saline solution, the effects of MNXS persisted after repeated washout attempts. Furthermore, after an initial exposure of segments of intact RMA to [35S] MNXS, greater than 30% of the radiolabel was retained 2 hr after removal of the drug. In contrast, retention of radiolabel was not detected with either [3H]MNXS (label on the piperidine ring of MNXS) or [3H]minoxidil (each less than 3% after a 2-hr washout). These data suggested that the sulfate moiety from MNXS was closely associated with the vascular tissue. To determine if proteins were the acceptors of sulfate from MNXS, intact RMAs were incubated with [35S]MNXS, and then 35S-labeled proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and analyzed by fluorography. Preferential labeling of a 116 kD protein was detected by 2 and 5 min of treatment. A 43 kD protein (resembling actin) also showed significant labeling. A similar profile of 35S-labeled proteins was observed in [35S] MNXS-treated A7r5 rat aortic smooth muscle cells, suggesting that the majority of proteins labeled by [35S]MNXS in intact RMA were components of smooth muscle cells
Directory of Open Access Journals (Sweden)
Kirill N. Demchenko
2014-03-01
Full Text Available Plasmodesmata (PD represent membrane-lined channels that link adjacent plant cells across the cell wall. PD of higher plants contain a central tube of endoplasmic reticulum called desmotubule. Membrane and lumen proteins seem to be able to move through the desmotubule, but most transport processes through PD occur through the cytoplasmic annulus (Brunkard et al., 2013. Calreticulin (CRT, a highly conserved Ca2+-binding protein found in all multi-cellular eukaryotes, predominantly located in the ER, was shown to localize to PD, though not all PD accumulate CRT. In nitrogen fixing actinorhizal root nodules of the Australian tree Casuarina glauca, the primary walls of infected cells containing the microsymbiont become lignified upon infection. TEM analysis of these nodules showed that during the differentiation of infected cells, PD connecting infected cells, and connecting infected and adjacent uninfected cells, were reduced in number as well as diameter (Schubert et al., 2013. In contrast with PD connecting young infected cells, and most PD connecting mature infected and adjacent uninfected cells, PD connecting mature infected cells did not accumulate CRT. Furthermore, as shown here, these PD were not associated with callose, and based on their diameter, they probably had lost their desmotubules. We speculate that either this is a slow path to PD degradation, or that the loss of callose accumulation and presumably also desmotubules leads to the PD becoming open channels and improves metabolite exchange between cells.
A Computer Model for the Hydraulic Analysis of Open Channel Cross Sections
Directory of Open Access Journals (Sweden)
W. H. Shayya
1996-01-01
Full Text Available Irrigation and hydraulic engineers are often faced with the difficulty of tedious trial solutions of the Manning equation to determine the various geometric elements of open channels. This paper addresses the development of a computer model for the design of the most commonly used channel-sections. The developed model is intended as an educational tool. It may be applied to the hydraulic design of trapezoidal , rectangular, triangular, parabolic, round-concered rectangular, and circular cross sections. Two procedures were utilized for the solution of the encountered implicit equations; the Newton-Raphson and the Regula-Falsi methods. In order to initiate the solution process , these methods require one and two initial guesses, respectively. Tge result revealed that the Regula-Flasi method required more iterations to coverage to the solution compared to the Newton-Raphson method, irrespective of the nearness of the initial guess to the actual solution. The average number of iterations for the Regula-Falsi method was approximately three times that of the Newton-Raphson method.
Biton, B; Sethuramanujam, S; Picchione, Kelly E; Bhattacharjee, A; Khessibi, N; Chesney, F; Lanneau, C; Curet, O; Avenet, P
2012-03-01
Sodium-activated potassium (K(Na)) channels have been suggested to set the resting potential, to modulate slow after-hyperpolarizations, and to control bursting behavior or spike frequency adaptation (Trends Neurosci 28:422-428, 2005). One of the genes that encodes K(Na) channels is called Slack (Kcnt1, Slo2.2). Studies found that Slack channels were highly expressed in nociceptive dorsal root ganglion neurons and modulated their firing frequency (J Neurosci 30:14165-14172, 2010). Therefore, Slack channel openers are of significant interest as putative analgesic drugs. We screened the library of pharmacologically active compounds with recombinant human Slack channels expressed in Chinese hamster ovary cells, by using rubidium efflux measurements with atomic absorption spectrometry. Riluzole at 500 μM was used as a reference agonist. The antipsychotic drug loxapine and the anthelmintic drug niclosamide were both found to activate Slack channels, which was confirmed by using manual patch-clamp analyses (EC(50) = 4.4 μM and EC(50) = 2.9 μM, respectively). Psychotropic drugs structurally related to loxapine were also evaluated in patch-clamp experiments, but none was found to be as active as loxapine. Loxapine properties were confirmed at the single-channel level with recombinant rat Slack channels. In dorsal root ganglion neurons, loxapine was found to behave as an opener of native K(Na) channels and to increase the rheobase of action potential. This study identifies new K(Na) channel pharmacological tools, which will be useful for further Slack channel investigations.
Syam, Bustami; Sebayang, Alexander; Sebayang, Septian; Muttaqin, Maraghi; Darmadi, Harry; Basuki, WS; Sabri, M.; Abda, S.
2018-03-01
Open channel conduit is designed and produced with the aims to reduce excess water, whether from rain, seepage, or excess irrigation water in an area. It is also included in one of the important components of urban infrastructure in tackling the problem of flooding and waterlogging. On the roadway, e.g. housing complex the open channel conduits should function the same, however conduit covers are needed. The covers should be also designed to function as parking bumper. This paper discusses the design and production of the stoppers using our newly invented materials; the stoppers are structurally tested under static, dynamic, and bump test. Response of the conduit cover are found from structural analysis using finite element software ANSYS MECHANICAL version 17.5. Two types of stoppers are introduced: flat and curvy configuration. It was obtained that both types are suitable for open channel conduit cover and parking bumper.
Prestrelo, L; Monteiro-Neto, C
2016-07-01
This study aimed to evaluate the human induced impact of a channel opening in a choked lagoon and attempted to establish the cause-effect links for the observed changes. The same lagoon system was sampled before and after the channel opening event, and the differences in fish and crustacean assemblages and environmental variables between these periods analysed. The opening of the artificial channel resulted in salinity increases, leading to a shift in species composition, favouring marine species and reducing abundance and diversity of previously dominant freshwater species. Furthermore, saltwater entrance into the choked lagoon caused an unexpected decrease in species richness and biomass, plus deterioration of ecosystem processes, reducing fishing capacity. The effects of salinity on the ecosystem vary depending on the ecosystem's composition and capacity to overcome salinity changes, thus specific monitoring projects are important strategies for developing coastal lagoon conservation management. © 2016 The Fisheries Society of the British Isles.
Tentative Study on Performance of Darriues-Type Hydroturbine Operated in Small Open Water Channel
Matsushita, D.; Moriyama, R.; Nakashima, K.; Watanabe, S.; Okuma, K.; Furukawa, A.
2014-03-01
The development of small hydropower is one of the realistic and preferable utilizations of renewable energy, but the extra-low head hydropower less than 2 m is almost undeveloped yet for some reasons. The authors have developed several types of Darrieus-type hydro-turbine system, and among them, the Darrieus-turbine with a wear and a nozzle installed upstream of turbine is so far in success to obtain more output power, i.e. more shaft torque, by gathering all water into the turbine. However, there can several cases exist, in which installing the wear covering all the flow channel width is unrealistic. Then, in the present study, the hydraulic performances of Darrieus-type hydro-turbine with the inlet nozzle is investigated, putting alone in a small open channel without upstream wear. In the experiment, the five-bladed Darrieus-type runner with the pitch-circle diameter of 300 mm and the blade span of 300 mm is vertically installed in the open channel with the width of 1,200 mm. The effectiveness of the shape of the inlet nozzle is also examined using two types of two-dimensional symmetric nozzle, the straight line nozzle (SL nozzle) with the converging angle of 45 degrees and the half diameter curved nozzle (HD nozzle) whose radius is a half diameter of runner pitch circle. Inlet and outlet nozzle widths are in common for the both nozzles, which are 540 mm and 240 mm respectively. All the experiments are carried out under the conditions with constant flow rate and downstream water level, and performances are evaluated by measured output torque and the measured head difference between the water levels upstream and downstream of the turbine. As a result, it is found that the output power is remarkably increased by installing the inlet nozzle, and the turbine with SL nozzle produces larger power than that with HD nozzle. However, the peak efficiency is deteriorated in both cases. The speed ratio defined by the rotor speed divided by the downstream water velocity at
Tentative Study on Performance of Darriues-Type Hydroturbine Operated in Small Open Water Channel
International Nuclear Information System (INIS)
Matsushita, D; Watanabe, S; Okuma, K; Moriyama, R; Nakashima, K; Furukawa, A
2014-01-01
The development of small hydropower is one of the realistic and preferable utilizations of renewable energy, but the extra-low head hydropower less than 2 m is almost undeveloped yet for some reasons. The authors have developed several types of Darrieus-type hydro-turbine system, and among them, the Darrieus-turbine with a wear and a nozzle installed upstream of turbine is so far in success to obtain more output power, i.e. more shaft torque, by gathering all water into the turbine. However, there can several cases exist, in which installing the wear covering all the flow channel width is unrealistic. Then, in the present study, the hydraulic performances of Darrieus-type hydro-turbine with the inlet nozzle is investigated, putting alone in a small open channel without upstream wear. In the experiment, the five-bladed Darrieus-type runner with the pitch-circle diameter of 300 mm and the blade span of 300 mm is vertically installed in the open channel with the width of 1,200 mm. The effectiveness of the shape of the inlet nozzle is also examined using two types of two-dimensional symmetric nozzle, the straight line nozzle (SL nozzle) with the converging angle of 45 degrees and the half diameter curved nozzle (HD nozzle) whose radius is a half diameter of runner pitch circle. Inlet and outlet nozzle widths are in common for the both nozzles, which are 540 mm and 240 mm respectively. All the experiments are carried out under the conditions with constant flow rate and downstream water level, and performances are evaluated by measured output torque and the measured head difference between the water levels upstream and downstream of the turbine. As a result, it is found that the output power is remarkably increased by installing the inlet nozzle, and the turbine with SL nozzle produces larger power than that with HD nozzle. However, the peak efficiency is deteriorated in both cases. The speed ratio defined by the rotor speed divided by the downstream water velocity at
Radaydeh, Redha; Zafar, Ammar; Al-Qahtani, Fawaz; Alouini, Mohamed-Slim
2016-01-01
This paper investigates low-complexity joint interference avoidance and desired link improvement for single channel allocation in multiuser multi-antenna access points (APs) for open-access small cells. It is considered that an active user is equipped with an atenna array that can be used to suppress interference sources but not to provide spatial diversity. On the other hand, the operation of APs can be coordinated to meet design requirements, and each of which can unconditionally utilize assigned physical channels. Moreover, each AP is equipped with uncorrelated antennas that can be reused simultaneously to serve many active users. The analysis provides new approaches to exploit physical channels, transmit antennas, and APs to mitigate interference, while providing the best possible link gain to an active user through the most suitable interference-free channel. The event of concurrent service requests placed by active users on a specific interference-free channel is discussed for either interference avoidance through identifying unshared channels or desired link improvement via multiuser scheduling. The applicability of the approaches to balance downlink loads is explained, and practical scenarios due to imperfect identification of interference-free channels and/or scheduled user are thoroughly investigated. The developed results are applicable for any statistical and geometric models of the allocated channel to an active user as well as channel conditions of interference users. They can be used to study various performance measures. Numerical and simulation results are presented to explain some outcomes of this work.
Radaydeh, Redha
2016-02-16
This paper investigates low-complexity joint interference avoidance and desired link improvement for single channel allocation in multiuser multi-antenna access points (APs) for open-access small cells. It is considered that an active user is equipped with an atenna array that can be used to suppress interference sources but not to provide spatial diversity. On the other hand, the operation of APs can be coordinated to meet design requirements, and each of which can unconditionally utilize assigned physical channels. Moreover, each AP is equipped with uncorrelated antennas that can be reused simultaneously to serve many active users. The analysis provides new approaches to exploit physical channels, transmit antennas, and APs to mitigate interference, while providing the best possible link gain to an active user through the most suitable interference-free channel. The event of concurrent service requests placed by active users on a specific interference-free channel is discussed for either interference avoidance through identifying unshared channels or desired link improvement via multiuser scheduling. The applicability of the approaches to balance downlink loads is explained, and practical scenarios due to imperfect identification of interference-free channels and/or scheduled user are thoroughly investigated. The developed results are applicable for any statistical and geometric models of the allocated channel to an active user as well as channel conditions of interference users. They can be used to study various performance measures. Numerical and simulation results are presented to explain some outcomes of this work.
A novel mechanism for fine-tuning open-state stability in a voltage-gated potassium channel
DEFF Research Database (Denmark)
Pless, Stephan Alexander; Niciforovic, Ana P; Galpin, Jason D
2013-01-01
stabilization is the consequence of the amelioration of an inherently repulsive open-state interaction between the partial negative charge on the face of Phe481 and a highly co-evolved acidic side chain, Glu395, and this interaction is potentially modulated through the Tyr485 hydroxyl. We propose...... fluorinated derivatives of aromatic residues previously implicated in the gating of Shaker potassium channels. Here we show that stepwise dispersion of the negative electrostatic surface potential of only one site, Phe481, stabilizes the channel open state. Furthermore, these data suggest that this apparent...
Energy Technology Data Exchange (ETDEWEB)
Bidart, A.; Caltagirone, J.P.; Parneix, S. [Laboratoire MASTER-ENSCPB, 33 - Talence (France)
1997-12-31
The MASTER laboratory has been involved since several years in the creation and utilization of modeling tools for the prediction of 3-D turbulent flows and heat transfers in turbine blades in order to optimize the cooling systems of turbo-machineries. This paper describes one of the test-cases that has been used for the validation of the `Aquilon` calculation code developed in this aim. Then, the modeling performed with the `Fluent` industrial code in order to evaluate the possible improvements of the Aquilon code, is presented. (J.S.) 5 refs.
Varseev, E.
2017-11-01
The present work is dedicated to verification of numerical model in standard solver of open-source CFD code OpenFOAM for two-phase flow simulation and to determination of so-called “baseline” model parameters. Investigation of heterogeneous coolant flow parameters, which leads to abnormal friction increase of channel in two-phase adiabatic “water-gas” flows with low void fractions, presented.
Lakehal, D.; Métrailler, D.; Reboux, S.
2017-06-01
This paper presents Direct Numerical Simulation (DNS) results of a turbulent water flow in a channel at Reτ = 400 laden with 0.25 mm diameter air bubbles clustered near the wall (maximum void fraction of α = 8% at y+ ˜ 20). The bubbles were fully resolved using the level set approach built within the CFD/CMFD code TransAT. The fluid properties (air and water) were kept real, including density, viscosity, and surface tension coefficient. The aim of this work is to understand the effects of the bubbles on near-wall turbulence, paving the way towards convective wall-boiling flow studies. The interactions between the gas bubbles and the water stream were studied through an in-depth analysis of the turbulence statistics. The near-wall flow is overall affected by the bubbles, which act like roughness elements during the early phase, prior to their departure from the wall. The average profiles are clearly altered by the bubbles dynamics near the wall, which somewhat contrasts with the findings from similar studies [J. Lu and G. Tryggvason, "Dynamics of nearly spherical bubbles in a turbulent channel upflow," J. Fluid Mech. 732, 166 (2013)], most probably because the bubbles were introduced uniformly in the flow and not concentrated at the wall. The shape of the bubbles measured as the apparent to initial diameter ratio is found to change by a factor of at least two, in particular at the later stages when the bubbles burst out from the boundary layer. The clustering of the bubbles seems to be primarily localized in the zone populated by high-speed streaks and independent of their size. More importantly, the bubbly flow seems to differ from the single-phase flow in terms of turbulent stress distribution and energy exchange, in which all the stress components seem to be increased in the region very close to the wall, by up to 40%. The decay in the energy spectra near the wall was found to be significantly slower for the bubbly flow than for a single-phase flow, which
Plasma Diagnostics by Microwave Interferometry in MHD Channels with the Aid of an Open Waveguide
Energy Technology Data Exchange (ETDEWEB)
Muenkel, J. [Rheinische-Westfalische Technische Hochschule Aachen, Federal Republic of Germany (Germany)
1966-10-15
Plasma diagnostics of a novel kind, using microwave interferometry, is described. Use is made of an open non-conventional waveguide in the test path of the microwave bridge. Guiding the microwave has several advantages over free transmission of the test h.f. beam between two horn antennas if there are small plasma streams bounded by ceramics and metals as in the case of MHD channels. There are less unknown and uncontrolled disturbances of the electromagnetic waves introduced by the boundaries. On the other hand most guiding structures disturb the homogeneity of the streaming plasma (cf. arrangements with Lecher wires, dielectric rods, etc.); the waveguide used here does not do so. This waveguide, a so-called groove guide, consists of two parallel metal plates or bands with a shallow axially-directed groove in each. The plasma stream to be tested flows between these plates in a direction perpendicular to the direction of propagation of the microwaves. The groove guide has properties similar to the ideal parallel-plate guide with infinite side wards extension, but the energy flow is concentrated in the middle region by the grooves. An approximate analysis, the transverse resonance analysis, has been used to calculate the field distribution and propagation characteristics of the guide. Because of the cross-sectional dimensions of the MHD channel in question (height 16 mm) and the wavelength (4 mm) chosen, considering the expected electron density, the groove guide had to be built for use in an oversized quasi-optical technique. The transition from rectangular (hollow pipe) guide to the open guide is done in two steps. With a good knowledge of the groove guide data and an appropriate theory of propagation of electromagnetic waves in ionized media, measuring phase shift and additional damping of the microwaves by introduction of the ionized gas allows the electron density and collision frequency, two of the most important plasma parameters, to be evaluated. The system
A lattice Boltzmann model for solute transport in open channel flow
Wang, Hongda; Cater, John; Liu, Haifei; Ding, Xiangyi; Huang, Wei
2018-01-01
A lattice Boltzmann model of advection-dispersion problems in one-dimensional (1D) open channel flows is developed for simulation of solute transport and pollutant concentration. The hydrodynamics are calculated based on a previous lattice Boltzmann approach to solving the 1D Saint-Venant equations (LABSVE). The advection-dispersion model is coupled with the LABSVE using the lattice Boltzmann method. Our research recovers the advection-dispersion equations through the Chapman-Enskog expansion of the lattice Boltzmann equation. The model differs from the existing schemes in two points: (1) the lattice Boltzmann numerical method is adopted to solve the advection-dispersion problem by meso-scopic particle distribution; (2) and the model describes the relation between discharge, cross section area and solute concentration, which increases the applicability of the water quality model in practical engineering. The model is verified using three benchmark tests: (1) instantaneous solute transport within a short distance; (2) 1D point source pollution with constant velocity; (3) 1D point source pollution in a dam break flow. The model is then applied to a 50-year flood point source pollution accident on the Yongding River, which showed good agreement with a MIKE 11 solution and gauging data.
Directory of Open Access Journals (Sweden)
Khalid Hussain Janbaz
2016-06-01
Full Text Available Symplocos paniculata is a medicinal plant used by native healers to manage gastrointestinal ailments. The crude methanolic extract of S. paniculata was screened pharmacologically both in vitro and in vivo for the validation of its therapeutic potential. It suppressed the spontaneous activity of isolated rabbit jejunum preparations and also caused inhibition of the low K+ (20 mM- induced spastic contractions in isolated rabbit jejunum preparations in a manner comparable to cromakalim. The relaxant effect was found to be blocked following glibenclamide exposure of the isolated tissue preparations similar to cromakalim, suggesting that observed response was likely to be mediated through opening of ATP dependent K+ channels. Following oral administration to mice provided protection against castor oil-induced diarrhea in a manner similar to loperamide. The plant material was found safe in toxicity study up to oral dose of 8 g/kg in mice. Hence, present study provides a scientific basis for the vernacular use of S. paniculata in gastro-intestinal system.
Roughness coefficients for stream channels in Arizona
Aldridge, B.N.; Garrett, J.M.
1973-01-01
When water flows in an open channel, energy is lost through friction along the banks and bed of the channel and through turbulence within the channel. The amount of energy lost is governed by channel roughness, which is expressed in terms of a roughness coefficient. An evaluation of the roughness coefficient is necessary in many hydraulic computations that involve flow in an open channel. Owing to the lack of satisfactory quantitative procedure, the ability of evaluate roughness coefficients can be developed only through experience; however, a basic knowledge of the methods used to assign the coefficients and the factors affecting them will be a great help. One of the most commonly used equations in open-channel hydraulics is that of Manning. The Manning equation is 1.486
Adib, M. R. M.; Amirza, A. R. M.; Wardah, T.; Junaidah, A.
2016-07-01
Hydraulic control gate structure plays an important role in regulating the flow of water in river, canal or water reservoir. One of the most appropriate structures in term of resolving the problem of flood occured is the construction of circular fibre steel flap gate. Therefore, an experiment has been conducted by using an open channel model at laboratory. In this case, hydraulic jump and backwater were the method to determined the hydraulic characteristics of circular fibre steel flap gate in an open channel model. From the experiment, the opening angle of flap gate can receive discharges with the highest flow rate of 0.035 m3/s with opening angle was 47°. The type of jump that occurs at the slope of 1/200 for a distance of 5.0 m is a standing jump or undulating wave. The height of the backwater can be identified based on the differences of specific force which is specific force before jump, F1 and specific force after jump, F2 from the formation of backwater. Based on the research conducted, the tendency of incident backwater wave occurred was high in every distance of water control location from water inlet is flap slope and the slope of 1/300 which is 0.84 m/s and 0.75 m/s of celerity in open channel model.
The structure of turbulence in a rapid tidal flow.
Milne, I A; Sharma, R N; Flay, R G J
2017-08-01
The structure of turbulence in a rapid tidal flow is characterized through new observations of fundamental statistical properties at a site in the UK which has a simple geometry and sedate surface wave action. The mean flow at the Sound of Islay exceeded 2.5 m s -1 and the turbulent boundary layer occupied the majority of the water column, with an approximately logarithmic mean velocity profile identifiable close to the seabed. The anisotropic ratios, spectral scales and higher-order statistics of the turbulence generally agree well with values reported for two-dimensional open channels in the laboratory and other tidal channels, therefore providing further support for the application of universal models. The results of the study can assist in developing numerical models of turbulence in rapid tidal flows such as those proposed for tidal energy generation.
The Effect of Confluence Angle on the Flow Pattern at a Rectangular Open-Channel
Directory of Open Access Journals (Sweden)
F. Rooniyan
2014-02-01
Full Text Available Flow connection in channels is a phenomenon which frequently happens in rivers, water and drainage channels and urban sewage systems. The phenomenon appears to be more complex in rivers than in channels, especially at the y-junction bed joint that causes erosion and sedimentation at some areas resulting to morphological changes. Flow behavior at the channel junction area depends on variables such as channel geometry, discharge ratio, tributary width and y-junction connection angle of the channel, bed level changes at the bed joint, flow characteristic at the bed joint upstream and flow Froude number in different sections. In this research, fluent numerical model and junction angles of 30o, 45o & 60o are used to analyze and evaluate the effect of channel junction geometry on the flow pattern and the flow separation zone dimensions in different ratios of flow discharge (upstream channel discharge to total discharge of the flow. Results for two ratios of flow discharge are represented. Results are in agreement with earlier studies and it is shown that the change of the channel crossing angle affects the flow pattern in the main channel and also that the dimensions of the created separation zone in the main channel become larger when the crossing angle increases. This phenomenon can also be observed when the flow discharge ratio is lower. Analysis showed that the least dimension of the separation zone will be at the crossing angle of 45o .
International Nuclear Information System (INIS)
Dritselis, Chris D
2016-01-01
The budgets of the Reynolds stress and streamwise enstrophy are evaluated through direct numerical simulations for the turbulent particle-laden flow in a vertical channel with momentum exchange between the two phases. The influence of the dispersed particles on the budgets is examined through a comparison of the particle-free and the particle-laden cases at the same Reynolds number of Re b = 5600 based on the bulk fluid velocity and the distance between the channel walls. Results are obtained for particle ensembles with four response times in simulations with and without streamwise gravity and inter-particle collisions at average mass (volume) fractions of 0.2 (2.7 × 10 −5 ) and 0.5 (6.8 × 10 −5 ). The particle feedback force on the flow of the carrier phase is modeled by a point-force approximation (PSIC-method). It is shown that all the terms in the budgets of the Reynolds stress components are decreased in the presence of particles. The level of reduction depends on the particle response time and it is higher under the effects of gravity and inter-particle collisions. A considerable reduction in all the terms of the streamwise enstrophy budget is also observed. In particular, all production mechanisms, and mainly vortex stretching, are inhibited in the particulate flows and thus the production of streamwise vorticity is significantly damped. A further insight into the direct particle effects on the fluid turbulence is provided by analyzing in detail the fluid–fluid, fluid–particle and particle–particle correlations, and the spectra of the fluid–particle energy exchange rate. The present results indicate that the turbulence production, dissipation and pressure–strain term are generally large quantities, but their summation is relatively small and comparable to the fluid–particle direct energy exchange rate. Consequently, the particle contribution can potentially increase or decrease the fluctuating fluid velocities and eventually control the
International Nuclear Information System (INIS)
Liu, J T; Zuo, Z G; Liu, S H; Wu, Y L
2014-01-01
In this paper, a new nonlinear k-ε turbulence model based on RNG k-ε turbulence model and Wilcox's k-ω turbulence model was proposed to simulate the unsteady flow and to predict the pressure fluctuation through a model pump turbine for engineering application. Calculations on a curved rectangular duct proved that the nonlinear k-ε turbulence model is applicable for high pressure gradient flows and large curvature flows. The numerically predicted relative pressure amplitude (peak to peak) in time domain to the pump turbine head at no load condition is very close to the experimental data. It is indicated that the prediction of the pressure fluctuation is valid by the present nonlinear k-ε method. The high pressure fluctuation in this area is the main issue for pump turbine design, especially at high head condition
Low pressure drop filtration of airborne molecular organic contaminants using open-channel networks
Dallas, Andrew J.; Joriman, Jon; Ding, Lefei; Weineck, Gerald; Seguin, Kevin
2007-03-01
Airborne molecular contamination (AMC) continues to play a very decisive role in the performance of many microelectronic devices and manufacturing processes. Besides airborne acids and bases, airborne organic contaminants such as 1-methyl-2-pyrrolidinone (NMP), hexamethyldisiloxane (HMDSO), trimethylsilanol (TMS), perfluoroalkylamines and condensables are of primary concern in these applications. Currently, the state of the filtration industry is such that optimum filter life and removal efficiency for organics is offered by granular carbon filter beds. However, the attributes that make packed beds of activated carbon extremely efficient also impart issues related to elevated filter weight and pressure drop. Most of the lower pressure drop AMC filters currently offered are quite expensive and are simply pleated combinations of various adsorptive and reactive media. On the other hand, low pressure drop filters, such as those designed as open-channel networks (OCN's), offer good filter life and removal efficiency with the additional benefits of significant reductions in overall filter weight and pressure drop. Equally important for many applications, the OCN filters can reconstruct the airflow so as to enhance the operation of a tool or process. For tool mount assemblies and fan filter units (FFUs) this can result in reduced fan and blower speeds, which subsequently can provide reduced vibration and energy costs. Additionally, these low pressure drop designs can provide a cost effective way of effectively removing AMC in full fab (or HVAC) filtration applications without significantly affecting air-handling requirements. Herein, we will present a new generation of low pressure drop OCN filters designed for the removal of airborne organics in a wide range of applications.
Balaji, K. A.; Prabu, K.
2018-03-01
There is an immense demand for high bandwidth and high data rate systems, which is fulfilled by wireless optical communication or free space optics (FSO). Hence FSO gained a pivotal role in research which has a added advantage of both cost-effective and licence free huge bandwidth. Unfortunately the optical signal in free space suffers from irradiance and phase fluctuations due to atmospheric turbulence and pointing errors which deteriorates the signal and degrades the performance of communication system over longer distance which is undesirable. In this paper, we have considered polarization shift keying (POLSK) system applied with wavelength and time diversity technique over Malaga(M)distribution to mitigate turbulence induced fading. We derived closed form mathematical expressions for estimating the systems outage probability and average bit error rate (BER). Ultimately from the results we can infer that wavelength and time diversity schemes enhances these systems performance.
International Nuclear Information System (INIS)
Tian Wenxi; Su, G.H.; Qiu Suizheng; Jia Dounan
2004-01-01
The field synergy principle was proposed by Guo(1998) which is based on 2-D boundary laminar flow and it resulted from a second look at the mechanism of convective heat transfer. Numerical verification of this principle's validity for turbulent flow has been carried out by very few researchers, and mostly commercial software such as FLUENT, CFX etc. were used in their study. In this paper, numerical simulation of turbulent flow with recirculation was developed using SIMPLE algorithm with two-equation k-ε model. Extension of computational region method and wall function method were quoted to regulate the whole computational region geometrically. Given the inlet Reynold number keeps constant: 10000, by changing the height of the solid obstacle, simulation was conducted and the result showed that the wall heat flux decreased with the angle between the velocity vector and the temperature gradient. Thus it is validated that the field synergy principle based on 2-D boundary laminar flow can also be applied to complex turbulent flow even with recirculation. (author)
Directory of Open Access Journals (Sweden)
R. Ghobadian
2016-10-01
Full Text Available Introduction: Flow and sediment transport has an important role in entrance deformation of open channel junctions. As water moved through a drainage network, it forced to converge at confluence. Due to increasing of water discharge and collision of converging flows, a complex three-dimensional and most highly turbulent location were occurred in the vicinity of the junction. Therefore a deep scour hole and point bar has developed in this area that caused the change in rivers morphology. Despite the large amount of research carried out on flow patterns in river confluences, only a few researches have focused on sediment transport. Materials and methods: In this research three dimensional model (SSIIM1 was used to study of flow pattern and sediment and erosion pattern at 60 degree Junction .the Navier-Stockes equation of turbulent flow in a general three-dimensional geometry are solved to obtain the water velocity: , (1 Where U is average velocity, ρ is density of water, is pressure, the Kronecker delta, which is 1 if i is equal to j and 0 otherwise and general space dimension. The last term is Reynolds stress, often modeled with the following equation: (2 Where and k are eddy viscosity and turbulent kinetic energy respectively. Van Rijn's relations were used to calculate sediment suspended and bed load transport. Dirichlet and zero gradients boundary conditions were used at inflow and outflow boundary respectively. fixed-lid approach was used to computed free surface by using zero gradient for all variables. The wall law for rough boundaries was also used as a boundary condition for bed and wall. In equilibrium situation, The sediment concentration for the cell closet to the bed was specified as the bed boundary condition. Specified value was used for sediment concentration of other boundary conditions at upstream boundary and zero gradients for the water surface, outlet, and the sides. the only simulation of local scouring and sedimentation at
Zheng, Shou-Tian; Zhao, Xiang; Lau, Samuel; Fuhr, Addis; Feng, Pingyun; Bu, Xianhui
2013-07-17
Reported here are the new concept of utilizing open metal sites (OMSs) for architectural pore design and its practical implementation. Specifically, it is shown here that OMSs can be used to run extended hooks (isonicotinates in this work) from the framework walls to the channel centers to effect the capture of single metal ions or clusters, with the concurrent partitioning of the large channel spaces into multiple domains, alteration of the host-guest charge relationship and associated guest-exchange properties, and transfer of OMSs from the walls to the channel centers. The concept of the extended hook, demonstrated here in the multicomponent dual-metal and dual-ligand system, should be generally applicable to a range of framework types.
Effects of free-surface on design charts for open channels
African Journals Online (AJOL)
2011-12-14
Dec 14, 2011 ... Normal depth is an important parameter for the design of channels and canals. For rectangular, trapezoidal, and circular channel sections it is possible to express normal depth by a trial-and-error procedure or analytically. However, the effects of free-surface on the design charts for determination of the ...
Velocity-based analysis of sediment incipient deposition in rigid boundary open channels.
Aksoy, Hafzullah; Safari, Mir Jafar Sadegh; Unal, Necati Erdem; Mohammadi, Mirali
2017-11-01
Drainage systems must be designed in a way to minimize undesired problems such as decrease in hydraulic capacity of the channel, blockage and transport of pollutants due to deposition of sediment. Channel design considering self-cleansing criteria are used to solve the sedimentation problem. Incipient deposition is one of the non-deposition self-cleansing design criteria that can be used as a conservative method for channel design. Experimental studies have been carried out in five different cross-section channels, namely trapezoidal, rectangular, circular, U-shape and V-bottom. Experiments were performed in a tilting flume using four different sizes of sands as sediment in nine different channel bed slopes. Two well-known methods, namely the Novak & Nalluri and Yang methods are considered for the analysis of sediment motion. Equations developed using experimental data are found to be in agreement with the literature. It is concluded that the design velocity depends on the shape of the channel cross-section. Rectangular and V-bottom channels need lower and higher incipient deposition velocities, respectively, in comparison with other channels.
Black, John H.; Woodman, Nicholas D.; Barker, John A.
2017-03-01
Rethinking an old tracer experiment in fractured crystalline rock suggests a concept of groundwater flow in sparse networks of long channels that is supported by results from an innovative lattice network model. The model, HyperConv, can vary the mean length of `strings' of connected bonds, and the gaps between them, using two independent probability functions. It is found that networks of long channels are able to percolate at lower values of (bond) density than networks of short channels. A general relationship between mean channel length, mean gap length and probability of percolation has been developed which incorporates the well-established result for `classical' lattice network models as a special case. Using parameters appropriate to a 4-m diameter drift located 360 m below surface at Stripa Mine Underground Research Laboratory in Sweden, HyperConv is able to reproduce values of apparent positive skin, as observed in the so-called Macropermeability Experiment, but only when mean channel length exceeds 10 m. This implies that such channel systems must cross many fracture intersections without bifurcating. A general relationship in terms of flow dimension is suggested. Some initial investigations using HyperConv show that the commonly observed feature, `compartmentalization', only occurs when channel density is just above the percolation threshold. Such compartments have been observed at Kamaishi Experimental Mine (Japan) implying a sparse flow network. It is suggested that compartments and skin are observable in the field, indicate sparse channel systems, and could form part of site characterization for deep nuclear waste repositories.
Energy Technology Data Exchange (ETDEWEB)
Gong, Jianying; Li, Guojun; Gao, Tieyu [Xian Jiaotong University, Xian (China)
2014-09-15
The present experiment compares the heat transfer and friction characteristics in steam cooled and air cooled rectangular channels (simulating a gas turbine blade cooling passage) with two opposite rib-roughened walls. The Reynolds number (Re) whose length scale is the hydraulic diameter of the passage is set within the range of 10000-60000. The channel length is 1000 mm. The pitch-to-rib height ratio, the channel aspect ratio and the channel blockage ratio is 10, 0.5 and 0.047, respectively. It is found that the average Nu, the average friction coefficient, and the heat transfer performance of both steam and air in the ribbed channels show almost the same change trend with the increase of Re. Under the same test conditions, the average Nu of steam is 30.2% higher than that of air, the average friction coefficient is 18.4% higher, and the heat transfer performances of steam on the ribbed and the smooth walls are 8.4% and 7.3% higher than those of air, respectively. In addition, semi-empirical correlations for the two test channels are developed, which can predict the Nu under the given test condition. The correlations can be used in the design of the internal cooling passage of new generation steam cooled gas turbine blade/vane.
User's Guide for Mixed-Size Sediment Transport Model for Networks of One-Dimensional Open Channels
Bennett, James P.
2001-01-01
This user's guide describes a mathematical model for predicting the transport of mixed sizes of sediment by flow in networks of one-dimensional open channels. The simulation package is useful for general sediment routing problems, prediction of erosion and deposition following dam removal, and scour in channels at road embankment crossings or other artificial structures. The model treats input hydrographs as stepwise steady-state, and the flow computation algorithm automatically switches between sub- and supercritical flow as dictated by channel geometry and discharge. A variety of boundary conditions including weirs and rating curves may be applied both external and internal to the flow network. The model may be used to compute flow around islands and through multiple openings in embankments, but the network must be 'simple' in the sense that the flow directions in all channels can be specified before simulation commences. The location and shape of channel banks are user specified, and all bedelevation changes take place between these banks and above a user-specified bedrock elevation. Computation of sediment-transport emphasizes the sand-size range (0.0625-2.0 millimeter) but the user may select any desired range of particle diameters including silt and finer (user may set the original bed-sediment composition of any number of layers of known thickness. The model computes the time evolution of total transport and the size composition of bed- and suspended-load sand through any cross section of interest. It also tracks bed -surface elevation and size composition. The model is written in the FORTRAN programming language for implementation on personal computers using the WINDOWS operating system and, along with certain graphical output display capability, is accessed from a graphical user interface (GUI). The GUI provides a framework for selecting input files and parameters of a number of components of the sediment-transport process. There are no restrictions in the
Energy Technology Data Exchange (ETDEWEB)
Gunawan, Budi [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Neary, Vincent Sinclair [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Mortensen, Josh [United States Bureau of Reclamation, Denver, CO (United States); Roberts, Jesse D. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2017-05-01
Hydrokinetic energy from flowing water in open channels has the potential to support local electricity needs with lower regulatory or capital investment than impounding water with more conventional means. MOU agencies involved in federal hydropower development have identified the need to better understand the opportunities for hydrokinetic (HK) energy development within existing canal systems that may already have integrated hydropower plants. This document provides an overview of the main considerations, tools, and assessment methods, for implementing field tests in an open-channel water system to characterize current energy converter (CEC) device performance and hydrodynamic effects. It describes open channel processes relevant to their HK site and perform pertinent analyses to guide siting and CEC layout design, with the goal of streamlining the evaluation process and reducing the risk of interfering with existing uses of the site. This document outlines key site parameters of interest and effective tools and methods for measurement and analysis with examples drawn from the Roza Main Canal, in Yakima, WA to illustrate a site application.
Energy Technology Data Exchange (ETDEWEB)
Tryggvason, Gretar [Univ. of Notre Dame, IN (United States); Bolotnov, Igor [North Carolina State Univ., Raleigh, NC (United States); Fang, Jun [North Carolina State Univ., Raleigh, NC (United States); Lu, Jiacai [Univ. of Notre Dame, IN (United States)
2017-03-30
Direct numerical simulation (DNS) has been regarded as a reliable data source for the development and validation of turbulence models along with experiments. The realization of DNS usually involves a very fine mesh that should be able to resolve all relevant turbulence scales down to Kolmogorov scale [1]. As the most computationally expensive approach compared to other CFD techniques, DNS applications used to be limited to flow studies at very low Reynolds numbers. Thanks to the tremendous growth of computing power over the past decades, the simulation capability of DNS has now started overlapping with some of the most challenging engineering problems. One of those examples in nuclear engineering is the turbulent coolant flow inside reactor cores. Coupled with interface tracking methods (ITM), the simulation capability of DNS can be extended to more complicated two-phase flow regimes. Departure from nucleate boiling (DNB) is the limiting critical heat flux phenomena for the majority of accidents that are postulated to occur in pressurized water reactors (PWR) [2]. As one of the major modeling and simulation (M&S) challenges pursued by CASL, the prediction capability is being developed for the onset of DNB utilizing multiphase-CFD (M-CFD) approach. DNS (coupled with ITM) can be employed to provide closure law information for the multiphase flow modeling at CFD scale. In the presented work, research groups at NCSU and UND will focus on applying different ITM to different geometries. Higher void fraction flow analysis at reactor prototypical conditions will be performed, and novel analysis methods will be developed, implemented and verified for the challenging flow conditions.
Directory of Open Access Journals (Sweden)
Theodore D. Katsilieris
2017-03-01
Full Text Available The terrestrial optical wireless communication links have attracted significant research and commercial worldwide interest over the last few years due to the fact that they offer very high and secure data rate transmission with relatively low installation and operational costs, and without need of licensing. However, since the propagation path of the information signal, i.e., the laser beam, is the atmosphere, their effectivity affects the atmospheric conditions strongly in the specific area. Thus, system performance depends significantly on the rain, the fog, the hail, the atmospheric turbulence, etc. Due to the influence of these effects, it is necessary to study, theoretically and numerically, very carefully before the installation of such a communication system. In this work, we present exactly and accurately approximate mathematical expressions for the estimation of the average capacity and the outage probability performance metrics, as functions of the link’s parameters, the transmitted power, the attenuation due to the fog, the ambient noise and the atmospheric turbulence phenomenon. The latter causes the scintillation effect, which results in random and fast fluctuations of the irradiance at the receiver’s end. These fluctuations can be studied accurately with statistical methods. Thus, in this work, we use either the lognormal or the gamma–gamma distribution for weak or moderate to strong turbulence conditions, respectively. Moreover, using the derived mathematical expressions, we design, accomplish and present a computational tool for the estimation of these systems’ performances, while also taking into account the parameter of the link and the atmospheric conditions. Furthermore, in order to increase the accuracy of the presented tool, for the cases where the obtained analytical mathematical expressions are complex, the performance results are verified with the numerical estimation of the appropriate integrals. Finally, using
Awasthi, Ankit; Anderson, William
2018-04-01
We have studied the effects of topographically driven secondary flows on inner-outer interaction in turbulent channel flow. Recent studies have revealed that large-scale motions in the logarithmic region impose an amplitude and frequency modulation on the dynamics of small-scale structures near the wall. This led to development of a predictive model for near-wall dynamics, which has practical relevance for large-eddy simulations. Existing work on amplitude modulation has focused on smooth-wall flows; however, Anderson [J. Fluid Mech. 789, 567 (2016), 10.1017/jfm.2015.744] addressed the problem of rough-wall turbulent channel flow in which the correlation profiles for amplitude modulation showed trends similar to those reported by Mathis et al. [Phys. Fluids 21, 111703 (2009), 10.1063/1.3267726]. For the present study, we considered flow over surfaces with a prominent spanwise heterogeneity, such that domain-scale turbulent secondary flows in the form of counter-rotating vortices are sustained within the flow. (We also show results for flow over a homogeneous roughness, which serves as a benchmark against the spanwise-perturbed cases.) The vortices are anchored to the topography such that prominent upwelling and downwelling occur above the low and high roughness, respectively. We have quantified the extent to which such secondary flows disrupt the distribution of spectral density across constituent wavelengths throughout the depth of the flow, which has direct implications for the existence of amplitude and frequency modulation. We find that the distinct outer peak associated with large-scale motions—the "modulators"—is preserved within the upwelling zone but vanishes in the downwelling zone. Within the downwelling zones, structures are steeper and shorter. Single- and two-point correlations for inner-outer amplitude and frequency modulation demonstrate insensitivity to resolution across cases. We also show a pronounced crossover between the single- and two
International Nuclear Information System (INIS)
Abdeen, Mostafa A. M.; Abdin, Alla E.
2007-01-01
The existence of hydraulic structures in a branched open channel system urges the need for considering the gradually varied flow criterion in evaluating the different hydraulic characteristics in this type of open channel system. Computations of hydraulic characteristics such as flow rates and water surface profiles in branched open channel system with hydraulic structures require tremendous numerical effort especially when the flow cannot be assumed uniform. In addition, the existence of submerged aquatic weeds in this branched open channel system adds to the complexity of the evaluation of the different hydraulic characteristics for this system. However, this existence of aquatic weeds can not be neglected since it is very common in Egyptian open channel systems. Artificial Neural Network (ANN) has been widely utilized in the past decade in civil engineering applications for the simulation and prediction of the different physical phenomena and has proven its capabilities in the different fields. The present study aims towards introducing the use of ANN technique to model and predict the impact of submerged aquatic weeds existence on the hydraulic performance of branched open channel system. Specifically the current paper investigates a branched open channel system that consists of main channel supplies water to two branch channels that are infested by submerged aquatic weeds and have water structures such as clear over fall weirs and sluice gates. The results of this study showed that ANN technique was capable, with small computational effort and high accuracy, of predicting the impact of different infestation percentage for submerged aquatic weeds on the hydraulic performance of branched open channel system with two different hydraulic structures
Energy Technology Data Exchange (ETDEWEB)
Sotela Avila, Gilberto [Universidad Nacional Autonoma de Mexico (Mexico)
2001-03-01
The author shows that the computation of gradually-varied-flow profiles in prismatic compound channels involves the solution of the dynamic equation, but using the compound channel Froude number defined by Blalock and Sturm. The same equation is used for non-prismatic channels by dividing the channel into short reaches and carrying the computation step by step through an iterative process. [Spanish] El autor demuestra que los perfiles del flujo gradualmente variado en canales prismaticos de seccion compuesta se pueden determinar mediante la integracion de la llamada ecuacion dinamica, pero usando el numero de Froude definido por Blalock y Sturm para este tipo de canales. Cuando no son prismaticos, tambien se aplica la ecuacion de la energia por tramos y el calculo sigue un proceso iterativo una vez definidos los tirantes criticos multiples y la zona en que se desarrolla el perfil.
Directory of Open Access Journals (Sweden)
Zeineb Es-Salah-Lamoureux
2010-05-01
Full Text Available hERG channels are physiologically important ion channels which mediate cardiac repolarization as a result of their unusual gating properties. These are very slow activation compared with other mammalian voltage-gated potassium channels, and extremely rapid inactivation. The mechanism of slow activation is not well understood and is investigated here using fluorescence as a direct measure of S4 movement and pore opening.Tetramethylrhodamine-5-maleimide (TMRM fluorescence at E519 has been used to track S4 voltage sensor movement, and channel opening and closing in hERG channels. Endogenous cysteines (C445 and C449 in the S1-S2 linker bound TMRM, which caused a 10 mV hyperpolarization of the V((1/2 of activation to -27.5+/-2.0 mV, and showed voltage-dependent fluorescence signals. Substitution of S1-S2 linker cysteines with valines allowed unobstructed recording of S3-S4 linker E519C and L520C emission signals. Depolarization of E519C channels caused rapid initial fluorescence quenching, fit with a double Boltzmann relationship, F-V(ON, with V((1/2 (,1 = -37.8+/-1.7 mV, and V((1/2 (,2 = 43.5+/-7.9 mV. The first phase, V((1/2 (,1, was approximately 20 mV negative to the conductance-voltage relationship measured from ionic tail currents (G-V((1/2 = -18.3+/-1.2 mV, and relatively unchanged in a non-inactivating E519C:S620T mutant (V((1/2 = -34.4+/-1.5 mV, suggesting the fast initial fluorescence quenching tracked S4 voltage sensor movement. The second phase of rapid quenching was absent in the S620T mutant. The E519C fluorescence upon repolarization (V((1/2 = -20.6+/-1.2, k = 11.4 mV and L520C quenching during depolarization (V((1/2 = -26.8+/-1.0, k = 13.3 mV matched the respective voltage dependencies of hERG ionic tails, and deactivation time constants from -40 to -110 mV, suggesting they detected pore-S4 rearrangements related to ionic current flow during pore opening and closing.THE DATA INDICATE: 1 that rapid environmental changes occur at the
Effects of potassium channel opener on the kinetics of thallium-201 in in-vitro and in-vivo
International Nuclear Information System (INIS)
Lee, J.; Kim, E. J.; Ahn, B. C.; Chae, S. C.; Lee, K. B.; Kim, C. K.
1997-01-01
Potassium channel opener (K-opener) opens membrane ATP-sensitive K + -channel and induces and increase in potassium efflux from cells. K-openers are powerful smooth muscle relaxants and currently used as antihypertensive, antianginal drugs or bronchodilators in clinic. Pharmacologic potency of newly synthesized K-opener is being evaluated with efflux capacity of preincubated Rb-83 from the isolated aortic vascular tissue preparation. Thallium has similar characteristics to those of rubidium and potassium in vivo. To evaluate the effect of pinacidil (a potent K-opener) on Tl-201 biokinetics, we have performed uptake/washout studies in cultured myocytes, and mice biodistribution study. Primary culture of spontaneous contracting myocytes was undertake from hearts of newborn Sprague-Dawley rat. Different concentration of pinacidil (100nM or 10uM) was co-incubated with Tl-201 in HBSS buffer to evaluate its effect on cellular uptake, or challenged to myocyte preparations pre-incubated with Tl-201 for washout study. Pinacidil was injected into mice simultaneous or 10-min after Tl-201 injection, and organ uptake and whole body retention ratio was measured using gamma counter or dose calibrator. Co-incubation of pinacidil with Tl-201 resulted in a decrease in Tl uptake into myocytes by 1.6 - 2.5 times, and an increase in washout by 1.6 - 3.1 times. Pinacidil injection resulted in mild decrease in blood, heart and liver uptake in mice, bur renal uptake was markedly decreased in a dose dependent manner. These results suggest that the pinacidil Tl-201 kinetics and may potentially affect the interpretation of Tl-201 myocardial imaging
Energy Technology Data Exchange (ETDEWEB)
Rosendahl, Uwe; Dreyer, Michael E. [University of Bremen, Sounding Rocket Experiment TEXUS-41 Center of Applied Space Technology and Microgravity (ZARM), Bremen (Germany)
2007-05-15
In this paper we report on the set-up and the performance of an experiment for the investigation of flow-rate limitations in open capillary channels under low-gravity conditions (microgravity). The channels consist of two parallel plates bounded by free liquid surfaces along the open sides. In the case of steady flow the capillary pressure of the free surface balances the differential pressure between the liquid and the surrounding constant-pressure gas phase. A maximum flow rate is achieved when the adjusted volumetric flow rate exceeds a certain limit leading to a collapse of the free surfaces. The flow is convective (inertia) dominated, since the viscous forces are negligibly small compared to the convective forces. In order to investigate this type of flow an experiment aboard the sounding rocket TEXUS-41 was performed. The aim of the investigation was to achieve the profiles of the free liquid surfaces and to determine the maximum flow rate of the steady flow. For this purpose a new approach to the critical flow condition by enlarging the channel length was applied. The paper is focussed on the technical details of the experiment and gives a review of the set-up, the preparation of the flight procedures and the performance. Additionally the typical appearance of the flow indicated by the surface profiles is presented as a basis for a separate continuative discussion of the experimental results. (orig.)
Basal interstitial water pressure in laboratory debris flows over a rigid bed in an open channel
Directory of Open Access Journals (Sweden)
N. Hotta
2012-08-01
Full Text Available Measuring the interstitial water pressure of debris flows under various conditions gives essential information on the flow stress structure. This study measured the basal interstitial water pressure during debris flow routing experiments in a laboratory flume. Because a sensitive pressure gauge is required to measure the interstitial water pressure in shallow laboratory debris flows, a differential gas pressure gauge with an attached diaphragm was used. Although this system required calibration before and after each experiment, it showed a linear behavior and a sufficiently high temporal resolution for measuring the interstitial water pressure of debris flows. The values of the interstitial water pressure were low. However, an excess of pressure beyond the hydrostatic pressure was observed with increasing sediment particle size. The measured excess pressure corresponded to the theoretical excess interstitial water pressure, derived as a Reynolds stress in the interstitial water of boulder debris flows. Turbulence was thought to induce a strong shear in the interstitial space of sediment particles. The interstitial water pressure in boulder debris flows should be affected by the fine sediment concentration and the phase transition from laminar to turbulent debris flow; this should be the subject of future studies.
Wickenden, A. D.; Grimwood, S.; Grant, T. L.; Todd, M. H.
1991-01-01
1 The actions of the potassium channel openers, cromakalim and minoxidil sulphate, were compared in a range of isolated blood vessel preparations. 2 Cromakalim and minoxidil sulphate inhibited spontaneous mechanical activity of the guinea-pig portal vein and relaxed the noradrenaline precontracted rat aorta with similar potency. In contrast, minoxidil sulphate was less potent than cromakalim in inhibiting spontaneous activity in the rat portal vein and was essentially inactive in the noradrenaline precontracted rat mesenteric artery and rabbit aorta. 3 Minoxidil sulphate did not antagonize the effects of cromakalim in the rabbit aorta indicating it was not acting as a partial 'agonist'. 4 Charybdotoxin, noxiustoxin and rubidium failed to discriminate between cromakalim and minoxidil sulphate indicating that the apparently selective effects of minoxidil sulphate were not mediated by either Ca(2+)-activated potassium channels, delayed rectifiers or rubidium impermeable potassium channels. 5 Glibenclamide antagonized the effects of cromakalim in an apparently competitive manner whereas the effects of minoxidil sulphate were antagonized in a non-competitive manner. The involvement of subtypes of ATP-sensitive potassium channels is discussed. PMID:1878752
Baetz, Ulrike; Huck, Nicola V.; Zhang, Jingbo
2017-01-01
Stomatal pores are formed between a pair of guard cells and allow plant uptake of CO2 and water evaporation. Their aperture depends on changes in osmolyte concentration of guard cell vacuoles, specifically of K+ and Mal2−. Efflux of Mal2− from the vacuole is required for stomatal closure; however, it is not clear how the anion is released. Here, we report the identification of ALMT4 (ALUMINUM ACTIVATED MALATE TRANSPORTER4) as an Arabidopsis thaliana ion channel that can mediate Mal2− release from the vacuole and is required for stomatal closure in response to abscisic acid (ABA). Knockout mutants showed impaired stomatal closure in response to the drought stress hormone ABA and increased whole-plant wilting in response to drought and ABA. Electrophysiological data show that ALMT4 can mediate Mal2− efflux and that the channel activity is dependent on a phosphorylatable C-terminal serine. Dephosphomimetic mutants of ALMT4 S382 showed increased channel activity and Mal2− efflux. Reconstituting the active channel in almt4 mutants impaired growth and stomatal opening. Phosphomimetic mutants were electrically inactive and phenocopied the almt4 mutants. Surprisingly, S382 can be phosphorylated by mitogen-activated protein kinases in vitro. In brief, ALMT4 likely mediates Mal2− efflux during ABA-induced stomatal closure and its activity depends on phosphorylation. PMID:28874508
Automatic tracking of red blood cells in micro channels using OpenCV
Rodrigues, Vânia; Rodrigues, Pedro J.; Pereira, Ana I.; Lima, Rui
2013-10-01
The present study aims to developan automatic method able to track red blood cells (RBCs) trajectories flowing through a microchannel using the Open Source Computer Vision (OpenCV). The developed method is based on optical flux calculation assisted by the maximization of the template-matching product. The experimental results show a good functional performance of this method.
Turbulence generation by waves
Energy Technology Data Exchange (ETDEWEB)
Kaftori, D.; Nan, X.S.; Banerjee, S. [Univ. of California, Santa Barbara, CA (United States)
1995-12-31
The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased. Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.
Rapid fabrication of pressure-driven open-channel microfluidic devices in omniphobic R(F) paper.
Glavan, Ana C; Martinez, Ramses V; Maxwell, E Jane; Subramaniam, Anand Bala; Nunes, Rui M D; Soh, Siowling; Whitesides, George M
2013-08-07
This paper describes the fabrication of pressure-driven, open-channel microfluidic systems with lateral dimensions of 45-300 microns carved in omniphobic paper using a craft-cutting tool. Vapor phase silanization with a fluorinated alkyltrichlorosilane renders paper omniphobic, but preserves its high gas permeability and mechanical properties. When sealed with tape, the carved channels form conduits capable of guiding liquid transport in the low-Reynolds number regime (i.e. laminar flow). These devices are compatible with complex fluids such as droplets of water in oil. The combination of omniphobic paper and a craft cutter enables the development of new types of valves and switches, such as "fold valves" and "porous switches," which provide new methods to control fluid flow.
Directory of Open Access Journals (Sweden)
Kyong Oh Baek
2018-04-01
Full Text Available There are a number of methods for observing and estimating the transverse dispersion coefficient in an analysis of the solute transport in open channel flow. It may be difficult to select an optimal method to calculate dispersion coefficients from tracer data among numerous methodologies. A flowchart was proposed in this study to select an appropriate method under the transport situation of either time-variant or steady condition. When making the flowchart, the strengths and limitations of the methods were evaluated based on its derivation procedure which was conducted under specific assumptions. Additionally, application examples of these methods on experimental data were illustrated using previous works. Furthermore, the observed dispersion coefficients in a laboratory channel were validated by using transport numerical modeling, and the simulation results were compared with the experimental results from tracer tests. This flowchart may assist in choosing the better methods for determining the transverse dispersion coefficient in various river mixing situations.
Directory of Open Access Journals (Sweden)
Tzilhav Shem-Ad
Full Text Available The tight electro-mechanical coupling between the voltage-sensing and pore domains of Kv channels lies at the heart of their fundamental roles in electrical signaling. Structural data have identified two voltage sensor pore inter-domain interaction surfaces, thus providing a framework to explain the molecular basis for the tight coupling of these domains. While the contribution of the intra-subunit lower domain interface to the electro-mechanical coupling that underlies channel opening is relatively well understood, the contribution of the inter-subunit upper interface to channel gating is not yet clear. Relying on energy perturbation and thermodynamic coupling analyses of tandem-dimeric Shaker Kv channels, we show that mutation of upper interface residues from both sides of the voltage sensor-pore domain interface stabilizes the closed channel state. These mutations, however, do not affect slow inactivation gating. We, moreover, find that upper interface residues form a network of state-dependent interactions that stabilize the open channel state. Finally, we note that the observed residue interaction network does not change during slow inactivation gating. The upper voltage sensing-pore interaction surface thus only undergoes conformational rearrangements during channel activation gating. We suggest that inter-subunit interactions across the upper domain interface mediate allosteric communication between channel subunits that contributes to the concerted nature of the late pore opening transition of Kv channels.
Shem-Ad, Tzilhav; Irit, Orr; Yifrach, Ofer
2013-01-01
The tight electro-mechanical coupling between the voltage-sensing and pore domains of Kv channels lies at the heart of their fundamental roles in electrical signaling. Structural data have identified two voltage sensor pore inter-domain interaction surfaces, thus providing a framework to explain the molecular basis for the tight coupling of these domains. While the contribution of the intra-subunit lower domain interface to the electro-mechanical coupling that underlies channel opening is relatively well understood, the contribution of the inter-subunit upper interface to channel gating is not yet clear. Relying on energy perturbation and thermodynamic coupling analyses of tandem-dimeric Shaker Kv channels, we show that mutation of upper interface residues from both sides of the voltage sensor-pore domain interface stabilizes the closed channel state. These mutations, however, do not affect slow inactivation gating. We, moreover, find that upper interface residues form a network of state-dependent interactions that stabilize the open channel state. Finally, we note that the observed residue interaction network does not change during slow inactivation gating. The upper voltage sensing-pore interaction surface thus only undergoes conformational rearrangements during channel activation gating. We suggest that inter-subunit interactions across the upper domain interface mediate allosteric communication between channel subunits that contributes to the concerted nature of the late pore opening transition of Kv channels.
Surof, Janis; Poliak, Juraj; Calvo, Ramon Mata
2017-06-01
Binary phase-shift keying optical transmission in the C-band with coherent intradyne reception is demonstrated over a long-range (10.45 km) link through the atmosphere. The link emulates representative channel conditions for geostationary optical feeder uplinks in satellite communications. The digital signal processing used in recovering the transmitted data and the performed measurements are described. Finally, the bit error rate results for 10 Gbit/s, 20 Gbit/s, and 30 Gbit/s of the outdoor experiments are presented and compared with back-to-back measurements and theory.
Ketogenic diet metabolites reduce firing in central neurons by opening K(ATP) channels.
Ma, Weiyuan; Berg, Jim; Yellen, Gary
2007-04-04
A low-carbohydrate ketogenic diet remains one of the most effective (but mysterious) treatments for severe pharmacoresistant epilepsy. We have tested for an acute effect of physiological ketone bodies on neuronal firing rates and excitability, to discover possible therapeutic mechanisms of the ketogenic diet. Physiological concentrations of ketone bodies (beta-hydroxybutyrate or acetoacetate) reduced the spontaneous firing rate of neurons in slices from rat or mouse substantia nigra pars reticulata. This region is thought to act as a "seizure gate," controlling seizure generalization. Consistent with an anticonvulsant role, the ketone body effect is larger for cells that fire more rapidly. The effect of ketone bodies was abolished by eliminating the metabolically sensitive K(ATP) channels pharmacologically or by gene knock-out. We propose that ketone bodies or glycolytic restriction treat epilepsy by augmenting a natural activity-limiting function served by K(ATP) channels in neurons.
Radiation heat transfer within an open-cycle MHD generator channel
Delil, A. A. M.
1983-05-01
Radiation heat transfer in an MHD generator was modeled using the Sparrow and Cess model for radiation in an emitting, absorbing and scattering medium. The resulting general equations can be considerably reduced by introducing simplifying approximations for the channel and MHD gas properties. The simplifications lead to an engineering model, which is very useful for one-dimensional channel flow approximation. The model can estimate thermo-optical MHD gas properties, which can be substituted in the energy equation. The model considers the contribution of solid particles in the MHD gas to radiation heat transfer, considerable in coal-fired closed cycle MHD generators. The modeling is applicable also for other types of flow at elevated temperatures, where radiation heat transfer is an important quantity.
Bartoletti, Theodore M; Jackman, Skyler L; Babai, Norbert; Mercer, Aaron J; Kramer, Richard H; Thoreson, Wallace B
2011-12-01
Light hyperpolarizes cone photoreceptors, causing synaptic voltage-gated Ca(2+) channels to open infrequently. To understand neurotransmission under these conditions, we determined the number of L-type Ca(2+) channel openings necessary for vesicle fusion at the cone ribbon synapse. Ca(2+) currents (I(Ca)) were activated in voltage-clamped cones, and excitatory postsynaptic currents (EPSCs) were recorded from horizontal cells in the salamander retina slice preparation. Ca(2+) channel number and single-channel current amplitude were calculated by mean-variance analysis of I(Ca). Two different comparisons-one comparing average numbers of release events to average I(Ca) amplitude and the other involving deconvolution of both EPSCs and simultaneously recorded cone I(Ca)-suggested that fewer than three Ca(2+) channel openings accompanied fusion of each vesicle at the peak of release during the first few milliseconds of stimulation. Opening fewer Ca(2+) channels did not enhance fusion efficiency, suggesting that few unnecessary channel openings occurred during strong depolarization. We simulated release at the cone synapse, using empirically determined synaptic dimensions, vesicle pool size, Ca(2+) dependence of release, Ca(2+) channel number, and Ca(2+) channel properties. The model replicated observations when a barrier was added to slow Ca(2+) diffusion. Consistent with the presence of a diffusion barrier, dialyzing cones with diffusible Ca(2+) buffers did not affect release efficiency. The tight clustering of Ca(2+) channels, along with a high-Ca(2+) affinity release mechanism and diffusion barrier, promotes a linear coupling between Ca(2+) influx and vesicle fusion. This may improve detection of small light decrements when cones are hyperpolarized by bright light.
Stirring turbulence with turbulence
Cekli, H.E.; Joosten, R.; van de Water, W.
2015-01-01
We stir wind-tunnel turbulence with an active grid that consists of rods with attached vanes. The time-varying angle of these rods is controlled by random numbers. We study the response of turbulence on the statistical properties of these random numbers. The random numbers are generated by the
Boni, Enrico; Bassi, Luca; Dallai, Alessandro; Guidi, Francesco; Meacci, Valentino; Ramalli, Alessandro; Ricci, Stefano; Tortoli, Piero
2016-10-01
Open scanners offer an increasing support to the ultrasound researchers who are involved in the experimental test of novel methods. Each system presents specific performance in terms of number of channels, flexibility, processing power, data storage capability, and overall dimensions. This paper reports the design criteria and hardware/software implementation details of a new 256-channel ultrasound advanced open platform. This system is organized in a modular architecture, including multiple front-end boards, interconnected by a high-speed (80 Gb/s) ring, capable of finely controlling all transmit (TX) and receive (RX) signals. High flexibility and processing power (equivalent to 2500 GFLOP) are guaranteed by the possibility of individually programming multiple digital signal processors and field programmable gate arrays. Eighty GB of on-board memory are available for the storage of prebeamforming, postbeamforming, and baseband data. The use of latest generation devices allowed to integrate all needed electronics in a small size ( 34 cm ×30 cm ×26 cm). The system implements a multiline beamformer that allows obtaining images of 96 lines by 2048 depths at a frame rate of 720 Hz (expandable to 3000 Hz). The multiline beamforming capability is also exploited to implement a real-time vector Doppler scheme in which a single TX and two independent RX apertures are simultaneously used to maintain the analysis over a full pulse repetition frequency range.
PyFLOWGO: An open-source platform for simulation of channelized lava thermo-rheological properties
Chevrel, Magdalena Oryaëlle; Labroquère, Jérémie; Harris, Andrew J. L.; Rowland, Scott K.
2018-02-01
Lava flow advance can be modeled through tracking the evolution of the thermo-rheological properties of a control volume of lava as it cools and crystallizes. An example of such a model was conceived by Harris and Rowland (2001) who developed a 1-D model, FLOWGO, in which the velocity of a control volume flowing down a channel depends on rheological properties computed following the thermal path estimated via a heat balance box model. We provide here an updated version of FLOWGO written in Python that is an open-source, modern and flexible language. Our software, named PyFLOWGO, allows selection of heat fluxes and rheological models of the user's choice to simulate the thermo-rheological evolution of the lava control volume. We describe its architecture which offers more flexibility while reducing the risk of making error when changing models in comparison to the previous FLOWGO version. Three cases are tested using actual data from channel-fed lava flow systems and results are discussed in terms of model validation and convergence. PyFLOWGO is open-source and packaged in a Python library to be imported and reused in any Python program (https://github.com/pyflowgo/pyflowgo)
DEFF Research Database (Denmark)
Hansen, Henrik H; Weikop, Pia; Mikkelsen, Maria D
2017-01-01
Central Kv7 (KCNQ) channels are voltage-dependent potassium channels composed of different combinations of four Kv7 subunits, being differently expressed in the brain. Notably, striatal dopaminergic neurotransmission is strongly suppressed by systemic administration of the pan-Kv7 channel opener ...... by acute systemic haloperidol administration in the rat. The relative mRNA levels of Kv7 subunits in the rat striatum were found to be Kv7.2 = Kv7.3 = Kv7.5 > >Kv7.4. These data suggest that intrastriatal Kv7 channels play a direct role in regulating striatal excitability in vivo....
International Nuclear Information System (INIS)
Cash, D.J.; Subbarao, K.
1987-01-01
The function of γ-aminobutyric acid (GABA) receptors, which mediate transmembrane chloride flux, can be studied by use of 36 Cl - isotope tracer with membrane from mammalian brain by quench-flow technique, with reaction times that allow resolution of the receptor desensitization rates from the ion flux rates. The rates of chloride exchange into the vesicles in the absence and presence of GABA were characterized with membrane from rat cerebral cortex. Unspecific 36 Cl - influx was completed in three phases of ca. 3% (t/sub 1/2/ = 0.6 s), 56% (t/sub 1/2 = 82 s), and 41% (t/sub 1/2 = 23 min). GABA-mediated, specific chloride exchange occurred with 6.5% of the total vesicular internal volume. The GABA-dependent 36 Cl - influx proceeded in two phases, each progressively slowed by desensitization. The measurements supported the presence of two distinguishable active GABA receptors on the same membrane mediating chloride exchange into the vesicles. The half-response concentrations were similar for both receptors. The two receptors were present in the activity ratio of ca. 4/1, similar to the ratio of low affinity to high-affinity GABA sites found in ligand binding experiments. The desensitization rates have a different dependence on GABA concentration than the channel-opening equilibria. For both receptors, the measurements over a 2000-fold GABA concentration range required a minimal mechanism involving the occupation of both of the two GABA binding sites for significant channel opening; then the receptors were ca. 80% open. Similarly for both receptors, desensitization was mediated by a different pair of binding sites, although desensitization with only one ligand molecule bound could occur at a 20-fold slower rate
2012-04-01
Both flame lengths shrink and large scale disruptions occur downstream with vortex shedding carrying reaction zones. Flames in both flameholders...9) the flame structure changes dramatically for both regular and open-slit V-gutter. Both flame lengths shrink and large scale disruptions occur...reduces the flame length . However, qualitatively the open-slit V-gutter appears to be more sensitive than the regular V-gutter. Both flames remain
Compressible turbulent flows: aspects of prediction and analysis
Energy Technology Data Exchange (ETDEWEB)
Friedrich, R. [TU Muenchen, Garching (Germany). Fachgebiet Stroemungsmechanik
2007-03-15
Compressible turbulent flows are an important element of high-speed flight. Boundary layers developing along fuselage and wings of an aircraft and along engine compressor and turbine blades are compressible and mostly turbulent. The high-speed flow around rockets and through rocket nozzles involves compressible turbulence and flow separation. Turbulent mixing and combustion in scramjet engines is another example where compressibility dominates the flow physics. Although compressible turbulent flows have attracted researchers since the fifties of the last century, they are not completely understood. Especially interactions between compressible turbulence and combustion lead to challenging, yet unsolved problems. Direct numerical simulation (DNS) and large-eddy simulation (LES) represent modern powerful research tools which allow to mimic such flows in great detail and to analyze underlying physical mechanisms, even those which cannot be accessed by the experiment. The present lecture provides a short description of these tools and some of their numerical characteristics. It then describes DNS and LES results of fully-developed channel and pipe flow and highlights effects of compressibility on the turbulence structure. The analysis of pressure fluctuations in such flows with isothermal cooled walls leads to the conclusion that the pressure-strain correlation tensor decreases in the wall layer and that the turbulence anisotropy increases, since the mean density falls off relative to the incompressible flow case. Similar increases in turbulence anisotropy due to compressibility are observed in inert and reacting temporal mixing layers. The nature of the pressure fluctuations is however two-facetted. While inert compressible mixing layers reveal wave-propagation effects in the pressure and density fluctuations, compressible reacting mixing layers seem to generate pressure fluctuations that are controlled by the time-rate of change of heat release and mean density
Offset-Free Model Predictive Control of Open Water Channel Based on Moving Horizon Estimation
Ekin Aydin, Boran; Rutten, Martine
2016-04-01
Model predictive control (MPC) is a powerful control option which is increasingly used by operational water managers for managing water systems. The explicit consideration of constraints and multi-objective management are important features of MPC. However, due to the water loss in open water systems by seepage, leakage and evaporation a mismatch between the model and the real system will be created. These mismatch affects the performance of MPC and creates an offset from the reference set point of the water level. We present model predictive control based on moving horizon estimation (MHE-MPC) to achieve offset free control of water level for open water canals. MHE-MPC uses the past predictions of the model and the past measurements of the system to estimate unknown disturbances and the offset in the controlled water level is systematically removed. We numerically tested MHE-MPC on an accurate hydro-dynamic model of the laboratory canal UPC-PAC located in Barcelona. In addition, we also used well known disturbance modeling offset free control scheme for the same test case. Simulation experiments on a single canal reach show that MHE-MPC outperforms disturbance modeling offset free control scheme.
Hydrodynamic and Sediment Responses of Open Channels to Exposed Pipe Encasements.
Directory of Open Access Journals (Sweden)
J Q Mao
Full Text Available The effects of exposed pipe encasements on the local variation of hydrodynamic and sediment conditions in a river channel are examined. Laboratory experiments are performed to assess the response of water level, flow regime and bed deformation to several representative types of concrete encasements. The experimental conditions considered are: three types of exposed pipe encasements exposed on the bed, including trapezoidal shape, circular-arc shape and polygonal shape, and three sets of discharges, including annual discharge, once-in-3-year flood, and once-in-50-year flood. Our experiments show that: (1 the amount of backwater definitely depends on the encasement geometric shape and the background discharge; (2 smaller discharges generally tend to induce local scour of river bed downstream of the encasement, and the order of sensitivity of bed deformation to the encasement geometric shape is trapezoidal > circular-arc > polygonal; (3 comparatively speaking, the polygonal encasement may be considered as a suitable protective structure for pipelines across alluvial rivers, with relatively modest effects on the local hydrodynamic conditions and bed stabilization.
Hydrodynamic and Sediment Responses of Open Channels to Exposed Pipe Encasements.
Mao, J Q; Zhang, H Q; Dai, H C; Yuan, B H; Hu, T F
2015-01-01
The effects of exposed pipe encasements on the local variation of hydrodynamic and sediment conditions in a river channel are examined. Laboratory experiments are performed to assess the response of water level, flow regime and bed deformation to several representative types of concrete encasements. The experimental conditions considered are: three types of exposed pipe encasements exposed on the bed, including trapezoidal shape, circular-arc shape and polygonal shape, and three sets of discharges, including annual discharge, once-in-3-year flood, and once-in-50-year flood. Our experiments show that: (1) the amount of backwater definitely depends on the encasement geometric shape and the background discharge; (2) smaller discharges generally tend to induce local scour of river bed downstream of the encasement, and the order of sensitivity of bed deformation to the encasement geometric shape is trapezoidal > circular-arc > polygonal; (3) comparatively speaking, the polygonal encasement may be considered as a suitable protective structure for pipelines across alluvial rivers, with relatively modest effects on the local hydrodynamic conditions and bed stabilization.
Haythorne, Elizabeth; Hamilton, D Lee; Findlay, John A; Beall, Craig; McCrimmon, Rory J; Ashford, Michael L J
2016-12-01
Individuals with Type 1 diabetes (T1D) are often exposed to recurrent episodes of hypoglycaemia. This reduces hormonal and behavioural responses that normally counteract low glucose in order to maintain glucose homeostasis, with altered responsiveness of glucose sensing hypothalamic neurons implicated. Although the molecular mechanisms are unknown, pharmacological studies implicate hypothalamic ATP-sensitive potassium channel (K ATP ) activity, with K ATP openers (KCOs) amplifying, through cell hyperpolarization, the response to hypoglycaemia. Although initial findings, using acute hypothalamic KCO delivery, in rats were promising, chronic exposure to the KCO NN414 worsened the responses to subsequent hypoglycaemic challenge. To investigate this further we used GT1-7 cells to explore how NN414 affected glucose-sensing behaviour, the metabolic response of cells to hypoglycaemia and K ATP activity. GT1-7 cells exposed to 3 or 24 h NN414 exhibited an attenuated hyperpolarization to subsequent hypoglycaemic challenge or NN414, which correlated with diminished K ATP activity. The reduced sensitivity to hypoglycaemia was apparent 24 h after NN414 removal, even though intrinsic K ATP activity recovered. The NN414-modified glucose responsiveness was not associated with adaptations in glucose uptake, metabolism or oxidation. K ATP inactivation by NN414 was prevented by the concurrent presence of tolbutamide, which maintains K ATP closure. Single channel recordings indicate that NN414 alters K ATP intrinsic gating inducing a stable closed or inactivated state. These data indicate that exposure of hypothalamic glucose sensing cells to chronic NN414 drives a sustained conformational change to K ATP , probably by binding to SUR1, that results in loss of channel sensitivity to intrinsic metabolic factors such as MgADP and small molecule agonists. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.
Rouhi, Amirreza; Chung, Daniel; Hutchins, Nicholas
2017-11-01
Direct numerical simulations (DNSs) are reported for open channel flow over streamwise-alternating patches of smooth and fully rough walls. Owing to the streamwise periodicity, the flow configuration is composed of a step change from smooth to rough, and a step change from rough to smooth. The friction Reynolds number varies from 443 over the smooth patch to 715 over the rough patch. The flow is thoroughly studied by mean and fluctuation profiles, and spectrograms. The detailed flow from DNS reveals discrepancies of up to 50% among the various definitions of the internal-layer thickness, with apparent power-law exponents differing by up to 60%. The definition based on the logarithmic slope of the velocity profile, as proposed by Chamorro et al. (Boundary-Layer Meteorol., vol. 130, 2009, pp. 29-41), is most consistent with the physical notion of the internal layer; this is supported by the defect similarity based on this internal-layer thickness, and the streamwise homogeneity of the dissipation length-scale within this internal layer. The statistics inside this internal-layer, and the growth of the internal layer itself, are minimally affected by the streamwise periodicity when the patch length is at least six times the channel height.
Comment on "Modified quantum-speed-limit bounds for open quantum dynamics in quantum channels"
Mirkin, Nicolás; Toscano, Fabricio; Wisniacki, Diego A.
2018-04-01
In a recent paper [Phys. Rev. A 95, 052118 (2017), 10.1103/PhysRevA.95.052118], the authors claim that our criticism, in Phys. Rev. A 94, 052125 (2016), 10.1103/PhysRevA.94.052125, to some quantum speed limit bounds for open quantum dynamics that appeared recently in literature are invalid. According to the authors, the problem with our analysis would be generated by an artifact of the finite-precision numerical calculations. We analytically show here that it is not possible to have any inconsistency associated with the numerical precision of calculations. Therefore, our criticism of the quantum speed limit bounds continues to be valid.
Experimental study on unsteady open channel flow and bedload transport based on a physical model
Cao, W.
2015-12-01
Flow in a nature river are usually unsteady, while nearly all the theories about bedload transport are on the basis of steady, uniform flow, and also with supposed equilibrium state of sediment transport. This is may be one of the main reasons why the bedload transport formulas are notoriously poor accuracy to predict the bedload. The aim of this research is to shed light on the effect of unsteadiness on the bedload transport based on experimental studies. The novel of this study is that the experiments were not carried out in a conventional flume but in a physical model, which are more similar to the actual river. On the other hand, in our experiments, multiple consecutive flood wave were reproduced in the physical model, and all the flow and sediment parameters are based on a large number of data obtained from many of identical flood waves. This method allow us to get more data for one flood, efficiently avoids the uncertainty of bedload rate only for one single flood wave, due to the stochastic fluctuation of the bedload transport. Three different flood waves were selected in the experiments. During each run of experiment, the water level of five different positions along the model were measured by ultrasonic water level gauge, flow velocity at the middle of the channel were measured by two dimensional electromagnetic current meter. Moreover, the bedload transport rate was measured by a unique automatic trap collecting and weighing system at the end of the physical model. The results shows that the celerity of flood wave propagate varies for different flow conditions. The velocity distribution was approximately accord with log-law profile during the entire rising and falling limb of flood. The bedload transport rate show intensity fluctuation in all the experiments, moreover, for different flood waves, the moment when the shear stress reaches its maximum value is not the exact moment when the sediment transport rate reaches its maximum value, which indicates
Open Channel Natural Convection Heat Transfer on a Vertical Finned Plate
International Nuclear Information System (INIS)
Park, Joo Hyun; Heo, Jeong Hwan; Chung, Bum Jin
2013-01-01
The natural convection heat transfer of vertical plate fin was investigated experimentally. Heat transfer systems were replaced by mass-transfer systems, based on the analogy concept. The experimental results lie within the predictions of the existing heat transfer correlations of plate-fin for the natural convections. An overlapped thermal boundary layers caused increasing heat transfer, and an overlapped momentum boundary layers caused decreasing heat transfer. As the fin height increases, heat transfer was enhanced due to increased inflow from the open side of the fin spacing. When fin spacing and fin height are large, heat transfer was unaffected by the fin spacing and fin height. Passive cooling by natural convection becomes more and more important for the nuclear systems as the station black out really happened at the Fukushima NPPs. In the RCCS (Reactor Cavity Cooling System) of a VHTR (Very High Temperature Reactor), natural convection cooling through duct system is adopted. In response to the stack failure event, extra cooling capacity adopting the fin array has to be investigated. The finned plate increases the surface area and the heat transfer increases. However, the plate of fin arrays may increase the pressure drop and the heat transfer decreases. Therefore, in order to enhance the passive cooling with fin arrays, the parameters for the fin arrays should be optimized. According to Welling and Wooldridge, a natural convection on vertical plate fin is function of Gr, Pr, L, t, S, and H. The present work investigated the natural convection heat transfer of a vertical finned plate with varying the fin height and the fin spacing. In order achieve high Rayleigh numbers, an electroplating system was employed and the mass transfer rates were measured using a copper sulfate electroplating system based on the analogy concept
Turbulence modelling; Modelisation de la turbulence isotherme
Energy Technology Data Exchange (ETDEWEB)
Laurence, D. [Electricite de France (EDF), Direction des Etudes et Recherches, 92 - Clamart (France)
1997-12-31
This paper is an introduction course in modelling turbulent thermohydraulics, aimed at computational fluid dynamics users. No specific knowledge other than the Navier Stokes equations is required beforehand. Chapter I (which those who are not beginners can skip) provides basic ideas on turbulence physics and is taken up in a textbook prepared by the teaching team of the ENPC (Benque, Viollet). Chapter II describes turbulent viscosity type modelling and the 2k-{epsilon} two equations model. It provides details of the channel flow case and the boundary conditions. Chapter III describes the `standard` (R{sub ij}-{epsilon}) Reynolds tensions transport model and introduces more recent models called `feasible`. A second paper deals with heat transfer and the effects of gravity, and returns to the Reynolds stress transport model. (author). 37 refs.
Large-Eddy-Simulation of turbulent magnetohydrodynamic flows
Directory of Open Access Journals (Sweden)
Woelck Johannes
2017-01-01
Full Text Available A magnetohydrodynamic turbulent channel flow under the influence of a wallnormal magnetic field is investigated using the Large-Eddy-Simulation technique and k-equation subgrid-scale-model. Therefore, the new solver MHDpisoFoam is implemented in the OpenFOAM CFD-Code. The temporal decay of an initial turbulent field for different magnetic parameters is investigated. The rms values of the averaged velocity fluctuations show a similar, trend for each coordinate direction. 80% of the fluctuations are damped out in the range between 0 < Ha < < 75 at Re = 6675. The trend can be approximated via an exponential of the form exp(−a·Ha, where a is a scaling parameter. At higher Hartmann numbers the fluctuations decrease in an almost linear way. Therefore, the results of this study show that it may be possible to construct a general law for the turbulence damping due to action of magnetic fields.
Directory of Open Access Journals (Sweden)
A. M. Berta
2010-05-01
Full Text Available During the floods, the effects of sediment transport in river beds are particulary significant and can be studied through the evolution of the water-sediment layer which moves in the lower part of a flow, named "moving layer". Moving layer variations along rivers lead to depositions and erosions and are typically unsteady, but are often tackled with expressions developed for steady (equilibrium conditions. In this paper, we develop an expression for the moving layer in unsteady conditions and calibrate it with experimental data. During laboratory tests, we have in fact reproduced a rapidly changing unsteady flow by the erosion of a granular steep slope. Results have shown a clear tendency of the moving layer, for fixed discharges, toward equilibrium conditions. Knowing the equilibrium achievement has presented many difficulties, being influenced by the choice of the equilibrium expression and moreover by the estimation of the parameters involved (for example friction angle. Since we used only data relevant to hyper-concentrated mono-dimensional flows for the calibration – occurring for slope gradients in the range 0.03–0.20 – our model can be applied both on open channels and on embankments/dams, providing that the flows can be modelled as mono-dimensional, and that slopes and applied shear stress levels fall within the considered ranges.
Magnetohydrodynamic turbulence
Biskamp, Dieter
2003-01-01
This book presents an introduction to, and modern account of, magnetohydrodynamic (MHD) turbulence, an active field both in general turbulence theory and in various areas of astrophysics. The book starts by introducing the MHD equations, certain useful approximations and the transition to turbulence. The second part of the book covers incompressible MHD turbulence, the macroscopic aspects connected with the different self-organization processes, the phenomenology of the turbulence spectra, two-point closure theory, and intermittency. The third considers two-dimensional turbulence and compressi
International Nuclear Information System (INIS)
Chen Xinxiang; Cao Yanning; Zhang Hanhui; Chen Yiping; Chen Xuehuan; Chai Xiaochuan
2008-01-01
Two new 3-D porous bismuth coordination polymers, (C 5 NH 6 ) 2 [Bi 2 (H 2 O) 2 (C 2 O 4 ) 4 ].2H 2 O 1 and (NH 4 )[Bi(C 2 O 4 ) 2 ].3H 2 O 2, have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic symmetry, P2 1 /c space group with a=10.378(2) A, b=17.285(3) A, c=16.563(5) A, α=90 deg., β=119.66(2) deg., γ=90 deg., V=2581.8(10) A 3 , Z=4, R 1 =0.0355 and wR 2 =0.0658 for unique 4713 reflections I >2σ(I). Compound 2 crystallizes in the tetragonal symmetry, I4 1 /amd space group with a=11.7026(17) A, b=11.7026(17) A, c=9.2233(18) A, α=90 deg., β=90 deg., γ=90 deg., V=1263.1(4) A 3 , Z=32, R 1 =0.0208 and wR 2 =0.0518 for unique 359 reflections I> 2σ(I). Compounds 1 and 2 are 3-D open-framework structures with a 6 6 uniform net, which consist of honeycomb-like layers connected to each other by oxalate units. While different guest molecules fill in their cavities of honeycomb-like layers, study of ultrasonic treatment on 2 indicates the replacement of NH 4 + by K + on potassium ion exchange. Thermogravimetric analysis indicates that the open-channel frameworks are thermally stable up to 200 deg. C, and other characterizations are also described by elemental analysis, IR and ultraviolet-visible diffuse reflectionintegral spectrum (UV-Vis DRIS). - Graphical abstract: Two novel 3-D extended porous coordination polymers have been synthesized by hydrothermal method. Both compounds are 3-D open-framework structures with a 6 6 uniform net, which consist of honeycomb-like layers connected to each other by oxalate units. While different guest molecules fill in their cavities of honeycomb-like layers. Study of ultrasonic treatment on 2 indicates the replacement of NH 4 + by K + on potassium ion exchange
Swillens, S; Champeil, P; Combettes, L; Dupont, G
1998-05-01
Confocal microscope studies with fluorescent dyes of inositol 1,4,5-trisphosphate (InsP3)-induced intracellular Ca2+ mobilization recently established the existence of 'elementary' events, dependent on the activity of individual InsP3-sensitive Ca2+ channels. In the present work, we try by theoretical stochastic simulation to explain the smallest signals observed in those studies, which were referred to as Ca2+ 'blips' [Parker I., Yao Y. Ca2+ transients associated with openings of inositol trisphosphate-gated channels in Xenopus oocytes. J Physiol Lond 1996; 491: 663-668]. For this purpose, we assumed a simple molecular model for the InsP3-sensitive Ca2+ channel and defined a set of parameter values accounting for the results obtained in electrophysiological bilayer experiments [Bezprozvanny I., Watras J., Ehrlich B.E. Bell-shaped calcium-response curves of Ins(1,4,5)P3- and calcium-gated channels from endoplasmic reticulum of cerebellum. Nature 1991; 351: 751-754; Bezprozvanny I., Ehrlich B.E. Inositol (1,4,5)-trisphosphate (InsP3)-gated Ca channels from cerebellum: conduction properties for divalent cations and regulation by intraluminal calcium. J Gen Physiol 1994; 104: 821-856]. With a stochastic procedure which considered cytosolic Ca2+ diffusion explicitly, we then simulated the behaviour of a single channel, placed in a realistic physiological environment. An attractive result was that the simulated channel exhibited bursts of activity, arising from repetitive channel openings, which were responsible for transient rises in Ca2+ concentration and were reminiscent of the relatively long-duration experimental Ca2+ blips. The influence of the values chosen for the various parameters (affinity and diffusion coefficient of the buffers, luminal Ca2+ concentration) on the kinetic characteristics of these theoretical blips is analyzed.
International Nuclear Information System (INIS)
Donnelly, R.J.
1988-01-01
Most flows of fluids, in nature and in technology, are turbulent. Since much of the energy expended by machines and devices that involve fluid flows is spent in overcoming drag caused by turbulence, there is a strong motivation to understand the phenomena. Surprisingly, the peculiar, quantum-mechanical form of turbulence that can form in superfluid helium may turn out to be much simpler to understand that the classical turbulence that forms in normal fluids. It now seems that the study of superfluid turbulence may provide simplified model systems for studying some forms of classical turbulence. There are also practical motivations for studying superfluid turbulence. For example, superfuid helium is often used as a coolant in superconducting machinery. Superfluid turbulence is the primary impediment to the transfer of heat by superfluid helium; an understanding of the phenomena may make it possible to design more efficient methods of refrigeration for superconducting devices. 8 figs
International Nuclear Information System (INIS)
Law, J K Y; Chan, M; Yeung, C K; Rudd, J A; Hofmann, B; Ingebrandt, S; Offenhäusser, A
2009-01-01
The microelectrode array (MEA) was used to evaluate the cardioprotective effects of adenosine triphosphate sensitive potassium (K ATP ) channel activation using potassium channel openers (KCOs) on HL-1 cardiomyocytes subjected to acute chemically induced metabolic inhibition. Beat frequency and extracellular action potential (exAP) amplitude were measured in the presence of metabolic inhibitors (sodium azide (NaN 3 ) or 2-deoxyglucose (2-DG)) or KCOs (pinacidil (PIN, a cyanoguanidine derivative, activates sarcolemmal K ATP channels) or SDZ PCO400 (SDZ, a benzopyran derivative, activates mitochondrial K ATP channels)). The protective effects of these KCOs on metabolically inhibited HL-1 cells were subsequently investigated. Signal shapes indicated that NaN 3 and 2-DG reduced the rate of the sodium (Na + ) influx signal as reflected by a reduction in beat frequency. PIN and SDZ appeared to reduce both rate of depolarization and extent of the Na + influx signals. Pre-treating cardiomyocytes with PIN (0.1 mM), but not SDZ, prevented the reduction of beat frequency associated with NaN 3 - or 2-DG-induced metabolic inhibition. The exAP amplitude was not affected by either KCO. The cardioprotective effect of PIN relative to SDZ may be due to the opening of different K ATP channels. This metabolic inhibition model on the MEA may provide a stable platform for the study of cardiac pathophysiology in the future
Cash, D J; Subbarao, K
1987-12-01
The function of gamma-aminobutyric acid (GABA) receptors, which mediate transmembrane chloride flux, can be studied by use of 36Cl- isotope tracer with membrane from mammalian brain by quench-flow technique, with reaction times that allow resolution of the receptor desensitization rates from the ion flux rates. The rates of chloride exchange into the vesicles in the absence and presence of GABA were characterized with membrane from rat cerebral cortex. Unspecific 36Cl- influx was completed in three phases of ca. 3% (t 1/2 = 0.6 s), 56% (t 1/2 = 82 s), and 41% (t 1/2 = 23 min). GABA-mediated, specific chloride exchange occurred with 6.5% of the total vesicular internal volume. The GABA-dependent 36Cl- influx proceeded in two phases, each progressively slowed by desensitization. The measurements supported the presence of two distinguishable active GABA receptors on the same membrane mediating chloride exchange into the vesicles with initial first-order rate constants of 9.5 s-1 and 2.3 s-1 and desensitizing with first-order rate constants of 21 s-1 and 1.4 s-1, respectively, at saturation. The half-response concentrations were similar for both receptors, 150 microM and 114 microM GABA for desensitization and 105 microM and 82 microM for chloride exchange, for the faster and slower desensitizing receptors, respectively. The two receptors were present in the activity ratio of ca. 4/1, similar to the ratio of "low-affinity" to "high-affinity" GABA sites found in ligand binding experiments. The desensitization rates have a different dependence on GABA concentration than the channel-opening equilibria.(ABSTRACT TRUNCATED AT 250 WORDS)
Mbuagbaw, Lawrence; Thabane, Lehana; Ongolo-Zogo, Pierre
2013-04-04
Using two-way mobile phone text messages to improve adherence to antiretroviral medication enhances communication between patients and health workers. We describe the implications of participants' responses to text messages in the Cameroon Mobile Phone SMS (CAMPS) trial. This is a cross-sectional analysis of data from the intervention arm of the CAMPS trial. CAMPS was a randomized controlled trial of motivational text messaging versus usual care to improve adherence to antiretroviral medication among people living with HIV in Yaounde, Cameroon (n = 200) over a 6 month period. Participants in the intervention arm (n = 101) were given a contact phone number, but were not required to respond to their reminder messages. If they did, their responses were noted and reported as counts and percentages. We received 99 phone calls and 55 text messages (154 responses) from 48 participants during the study period. The median number of responses was 1 (first quartile [Q1]: 1; third quartile [Q3]: 3). Half (n = 79, 51.1%) of them were expressions of gratitude. The rest included requests for logistical (n = 21, 13.6%), medical (n = 20, 12.9%) and financial (n = 11, 7.1%) support. Initiating two-way mobile communication opens more channels for people living with HIV to express unmet needs. Researchers, policy makers and clinicians should be ready to respond to the needs expressed by patients who respond to text messages. Pan-African Clinical Trials Registry: PACTR201011000261458;
Energy Technology Data Exchange (ETDEWEB)
Tian, W.; Aye, M.; Qiu, S.; Jia, D. [Xi' an Jiaotong Univ., Dept. of Nuclear and Thermal Power Engineering, Xi' an (China)]. E-mail: wxtian_xjtu@163.com
2004-07-01
The field synergy principle was proposed by Guo Z. Y based on 2-D boundary laminar flow and it resulted from a second look at the mechanism of convective heat transfer. The objective of this paper is to numerically verify the applicability of this theory under turbulent flow or even with recirculating flow condition. (author)
Direct Numerical Simulation of heat transfer in a turbulent flume
International Nuclear Information System (INIS)
Bergant, R.; Tiselj, I.
2001-01-01
Direct Numerical Simulation (DNS) can be used for the description of turbulent heat transfer in the fluid at low Reynolds numbers. DNS means precise solving of Navier-Stoke's equations without any extra turbulent models. DNS should be able to describe all relevant length scales and time scales in observed turbulent flow. The largest length scale is actually dimension of system and the smallest length and time scale is equal to Kolmogorov scale. In the present work simulations of fully developed turbulent velocity and temperature fields were performed in a turbulent flume (open channel) with pseudo-spectral approach at Reynolds number 2670 (friction Reynolds number 171) and constant Prandtl number 5.4, considering the fluid temperature as a passive scalar. Two ideal thermal boundary conditions were taken into account on the heated wall. The first one was an ideal isothermal boundary condition and the second one an ideal isoflux boundary condition. We observed different parameters like mean temperature and velocity, fluctuations of temperature and velocity, and auto-correlation functions.(author)
Stochastic modelling of turbulence
DEFF Research Database (Denmark)
Sørensen, Emil Hedevang Lohse
previously been shown to be closely connected to the energy dissipation. The incorporation of the small scale dynamics into the spatial model opens the door to a fully fledged stochastic model of turbulence. Concerning the interaction of wind and wind turbine, a new method is proposed to extract wind turbine...
EuHIT, Collaboration
2015-01-01
As a member of the EuHIT (European High-Performance Infrastructures in Turbulence - see here) consortium, CERN is participating in fundamental research on turbulence phenomena. To this end, the Laboratory provides European researchers with a cryogenic research infrastructure (see here), where the first tests have just been performed.
International Nuclear Information System (INIS)
Horton, W.
1998-07-01
The origin of plasma turbulence from currents and spatial gradients in plasmas is described and shown to lead to the dominant transport mechanism in many plasma regimes. A wide variety of turbulent transport mechanism exists in plasmas. In this survey the authors summarize some of the universally observed plasma transport rates
Energy Technology Data Exchange (ETDEWEB)
Nazarenko, Sergey [Warwick Univ., Coventry (United Kingdom). Mathematics Inst.
2011-07-01
Wave Turbulence refers to the statistical theory of weakly nonlinear dispersive waves. There is a wide and growing spectrum of physical applications, ranging from sea waves, to plasma waves, to superfluid turbulence, to nonlinear optics and Bose-Einstein condensates. Beyond the fundamentals the book thus also covers new developments such as the interaction of random waves with coherent structures (vortices, solitons, wave breaks), inverse cascades leading to condensation and the transitions between weak and strong turbulence, turbulence intermittency as well as finite system size effects, such as ''frozen'' turbulence, discrete wave resonances and avalanche-type energy cascades. This book is an outgrow of several lectures courses held by the author and, as a result, written and structured rather as a graduate text than a monograph, with many exercises and solutions offered along the way. The present compact description primarily addresses students and non-specialist researchers wishing to enter and work in this field. (orig.)
International Nuclear Information System (INIS)
Carrilho, R.J.; Marins, J.E.R.
1981-01-01
A new instrument for the channel opening command, synchronized to the movement, is designed, developed and produced, together with a new and complete amplifier for the transducer activation. (L.C.) [pt
DEFF Research Database (Denmark)
Peitersen, Torben; Grunnet, Morten; Benson, Alan P
2008-01-01
BACKGROUND: Dysfunction or pharmacologic inhibition of repolarizing cardiac ionic currents can lead to fatal arrhythmias. The hERG potassium channel underlies the repolarizing current I(Kr), and mutations therein can produce both long and short QT syndromes (LQT2 and SQT1). We previously reported...
Bai, Qifeng; Pérez-Sánchez, Horacio; Zhang, Yang; Shao, Yonghua; Shi, Danfeng; Liu, Huanxiang; Yao, Xiaojun
2014-08-14
The reported crystal structures of β2 adrenergic receptor (β2AR) reveal that the open and closed states of the water channel are correlated with the inactive and active conformations of β2AR. However, more details about the process by which the water channel states are affected by the active to inactive conformational change of β2AR remain illusive. In this work, molecular dynamics simulations are performed to study the dynamical inactive and active conformational change of β2AR induced by inverse agonist ICI 118,551. Markov state model analysis and free energy calculation are employed to explore the open and close states of the water channel. The simulation results show that inverse agonist ICI 118,551 can induce water channel opening during the conformational transition of β2AR. Markov state model (MSM) analysis proves that the energy contour can be divided into seven states. States S1, S2 and S5, which represent the active conformation of β2AR, show that the water channel is in the closed state, while states S4 and S6, which correspond to the intermediate state conformation of β2AR, indicate the water channel opens gradually. State S7, which represents the inactive structure of β2AR, corresponds to the full open state of the water channel. The opening mechanism of the water channel is involved in the ligand-induced conformational change of β2AR. These results can provide useful information for understanding the opening mechanism of the water channel and will be useful for the rational design of potent inverse agonists of β2AR.
Turbulence models development and engineering applications
International Nuclear Information System (INIS)
Groetzbach, G.; Ammann, T.; Dorr, B.; Hiltner, I.; Hofmann, S.; Kampczyk, M.; Kimhi, Y.; Seiter, C.; Woerner, M.; Alef, M.; Hennemuth, A.
1995-01-01
The FLUTAN code is used for analyzing the decay heat removal in new reactor concepts. The turbulence models applied in FLUTAN are improved by the development of the TURBIT code. TURBIT serves for a numerical simulation of turbulent channel flow. (orig.)
Subcooled He II heat transport in the channel with abrupt contractions/enlargements
International Nuclear Information System (INIS)
Maekawa, R.; Iwamoto, A.; Hamaguchi, S.; Mito, T.
2002-01-01
Heat transport mechanisms for subcooled He II in the channel with abrupt contractions and/or enlargements have been investigated under steady state conditions. The channel, made of G-10, contains various contraction geometries to simulate the cooling channel of a superconducting magnet. In other words, contractions are periodically placed along the channel to simulate the spacers within the magnet winding. A copper block heater inputs the heat to the channel from one end, while the other end is open to the He II bath. Temperature profiles were measured with temperature sensors embedded in the channel as a function of heat input. Calculations were performed using a simple one-dimensional turbulent heat transport equation and with geometric factor consideration. The effects on heat transport mechanisms in He II caused by abrupt change of channel geometry and size are discussed
Molokov, S. Y.; Allen, J. E.
Magnetohydrodynamic (MHD) flows of viscous incompressible fluid in strong magnetic fields parallel to a free surface of fluid are investigated. The problem of flow in an open channel due to a moving side wall in uniform magnetic field is considered, and treated by means of matched asymptotic expansions method. The flow region is divided into various subregions and leading terms of asymptotic expansions as M tends towards infinity (M is the Hartmann number) of solutions of correspondent problems in each subregion are obtained. An exact analytic solution of equations governing the free-surface layer of thickness of order M to the minus 1/2 power is obtained.
Hill, Craig Steven
Accelerating marine hydrokinetic (MHK) renewable energy development towards commercial viability requires investigating interactions between the engineered environment and its surrounding physical and biological environments. Complex and energetic hydrodynamic and morphodynamic environments desired for such energy conversion installations present difficulties for designing efficient yet robust sustainable devices, while permitting agency uncertainties regarding MHK device environmental interactions result in lengthy and costly processes prior to installing and demonstrating emerging technologies. A research program at St. Anthony Falls Laboratory (SAFL), University of Minnesota, utilized multi-scale physical experiments to study the interactions between axial-flow hydrokinetic turbines, turbulent open channel flow, sediment transport, turbulent turbine wakes, and complex hydro-morphodynamic processes in channels. Model axial-flow current-driven three-bladed turbines (rotor diameters, dT = 0.15m and 0.5m) were installed in open channel flumes with both erodible and non-erodible substrates. Device-induced local scour was monitored over several hydraulic conditions and material sizes. Synchronous velocity, bed elevation and turbine performance measurements provide an indication into the effect channel topography has on device performance. Complimentary experiments were performed in a realistic meandering outdoor research channel with active sediment transport to investigate device interactions with bedform migration and secondary turbulent flow patterns in asymmetric channel environments. The suite of experiments undertaken during this research program at SAFL in multiple channels with stationary and mobile substrates under a variety of turbine configurations provides an in-depth investigation into how axial-flow hydrokinetic devices respond to turbulent channel flow and topographic complexity, and how they impact local and far-field sediment transport characteristics
International Nuclear Information System (INIS)
You, Byunghyun; Jeong, Yong Hoon
2014-01-01
A fuel assembly had hexagonal structure adjacent to 6 fuel assemblies, which influence to the target fuel assembly due to elimination of duct. For calculating the influence, 6 additional channels were generated between the adjacent fuel assemblies and cross flow model was applied to the channels. The adjacent fuel assemblies were analyzed and the results were used in the additional channel as boundary condition of the target fuel assembly. To design the specifications of duct-less assembly, modified or brand-new thermal-hydraulic methodology is needed which is using MATRA-LMR and CFD codes in this study. The MATRA-LMR is a sub-channel analysis code for LMR that has been developed in Korea Atomic Energy Research Institute. It is designed to analyze a fuel assembly with wire-wrap and duct structure. However, the duct-less core is not able to be analyzed by the MATRA-LMR which doesn't consider cross flow between the fuel assemblies and effect of grid spacer. The code need improvement by editing source code to eliminate effect of duct and analyze pressure drop and mixing between the sub-channels caused by grid spacer and cross flow between the fuel assemblies. To validate reformed pressure drop model and cross flow model in MATRA-LMR, CFD analysis is performed. For verifying the results of CFD, LMR subchannel experimental data is benchmarked which is done by ORNL. The verified CFD for thermalhydraulic analysis calculated pressure drop and mixing caused by grid spacer and cross flow between fuel assemblies
Oxidizing reagent copper-o-phenanthroline is an open channel blocker of the vanilloid receptor TRPV1
Czech Academy of Sciences Publication Activity Database
Toušová, Karolina; Sušánková, Klára; Teisinger, Jan; Vyklický st., Ladislav; Vlachová, Viktorie
2004-01-01
Roč. 47, č. 2 (2004), s. 273-285 ISSN 0028-3908 R&D Projects: GA ČR GA305/03/0802; GA ČR GA309/02/1479; GA MŠk LN00B122 Institutional research plan: CEZ:AV0Z5011922 Keywords : vanilloid receptor * TRP channels * capsaicin Subject RIV: ED - Physiology Impact factor: 3.734, year: 2004
A 1D-2D coupled SPH-SWE model applied to open channel flow simulations in complicated geometries
Chang, Kao-Hua; Sheu, Tony Wen-Hann; Chang, Tsang-Jung
2018-05-01
In this study, a one- and two-dimensional (1D-2D) coupled model is developed to solve the shallow water equations (SWEs). The solutions are obtained using a Lagrangian meshless method called smoothed particle hydrodynamics (SPH) to simulate shallow water flows in converging, diverging and curved channels. A buffer zone is introduced to exchange information between the 1D and 2D SPH-SWE models. Interpolated water discharge values and water surface levels at the internal boundaries are prescribed as the inflow/outflow boundary conditions in the two SPH-SWE models. In addition, instead of using the SPH summation operator, we directly solve the continuity equation by introducing a diffusive term to suppress oscillations in the predicted water depth. The performance of the two approaches in calculating the water depth is comprehensively compared through a case study of a straight channel. Additionally, three benchmark cases involving converging, diverging and curved channels are adopted to demonstrate the ability of the proposed 1D and 2D coupled SPH-SWE model through comparisons with measured data and predicted mesh-based numerical results. The proposed model provides satisfactory accuracy and guaranteed convergence.
Separation of Particles in Channels Rotary Engine
Directory of Open Access Journals (Sweden)
Zyatikov Pavel
2015-01-01
Full Text Available The article considers the separation of particles in channels with different relative length. It is shown that the intensity of turbulence at the inlet section of the channel varies considerably in its length. The dependence of the turbulence damping along the channel expressing by fraction of the distance is shown. The ratio of the particle separation efficiency out the gas flow in the rotor channel is defined. The values of particle separation efficiency in the channel for the angle α=π/4 in turbulent aerosol flow is shows, including without mixing the particles.
Hanratty, Thomas J.
1980-01-01
This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)
CERN. Geneva. Audiovisual Unit
2005-01-01
Understanding turbulence is vital in astrophysics, geophysics and many engineering applications, with thermal convection playing a central role. I shall describe progress that has recently been made in understanding this ubiquitous phenomenon by making controlled experiments using low-temperature helium, and a brief account of the frontier topic of superfluid turbulence will also be given. CERN might be able to play a unique role in experiments to probe these two problems.
DEFF Research Database (Denmark)
Li, Jinzhao; Qi, Meilan; Fuhrman, David R.
2018-01-01
-normal distribution for uniform channel-open flows. The comparisons of sediment transport rates where turbulent fluctuations in the bed shear stress are, or are not, taken into account show that the sediment transport rates calculated by the mean bed shear stress are under-predicted. Furthermore, a new sediment......This study concerns the flow and associated sediment transport in front of a cylinder in steady currents. The study comprises (i) flow characteristics induced by the turbulent horseshoe vortex (THV), (ii) bed shear stress within the THV region, and (iii) predicted sediment transport rates...
Turbulence optimisation in stellarator experiments
Energy Technology Data Exchange (ETDEWEB)
Proll, Josefine H.E. [Max-Planck/Princeton Center for Plasma Physics (Germany); Max-Planck-Institut fuer Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald (Germany); Faber, Benjamin J. [HSX Plasma Laboratory, University of Wisconsin-Madison, Madison, WI 53706 (United States); Helander, Per; Xanthopoulos, Pavlos [Max-Planck/Princeton Center for Plasma Physics (Germany); Lazerson, Samuel A.; Mynick, Harry E. [Plasma Physics Laboratory, Princeton University, P.O. Box 451 Princeton, New Jersey 08543-0451 (United States)
2015-05-01
Stellarators, the twisted siblings of the axisymmetric fusion experiments called tokamaks, have historically suffered from confining the heat of the plasma insufficiently compared with tokamaks and were therefore considered to be less promising candidates for a fusion reactor. This has changed, however, with the advent of stellarators in which the laminar transport is reduced to levels below that of tokamaks by shaping the magnetic field accordingly. As in tokamaks, the turbulent transport remains as the now dominant transport channel. Recent analytical theory suggests that the large configuration space of stellarators allows for an additional optimisation of the magnetic field to also reduce the turbulent transport. In this talk, the idea behind the turbulence optimisation is explained. We also present how an optimised equilibrium is obtained and how it might differ from the equilibrium field of an already existing device, and we compare experimental turbulence measurements in different configurations of the HSX stellarator in order to test the optimisation procedure.
Optimizing Stellarators for Turbulent Transport
International Nuclear Information System (INIS)
Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.
2010-01-01
Up to now, the term 'transport-optimized' stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.
Tarrab, Leticia; Garcia, Carlos M.; Cantero, Mariano I.; Oberg, Kevin
2012-01-01
This work presents a systematic analysis quantifying the role of the presence of turbulence fluctuations on uncertainties (random errors) of acoustic Doppler current profiler (ADCP) discharge measurements from moving platforms. Data sets of three-dimensional flow velocities with high temporal and spatial resolution were generated from direct numerical simulation (DNS) of turbulent open channel flow. Dimensionless functions relating parameters quantifying the uncertainty in discharge measurements due to flow turbulence (relative variance and relative maximum random error) to sampling configuration were developed from the DNS simulations and then validated with field-scale discharge measurements. The validated functions were used to evaluate the role of the presence of flow turbulence fluctuations on uncertainties in ADCP discharge measurements. The results of this work indicate that random errors due to the flow turbulence are significant when: (a) a low number of transects is used for a discharge measurement, and (b) measurements are made in shallow rivers using high boat velocity (short time for the boat to cross a flow turbulence structure).
Three-dimensional laser-induced fluorescence measurements of turbulent chemical plumes
True, Aaron; Crimaldi, John
2017-11-01
In order to find prey, mates, and suitable habitat, many organisms must navigate through complex chemical plume structures in turbulent flow environments. In this context, we investigate the spatial and temporal structure of chemical plumes released isokinetically into fractal-grid-generated turbulence in an open channel flow. We first utilized particle image velocimetry (PIV) to characterize flow conditions (mean free stream velocities, turbulence intensities, turbulent kinetic energy dissipation rates, Taylor Reynolds numbers). We then implemented a newly developed high-resolution, high-speed, volumetric scanning laser-induced fluorescence (LIF) system for near time-resolved measurements of three-dimensional chemical plume structures. We investigated cases with and without a cylinder wake, and compare statistical (mean, variance, intermittency, probability density functions) and spectral (power spectrum of concentration fluctuations) characteristics of the chemical plume structure. Stretching and folding of complex three-dimensional filament structures during chaotic turbulent mixing is greatly enhanced in the cylinder wake case. In future experiments, we will implement simultaneous PIV and LIF, enabling computation of the covariance of the velocity and chemical concentration fluctuations and thus estimation of turbulent eddy diffusivities. NSF PHY 1555862.
Dmitriev, S. S.; Vasil'ev, K. E.; Mokhamed, S. M. S. O.; Gusev, A. A.; Barbashin, A. V.
2017-11-01
In modern combined cycle gas turbines (CCGT), when designing the reducers from the output diffuser of a gas turbine to a boiler-utilizer, wide-angle diffusers are used, in which practically from the input a flow separation and transition to jet stream regime occurs. In such channels, the energy loss in the field of velocities sharply rise and the field of velocities in the output from them is characterized by considerable unevenness that worsens the heat transfer process in the first by motion tube bundles of the boiler-utilizer. The results of experimental research of the method for reducing the energy loss and alignment of the field of velocities at the output from a flat asymmetrical diffuser channel with one deflecting wall with the opening angle of 40° by means of placing inside the channel the flat plate parallel to the deflecting wall are presented in the paper. It is revealed that, at this placement of the plate in the channel, it has a chance to reduce the energy loss by 20%, considerably align the output field of velocities, and decrease the dynamic loads on the walls in the output cross-section. The studied method of resistance reduction and alignment of the fields of velocities in the flat diffuser channels was used for optimization of the reducer from the output diffuser of the gas turbine to the boiler-utilizer of CCGT of PGU-450T type of Kaliningrad Thermal Power Plant-2. The obtained results are evidence that the configuration of the reducer installed in the PGU-450T of Kaliningrad Thermal Power Plant-2 is not optimal. It follows also from the obtained data that working-off the reducer should be necessarily conducted by the test results of the channel consisting of the model of reducer with the model of boiler-utilizer installed behind it. Application of the method of alignment of output field of velocities and reducing the resistance in the wide-angle diffusers investigated in the work made it possible—when using the known model of diffusion
Mastracci, Brian; Guo, Wei
2018-01-01
The superfluid phase of helium-4, known as He ii, exhibits extremely small kinematic viscosity and may be a useful tool for economically producing and studying high Reynolds number turbulent flow. Such applications are not currently possible because a comprehensive understanding of the complex two-fluid behavior of He ii is lacking. This situation could be remedied by a systematic investigation of simple, well controlled turbulence that can be directly compared with theoretical models. To this end, we have developed a new apparatus that combines flow visualization with second sound attenuation to study turbulence in the wake of a mesh grid towed through a He ii filled channel. One of three mesh grids (mesh number M = 3, 3.75, or 5 mm) can be pulled at speeds between 0.1 and 60 cm/s through a cast acrylic flow channel which has a 16 mm × 16 mm cross section and measures 330 mm long. The motion of solidified deuterium tracer particles, with diameter of the order 1 μm, in the resulting flow is captured by a high speed camera, and a particle tracking velocimetry algorithm resolves the Lagrangian particle trajectories through the turbulent flow field. A pair of oscillating superleak second sound transducers installed in the channel allows complementary measurement of vortex line density in the superfluid throughout the turbulent decay process. Success in early experiments demonstrates the effectiveness of both probes, and preliminary analysis of the data shows that both measurements strongly correlate with each other. Further investigations will provide comprehensive information that can be used to address open questions about turbulence in He ii and move toward the application of this fluid to high Reynolds number fluid research.
International Nuclear Information System (INIS)
Buchner, Abel-John; Kitsios, Vassili; Atkinson, Callum; Soria, Julio; Lozano-Durán, Adrián
2016-01-01
Previous works have shown that momentum transfer in the wall–normal direction within turbulent wall–bounded flows occurs primarily within coherent structures defined by regions of intense Reynolds stress [1]. Such structures may be classified into wall–attached and wall–detached structures with the latter being typically weak, small–scale, and isotropically oriented, while the former are larger and carry most of the Reynolds stresses. The mean velocity fluctuation within each structure may also be used to separate structures by their dynamic properties. This study aims to extract information regarding the scales, kinematics and dynamics of these structures within the topological framework of the invariants of the velocity gradient tensor (VGT). The local topological characteristics of these intense Reynolds stress structures are compared to the topological characteristics of vortex clusters defined by the discriminant of the velocity gradient tensor. The alignment of vorticity with the principal strain directions within these structures is also determined, and the implications of these findings are discussed. (paper)
Energy Technology Data Exchange (ETDEWEB)
Mimouni, S., E-mail: stephane.mimouni@edf.f [Electricite de France R and D Division, 6 Quai Watier, F-78400 Chatou (France); Archambeau, F.; Boucker, M.; Lavieville, J. [Electricite de France R and D Division, 6 Quai Watier, F-78400 Chatou (France); Morel, C. [Commissariat a l' Energie Atomique, 17 rue des Martyrs, F-38000 Grenoble (France)
2010-09-15
High-thermal performance PWR (pressurized water reactor) spacer grids require both low pressure loss and high critical heat flux (CHF) properties. Numerical investigations on the effect of angles and position of mixing vanes and to understand in more details the main physical phenomena (wall boiling, entrainment of bubbles in the wakes, recondensation) are required. In the field of fuel assembly analysis or design by means of CFD codes, the overwhelming majority of the studies are carried out using two-equation eddy viscosity models (EVM), especially the standard K-{epsilon} model, while the use of Reynolds Stress Transport Models (RSTM) remains exceptional. But extensive testing and application over the past three decades have revealed a number of shortcomings and deficiencies in eddy viscosity models. In fact, the K-{epsilon} model is totally blind to rotation effects and the swirling flows can be regarded as a special case of fluid rotation. This aspect is crucial for the simulation of a hot channel in a fuel assembly. In fact, the mixing vanes of the spacer grids generate a swirl in the coolant water, to enhance the heat transfer from the rods to the coolant in the hot channels and to limit boiling. First, we started to evaluate computational fluid dynamics results against the AGATE-mixing experiment: single-phase liquid water tests, with Laser-Doppler liquid velocity measurements upstream and downstream of mixing blades. The comparison of computed and experimental azimuthal (circular component in a horizontal plane) liquid velocity downstream of a mixing vane for the AGATE-mixing test shows that the rotating flow is qualitatively well reproduced by CFD calculations but azimuthal liquid velocity is underestimated with the K-{epsilon} model. Before comparing performance of EVM and RSTM models on fuel assembly geometry, we performed calculations with a simpler geometry, the ASU-annular channel case. A wall function model dedicated to boiling flows is also
Tchen, C. M.
1986-01-01
Theoretical and numerical works in atmospheric turbulence have used the Navier-Stokes fluid equations exclusively for describing large-scale motions. Controversy over the existence of an average temperature gradient for the very large eddies in the atmosphere suggested that a new theoretical basis for describing large-scale turbulence was necessary. A new soliton formalism as a fluid analogue that generalizes the Schrodinger equation and the Zakharov equations has been developed. This formalism, processing all the nonlinearities including those from modulation provided by the density fluctuations and from convection due to the emission of finite sound waves by velocity fluctuations, treats large-scale turbulence as coalescing and colliding solitons. The new soliton system describes large-scale instabilities more explicitly than the Navier-Stokes system because it has a nonlinearity of the gradient type, while the Navier-Stokes has a nonlinearity of the non-gradient type. The forced Schrodinger equation for strong fluctuations describes the micro-hydrodynamical state of soliton turbulence and is valid for large-scale turbulence in fluids and plasmas where internal waves can interact with velocity fluctuations.
Lieb, Andreas; Ortner, Nadine; Striessnig, Jörg
2014-04-01
Activity of voltage-gated Cav1.3 L-type Ca(2+) channels is required for proper hearing as well as sinoatrial node and brain function. This critically depends on their negative activation voltage range, which is further fine-tuned by alternative splicing. Shorter variants miss a C-terminal regulatory domain (CTM), which allows them to activate at even more negative potentials than C-terminally long-splice variants. It is at present unclear whether this is due to an increased voltage sensitivity of the Cav1.3 voltage-sensing domain, or an enhanced coupling of voltage-sensor conformational changes to the subsequent opening of the activation gate. We studied the voltage-dependence of voltage-sensor charge movement (QON-V) and of current activation (ICa-V) of the long (Cav1.3L) and a short Cav1.3 splice variant (Cav1.342A) expressed in tsA-201 cells using whole cell patch-clamp. Charge movement (QON) of Cav1.3L displayed a much steeper voltage-dependence and a more negative half-maximal activation voltage than Cav1.2 and Cav3.1. However, a significantly higher fraction of the total charge had to move for activation of Cav1.3 half-maximal conductance (Cav1.3: 68%; Cav1.2: 52%; Cav3.1: 22%). This indicated a weaker coupling of Cav1.3 voltage-sensor charge movement to pore opening. However, the coupling efficiency was strengthened in the absence of the CTM in Cav1.342A, thereby shifting ICa-V by 7.2 mV to potentials that were more negative without changing QON-V. We independently show that the presence of intracellular organic cations (such as n-methyl-D-glucamine) induces a pronounced negative shift of QON-V and a more negative activation of ICa-V of all three channels. These findings illustrate that the voltage sensors of Cav1.3 channels respond more sensitively to depolarization than those of Cav1.2 or Cav3.1. Weak coupling of voltage sensing to pore opening is enhanced in the absence of the CTM, allowing short Cav1.342A splice variants to activate at lower voltages
International Nuclear Information System (INIS)
Drury, L.O.; Stewart, J.M.
1976-01-01
A generalization of a transformation due to Kurskov and Ozernoi is used to rewrite the usual equations governing subsonic turbulence in Robertson-Walker cosmological models as Navier-Stokes equations with a time-dependent viscosity. This paper first rederives some well-known results in a very simple way by means of this transformation. The main result however is that the establishment of a Kolmogorov spectrum at recombination appears to be incompatible with subsonic turbulence. The conditions after recombination are also discussed briefly. (author)
Turbulent flow in a partially filled pipe
Ng, Henry; Cregan, Hope; Dodds, Jonathan; Poole, Robert; Dennis, David
2017-11-01
Turbulent flow in a pressure driven pipe running partially full has been investigated using high-speed 2D-3C Stereoscopic Particle Imaging Velocimetry. With the field-of-view spanning the entire pipe cross section we are able to reconstruct the full three dimensional quasi-instantaneous flow field by invoking Taylor's hypothesis. The measurements were carried out over a range of flow depths at a constant Reynolds number based on hydraulic diameter and bulk velocity of Re = 32 , 000 . In agreement with previous studies, the ``velocity dip'' phenomenon, whereby the location of the maximum streamwise velocity occurs below the free surface was observed. A mean flow secondary current is observed near the free surface with each of the counter-rotating rollers filling the half-width of the pipe. Unlike fully turbulent flow in a rectangular open channel or pressurized square duct flow where the secondary flow cells appear in pairs about a corner bisector, the mean secondary motion observed here manifests only as a single pair of vortices mirrored about the pipe vertical centreline.
Structure and modeling of turbulence
International Nuclear Information System (INIS)
Novikov, E.A.
1995-01-01
The open-quotes vortex stringsclose quotes scale l s ∼ LRe -3/10 (L-external scale, Re - Reynolds number) is suggested as a grid scale for the large-eddy simulation. Various aspects of the structure of turbulence and subgrid modeling are described in terms of conditional averaging, Markov processes with dependent increments and infinitely divisible distributions. The major request from the energy, naval, aerospace and environmental engineering communities to the theory of turbulence is to reduce the enormous number of degrees of freedom in turbulent flows to a level manageable by computer simulations. The vast majority of these degrees of freedom is in the small-scale motion. The study of the structure of turbulence provides a basis for subgrid-scale (SGS) models, which are necessary for the large-eddy simulations (LES)
DEFF Research Database (Denmark)
Nielsen, Mogens Peter; Shui, Wan; Johansson, Jens
2011-01-01
term with stresses depending linearly on the strain rates. This term takes into account the transfer of linear momentum from one part of the fluid to another. Besides there is another term, which takes into account the transfer of angular momentum. Thus the model implies a new definition of turbulence...
Altered Expression of a Malate-Permeable Anion Channel, OsALMT4, Disrupts Mineral Nutrition1[OPEN
Delhaize, Emmanuel
2017-01-01
Aluminum-activated malate transporters (ALMTs) form a family of anion channels in plants, but little is known about most of its members. This study examined the function of OsALMT4 from rice (Oryza sativa). We show that OsALMT4 is expressed in roots and shoots and that the OsALMT4 protein localizes to the plasma membrane. Transgenic rice lines overexpressing (OX) OsALMT4 released malate from the roots constitutively and had 2-fold higher malate concentrations in the xylem sap than nulls, indicating greater concentrations of malate in the apoplast. OX lines developed brown necrotic spots on the leaves that did not appear on nulls. These symptoms were not associated with altered concentrations of any mineral element in the leaves, although the OX lines had higher concentrations of Mn and B in their grain compared with nulls. While total leaf Mn concentrations were not different between the OX and null lines, Mn concentrations in the apoplast were greater in the OX plants. The OX lines also displayed increased expression of Mn transporters and were more sensitive to Mn toxicity than null plants. We showed that the growth of wild-type rice was unaffected by 100 µm Mn in hydroponics but, when combined with 1 mm malate, this concentration inhibited growth. We conclude that increasing OsALMT4 expression affected malate efflux and compartmentation within the tissues, which increased Mn concentrations in the apoplast of leaves and induced the toxicity symptoms. This study reveals new links between malate transport and mineral nutrition. PMID:29101278
Defensin-like ZmES4 mediates pollen tube burst in maize via opening of the potassium channel KZM1.
Directory of Open Access Journals (Sweden)
Suseno Amien
2010-06-01
Full Text Available In contrast to animals and lower plant species, sperm cells of flowering plants are non-motile and are transported to the female gametes via the pollen tube, i.e. the male gametophyte. Upon arrival at the female gametophyte two sperm cells are discharged into the receptive synergid cell to execute double fertilization. The first players involved in inter-gametophyte signaling to attract pollen tubes and to arrest their growth have been recently identified. In contrast the physiological mechanisms leading to pollen tube burst and thus sperm discharge remained elusive. Here, we describe the role of polymorphic defensin-like cysteine-rich proteins ZmES1-4 (Zea mays embryo sac from maize, leading to pollen tube growth arrest, burst, and explosive sperm release. ZmES1-4 genes are exclusively expressed in the cells of the female gametophyte. ZmES4-GFP fusion proteins accumulate in vesicles at the secretory zone of mature synergid cells and are released during the fertilization process. Using RNAi knock-down and synthetic ZmES4 proteins, we found that ZmES4 induces pollen tube burst in a species-preferential manner. Pollen tube plasma membrane depolarization, which occurs immediately after ZmES4 application, as well as channel blocker experiments point to a role of K(+-influx in the pollen tube rupture mechanism. Finally, we discovered the intrinsic rectifying K(+ channel KZM1 as a direct target of ZmES4. Following ZmES4 application, KZM1 opens at physiological membrane potentials and closes after wash-out. In conclusion, we suggest that vesicles containing ZmES4 are released from the synergid cells upon male-female gametophyte signaling. Subsequent interaction between ZmES4 and KZM1 results in channel opening and K(+ influx. We further suggest that K(+ influx leads to water uptake and culminates in osmotic tube burst. The species-preferential activity of polymorphic ZmES4 indicates that the mechanism described represents a pre-zygotic hybridization
Defensin-Like ZmES4 Mediates Pollen Tube Burst in Maize via Opening of the Potassium Channel KZM1
Márton, Mihaela L.; Debener, Thomas; Geiger, Dietmar; Becker, Dirk; Dresselhaus, Thomas
2010-01-01
In contrast to animals and lower plant species, sperm cells of flowering plants are non-motile and are transported to the female gametes via the pollen tube, i.e. the male gametophyte. Upon arrival at the female gametophyte two sperm cells are discharged into the receptive synergid cell to execute double fertilization. The first players involved in inter-gametophyte signaling to attract pollen tubes and to arrest their growth have been recently identified. In contrast the physiological mechanisms leading to pollen tube burst and thus sperm discharge remained elusive. Here, we describe the role of polymorphic defensin-like cysteine-rich proteins ZmES1-4 (Zea mays embryo sac) from maize, leading to pollen tube growth arrest, burst, and explosive sperm release. ZmES1-4 genes are exclusively expressed in the cells of the female gametophyte. ZmES4-GFP fusion proteins accumulate in vesicles at the secretory zone of mature synergid cells and are released during the fertilization process. Using RNAi knock-down and synthetic ZmES4 proteins, we found that ZmES4 induces pollen tube burst in a species-preferential manner. Pollen tube plasma membrane depolarization, which occurs immediately after ZmES4 application, as well as channel blocker experiments point to a role of K+-influx in the pollen tube rupture mechanism. Finally, we discovered the intrinsic rectifying K+ channel KZM1 as a direct target of ZmES4. Following ZmES4 application, KZM1 opens at physiological membrane potentials and closes after wash-out. In conclusion, we suggest that vesicles containing ZmES4 are released from the synergid cells upon male-female gametophyte signaling. Subsequent interaction between ZmES4 and KZM1 results in channel opening and K+ influx. We further suggest that K+ influx leads to water uptake and culminates in osmotic tube burst. The species-preferential activity of polymorphic ZmES4 indicates that the mechanism described represents a pre-zygotic hybridization barrier and may be a
Ihara, Yukiko; Tomonoh, Yuko; Deshimaru, Masanobu; Zhang, Bo; Uchida, Taku; Ishii, Atsushi; Hirose, Shinichi
2016-01-01
The hetero-tetrameric voltage-gated potassium channel Kv7.2/Kv7.3, which is encoded by KCNQ2 and KCNQ3, plays an important role in limiting network excitability in the neonatal brain. Kv7.2/Kv7.3 dysfunction resulting from KCNQ2 mutations predominantly causes self-limited or benign epilepsy in neonates, but also causes early onset epileptic encephalopathy. Retigabine (RTG), a Kv7.2/ Kv7.3-channel opener, seems to be a rational antiepileptic drug for epilepsies caused by KCNQ2 mutations. We therefore evaluated the effects of RTG on seizures in two strains of knock-in mice harboring different Kcnq2 mutations, in comparison to the effects of phenobarbital (PB), which is the first-line antiepileptic drug for seizures in neonates. The subjects were heterozygous knock-in mice (Kcnq2Y284C/+ and Kcnq2A306T/+) bearing the Y284C or A306T Kcnq2 mutation, respectively, and their wild-type (WT) littermates, at 63-100 days of age. Seizures induced by intraperitoneal injection of kainic acid (KA, 12mg/kg) were recorded using a video-electroencephalography (EEG) monitoring system. Effects of RTG on KA-induced seizures of both strains of knock-in mice were assessed using seizure scores from a modified Racine's scale and compared with those of PB. The number and total duration of spike bursts on EEG and behaviors monitored by video recording were also used to evaluate the effects of RTG and PB. Both Kcnq2Y284C/+ and Kcnq2A306T/+ mice showed significantly more KA-induced seizures than WT mice. RTG significantly attenuated KA-induced seizure activities in both Kcnq2Y284C/+ and Kcnq2A306T/+ mice, and more markedly than PB. This is the first reported evidence of RTG ameliorating KA-induced seizures in knock-in mice bearing mutations of Kcnq2, with more marked effects than those observed with PB. RTG or other Kv7.2-channel openers may be considered as first-line antiepileptic treatments for epilepsies resulting from KCNQ2 mutations.
Modelling of subcritical free-surface flow over an inclined backward-facing step in a water channel
Directory of Open Access Journals (Sweden)
Šulc Jan
2012-04-01
Full Text Available The contribution deals with the experimental and numerical modelling of subcritical turbulent flow in an open channel with an inclined backward-facing step. The step with the inclination angle α = 20° was placed in the water channel of the cross-section 200×200 mm. Experiments were carried out by means of the PIV and LDA measuring techniques. Numerical simulations were executed by means of the commercial software ANSYS CFX 12.0. Numerical results obtained for twoequation models and EARSM turbulence model completed by transport equations for turbulent energy and specific dissipation rate were compared with experimental data. The modelling was concentrated particularly on the development of the flow separation and on the corresponding changes of free surface.
Tkachenko, H M; Kurhaliuk, N M; Vovkanych, L S
2004-01-01
We have examined the influence of ATP-sensitive potassium (KATP) channel opener pinacidil (0.06 mg/kg) and inhibitor glibenclamide (1 mg/kg) on the changes of energy metabolism in the liver of rats under the stress conditions. The rats were divided in two groups with high and low resistance to hypoxia. The stress was modeled by placing the rats in a cage filled with water and closed with a net. The distance from water to the net was only 5 cm. The effects of KATP opener pinacidil (0.06 mg/kg) and inhibitor glibenclamide (1 mg/kg) on ADP-stimulating mitochondrial respiration by Chance, calcium capacity of organellas and processes of lipid peroxidation in the liver of rats with different resistance to hypoxia under the stress condition have been investigated. We have used the next substrates of oxidation: 0.35 mM succinate and 1 mM alpha-ketoglutarate. The additional analyses were conducted with the use of inhibitors: mitochondrial enzyme complex I 10 mM rotenone and succinate dehydrohenase 2 mM malonic acid. It was shown that the stress condition evoked the succinate oxidation and the decrease of alpha-ketoglutarate efficacy, the increase of calcium mitochondrial capacity and the intensification of lipid peroxidation processes. Under the presence of succinate, the increase of O2 uptake with simultaneous decrease of ADP/O ratio in rats with high resistance under stress was observed. Simultaneously, oxidation of alpha-ketoglutarate, a NAD-dependent substrate, was inhibited. Pinacidil caused the reorganization of mitochondrial energy metabolism in favour of NAD-dependent oxidation and the improvment of the protection against stress. The decrease of the efficacy of mitochondrial energy processes functioning was shown in animals with low resistance to hypoxia. KATP channel opener pinacidil has a protective effect on the processes of mitochondrial liver energy support under stress. These changes deal with the increase of alpha-ketoglutarate oxidation (respiratory rate and
Turbulence-Free Double-slit Interferometer
Smith, Thomas A.; Shih, Yanhua
2018-02-01
Optical turbulence can be detrimental for optical observations. For instance, atmospheric turbulence may reduce the visibility or completely blur out the interference produced by an interferometer in open air. However, a simple two-photon interference theory based on Einstein's granularity picture of light makes a turbulence-free interferometer possible; i.e., any refraction index, length, or phase variations along the optical paths of the interferometer do not have any effect on its interference. Applying this mechanism, the reported experiment demonstrates a two-photon double-slit interference that is insensitive to atmospheric turbulence. The turbulence-free mechanism and especially the turbulence-free interferometer would be helpful in optical observations that require high sensitivity and stability such as for gravitational-wave detection.
Turbulent breakage of ductile aggregates.
Marchioli, Cristian; Soldati, Alfredo
2015-05-01
In this paper we study breakage rate statistics of small colloidal aggregates in nonhomogeneous anisotropic turbulence. We use pseudospectral direct numerical simulation of turbulent channel flow and Lagrangian tracking to follow the motion of the aggregates, modeled as sub-Kolmogorov massless particles. We focus specifically on the effects produced by ductile rupture: This rupture is initially activated when fluctuating hydrodynamic stresses exceed a critical value, σ>σ(cr), and is brought to completion when the energy absorbed by the aggregate meets the critical breakage value. We show that ductile rupture breakage rates are significantly reduced with respect to the case of instantaneous brittle rupture (i.e., breakage occurs as soon as σ>σ(cr)). These discrepancies are due to the different energy values at play as well as to the statistical features of energy distribution in the anisotropic turbulence case examined.
Towards CFD modeling of turbulent pipeline material transportation
Shahirpour, Amir; Herzog, Nicoleta; Egbers, Cristoph
2013-04-01
Safe and financially efficient pipeline transportation of carbon dioxide is a critical issue in the developing field of the CCS Technology. In this part of the process, carbon dioxide is transported via pipes with diameter of 1.5 m and entry pressure of 150 bar, with Reynolds number of 107 and viscosity of 8×10(-5) Pa.s as dense fluid [1]. Presence of large and small scale structures in the pipeline, high Reynolds numbers at which CO2 should be transferred, and 3 dimensional turbulence caused by local geometrical modifications, increase the importance of simulation of turbulent material transport through the individual components of the CO2 chain process. In this study, incompressible turbulent channel flow and pipe flow have been modeled using OpenFoam, an open source CFD software. In the first step, simulation of a turbulent channel flow has been considered using LES for shear Reynolds number of 395. A simple geometry has been chosen with cyclic fluid inlet and outlet boundary conditions to simulate a fully developed flow. The mesh is gradually refined towards the wall to provide values close enough to the wall for the wall coordinate (y+). Grid resolution study has been conducted for One-Equation model. The accuracy of the results is analyzed with respect to the grid smoothness in order to reach an optimized resolution for carrying out the next simulations. Furthermore, three LES models, One-Equation, Smagorinsky and Dynamic Smagorinsky are applied for the grid resolution of (60 × 100 × 80) in (x, y, z) directions. The results are then validated with reference to the DNS carried out by Moser et al.[2] for the similar geometry using logarithmic velocity profile (U+) and Reynolds stress tensor components. In the second step the similar flow is modeled using Reynolds averaged method. Several RANS models, like K-epsilon and Launder-Reece-Rodi are applied and validated against DNS and LES results in a similar fashion. In the most recent step, it has been intended
Directory of Open Access Journals (Sweden)
Alexey S. Ladokhin
2017-09-01
Full Text Available Cellular entry of diphtheria toxin is a multistage process involving receptor targeting, endocytosis, and translocation of the catalytic domain across the endosomal membrane into the cytosol. The latter is ensured by the translocation (T domain of the toxin, capable of undergoing conformational refolding and membrane insertion in response to the acidification of the endosomal environment. While numerous now classical studies have demonstrated the formation of an ion-conducting conformation—the Open-Channel State (OCS—as the final step of the refolding pathway, it remains unclear whether this channel constitutes an in vivo translocation pathway or is a byproduct of the translocation. To address this question, we measure functional activity of known OCS-blocking mutants with H-to-Q replacements of C-terminal histidines of the T-domain. We also test the ability of these mutants to translocate their own N-terminus across lipid bilayers of model vesicles. The results of both experiments indicate that translocation activity does not correlate with previously published OCS activity. Finally, we determined the topology of TH5 helix in membrane-inserted T-domain using W281 fluorescence and its depth-dependent quenching by brominated lipids. Our results indicate that while TH5 becomes a transbilayer helix in a wild-type protein, it fails to insert in the case of the OCS-blocking mutant H322Q. We conclude that the formation of the OCS is not necessary for the functional translocation by the T-domain, at least in the histidine-replacement mutants, suggesting that the OCS is unlikely to constitute a translocation pathway for the cellular entry of diphtheria toxin in vivo.
Nonuniform quantum turbulence in superfluids
Nemirovskii, Sergey K.
2018-04-01
The problem of quantum turbulence in a channel with an inhomogeneous counterflow of superfluid turbulent helium is studied. The counterflow velocity Vns x(y ) along the channel is supposed to have a parabolic profile in the transverse direction y . Such statement corresponds to the recent numerical simulation by Khomenko et al. [Phys. Rev. B 91, 180504 (2015), 10.1103/PhysRevB.91.180504]. The authors reported about a sophisticated behavior of the vortex-line density (VLD) L (r ,t ) , different from L ∝Vns x(y) 2 , which follows from the straightforward application of the conventional Vinen theory. It is clear that Vinen theory should be refined by taking into account transverse effects, and the way it ought to be done is the subject of active discussion in the literature. In this work, we discuss several possible mechanisms of the transverse flux of VLD L (r ,t ) which should be incorporated in the standard Vinen equation to describe adequately the inhomogeneous quantum turbulence. It is shown that the most effective among these mechanisms is the one that is related to the phase-slippage phenomenon. The use of this flux in the modernized Vinen equation corrects the situation with an unusual distribution of the vortex-line density, and satisfactorily describes the behavior L (r ,t ) both in stationary and nonstationary situations. The general problem of the phenomenological Vinen theory in the case of nonuniform and nonstationary quantum turbulence is thoroughly discussed.
[Turbulence and spatio-temporal chaos
International Nuclear Information System (INIS)
1990-01-01
This report discusses Saffman-Taylor instability; cylinder wake; Levy walk and turbulent channel flow; bubble motion and bubble streams; spinal turbulent and wetting; collective behavior of a coupled map system with a conserved quantity; stability of temporally periodic states; generic nonergodic behavior in continuous systems; characterization of unstable periodic orbits; in low-dimensional chaotic attractors and repellers; and Ginzburg-Landau theory for oil-water-surfactant mixture
Composite asymptotic expansions and scaling wall turbulence.
Panton, Ronald L
2007-03-15
In this article, the assumptions and reasoning that yield composite asymptotic expansions for wall turbulence are discussed. Particular attention is paid to the scaling quantities that are used to render the variables non-dimensional and of order one. An asymptotic expansion is proposed for the streamwise Reynolds stress that accounts for the active and inactive turbulence by using different scalings. The idea is tested with the data from the channel flows and appears to have merit.
Sehlke, A.; Kobs-Nawotniak, S. E.; Hughes, S. S.; Sears, D. W. G.; Downs, M.; Whittington, A. G.; Lim, D. S. S.; Heldmann, J. L.
2017-12-01
microcrystals, strongly increasing the viscosity of the lava several orders of magnitude. The results of this study allows us to correlate T, X, η, φc, φb, and ρ to the lava flow morphology expressed as surface roughness, which can then be used as a tool to infer these physical properties of the rocks for open channel lava flows on other airless bodies, such as the Moon and Mercury, based on DTMs.
Advancements in engineering turbulence modeling
Shih, T.-H.
1991-01-01
Some new developments in two-equation models and second order closure models are presented. Two-equation models (k-epsilon models) have been widely used in computational fluid dynamics (CFD) for engineering problems. Most of low-Reynolds number two-equation models contain some wall-distance damping functions to account for the effect of wall on turbulence. However, this often causes the confusion and difficulties in computing flows with complex geometry and also needs an ad hoc treatment near the separation and reattachment points. A set of modified two-equation models is proposed to remove the aforementioned shortcomings. The calculations using various two-equation models are compared with direct numerical simulations of channel flow and flat boundary layers. Development of a second order closure model is also discussed with emphasis on the modeling of pressure related correlation terms and dissipation rates in the second moment equations. All the existing models poorly predict the normal stresses near the wall and fail to predict the 3-D effect of mean flow on the turbulence (e.g. decrease in the shear stress caused by the cross flow in the boundary layer). The newly developed second order near-wall turbulence model is described and is capable of capturing the near-wall behavior of turbulence as well as the effect of 3-D mean flow on the turbulence.
Turbulence near the wall in tokamaks
International Nuclear Information System (INIS)
Nedospasov, A.V.
1989-01-01
Causes of plasma turbulence in the shadow of poloidal limiter of tokamak are discussed. Current to limiter along the magnetic field plays the determining role. In this case the plasma on the external surrounding of torr is unstable relatively to channeled perturbations. Conditions of strong and weak recycling in limiter are considered. It is shown that in case of strong recycling, the amplitude and scale of turbulence pulsations and turbulent temperature conductivity of the plasma can be determined by low temperature of electrons near the limiter surface
Mean Flow and Turbulence Near a Series of Dikes
Yaeger, M. A.; Duan, J. G.
2008-12-01
Scour around various structures obstructing flow in an open channel is a common problem faced by river engineers. To better understand why this occurs, two questions must be answered: what are the mean flow and turbulence distributions around these structures and how do these two fields affect sediment transport? In addition, are the mean flow or turbulence properties more important in predicting the local transport rate? To answer these questions, a near-bed turbulence and shear stress study was conducted in a flat, fixed bed laboratory flume. Three dikes were placed on the left wall at right angles to the flow, extending partway into the flow, and remaining fully emerged throughout the experiment. A micro acoustic Doppler velocimeter (ADV) was used to measure velocities near the bed in the x, y, and z directions and then the turbulence intensities and Reynolds stresses were calculated from these measurements. Preliminary results showed that mean velocity has no relation to the formation of scour near the tips of the dikes but that Reynolds stresses and turbulence intensities do. It was shown that the horizontal component of the Reynolds stress near the bed contributed the most to the formation of scour. The maximum value of this component was over 200 times that of the mean bed shear stress of the incoming flow, whereas in a single dike field, the same Reynolds stress is about 60 times that of the incoming flow. The magnitudes of the other two components of the Reynolds stress were less than that of the horizontal component, with magnitudes about 20 times that of the incoming flow. This may be attributed to the very small contribution of the vertical velocity in these components. Turbulence intensity magnitudes were about 3 to 5 times that of the incoming flow, with the largest being u'. The largest values for both Reynolds stresses and turbulence intensities were seen at the tip of the second dike in the series. Better understanding of these flow processes will
Jin, Jin; Weber, Ewald; Destruel, Aurelien; O'Brien, Kieran; Henin, Bassem; Engstrom, Craig; Crozier, Stuart
2018-03-01
We present the initial in vivo imaging results of an open architecture eight-channel parallel transmission (pTx) transceive radiofrequency (RF) coil array that was designed and constructed for static and dynamic 7T MRI of the knee and ankle joints. The pTx coil has a U-shaped dual-row configuration (200 mm overall length longitudinally) that allows static and dynamic imaging of the knee and ankle joints at various postures and during active movements. This coil structure, in combination with B 1 shimming, allows flexible configuration of B 1 transmit profiles, with good homogeneity over 120-mm regions of interest. This coil enabled high-resolution gradient echo (e.g., 3D dual-echo steady state [DESS] and 3D multiecho data image combination [MEDIC]) and turbo spin echo (TSE) imaging (e.g., with proton density weighting [PDw], PDw with fat saturation, and T 1 and T 2 weightings) with local RF energy absorption rates well below regulatory limits. High-resolution 2D and 3D image series (e.g., 0.3 mm in-plane resolution for TSE, 0.47 mm isotropic for DESS and MEDIC) were obtained from the knee and ankle joints with excellent tissue contrast. Dynamic imaging during continuous knee and ankle flexion-extension cycles were successfully acquired. The new open pTx coil array provides versatility for high-quality static and dynamic MRI of the knee and ankle joints at 7T. Magn Reson Med 79:1804-1816, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.
National Oceanic and Atmospheric Administration, Department of Commerce — Forecast turbulence hazards identified by the Graphical Turbulence Guidance algorithm. The Graphical Turbulence Guidance product depicts mid-level and upper-level...
Graphical Turbulence Guidance - Composite
National Oceanic and Atmospheric Administration, Department of Commerce — Forecast turbulence hazards identified by the Graphical Turbulence Guidance algorithm. The Graphical Turbulence Guidance product depicts mid-level and upper-level...
Directory of Open Access Journals (Sweden)
Weijie Liang
2017-02-01
Full Text Available Background/Aims: Hyperglycemia activates multiple signaling molecules, including reactive oxygen species (ROS, toll-like receptor 4 (TLR4, receptor-interacting protein 3 (RIP3, a kinase promoting necroptosis, which mediate hyperglycemia-induced cardiac injury. This study explored whether inhibition of ROS-TLR4-necroptosis pathway contributed to the protection of ATP-sensitive K+ (KATP channel opening against high glucose-induced cardiac injury and inflammation. Methods: H9c2 cardiac cells were treated with 35 mM glucose (HG to establish a model of HG-induced insults. The expression of RIP3 and TLR4 were tested by western blot. Generation of ROS, cell viability, mitochondrial membrane potential (MMP and secretion of inflammatory cytokines were measured as injury indexes. Results: HG increased the expression of TLR4 and RIP3. Necrostatin-1 (Nec-1, an inhibitor of necroptosis or TAK-242 (an inhibitor of TLR4 co-treatment attenuated HG-induced up-regulation of RIP3. Diazoxide (DZ, a mitochondrial KATP channel opener or pinacidil (Pin, a non-selective KATP channel opener or N-acetyl-L-cysteine (NAC, a ROS scavenger pre-treatment blocked the up-regulation of TLR4 and RIP3. Furthermore, pre-treatment with DZ or Pin or NAC, or co-treatment with TAK-242 or Nec-1 attenuated HG-induced a decrease in cell viability, and increases in ROS generation, MMP loss and inflammatory cytokines secretion. However, 5-hydroxy decanoic acid (5-HD, a mitochondrial KATP channel blocker or glibenclamide (Gli, a non-selective KATP channel blocker pre-treatment did not aggravate HG-induced injury and inflammation. Conclusion: KATP channel opening protects H9c2 cells against HG-induced injury and inflammation by inhibiting ROS-TLR4-necroptosis pathway.
Magnetohydrodynamic Turbulence
Montgomery, David C.
2004-01-01
Magnetohydrodynamic (MHD) turbulence theory is modeled on neutral fluid (Navier-Stokes) turbulence theory, but with some important differences. There have been essentially no repeatable laboratory MHD experiments wherein the boundary conditions could be controlled or varied and a full set of diagnostics implemented. The equations of MHD are convincingly derivable only in the limit of small ratio of collision mean-free-paths to macroscopic length scales, an inequality that often goes the other way for magnetofluids of interest. Finally, accurate information on the MHD transport coefficients-and thus, the Reynolds-like numbers that order magnetofluid behavior-is largely lacking; indeed, the algebraic expressions used for such ingredients as the viscous stress tensor are often little more than wishful borrowing from fluid mechanics. The one accurate thing that has been done extensively and well is to solve the (strongly nonlinear) MHD equations numerically, usually in the presence of rectangular periodic boundary conditions, and then hope for the best when drawing inferences from the computations for those astrophysical and geophysical MHD systems for which some indisputably turbulent detailed data are available, such as the solar wind or solar prominences. This has led to what is perhaps the first field of physics for which computer simulations are regarded as more central to validating conclusions than is any kind of measurement. Things have evolved in this way due to a mixture of the inevitable and the bureaucratic, but that is the way it is, and those of us who want to work on the subject have to live with it. It is the only game in town, and theories that have promised more-often on the basis of some alleged ``instability''-have turned out to be illusory.
Energy Technology Data Exchange (ETDEWEB)
Groetzbach, G.; Ammann, T.; Dorr, B.; Hiltner, I.; Hofmann, S.; Kampczyk, M.; Kimhi, Y.; Seiter, C.; Woerner, M.; Alef, M.; Hennemuth, A.
1995-08-01
The FLUTAN code is used for analyzing the decay heat removal in new reactor concepts. The turbulence models applied in FLUTAN are improved by the development of the TURBIT code. TURBIT serves for a numerical simulation of turbulent channel flow. (orig.)
Sprung, D.; Eijk, A.M.J. van; Günter, W.; Griffith, D.; Eisele, C.; Sucher, E.; Seiffer, D.; Stein, K.
2017-01-01
Atmospheric turbulence impacts on the propagation of electro-optical radiation. Typical manifestations of optical turbulence are scintillation (intensity fluctuations), beam wander and (for laser systems) reduction of beam quality. For longer propagation channels, it is important to characterize the
Franz, Delbert D.; Melching, Charles S.
1997-01-01
The Full EQuations (FEQ) model is a computer program for solution of the full, dynamic equations of motion for one-dimensional unsteady flow in open channels and through control structures. A stream system that is simulated by application of FEQ is subdivided into stream reaches (branches), parts of the stream system for which complete information on flow and depth are not required (dummy branches), and level-pool reservoirs. These components are connected by special features; that is, hydraulic control structures, including junctions, bridges, culverts, dams, waterfalls, spillways, weirs, side weirs, and pumps. The principles of conservation of mass and conservation of momentum are used to calculate the flow and depth throughout the stream system resulting from known initial and boundary conditions by means of an implicit finite-difference approximation at fixed points (computational nodes). The hydraulic characteristics of (1) branches including top width, area, first moment of area with respect to the water surface, conveyance, and flux coefficients and (2) special features (relations between flow and headwater and (or) tail-water elevations, including the operation of variable-geometry structures) are stored in function tables calculated in the companion program, Full EQuations UTiLities (FEQUTL). Function tables containing other information used in unsteady-flow simulation (boundary conditions, tributary inflows or outflows, gate settings, correction factors, characteristics of dummy branches and level-pool reservoirs, and wind speed and direction) are prepared by the user as detailed in this report. In the iterative solution scheme for flow and depth throughout the stream system, an interpolation of the function tables corresponding to the computational nodes throughout the stream system is done in the model. FEQ can be applied in the simulation of a wide range of stream configurations (including loops), lateral-inflow conditions, and special features. The
Pressure atomizer having multiple orifices and turbulent generation feature
VanBrocklin, Paul G.; Geiger, Gail E.; Moran, Donald James; Fournier, Stephane
2002-01-01
A pressure atomizer includes a silicon plate having a top surface and a bottom surface. A portion of the top surface defines a turbulent chamber. The turbulent chamber is peripherally bounded by the top surface of the plate. The turbulent chamber is recessed a predetermined depth relative to the top surface. The silicon plate further defines at least one flow orifice. Each flow orifice extends from the bottom surface of the silicon plate to intersect with and open into the turbulent chamber. Each flow orifice is in fluid communication with the turbulent chamber.
International Nuclear Information System (INIS)
Zushi, H.; Hanada, K.; Nishino, N.
2010-11-01
Statistical features of fluctuations including blobs are investigated using the CCD imaging technique in open and closed magnetic configurations. In a simple open magnetic configuration with vertical (B z ) and toroidal fields (B t ) slab plasma produced by electron cyclotron waves is studied as a function of B z /B t . It is found that fluctuations become dominated by blobs depending on the ratio B z /B t . In the plasma source region R s helix-sinusoidal perturbations are exited, whose helix angle and vertical wavelength are consistent with pitch angle and turn distance of the magnetic field lines there. Steep gradient in the intermediate region R im outside R s triggers the plasma to expand radially as a blob ejection. Along the ridge line of the maximum inverse scale length a wave front of the helix perturbation moves outward. Acceleration of a blob is found in the source-free region R sf . It is found that the probability density function pdf of fluctuations in all B z /B t experiments is close to a gamma distribution. Ohmic plasma is ramped-up from the slab plasma and closed surface LCFS is formed. Fluctuations inboard side and outer scrape off layer SOL are studied in this process. Former one is characterized by small amplitude fluctuation level δI/I-a few %, but latter one shows intermittent large amplitude. Two dimensional structures of the higher moments (skewness S and kurtosis k) representing the shape of pdf are studied. In the former it is observed that these structures consistent with the LCFS, and the pdf is close to a Gaussian distribution. The numerical coefficients characterizing the Pearson system are also derived. In the outboard SOL, it is found that S and k are not only a function of the magnetic flux, but also the magnetic field lines. The pdf is consistent with the Gaussian one for 0.1m from the LCFS, and becomes beta and gamma ones far from the LCFS. Based on the observed numerical coefficients in the Pearson system a relation between
International Nuclear Information System (INIS)
Cash, D.J.; Subbarao, K.
1988-01-01
The effect of pentobarbital on the responses of the γ-aminobutyric acid (GABA) receptor from rat brain was studied in quantitative measurements of GABA-mediated chloride-exchange rates (reflecting channel-opening equilibrium) and receptor desensitization rates by using 36 Cl - tracer ion with negative membrane vesicles. Pentobarbital effected the two phases of 36 Cl - influx in different ways, supporting previous evidence that these are mediated by two different receptors. Both the chloride-exchange rate and the desensitization rate of the faster desensitizing receptor were increased by pentobarbital at concentrations above 20 μM by an allosteric effect shifting the response curve to lower GABA concentrations. A similar enhancement of the responses of the slower desensitizing receptor occurred up to 200 μM pentobarbital. Two pentobarbital effector sites were involved in the allosteric mechanism. Above 500 μM pentobarbital, both the initial chloride-exchange rate and the desensitization rate of the slower desensitizing receptor were decreased. This inhibition, which was immediate, occurred with saturating as well as low GABA concentrations and therefore was not attributed to decreased GABA binding but to inhibitory sites for pentobarbital, different from the allosteric activating sites and the GABA binding sites. The chloride ion exchange activity was seen to recover with time, at concentrations above 1000 μM pentobarbital, in a process with a very steep dependence on pentobarbital concentration. This reactivation was attributed to the conversion of an initial form of the receptor to a final form that was less inhibited by pentobarbital. Comparisons of the effects of pentobarbital on desensitization and on high-affinity ligand binding measurements suggest that increased GABA binding at equilibrium reflects an increased conversion to the desensitized state
Yamada, Jun; Ohgomori, Tomohiro; Jinno, Shozo
2017-06-15
The perineuronal net (PNN), a specialized aggregate of the extracellular matrix, is involved in neuroprotection against oxidative stress, which is now recognized as a major contributor to age-related decline in brain functions. In this study, we investigated the age-related molecular changes of PNNs using monoclonal antibody Cat-315, which recognizes human natural killer-1 (HNK-1) glycan on aggrecan-based PNNs. Western blot analysis showed that the expression levels of Cat-315 epitope in the hippocampus were higher in middle-aged (MA, 12-month-old) mice than in young adult (YA, 2-month-old) mice. Although there were no differences in the expression levels of Cat-315 epitope between old age (OA, 20-month-old) and MA mice, Cat-315 immunoreactivity was also detected in astrocytes of OA mice. To focus on Cat-315 epitope in PNNs, we used YA and MA mice in the following experiments. Optical disector analysis showed that there were no differences in the numbers of Cat-315-positive (Cat-315 + ) PNNs between YA and MA mice. Fluorescence intensity analysis indicated that Cat-315 immunoreactivity in PNNs increased with age in the dorsal hippocampus, which is mainly involved in cognitive functions. Administration of an open-channel blocker of NMDA receptor, memantine, reduced the expression levels of Cat-315 epitope in the hippocampus. Furthermore, the numbers of glutamatergic and GABAergic terminals colocalized with Cat-315 epitope around parvalbumin-positive neurons were decreased by memantine. These findings provide novel insight into the involvement of PNNs in normal brain ageing, and suggest that memantine may counteract the age-related alterations in expression levels of Cat-315 epitope via regulation of its subcellular localization. © 2017 Wiley Periodicals, Inc.
Felder, Stefan; Chanson, Hubert
2009-07-01
In high-velocity free-surface flows, air entrainment is common through the interface, and intense interactions take place between turbulent structures and entrained bubbles. Two-phase flow properties were measured herein in high-velocity open channel flows above a stepped chute. Detailed turbulence measurements were conducted in a large-size facility, and a comparative analysis was applied to test the validity of the Froude and Reynolds similarities. The results showed consistently that the Froude similitude was not satisfied using a 2:1 geometric scaling ratio. Lesser number of entrained bubbles and comparatively greater bubble sizes were observed at the smaller Reynolds numbers, as well as lower turbulence levels and larger turbulent length and time scales. The results implied that small-size models did underestimate the rate of energy dissipation and the aeration efficiency of prototype stepped spillways for similar flow conditions. Similarly a Reynolds similitude was tested. The results showed also some significant scale effects. However a number of self-similar relationships remained invariant under changes of scale and confirmed the analysis of Chanson and Carosi (Exp Fluids 42:385-401, 2007). The finding is significant because self-similarity may provide a picture general enough to be used to characterise the air-water flow field in large prototype channels.
Surface roughness effects on turbulent Couette flow
Lee, Young Mo; Lee, Jae Hwa
2017-11-01
Direct numerical simulation of a turbulent Couette flow with two-dimensional (2-D) rod roughness is performed to examine the effects of the surface roughness. The Reynolds number based on the channel centerline laminar velocity (Uco) and channel half height (h) is Re =7200. The 2-D rods are periodically arranged with a streamwise pitch of λ = 8 k on the bottom wall, and the roughness height is k = 0.12 h. It is shown that the wall-normal extent for the logarithmic layer is significantly shortened in the rough-wall turbulent Couette flow, compared to a turbulent Couette flow with smooth wall. Although the Reynolds stresses are increased in a turbulent channel flow with surface roughness in the outer layer due to large-scale ejection motions produced by the 2-D rods, those of the rough-wall Couette flow are decreased. Isosurfaces of the u-structures averaged in time suggest that the decrease of the turbulent activity near the centerline is associated with weakened large-scale counter-rotating roll modes by the surface roughness. This research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A1A09000537) and the Ministry of Science, ICT & Future Planning (NRF-2017R1A5A1015311).
International Nuclear Information System (INIS)
Song, Woo Seog; Lee, Seung Bae; Shin, Dong Shin; Na, Yang
2006-01-01
The piezoelectric bimorph film, which, as an actuator, can generate more effective displacement than the usual PVDF film, is used to control the turbulent boundary-layer flow. The change of wall pressures inside the turbulent boundary layer is observed by using the multi-channel microphone array flush-mounted on the surface when actuation at the non-dimensional frequency f b + =0.008 and 0.028 is applied to the turbulent boundary layer. The wall pressure characteristics by the actuation to produce local displacement are more dominantly influenced by the size of the actuator module than the actuation frequency. The movement of large-scale turbulent structures to the upper layer is found to be the main mechanism of the reduction in the wall-pressure energy spectrum when the 700ν/u τ -long bimorph film is periodically actuated at the non-dimensional frequency f b + =0.008 and 0.028. The bimorph actuator is triggered with the time delay for the active forcing at a single frequency when a 1/8' pressure-type, pin-holed microphone sensor detects the large-amplitude pressure event by the turbulent spot. The wall-pressure energy in the late-transitional boundary layer is partially reduced near the convection wavenumber by the open-loop control based on the large amplitude event
Experimental investigations of turbulent temperature fluctuations and phase angles in ASDEX Upgrade
Freethy, Simon
2017-10-01
A complete experimental understanding of the turbulent fluctuations in tokamak plasmas is essential for providing confidence in the extrapolation of heat transport models to future experimental devices and reactors. Guided by ``predict first'' nonlinear gyrokinetic simulations with the GENE code, two new turbulence diagnostics were designed and have been installed on ASDEX Upgrade (AUG) to probe the fundamentals of ion-scale turbulent electron heat transport. The first, a 30-channel correlation ECE (CECE) radiometer, measures radial profiles (0.5 a levels are in the range 0.3 - 0.8%. The second is formed by the addition of a reflectometer on the same line of sight to enable measurements of the phase angle between turbulent density and temperature fluctuations. Design predictions are followed by a more traditional ``post-diction'' validation study with GENE. Using a cutting edge synthetic diagnostic GENE shows a factor 1.6 - 2 over-prediction of the fluctuation amplitude, while matching both ion and electron heat fluxes within experimental error. Detailed sensitivity scans are underway to understand the robustness of this disagreement and a detailed assessment of the experimental errors has been carried out. The discrepancy opens questions about the role of multi-scale turbulence physics, but also indicates the need for the comparison of more experimental turbulence properties to have a more complete validation hierarchy. In an effort to understand the discrepancy, predictions of the nT-phase and the radial correlation length have been made along with an assessment of their sensitivity to experimental errors. Comparison to experimental measurements will be discussed. This work is supported in part by the US DOE under Grants DE-SC0006419 and DE-SC0017381. This work has also received funding from the European Union's Horizon 2020 research and innovation programme under Grant agreement number 633053.
Numerical investigation of the effects of large particles on wall-turbulence
International Nuclear Information System (INIS)
Pan, Y.; Banerjee, S.
1997-01-01
Particle-laden turbulent flows, at average volume fraction less than 4x10 -4 , in open channels are numerically simulated by using a pseudospectral method. The motion of particles, that are large compared with the dissipative length scale, is coupled to the fluid motion by a method that generates a open-quotes virtualclose quotes no-slip boundary on the particle surface by imposition of an external force field on the grid-points enclosed by the particle. Cases for both moving and stationary particles, lying on the wall, are simulated. The investigations focus on particle-turbulence interaction. It is found that particles increase turbulence intensities and Reynolds stress. By examining higher order turbulence statistics and doing a quadrant analysis of the Reynolds stress, it is found that the ejection-sweep cycle is affected emdash primarily through suppression of sweeps by the smaller particles and enhancement of sweep activity by the larger particles. An assessment of the impact of these findings on scalar transfer is made, as enhancement of wall heat/mass transfer rates is a motivation of the overall work on this subject. In the cases considered, comparison of the calculations with an existing experiment was possible, and shows good agreement. At present, due to limitations in available computational resources, this method cannot be used when the particle diameter is smaller than the smallest turbulence scale (e.g. the Kolmogorov length scale) and the volume fraction is of the same order as studied in this paper, i.e. between 10 -3 and 10 -4 . copyright 1997 American Institute of Physics
Influence of atmospheric turbulence on the quantum polarization state
Yang, Ru; Xue, Yang; Li, Yunxia; Shi, Lei; Zhu, Yu; Zhu, Qiuli
2018-03-01
In order to study the influence of atmospheric turbulence on the polarization state of the free space quantum communication, the relationship between the refractive index and altitude, the refractive index structure constant and the turbulence dimension is deduced based on two different atmospheric refractive index structural constants models. The turbulence intensity factor κ is introduced and the equation of the variation of the quantum polarization degree with turbulence intensity is established. Through the simulation of the turbulent refractive index and the performance of four different polarization states in the low altitude turbulence environment, the results show that the atmospheric turbulence in the near ground will affect the fluctuation of the degree of polarization, and the degree of polarization varies linearly with the change of turbulence intensity. In the case of polarization |H>, the range of polarization |H> varies from 0 to 0.14 with the change of turbulence intensity. The influence of atmospheric turbulence on four different polarization states is different, and the degree of |H> and |V> depolarization is greater in the daytime and back. The depolarization degree of |-> at night is greater. The relationship between the degree of polarization and the change of turbulence intensity is analyzed by mathematical modeling, which is helpful to select the reasonable experimental scheme and compensate the change of polarization state in the aviation quantum Secure communication channel.
The role of the sheath in magnetized plasma turbulence and flows
International Nuclear Information System (INIS)
Loizu, J.
2013-01-01
Controlled nuclear fusion could provide our society with a clean, safe, and virtually inexhaustible source of electric power production. The tokamak has proven to be capable of producing large amounts of fusion reactions by conning magnetically the fusion fuel at sufficiently high density and temperature, thus in the plasma state. Because of turbulence, however, high temperature plasma reaches the outermost region of the tokamak, the Scrape-Off Layer (SOL), which features open magnetic field lines that channel particles and heat into a dedicated region of the vacuum vessel. The plasma dynamics in the SOL is crucial in determining the performance of tokamak devices, and constitutes one of the greatest uncertainties in the success of the fusion program. In the last few years, the development of numerical codes based on reduced fluid models has provided a tool to study turbulence in open field line configurations. In particular, the GBS (Global Braginskii Solver) code has been developed at CRPP and is used to perform global, three-dimensional, full-n, flux-driven simulations of plasma turbulence in open field lines. Reaching predictive capabilities is an outstanding challenge that involves a proper treatment of the plasma-wall interactions at the end of the field lines, to well describe the particle and energy losses. This involves the study of plasma sheaths, namely the layers forming at the interface between plasmas and solid surfaces, where the drift and quasi neutrality approximations break down. This is an investigation of general interest, as sheaths are present in all laboratory plasmas. This thesis presents progress in the understanding of plasma sheaths and their coupling with the turbulence in the main plasma. A kinetic code is developed to study the magnetized plasma-wall transition region and derive a complete set of analytical boundary conditions that supply the sheath physics to fluid codes. These boundary conditions are implemented in the GBS code and
Macro-scale turbulence modelling for flows in porous media
International Nuclear Information System (INIS)
Pinson, F.
2006-03-01
- This work deals with the macroscopic modeling of turbulence in porous media. It concerns heat exchangers, nuclear reactors as well as urban flows, etc. The objective of this study is to describe in an homogenized way, by the mean of a spatial average operator, turbulent flows in a solid matrix. In addition to this first operator, the use of a statistical average operator permits to handle the pseudo-aleatory character of turbulence. The successive application of both operators allows us to derive the balance equations of the kind of flows under study. Two major issues are then highlighted, the modeling of dispersion induced by the solid matrix and the turbulence modeling at a macroscopic scale (Reynolds tensor and turbulent dispersion). To this aim, we lean on the local modeling of turbulence and more precisely on the k - ε RANS models. The methodology of dispersion study, derived thanks to the volume averaging theory, is extended to turbulent flows. Its application includes the simulation, at a microscopic scale, of turbulent flows within a representative elementary volume of the porous media. Applied to channel flows, this analysis shows that even within the turbulent regime, dispersion remains one of the dominating phenomena within the macro-scale modeling framework. A two-scale analysis of the flow allows us to understand the dominating role of the drag force in the kinetic energy transfers between scales. Transfers between the mean part and the turbulent part of the flow are formally derived. This description significantly improves our understanding of the issue of macroscopic modeling of turbulence and leads us to define the sub-filter production and the wake dissipation. A f - f - w >f model is derived. It is based on three balance equations for the turbulent kinetic energy, the viscous dissipation and the wake dissipation. Furthermore, a dynamical predictor for the friction coefficient is proposed. This model is then successfully applied to the study of
Randomness Representation of Turbulence in Canopy Flows Using Kolmogorov Complexity Measures
Directory of Open Access Journals (Sweden)
Dragutin Mihailović
2017-09-01
Full Text Available Turbulence is often expressed in terms of either irregular or random fluid flows, without quantification. In this paper, a methodology to evaluate the randomness of the turbulence using measures based on the Kolmogorov complexity (KC is proposed. This methodology is applied to experimental data from a turbulent flow developing in a laboratory channel with canopy of three different densities. The methodology is even compared with the traditional approach based on classical turbulence statistics.
Watanabe, Y; Suzuki, A; Suzuki, H; Itoh, T
1996-03-01
1. The role of membrane hyperpolarization on agonist-induced contraction was investigated in intact and alpha-toxin-skinned smooth muscles of rabbit mesenteric artery by use of the ATP-sensitive K+ channel opener, (-)-(3S,4R)-4-(N-acetyl-N-hydroxyamino)-6-cyano-3,4-dihydro-2,2- dimethyl-2H-1-benzopyran-3-ol (Y-26763), and either histamine (Hist) or noradrenaline (NA). 2. Hist (3 microM) and NA (10 microM) both produced a phasic, followed by a tonic increase in intracellular Ca2+ concentration ([Ca2+]i) and force. Y-26763 (10 microM) potently inhibited the NA-induced phasic and tonic increase in [Ca2+]i and force. In contrast, Y-26763 attenuated the Hist-induced phasic increase in [Ca2+]i and force but had almost no effect on the tonic response. However, ryanodine-treatment of muscles in order to inhibit the function of intracellular Ca2+ storage sites altered the action of Y-26763 which now attenuated the Hist-induced tonic increase in [Ca2+]i and force in a concentration-dependent manner (at concentrations > 1 microM). Glibenclamide (10 microM) attenuated the inhibitory action of Y-26763. 3. Hist (3 microM) depolarized the smooth muscle cells to the same extent as NA (10 microM). In the absence of either agonist, Y-26763 (over 30 nM) hyperpolarized the membrane and glibenclamide inhibited this hyperpolarization. Y-26763 (10 microM) almost abolished the NA-induced membrane depolarization, but only slightly attenuated the Hist-induced membrane depolarization in which the delta (delta) value (the difference before and after application of Hist) was not modified by any concentration of Y-26763. In ryanodine-treated smooth muscle cells, Y-26763 hyperpolarized the membrane and potently inhibited the membrane depolarization induced by Hist. 4. In ryanodine-treated muscle, Y-26763 had no measurable effect on the Hist-induced [Ca2+]i-force relationship. Y-26763 also had no apparent effect on the myofilament Ca(2+)-sensitivity in the presence of Hist in alpha
Kolmogorov Behavior of Near-Wall Turbulence and Its Application in Turbulence Modeling
Shih, Tsan-Hsing; Lumley, John L.
1992-01-01
The near-wall behavior of turbulence is re-examined in a way different from that proposed by Hanjalic and Launder and followers. It is shown that at a certain distance from the wall, all energetic large eddies will reduce to Kolmogorov eddies (the smallest eddies in turbulence). All the important wall parameters, such as friction velocity, viscous length scale, and mean strain rate at the wall, are characterized by Kolmogorov microscales. According to this Kolmogorov behavior of near-wall turbulence, the turbulence quantities, such as turbulent kinetic energy, dissipation rate, etc. at the location where the large eddies become Kolmogorov eddies, can be estimated by using both direct numerical simulation (DNS) data and asymptotic analysis of near-wall turbulence. This information will provide useful boundary conditions for the turbulent transport equations. As an example, the concept is incorporated in the standard k-epsilon model which is then applied to channel and boundary flows. Using appropriate boundary conditions (based on Kolmogorov behavior of near-wall turbulence), there is no need for any wall-modification to the k-epsilon equations (including model constants). Results compare very well with the DNS and experimental data.
LES Modeling with Experimental Validation of a Compound Channel having Converging Floodplain
Mohanta, Abinash; Patra, K. C.
2018-04-01
Computational fluid dynamics (CFD) is often used to predict flow structures in developing areas of a flow field for the determination of velocity field, pressure, shear stresses, effect of turbulence and others. A two phase three-dimensional CFD model along with the large eddy simulation (LES) model is used to solve the turbulence equation. This study aims to validate CFD simulations of free surface flow or open channel flow by using volume of fluid method by comparing the data observed in hydraulics laboratory of the National Institute of Technology, Rourkela. The finite volume method with a dynamic sub grid scale was carried out for a constant aspect ratio and convergence condition. The results show that the secondary flow and centrifugal force influence flow pattern and show good agreement with experimental data. Within this paper over-bank flows have been numerically simulated using LES in order to predict accurate open channel flow behavior. The LES results are shown to accurately predict the flow features, specifically the distribution of secondary circulations both for in-bank channels as well as over-bank channels at varying depth and width ratios in symmetrically converging flood plain compound sections.
PDF modeling of turbulent flows on unstructured grids
Bakosi, Jozsef
modeling the dispersion of passive scalars in inhomogeneous turbulent flows. Two different micromixing models are investigated that incorporate the effect of small scale mixing on the transported scalar: the widely used interaction by exchange with the mean and the interaction by exchange with the conditional mean model. An adaptive algorithm to compute the velocity-conditioned scalar mean is proposed that homogenizes the statistical error over the sample space with no assumption on the shape of the underlying velocity PDF. The development also concentrates on a generally applicable micromixing timescale for complex flow domains. Several newly developed algorithms are described in detail that facilitate a stable numerical solution in arbitrarily complex flow geometries, including a stabilized mean-pressure projection scheme, the estimation of conditional and unconditional Eulerian statistics and their derivatives from stochastic particle fields employing finite element shapefunctions, particle tracking through unstructured grids, an efficient particle redistribution procedure and techniques related to efficient random number generation. The algorithm is validated and tested by computing three different turbulent flows: the fully developed turbulent channel flow, a street canyon (or cavity) flow and the turbulent wake behind a circular cylinder at a sub-critical Reynolds number. The solver has been parallelized and optimized for shared memory and multi-core architectures using the OpenMP standard. Relevant aspects of performance and parallelism on cache-based shared memory machines are discussed and presented in detail. The methodology shows great promise in the simulation of high-Reynolds-number incompressible inert or reactive turbulent flows in realistic configurations.
High Reynolds Number Turbulence
National Research Council Canada - National Science Library
Smits, Alexander J
2007-01-01
The objectives of the grant were to provide a systematic study to fill the gap between existing research on low Reynolds number turbulent flows to the kinds of turbulent flows encountered on full-scale vehicles...
1997-01-01
A color image of fine channel networks on Mars; north toward top. The scene shows heavily cratered highlands dissected by dendritic open channel networks that dissect steep slopes of impact crater walls. This image is a composite of Viking high-resolution images in black and white and low-resolution images in color. The image extends from latitude 9 degrees S. to 5 degrees S. and from longitude 312 degrees to 320 degrees; Mercator projection. The dendritic pattern of the fine channels and their location on steep slopes leads to the interpretation that these are runoff channels. The restriction of these types of channels to ancient highland rocks suggests that these channels are old and date from a time on Mars when conditions existed for precipitation to actively erode rocks. After the channels reach a low plain, they appear to end. Termination may have resulted from burial by younger deposits or perhaps the flows percolated into the surface materials and continued underground.
Dip Phenomenon in High-Curved Turbulent Flows and Application of Entropy Theory
Directory of Open Access Journals (Sweden)
Donatella Termini
2018-03-01
Full Text Available The estimation of velocity profile in turbulent open channels is a difficult task due to the significant effects of the secondary flow. The present paper investigates the mechanism of the velocity-dip phenomenon, whereby the location of the maximum velocity appears to be below the free surface. Previous studies conducted in straight channels relate the mechanism of the velocity-dip phenomenon to secondary flow induced by anisotropy of turbulence. This work focuses on high-curved channels where the secondary motion, which is also induced by the channel’s curvature, evolves along the bend. The width-to-depth ratio, B/h, is one of the most important parameters that are affecting the secondary motion entity. In particular, the present study aims to investigate the evolution of the velocity-dip along the bend for two values of the width-to-depth ratio and the applicability of the entropic model for the dip-phenomenon estimation. The results show that the velocity-dip is more accentuated for low values of the width-to-depth ratio, where the secondary motion plays a fundamental role in the distribution of the downstream flow velocity, although the velocity-dip is also present when the aspect ratio is higher than 10. Furthermore, the velocity profiles that were estimated by applying the entropic model are in good agreement with the measured ones, especially for B/h < 10.
DEFF Research Database (Denmark)
Brand, Arno J.; Peinke, Joachim; Mann, Jakob
2011-01-01
The nature of turbulent flow towards, near and behind a wind turbine, the effect of turbulence on the electricity production and the mechanical loading of individual and clustered wind turbines, and some future issues are discussed.......The nature of turbulent flow towards, near and behind a wind turbine, the effect of turbulence on the electricity production and the mechanical loading of individual and clustered wind turbines, and some future issues are discussed....
Regeneration of near-wall turbulence structures
Hamilton, James M.; Kim, John J.; Waleffe, Fabian A.
1993-01-01
An examination of the regeneration mechanisms of near-wall turbulence and an attempt to investigate the critical Reynolds number conjecture of Waleffe & Kim is presented. The basis is an extension of the 'minimal channel' approach of Jimenez and Moin which emphasizes the near-wall region and further reduces the complexity of the turbulent flow. Reduction of the flow Reynolds number to the minimum value which will allow turbulence to be sustained has the effect of reducing the ratio of the largest scales to the smallest scales or, equivalently, of causing the near-wall region to fill more of the area between the channel walls. In addition, since each wall may have an active near-wall region, half of the channel is always somewhat redundant. If a plane Couette flow is instead chosen as the base flow, this redundancy is eliminated: the mean shear of a plane Couette flow has a single sign, and at low Reynolds numbers, the two wall regions share a single set of structures. A minimal flow with these modifications possesses, by construction, the strongest constraints which allow sustained turbulence, producing a greatly simplified flow in which the regeneration process can be examined.
Creely, A. J.; Freethy, S. J.; Burke, W. M.; Conway, G. D.; Leccacorvi, R.; Parkin, W. C.; Terry, D. R.; White, A. E.
2018-05-01
A newly upgraded correlation electron cyclotron emission (CECE) diagnostic has been installed on the ASDEX Upgrade tokamak and has begun to perform experimental measurements of electron temperature fluctuations. CECE diagnostics measure small amplitude electron temperature fluctuations by correlating closely spaced heterodyne radiometer channels. This upgrade expanded the system from six channels to thirty, allowing simultaneous measurement of fluctuation level radial profiles without repeat discharges, as well as opening up the possibility of measuring radial turbulent correlation lengths. Newly refined statistical techniques have been developed in order to accurately analyze the fluctuation data collected from the CECE system. This paper presents the hardware upgrades for this system and the analysis techniques used to interpret the raw data, as well as measurements of fluctuation spectra and fluctuation level radial profiles.
International Nuclear Information System (INIS)
Goldman, M.V.
1984-01-01
After a brief discussion of beam-excited Langmuir turbulence in the solar wind, we explain the criteria for wave-particle, three-wave and strong turbulence interactions. We then present the results of a numerical integration of the Zakharov equations, which describe the strong turbulence saturation of a weak (low-density) high energy, bump-on-tail beam instability. (author)
Near wall turbulence: An experimental view
Stanislas, Michel
2017-10-01
The present paper draws upon the experience of the author to illustrate the potential of advanced optical metrology for understanding near-wall-turbulence physics. First the canonical flat plate boundary layer problem is addressed, initially very near to the wall and then in the outer region when the Reynolds number is high enough to generate an outer turbulence peak. The coherent structure organization is examined in detail with the help of stereoscopic particle image velocimetry (PIV). Then the case of a turbulent boundary layer subjected to a mild adverse pressure gradient is considered. The results obtained show the great potential of a joint experimental-numerical approach. The conclusion is that the insight provided by today's optical metrology opens the way for significant improvements in turbulence modeling in upcoming years.
Advances in fluid modeling and turbulence measurements
International Nuclear Information System (INIS)
Wada, Akira; Ninokata, Hisashi; Tanaka, Nobukazu
2002-01-01
The context of this book consists of four fields: Environmental Fluid Mechanics; Industrial Fluid Mechanics; Fundamentals of Fluid Mechanics; and Turbulence Measurements. Environmental Fluid Mechanics includes free surface flows in channels, rivers, seas, and estuaries. It also discusses wind engineering issues, ocean circulation model and dispersion problems in atmospheric, water and ground water environments. In Industrial Fluid Mechanics, fluid phenomena in energy exchanges, modeling of turbulent two- or multi-phase flows, swirling flows, flows in combustors, variable density flows and reacting flows, flows in turbo-machines, pumps and piping systems, and fluid-structure interaction are discussed. In Fundamentals of Fluid Mechanics, progress in modeling turbulent flows and heat/mass transfers, computational fluid dynamics/numerical techniques, parallel computing algorithms, applications of chaos/fractal theory in turbulence are reported. In Turbulence Measurements, experimental studies of turbulent flows, experimental and post-processing techniques, quantitative and qualitative flow visualization techniques are discussed. Separate abstracts were presented for 15 of the papers in this issue. The remaining 89 were considered outside the subject scope of INIS. (J.P.N.)
Hairpin vortices in turbulent boundary layers
International Nuclear Information System (INIS)
Eitel-Amor, G; Schlatter, P; Flores, O
2014-01-01
The present work addresses the question whether hairpin vortices are a dominant feature of near-wall turbulence and which role they play during transition. First, the parent-offspring mechanism is investigated in temporal simulations of a single hairpin vortex introduced in a mean shear flow corresponding to turbulent channels and boundary layers up to Re τ = 590. Using an eddy viscosity computed from resolved simulations, the effect of a turbulent background is also considered. Tracking the vortical structure downstream, it is found that secondary hairpins are created shortly after initialization. Thereafter, all rotational structures decay, whereas this effect is enforced in the presence of an eddy viscosity. In a second approach, a laminar boundary layer is tripped to transition by insertion of a regular pattern of hairpins by means of defined volumetric forces representing an ejection event. The idea is to create a synthetic turbulent boundary layer dominated by hairpin-like vortices. The flow for Re τ < 250 is analysed with respect to the lifetime of individual hairpin-like vortices. Both the temporal and spatial simulations demonstrate that the regeneration process is rather short-lived and may not sustain once a turbulent background has formed. From the transitional flow simulations, it is conjectured that the forest of hairpins reported in former DNS studies is an outer layer phenomenon not being connected to the onset of near-wall turbulence.
Flow-induced separation in wall turbulence.
Nguyen, Quoc; Srinivasan, Chiranth; Papavassiliou, Dimitrios V
2015-03-01
One of the defining characteristics of turbulence is its ability to promote mixing. We present here a case where the opposite happens-simulation results indicate that particles can separate near the wall of a turbulent channel flow, when they have sufficiently different Schmidt numbers without use of any other means. The physical mechanism of the separation is understood when the interplay between convection and diffusion, as expressed by their characteristic time scales, is considered, leading to the determination of the necessary conditions for a successful separation between particles. Practical applications of these results can be found when very small particles need to be separated or removed from a fluid.
Neutrino Flavor Evolution in Turbulent Supernova Matter
Lund, Tina; Kneller, James P.
In order to decode the neutrino burst signal from a Galactic core-collapse supernova and reveal the complicated inner workings of the explosion, we need a thorough understanding of the neutrino flavor evolution from the proto-neutron-star outwards. The flavor content of the signal evolves due to both neutrino collective effects and matter effects which can lead to a highly interesting interplay and distinctive spectral features. In this paper we investigate the supernova neutrino flavor evolution by including collective flavor effects, the evolution of the Mikheyev, Smirnov & Wolfenstein (MSW) matter conversions due to the shock wave passing through the star, and the impact of turbulence. The density profiles utilized in our calculations represent a 10.8 MG progenitor and comes from a 1D numerical simulation by Fischer et al.[1]. We find that small amplitude turbulence, up to 10% of the average potential, leads to a minimal modification of the signal, and the emerging neutrino spectra retain both collective and MSW features. However, when larger amounts of turbulence are added, 30% and 50%, the features of collective and shock wave effects in the high density resonance channel are almost completely obscured at late times. At the same time we find the other mixing channels - the low density resonance channel and the non-resonant channels - begin to develop turbulence signatures. Large amplitude turbulent motions in the outer layers of massive, iron core-collapse supernovae may obscure the most obvious fingerprints of collective and shock wave effects in the neutrino signal but cannot remove them completely, and additionally bring about new features in the signal. We illustrate how the progression of the shock wave is reflected in the changing survival probabilities over time, and we show preliminary results on how some of these collective and shock wave induced signatures appear in a detector signal.
Hydraulics of combining flow in a right-angled compound open ...
Indian Academy of Sciences (India)
rectangular channels using Navier–Stokes equations based on Reynolds Stress Turbulence ... The chocking condition and breakdown of junction were also ..... cross-section by the turbulence-induced helical flow cells that cause transverse ...
DNS of fully developed turbulent heat transfer of a viscoelastic drag-reducing flow
Energy Technology Data Exchange (ETDEWEB)
Yu, Bo [Department of Oil and Gas Storage and Transportation Engineering, China University of Petroleum, Beijing 102249 (China); Kawaguchi, Yasuo [Department of Mechanical Engineering, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510 (Japan)
2005-10-01
A direct numerical simulation (DNS) of turbulent heat transfer in a channel flow with a Giesekus model was carried out to investigate turbulent heat transfer mechanism of a viscoelastic drag-reducing flow by additives. The configuration was a fully-developed turbulent channel flow with uniform heat flux imposed on both the walls. The temperature was considered as a passive scalar with the effect of buoyancy force neglected. The Reynolds number based on the friction velocity and half the channel height was 150. Statistical quantities such as root-mean-square temperature fluctuations, turbulent heat fluxes and turbulent Prandtl number were obtained and compared with those of a Newtonian fluid flow. Budget terms of the temperature variance and turbulent heat fluxes were also presented. (author)
DEFF Research Database (Denmark)
Thomas, Sobi; Bates, Alex; Park, Sam
2016-01-01
A minimum balance of plant (BOP) is desired for an open-cathode high temperature polymer electrolyte membrane (HTPEM) fuel cell to ensure low parasitic losses and a compact design. The advantage of an open-cathode system is the elimination of the coolant plate and incorporation of a blower for ox...
Progress in turbulence research
International Nuclear Information System (INIS)
Bradshaw, P.
1990-01-01
Recent developments in experiments and eddy simulations, as an introduction to a discussion of turbulence modeling for engineers is reviewed. The most important advances in the last decade rely on computers: microcomputers to control laboratory experiments, especially for multidimensional imaging, and supercomputers to simulate turbulence. These basic studies in turbulence research are leading to genuine breakthroughs in prediction methods for engineers and earth scientists. The three main branches of turbulence research: experiments, simulations (numerically-accurate three-dimensional, time-dependent solutions of the Navier-Stokes equations, with any empiricism confined to the smallest eddies), and modeling (empirical closure of time-averaged equations for turbulent flow) are discussed. 33 refs
Homogeneous turbulence dynamics
Sagaut, Pierre
2018-01-01
This book provides state-of-the-art results and theories in homogeneous turbulence, including anisotropy and compressibility effects with extension to quantum turbulence, magneto-hydodynamic turbulence and turbulence in non-newtonian fluids. Each chapter is devoted to a given type of interaction (strain, rotation, shear, etc.), and presents and compares experimental data, numerical results, analysis of the Reynolds stress budget equations and advanced multipoint spectral theories. The role of both linear and non-linear mechanisms is emphasized. The link between the statistical properties and the dynamics of coherent structures is also addressed. Despite its restriction to homogeneous turbulence, the book is of interest to all people working in turbulence, since the basic physical mechanisms which are present in all turbulent flows are explained. The reader will find a unified presentation of the results and a clear presentation of existing controversies. Special attention is given to bridge the results obta...
DEFF Research Database (Denmark)
Gilling, Lasse
of resolved inflow turbulence on airfoil simulations in CFD. The detached-eddy simulation technique is used because it can resolve the inflow turbulence without becoming too computationally expensive due to its limited requirements for mesh resolution in the boundary layer. It cannot resolve the turbulence......Wind turbines operate in inflow turbulence whether it originates from the shear in the atmospheric boundary layer or from the wake of other wind turbines. Consequently, the airfoils of the wings experience turbulence in the inflow. The main topic of this thesis is to investigate the effect...... that is formed in attached boundary layers, but the freestream turbulence can penetrate the boundary layer. The idea is that the resolved turbulence from the freestream should mix high momentum flow into the boundary layer and thereby increase the resistance against separation and increase the maximum lift...
Numerical simulation of sediment movement and deposition in a meandering channel
International Nuclear Information System (INIS)
Ghani, U.
2011-01-01
In this research work, predictions have been made for the transport and deposition of incoming sediments in an open channel. Attempt has been made to understand the behavior of sediments flowing in the channel. The geometry consisted of a meandering compound channel with a constant inflow of sediments. For this purpose, 3D version of CFD (Computational Fluid Dynamics) code FLUENT has been used as a research tool. The turbulence closure of Reynolds Averaged Navior-Stokes equation was performed with standard -turbulence model. The Lagrangian particle tracking technique available in the code has been used for modeling sediment movement and deposition. For this purpose, nine different ranges of the particle diameters were released at the inlet of the channel. Initially, the model was validated using point velocities in the downstream direction and discharge values at five cross sections along the meander wavelength. The channel used for simulation purposes had a rectangular section. Once the model validated, it was then used for simulation of sediments. The numerical modeling gave a detailed picture of sediment deposited and transported through the channel. As the model was used with - turbulence model and Lagrangian particle tracking technique and then validated, it showed that when this combination of particle tracking and turbulence closure option will be used, the prediction will be fairly good and trustworthy. A number of numerical experiments were conducted to get the impact of sediment inflow velocity and its diameter on deposition patterns. It showed that boundary shearing stresses and secondary flows had considerable impact on sediment deposition in a river bend. The current study revealed that CFD technique can be used for predicting sediment distribution patterns with reasonable confidence. Such prediction techniques are not only economical but also provide details of complex flow and sediment movement behavior which are difficult to get through
Heated water jet in coflowing turbulent stream
International Nuclear Information System (INIS)
Shirazi, M.A.; McQuivey, R.S.; Keefer, T.N.
1974-01-01
Effects of ambient turbulence on temperature and salinity distributions of heated water and neutrally buoyant saltwater jets were studied for a wide range of densimetric jet Froude numbers, jet discharge velocities, and ambient turbulence levels in a 4-ft-wide channel. Estimates of vertical and lateral diffusivity coefficients for heat and for salt were obtained from salinity and temperature distributions taken at several stations downstream of the injection point. Readily usable correlations are presented for plume center-line temperature, plume width, and trajectory. The ambient turbulence affects the gross behavior characteristics of the plume. The effects vary with the initial jet Froude number and the jet to ambient velocity ratio. Heat and salinity are transported similarly and the finite source dimensions and the initial jet characteristics alter the numerical value of the diffusivity
Reducing Turbulent Transport in Toroidal Configurations via Shaping
International Nuclear Information System (INIS)
Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.
2011-01-01
Recent progress in reducing turbulent transport in stellarators and tokamaks by 3D shaping using a stellarator optimization code in conjunction with a gyrokinetic code is presented. The original applications of the method focussed on ion temperature gradient transport in a quasi-axisymmetric stellarator design. Here, an examination of both other turbulence channels and other starting configurations is initiated. It is found that the designs evolved for transport from ion temperature gradient turbulence also display reduced transport from other transport channels whose modes are also stabilized by improved curvature, such as electron temperature gradient and ballooning modes. The optimizer is also applied to evolving from a tokamak, finding appreciable turbulence reduction for these devices as well. From these studies, improved understanding is obtained of why the deformations found by the optimizer are beneficial, and these deformations are related to earlier theoretical work in both stellarators and tokamaks.
Vincent, Thomas R.; Avramova, Marieta; Canham, James; Higgins, Peter; Bilkey, Natasha; Mugford, Sam T.; Pitino, Marco; Toyota, Masatsugu
2017-01-01
A transient rise in cytosolic calcium ion concentration is one of the main signals used by plants in perception of their environment. The role of calcium in the detection of abiotic stress is well documented; however, its role during biotic interactions remains unclear. Here, we use a fluorescent calcium biosensor (GCaMP3) in combination with the green peach aphid (Myzus persicae) as a tool to study Arabidopsis thaliana calcium dynamics in vivo and in real time during a live biotic interaction. We demonstrate rapid and highly localized plant calcium elevations around the feeding sites of M. persicae, and by monitoring aphid feeding behavior electrophysiologically, we demonstrate that these elevations correlate with aphid probing of epidermal and mesophyll cells. Furthermore, we dissect the molecular mechanisms involved, showing that interplay between the plant defense coreceptor BRASSINOSTEROID INSENSITIVE-ASSOCIATED KINASE1 (BAK1), the plasma membrane ion channels GLUTAMATE RECEPTOR-LIKE 3.3 and 3.6 (GLR3.3 and GLR3.6), and the vacuolar ion channel TWO-PORE CHANNEL1 (TPC1) mediate these calcium elevations. Consequently, we identify a link between plant perception of biotic threats by BAK1, cellular calcium entry mediated by GLRs, and intracellular calcium release by TPC1 during a biologically relevant interaction. PMID:28559475
Markfort, C. D.
2017-12-01
Aquatic ecosystems are integrators of nutrient and carbon from their watersheds. The effects of climate change in many cases will enhance the rate of these inputs and change the thermodynamics within aquatic environments. It is unclear the extent these changes will have on water quality and carbon assimilation, but the drivers of these processes will be determined by the complex interactions at the land-water and air-water interfaces. For example, flow over and beneath wind-driven surface waves generate turbulence that plays an important role in aquatic ecology and biogeochemistry, exchange of gases such as oxygen and carbon dioxide, and it is important for the transfer of energy and controlling evaporation. Energy transferred from the atmosphere promotes the generation and maintenance of waves. A fraction of the energy is transferred to the surface mixed layer through the generation of turbulence. Energy is also transferred back to the atmosphere by waves. There is a need to quantify the details of the coupled boundary layers of the air-water system to better understand how turbulence plays a role in the interactions. We have developed capabilities to conduct field and laboratory experiments using eddy covariance on tall-towers and rafts, UAS platforms integrated with remote sensing, and detailed wind-wave measurements with time-resolved PIV in a new boundary layer wind-wave tunnel. We will show measurements of the detailed structure of the air and water boundary layers under varying wind and wave conditions in the newly developed IIHR Boundary-Layer Wind-Wave Tunnel. The facility combines a 30-m long recirculating water channel with an open-return boundary layer wind tunnel. A thick turbulent boundary layer is developed in the 1 m high air channel, over the water surface, allowing for the study of boundary layer turbulence interacting with a wind-driven wave field. Results will help interpret remote sensing, energy budget measurements, and turbulence transport
Nonlinear wave collapse and strong turbulence
International Nuclear Information System (INIS)
Robinson, P.A.
1997-01-01
The theory and applications of wave self-focusing, collapse, and strongly nonlinear wave turbulence are reviewed. In the last decade, the theory of these phenomena and experimental realizations have progressed rapidly. Various nonlinear wave systems are discussed, but the simplest case of collapse and strong turbulence of Langmuir waves in an unmagnetized plasma is primarily used in explaining the theory and illustrating the main ideas. First, an overview of the basic physics of linear waves and nonlinear wave-wave interactions is given from an introductory perspective. Wave-wave processes are then considered in more detail. Next, an introductory overview of the physics of wave collapse and strong turbulence is provided, followed by a more detailed theoretical treatment. Later sections cover numerical simulations of Langmuir collapse and strong turbulence and experimental applications to space, ionospheric, and laboratory plasmas, including laser-plasma and beam-plasma interactions. Generalizations to self-focusing, collapse, and strong turbulence of waves in other systems are also discussed, including nonlinear optics, solid-state systems, magnetized auroral and astrophysical plasmas, and deep-water waves. The review ends with a summary of the main ideas of wave collapse and strong-turbulence theory, a collection of open questions in the field, and a brief discussion of possible future research directions. copyright 1997 The American Physical Society
Lewis, Bryan; Cimbala, John; Wouden, Alex
2011-11-01
Turbulence models are generally developed to study common academic geometries, such as flat plates and channels. Creating quality computational grids for such geometries is trivial, and allows stringent requirements to be met for boundary layer grid refinement. However, engineering applications, such as flow through hydroturbines, require the analysis of complex, highly curved geometries. To produce body-fitted grids for such geometries, the mesh quality requirements must be relaxed. Relaxing these requirements, along with the complexity of rotating flows, forces turbulence models to be employed beyond their developed scope. This study explores the solution sensitivity to boundary layer grid quality for various turbulence models and boundary conditions currently implemented in OpenFOAM. The following models are resented: k-omega, k-omega SST, k-epsilon, realizable k-epsilon, and RNG k-epsilon. Standard wall functions, adaptive wall functions, and sub-grid integration are compared using various grid refinements. The chosen geometry is the GAMM Francis Turbine because experimental data and comparison computational results are available for this turbine. This research was supported by a grant from the DoE and a National Defense Science and Engineering Graduate Fellowship.
The influence of turbulent bursting on sediment resuspension under unidirectional currents
Directory of Open Access Journals (Sweden)
S. Salim
2017-07-01
Full Text Available Laboratory experiments were conducted in an open channel flume with a flat sandy bed to examine the role of turbulence on sediment resuspension. An acoustic Doppler velocimeter (ADV was used to measure the instantaneous three-dimensional velocity components and acoustic backscatter as a proxy to suspended sediment concentration. Estimates of sediment transport assume that there is a mean critical velocity that needs to be exceeded before sediment transport is initiated. This approach does not consider the turbulent flow field that may initiate sediment resuspension through event-based processes such as the bursting phenomenon. In this paper, laboratory measurements were used to examine the sediment resuspension processes below and above the mean critical velocity. The results within a range above and below the measured mean critical velocity suggested that (1 the contribution of turbulent bursting events remained identical in both experimental conditions, (2 ejection and sweep events contributed more to the total sediment flux than up-acceleration and down-deceleration events, and (3 wavelet transform revealed a correlation between the momentum and sediment flux in both test conditions. Such similarities in conditions above and below the measured mean critical velocity highlight the need to re-evaluate the accuracy of a single time-averaged mean critical velocity for the initiation of sediment entrainment.
Modelling natural convection in a heated vertical channel for room ventilation
International Nuclear Information System (INIS)
Rodrigues, A.M.; Canha da Piedade, A.; Lahellec, A.; Grandpeix, J.Y.
2000-01-01
Solar-air collectors installed on the south-facing walls of school buildings have been tried out in Portugal as a passive means of improving indoor air quality without prejudice to thermal comfort requirements. A numerical investigation of the behaviour of these systems, typified as vertical channels opened at both ends, is presented for typical geometries and outdoor conditions. The study is carried out with natural convection and assumes that the induced flow is turbulent and two-dimensional. The fully averaged equations of motion and energy, added to a two-equation turbulence model, are discretized and solved following the concepts of TEF (Transfer Evolution Formalism) using a finite volume method. Flow and temperature fields are produced and results presented in terms of temperature and velocity distributions at the exit section of the duct. These enable a better understanding of the developing flow and can be helpful in the design phase of this type of system. (author)
Modeling channel interference in an orbital angular momentum-multiplexed laser link
Anguita, Jaime A.; Neifeld, Mark A.; Vasic, Bane V.
2009-08-01
We study the effects of optical turbulence on the energy crosstalk among constituent orbital angular momentum (OAM) states in a vortex-based multi-channel laser communication link and determine channel interference in terms of turbulence strength and OAM state separation. We characterize the channel interference as a function of C2n and transmit OAM state, and propose probability models to predict the random fluctuations in the received signals for such architecture. Simulations indicate that turbulence-induced channel interference is mutually correlated across receive channels.
Plasma Turbulence General Topics
Energy Technology Data Exchange (ETDEWEB)
Kadomtsev, B. B. [Nuclear Energy Institute, Academy of Sciences of the USSR, Moscow, USSR (Russian Federation)
1965-06-15
It is known that under experimental conditions plasma often shows chaotic motion. Such motion, when many degrees of freedom are excited to levels considerably above the thermal level, will be called turbulent. The properties of turbulent plasma in many respects differ from the properties of laminar plasma. It can be said that the appearance of various anomalies in plasma behaviour indicates the presence of turbulence in plasma. In order to verify directly the presence of turbulent motion in plasma we must, however, measure the fluctuation of some microscopic parameters in plasma.
A theoretical description of inhomogeneous turbulence
International Nuclear Information System (INIS)
Turner, L.
2000-01-01
This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). In this LDRD, we have developed a highly compact and descriptive formalism that allows us to broach the theoretically formidable morass of inhomogeneous turbulence. Our formalism has two novel aspects: (a) an adaptation of helicity basis functions to represent an arbitrary incompressible channel flow and (b) the invocation of a hypothesis of random phase. A result of this compact formalism is that the mathematical description of inhomogeneous turbulence looks much like that of homogeneous turbulence--at the moment, the most rigorously explored terrain in turbulence research. As a result, we can explore the effect of boundaries on such important quantities as the gradients of mean flow, mean pressure, triple-velocity correlations and pressure velocity correlations, all of which vanish under the conventional, but artificial, assumption that the turbulence is statistically spatially uniform. Under suitable conditions, we have predicted that a mean flow gradient can develop even when none is initially present
On the mechanism of elasto-inertial turbulence.
Dubief, Yves; Terrapon, Vincent E; Soria, Julio
2013-11-01
Elasto-inertial turbulence (EIT) is a new state of turbulence found in inertial flows with polymer additives. The dynamics of turbulence generated and controlled by such additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 (based on the bulk and the channel height) are used to study the formation and dynamics of elastic instabilities and their effects on the flow. The flow topology of EIT is found to differ significantly from Newtonian wall-turbulence. Structures identified by positive (rotational flow topology) and negative (extensional/compressional flow topology) second invariant Q a isosurfaces of the velocity gradient are cylindrical and aligned in the spanwise direction. Polymers are significantly stretched in sheet-like regions that extend in the streamwise direction with a small upward tilt. The Q a cylindrical structures emerge from the sheets of high polymer extension, in a mechanism of energy transfer from the fluctuations of the polymer stress work to the turbulent kinetic energy. At subcritical Reynolds numbers, EIT is observed at modest Weissenberg number ( Wi , ratio polymer relaxation time to viscous time scale). For supercritical Reynolds numbers, flows approach EIT at large Wi . EIT provides new insights on the nature of the asymptotic state of polymer drag reduction (maximum drag reduction), and explains the phenomenon of early turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian flows observed in some polymeric flows.