Topology optimization of Channel flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan; Sigmund, Ole; Haber, R. B.
2005-01-01
function which measures either some local aspect of the velocity field or a global quantity, such as the rate of energy dissipation. We use the finite element method to model the flow, and we solve the optimization problem with a gradient-based math-programming algorithm that is driven by analytical...... sensitivities. Our target application is optimal layout design of channels in fluid network systems. Using concepts borrowed from topology optimization of compliant mechanisms in solid mechanics, we introduce a method for the synthesis of fluidic components, such as switches, diodes, etc....
Selected problems of gas-liquid flow through the channels filled with metal foams
Directory of Open Access Journals (Sweden)
Dyga Roman
2017-01-01
Full Text Available Open-cell metal foams are relatively unknown type of cellular material, which is increasingly being used as structural packing in the industrial equipment. The paper presents an analysis of experimental results on heat transfer and hydrodynamics of gas-liquid two-phase flow through the channels filled with metal foams. The research included the registration of temperature and pressure changes on fluid flow path. Furthermore the phase void fraction was measured and flow patterns in present in the channel were observed. It was found that in two-phase flow, both from heat transfer and hydrodynamics of flow point of view, the liquid plays the dominant role. It was also found a significant influence of flow patterns on frictional pressure loss value and phase void fraction. Whereas the flow patterns and geometry of the foam in much lesser extent influence on the intensity of heat transfer. Type of gas-liquid flow patterns primarily depends on flow conditions, including the velocity and properties of fluids. On the other hand, it wasn’t stated any significant effect of geometrical parameters of foam on the type of flow and the value of phase void fraction. Among many flow patterns observed during the study, there have been identified four basic structures: plug, semi-slug, slug, and stratified.
On the solution of fluid flow and heat transfer problem in a 2D channel with backward-facing step
Directory of Open Access Journals (Sweden)
Alexander A. Fomin
2017-06-01
Full Text Available The stable stationary solutions of the test problem of hydrodynamics and heat transfer in a plane channel with the backward-facing step have been considered in the work for extremely high Reynolds numbers and expansion ratio of the stream $ER$. The problem has been solved by numerical integration of the 2D Navier–Stokes equations in ‘velocity-pressure’ formulation and the heat equation in the range of Reynolds number $500 \\leqslant \\mathrm{ Re} \\leqslant 3000$ and expansion ratio $1.43 \\leqslant ER \\leqslant 10$ for Prandtl number $\\mathrm{ Pr} = 0.71$. Validity of the results has been confirmed by comparing them with literature data. Detailed flow patterns, fields of stream overheating, and profiles of horizontal component of velocity and relative overheating of flow in the cross section of the channel have been presented. Complex behaviors of the coefficients of friction, hydrodynamic resistance and heat transfer (Nusselt number along the channel depending on the problem parameters have been analyzed.
Problem of Channel Utilization and Merging Flows in Buffered Optical Burst Switching Networks
Directory of Open Access Journals (Sweden)
Milos Kozak
2013-01-01
Full Text Available In the paper authors verify two problems of methods of operational research in optical burst switching. The first problem is at edge node, related to the medium access delay. The second problem is at an intermediate node related to buffering delay. A correction coefficient K of transmission speed is obtained from the first analysis. It is used in to provide a full-featured link of nominal data rate. Simulations of the second problem reveal interesting results. It is not viable to prepare routing and wavelength assignment based on end-to-end delay, i.e. link's length or number of hops, as commonly used in other frameworks (OCS, Ethernet, IP, etc. nowadays. Other parameters such as buffering probability must be taken into consideration as well. Based on the buffering probability an estimation of the number of optical/electrical converters can be made. This paper concentrates important traffic constraints of buffered optical burst switching. It allows authors to prepare optimization algorithms for regenerators placement in CAROBS networks using methods of operational research.
Precipitation patterns during channel flow
Jamtveit, B.; Hawkins, C.; Benning, L. G.; Meier, D.; Hammer, O.; Angheluta, L.
2013-12-01
Mineral precipitation during channelized fluid flow is widespread in a wide variety of geological systems. It is also a common and costly phenomenon in many industrial processes that involve fluid flow in pipelines. It is often referred to as scale formation and encountered in a large number of industries, including paper production, chemical manufacturing, cement operations, food processing, as well as non-renewable (i.e. oil and gas) and renewable (i.e. geothermal) energy production. We have studied the incipient stages of growth of amorphous silica on steel plates emplaced into the central areas of the ca. 1 meter in diameter sized pipelines used at the hydrothermal power plant at Hellisheidi, Iceland (with a capacity of ca 300 MW electricity and 100 MW hot water). Silica precipitation takes place over a period of ca. 2 months at approximately 120°C and a flow rate around 1 m/s. The growth produces asymmetric ca. 1mm high dendritic structures ';leaning' towards the incoming fluid flow. A novel phase-field model combined with the lattice Boltzmann method is introduced to study how the growth morphologies vary under different hydrodynamic conditions, including non-laminar systems with turbulent mixing. The model accurately predicts the observed morphologies and is directly relevant for understanding the more general problem of precipitation influenced by turbulent mixing during flow in channels with rough walls and even for porous flow. Reference: Hawkins, C., Angheluta, L., Hammer, Ø., and Jamtveit, B., Precipitation dendrites in channel flow. Europhysics Letters, 102, 54001
Mann, Philip H.; Suiter, Patricia A.
This teacher's guide contains a list of general auditory problem areas where students have the following problems: (a) inability to find or identify source of sound; (b) difficulty in discriminating sounds of words and letters; (c) difficulty with reproducing pitch, rhythm, and melody; (d) difficulty in selecting important from unimportant sounds;…
Free-Molecular Gas Flow in Narrow (Nanoscale) Channel
Levdansky, V.V.; Roldugin, V.I.; Žďanov, V.M.; V. Ždímal
2014-01-01
Free-molecular gas flow in cylindrical channels (capillaries) in various schemes of molecule scattering by channel walls in view of surface diffusion is considered. The problem of separation of gas mixtures in their flow through membranes with nanopores is studied. The problem of uniform deposition of thin films on the inner surface of the fine cylindrical channel is discussed.
Parameter estimation in channel network flow simulation
Directory of Open Access Journals (Sweden)
Han Longxi
2008-03-01
Full Text Available Simulations of water flow in channel networks require estimated values of roughness for all the individual channel segments that make up a network. When the number of individual channel segments is large, the parameter calibration workload is substantial and a high level of uncertainty in estimated roughness cannot be avoided. In this study, all the individual channel segments are graded according to the factors determining the value of roughness. It is assumed that channel segments with the same grade have the same value of roughness. Based on observed hydrological data, an optimal model for roughness estimation is built. The procedure of solving the optimal problem using the optimal model is described. In a test of its efficacy, this estimation method was applied successfully in the simulation of tidal water flow in a large complicated channel network in the lower reach of the Yangtze River in China.
Catalytic reaction in confined flow channel
Energy Technology Data Exchange (ETDEWEB)
Van Hassel, Bart A.
2016-03-29
A chemical reactor comprises a flow channel, a source, and a destination. The flow channel is configured to house at least one catalytic reaction converting at least a portion of a first nanofluid entering the channel into a second nanofluid exiting the channel. The flow channel includes at least one turbulating flow channel element disposed axially along at least a portion of the flow channel. A plurality of catalytic nanoparticles is dispersed in the first nanofluid and configured to catalytically react the at least one first chemical reactant into the at least one second chemical reaction product in the flow channel.
Improved convection cooling in steady channel flows
Alben, Silas
2017-10-01
A fundamental problem in heat transfer is the convective cooling of the heated walls of a channel. We find steady two-dimensional (2D) flows that maximize the heat removed from fixed-temperature walls for a given rate of energy used to drive the flow, Pe2 (Pe is the Peclet number, a dimensionless flow speed). For parabolic (Poiseuille) flow, the heat transfer scales as Pe1/3. Starting from Poiseuille flow, we compute a sequence of optima using Newton's method with continuation. Computed optimal flows are found to be approximately unidirectional and nearly uniform outside of sharp boundary layers at the channel walls. A linear approximation near Poiseuille flow shows how the thermal boundary layer generates a boundary layer in the optimal flow. We are thus led to compute optimal unidirectional flows with boundary layers, for which the heat transfer scales as Pe2/5, an improvement over the Pe1/3 Poiseuille flow scaling. The optimal flows have viscous dissipation concentrated in boundary layers of thickness ˜Pe-2/5 at the channel walls, and have a uniform velocity ˜Pe4/5 outside the boundary layers. We explain the scalings using physical and mathematical arguments. We also show that with channels of aspect ratio (length/height) L , the outer flow speed scales as L-1 /5 and the boundary layer thickness scales as L3 /5 in the unidirectional approximation. At the Reynolds numbers near the turbulent transition for 2D Poiseuille flow in air, we find a 60% increase in heat transferred over that of Poiseuille flow.
Interacting divided channel method for compound channel flow
Huthoff, Freek; Roos, Pieter C.; Augustijn, Dionysius C.M.; Hulscher, Suzanne J.M.H.
2008-01-01
A new method to calculate flow in compound channels is proposed: the interacting divided channel method (IDCM), based on a new parametrization of the interface stress between adjacent flow compartments, typically between the main channel and floodplain of a two-stage channel. This expression is
Turbulent flow in two-inlet channels
Energy Technology Data Exchange (ETDEWEB)
Kao, H.C. [NASA, Cleveland, OH (United States). Lewis Research Center
1993-12-01
The problem of turbulent flows in two-inlet channels has been studied numerically by solving the Reynolds-averaged Navier-Stokes equations with the {kappa}-{epsilon} model in a mapped domain. Both the high Reynolds number and the low Reynolds number form were used for this purpose. In general, the former predicts a weaker and smaller recirculation zone that the latter. Comparisons with experimental data, when applicable, were also made. The bulk of the present computations used, however, the high Reynolds number form to correlate different geometries and inflow conditions with the flow properties after turning.
Flow and sediment transport across oblique channels
DEFF Research Database (Denmark)
Hjelmager Jensen, Jacob; Madsen, Erik Østergaard; Fredsøe, Jørgen
1998-01-01
A 3D numerical investigation of flow across channels aligned obliquely to the main flow direction has been conducted. The applied numerical model solves the Reynolds-averaged Navier-Stokes equations using the k-ε model for turbulence closure on a curvilinear grid. Three momentum equations...... are solved, but the computational domain is 2D due to a uniformity along the channel alignment. Two important flow features arise when the flow crosses the channel: (i) the flow will be refracted in the direction of the channel alignment. This may be described by a depth-averaged model. (ii) due to shear...
Developing laminar flow in curved rectangular channels
De Vriend, H.J.
1978-01-01
As an intermediate step between earlier investigations on fully developed laminar flow in curved channels of shallow rectancular wet cross-section and the mathematical modeling of turbulent flow in river bends, a mathematical model of developing laminar flow in such channels is investigated. The
Computational open-channel hydraulics for movable-bed problems
Lai, Chintu; ,
1990-01-01
As a major branch of computational hydraulics, notable advances have been made in numerical modeling of unsteady open-channel flow since the beginning of the computer age. According to the broader definition and scope of 'computational hydraulics,' the basic concepts and technology of modeling unsteady open-channel flow have been systematically studied previously. As a natural extension, computational open-channel hydraulics for movable-bed problems are addressed in this paper. The introduction of the multimode method of characteristics (MMOC) has made the modeling of this class of unsteady flows both practical and effective. New modeling techniques are developed, thereby shedding light on several aspects of computational hydraulics. Some special features of movable-bed channel-flow simulation are discussed here in the same order as given by the author in the fixed-bed case.
HANARO core channel flow-rate measurement
Energy Technology Data Exchange (ETDEWEB)
Kim, Heon Il; Chae, Hee Tae; Im, Don Soon; Kim, Seon Duk [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)
1996-06-01
HANARO core consists of 23 hexagonal flow tubes and 16 cylindrical flow tubes. To get the core flow distribution, we used 6 flow-rate measuring dummy fuel assemblies (instrumented dummy fuel assemblies). The differential pressures were measured and converted to flow-rates using the predetermined relationship between AP and flow-rate for each instrumented dummy fuel assemblies. The flow-rate for the cylindrical flow channels shows +-7% relative errors and that for the hexagonal flow channels shows +-3.5% relative errors. Generally the flow-rates of outer core channels show smaller values compared to those of inner core. The channels near to the core inlet pipe and outlet pipes also show somewhat lower flow-rates. For the lower flow channels, the thermal margin was checked by considering complete linear power histories. From the experimental results, the gap flow-rate was estimated to be 49.4 kg/s (cf. design flow of 50 kg/s). 15 tabs., 9 figs., 10 refs. (Author) .new.
An experimental study of rip channel flow
DEFF Research Database (Denmark)
Drønen, Nils Kjetil; Karunarathna, H.; Fredsøe, Jørgen
2002-01-01
A laboratory study of the flow over a bar with a single rip channel has been performed. First, the well-known pattern of a bar circulation cell with a strong offshore-directed current out through the rip channel and a weaker onshore-directed return flow over the bar is documented. Then measurements...... of the three-dimensional structure of the flow in the area where the rip channel, the bar and the trough meet and well inside the rip channel are presented. These measurements reveal that 3D effects play an important role, and that a depth-integrated viewpoint may not always be sufficient for predicting...
Inertial (non-Darcian) channeled seepage flow
Foda, Mostafa A.
1994-10-01
A slow wave solution is identified for an infinite elastic medium intersected by a two-dimensional fluid channel. Because the wave speed is much slower than the medium's elastic shear wave, the response in the elastic medium is governed by elastostatics. The inertia of the wave is essentially focused in the fluid channel. Furthermore, wave damping is caused by fluid viscous friction on the channel in an elastic solid. It is proposed that these solutions may also be used in the case of a granular porous medium. The seepage channels would then represent a network of preferential flow paths. Therefore we would allow, in this case, the channel porosity to be different from the average granular porosity. For a strongly channel seepage flow or for a low channel porosity the solution is shown to approach that of a single-channel solution, giving rise to a slow propagating wave mode. On the other hand, for weak channeling or nearly `homogeneous' seepage flow the solution is shown to reproduce Biot's (1956) critically damped wave of the second kind. It is proposed that the resonance observed by Foda and Tzang (1994) are in the form of these strongly channeled wave modes.
Stability of flowing open fluidic channels
Directory of Open Access Journals (Sweden)
Jue Nee Tan
2013-02-01
Full Text Available Open fluidic systems have a distinct advantage over enclosed channels in that the fluids exposed nature makes for easy external interaction, this finds uses in introduction of samples by adding liquid droplets or from the surrounding gaseous medium. This work investigates flowing open channels and films, which can potentially make use of the open section of the system as an external interface, before bringing the sample into an enclosed channel. Clearly, in this scenario a key factor is the stability of the flowing open fluid. The open channels investigated include a straight open channel defined by a narrow strip of solid surface, the edges of which allow large contact angle hysteresis, and a wider structure allowing for multiple inputs and outputs. A model is developed for fluid flow, and the findings used to describe the process of failure in both cases.
Dual-view flow channel visualization
Hibara, A.; Kaxama, Y; Carlen, Edwin; van den Berg, Albert
2014-01-01
The concept of dual-view flow-channel visualization is proposed, where ordinary (top) and lateral images are available in a single view field. In order to obtain the top and lateral fluidic-channel images in a single view of the microscope observation, optical path lengths of these images were
Atlantic water flow through the Faroese Channels
Directory of Open Access Journals (Sweden)
B. Hansen
2017-11-01
Full Text Available Through the Faroese Channels – the collective name for a system of channels linking the Faroe–Shetland Channel, Wyville Thomson Basin, and Faroe Bank Channel – there is a deep flow of cold waters from Arctic regions that exit the system as overflow through the Faroe Bank Channel and across the Wyville Thomson Ridge. The upper layers, in contrast, are dominated by warm, saline water masses from the southwest, termed Atlantic water. In spite of intensive research over more than a century, there are still open questions on the passage of these waters through the system with conflicting views in recent literature. Of special note is the suggestion that there is a flow of Atlantic water from the Faroe–Shetland Channel through the Faroe Bank Channel, which circles the Faroes over the slope region in a clockwise direction. Here, we combine the observational evidence from ship-borne hydrography, moored current measurements, surface drifter tracks, and satellite altimetry to address these questions and propose a general scheme for the Atlantic water flow through this channel system. We find no evidence for a continuous flow of Atlantic water from the Faroe–Shetland Channel to the Faroe Bank Channel over the Faroese slope. Rather, the southwestward-flowing water over the Faroese slope of the Faroe–Shetland Channel is totally recirculated within the combined area of the Faroe–Shetland Channel and Wyville Thomson Basin, except possibly for a small release in the form of eddies. This does not exclude a possible westward flow over the southern tip of the Faroe Shelf, but even including that, we estimate that the average volume transport of a Circum-Faroe Current does not exceed 0.5 Sv (1 Sv = 106 m3 s−1. Also, there seems to be a persistent flow of Atlantic water from the western part of the Faroe Bank Channel into the Faroe–Shetland Channel that joins the Slope Current over the Scottish slope. These conclusions will affect
Atlantic water flow through the Faroese Channels
Hansen, Bogi; Poulsen, Turið; Margretha Húsgarð Larsen, Karin; Hátún, Hjálmar; Østerhus, Svein; Darelius, Elin; Berx, Barbara; Quadfasel, Detlef; Jochumsen, Kerstin
2017-11-01
Through the Faroese Channels - the collective name for a system of channels linking the Faroe-Shetland Channel, Wyville Thomson Basin, and Faroe Bank Channel - there is a deep flow of cold waters from Arctic regions that exit the system as overflow through the Faroe Bank Channel and across the Wyville Thomson Ridge. The upper layers, in contrast, are dominated by warm, saline water masses from the southwest, termed Atlantic water. In spite of intensive research over more than a century, there are still open questions on the passage of these waters through the system with conflicting views in recent literature. Of special note is the suggestion that there is a flow of Atlantic water from the Faroe-Shetland Channel through the Faroe Bank Channel, which circles the Faroes over the slope region in a clockwise direction. Here, we combine the observational evidence from ship-borne hydrography, moored current measurements, surface drifter tracks, and satellite altimetry to address these questions and propose a general scheme for the Atlantic water flow through this channel system. We find no evidence for a continuous flow of Atlantic water from the Faroe-Shetland Channel to the Faroe Bank Channel over the Faroese slope. Rather, the southwestward-flowing water over the Faroese slope of the Faroe-Shetland Channel is totally recirculated within the combined area of the Faroe-Shetland Channel and Wyville Thomson Basin, except possibly for a small release in the form of eddies. This does not exclude a possible westward flow over the southern tip of the Faroe Shelf, but even including that, we estimate that the average volume transport of a Circum-Faroe Current does not exceed 0.5 Sv (1 Sv = 106 m3 s-1). Also, there seems to be a persistent flow of Atlantic water from the western part of the Faroe Bank Channel into the Faroe-Shetland Channel that joins the Slope Current over the Scottish slope. These conclusions will affect potential impacts from offshore activities in the
Flow Through A Horizontal Porous Channel With A Harmonic ...
African Journals Online (AJOL)
In this research work we provide a finite element solution to the problem of the flow through a horizontal channel with a harmonic pressure gradient. Results obtained shows that the ... due to the viscous dissipation effect. Keywords: Asymptotic techniques, Maxwell fluid, constantly accelerating plates and velocity fields.
Convection surrounding mesoscale ionospheric flow channels
Rinne, Y.; Moen, J.; Baker, J. B. H.; Carlson, H. C.
2011-05-01
We evaluate data from the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and Defense Meteorological Satellite Program (DMSP) spacecraft coupled with data from the Super Dual Auroral Radar Network (SuperDARN) polar cap convection patterns in order to study how the ionospheric convection evolves around a sequence of transient, mesoscale flow channel events in the duskside of the cusp inflow region. On a northwestward convection background for the interplanetary magnetic field (IMF) BY positive and BZ negative, a sequence of three eastward flow channels formed over the course of 1 hour in response to three sharp IMF rotations to IMF BY negative and IMF BZ positive. The first and third channels, due to IMF BY negative periods of ˜13 min and >30 min, respectively, develop in a similar manner: they span the entire ESR field of view and widen poleward with increasing time elapsed since their first appearance until the IMF rotates back. The convection patterns are consistent with the line-of-sight data from the ESR and DMSP within a 10 min adaption time. The flow lines form a twin-vortex flow, with the observed channel being the twin vortices' center flow. The fitting algorithm was pushed to its limits in terms of spatial resolution in this study. During portions of the channel events, the suggested twin-cell flow is not in agreement with our physical interpretation of the flow channels being reconnection events because cell closure is suggested across an anticipated nonreconnecting open-closed boundary. For these segments, we present simulated patterns which have been arrived at by a combination of looking at the raw data and examining the fitted convection patterns.
Flow of MHD Carreau Fluid in a Curved Channel
Directory of Open Access Journals (Sweden)
Saima Noreen
2013-01-01
Full Text Available Analysis has been made for the curvature effects on the MHD peristaltic flow of an incompressible Carreau fluid in a channel. The flow problem is first reduced in the wave frame of reference and then solved after employing the long wavelength and low Reynolds number approximations. Expressions of stream function, pressure gradient, magnetic force function, induced magnetic field and current density are derived and then examined for various parameters of interest.
Application of the GRP scheme to open channel flow equations
Birman, A.; Falcovitz, J.
2007-03-01
The GRP (generalized Riemann problem) scheme, originally conceived for gasdynamics, is reformulated for the numerical integration of the shallow water equations in channels of rectangular cross-section, variable width and bed profile, including a friction model for the fluid-channel shear stress. This scheme is a second-order analytic extension of the first-order Godunov-scheme, based on time-derivatives of flow variables at cell-interfaces resulting from piecewise-linear data reconstruction in cells. The second-order time-integration is based on solutions to generalized Riemann problems at cell-interfaces, thus accounting for the full governing equations, including source terms. The source term due to variable bed elevation is treated in a well-balanced way so that quiescent flow is exactly replicated; this is done by adopting the Surface Gradient Method (SGM). Several problems of steady or unsteady open channel flow are considered, including the terms corresponding to variable channel width and bed elevation, as well as to shear stress at the fluid-channel interface (using the Manning friction model). In all these examples remarkable agreement is obtained between the numerical integration and the exact or accurate solutions.
Mathematical model of two-phase flow in accelerator channel
Directory of Open Access Journals (Sweden)
О.Ф. Нікулін
2010-01-01
Full Text Available The problem of two-phase flow composed of energy-carrier phase (Newtonian liquid and solid fine-dispersed phase (particles in counter jet mill accelerator channel is considered. The mathematical model bases goes on the supposition that the phases interact with each other like independent substances by means of aerodynamics’ forces in conditions of adiabatic flow. The mathematical model in the form of system of differential equations of order 11 is represented. Derivations of equations by base physical principles for cross-section-averaged quantity are produced. The mathematical model can be used for estimation of any kinematic and thermodynamic flow characteristics for purposely parameters optimization problem solving and transfer functions determination, that take place in counter jet mill accelerator channel design.
Turbulent channel flows over complex walls
Rosti, Marco Edoardo; Brandt, Luca
2017-11-01
We perform numerical simulations of turbulent channel flows over porous walls and deformable hyper-elastic walls. The flow over porous walls is simulated using volume-averaged Navier ``Stokes equations within the porous layers, while the multiphase flow over deformable walls is solved with a one-continuum formulation which allows the use of a fully Eulerian formulation. New insights on the effect of these complex walls on the turbulent flows in terms of friction, statistics and flow structures are discussed using a number of post-processing techniques. The turbulent flow in the channel is affected by the porous and moving walls in a similar manner even at low values of porosity and elasticity due to the non-zero fluctuations of vertical velocity at the interface that influence the flow dynamics. The near-wall streaks and the associated quasi-streamwise vortices are strongly reduced near porous and deformable isotropic wall while the flow becomes more correlated in the spanwise direction. On the contrary, an opposite behavior is noticed in the case of anisotropic porous layers, with an increase of streamwise correlation due to a strengthening of the low- and high-speed streaks.
Central schemes for open-channel flow
Gottardi, Guido; Venutelli, Maurizio
2003-03-01
The resolution of the Saint-Venant equations for modelling shock phenomena in open-channel flow by using the second-order central schemes of Nessyahu and Tadmor (NT) and Kurganov and Tadmor (KT) is presented. The performances of the two schemes that we have extended to the non-homogeneous case and that of the classical first-order Lax-Friedrichs (LF) scheme in predicting dam-break and hydraulic jumps in rectangular open channels are investigated on the basis of different numerical and physical conditions. The efficiency and robustness of the schemes are tested by comparing model results with analytical or experimental solutions.
Flow through a very porous obstacle in a shallow channel
Creed, M. J.; Draper, S.; Nishino, T.; Borthwick, A. G. L.
2017-04-01
A theoretical model, informed by numerical simulations based on the shallow water equations, is developed to predict the flow passing through and around a uniform porous obstacle in a shallow channel, where background friction is important. This problem is relevant to a number of practical situations, including flow through aquatic vegetation, the performance of arrays of turbines in tidal channels and hydrodynamic forces on offshore structures. To demonstrate this relevance, the theoretical model is used to (i) reinterpret core flow velocities in existing laboratory-based data for an array of emergent cylinders in shallow water emulating aquatic vegetation and (ii) reassess the optimum arrangement of tidal turbines to generate power in a tidal channel. Comparison with laboratory-based data indicates a maximum obstacle resistance (or minimum porosity) for which the present theoretical model is valid. When the obstacle resistance is above this threshold the shallow water equations do not provide an adequate representation of the flow, and the theoretical model over-predicts the core flow passing through the obstacle. The second application of the model confirms that natural bed resistance increases the power extraction potential for a partial tidal fence in a shallow channel and alters the optimum arrangement of turbines within the fence.
Partial obstruction of flow through a channel
Araújo, A. D.; Lima, Izael A.; Almeida, M. P.; Grotberg, J. B.; Andrade, José S.
2018-02-01
We study the disturbance on two-dimensional flow generated by a circular obstacle of radius r placed downwind in front of a duct of width w at a distance λ between the center of the obstacle and the inlet position of the channel. Our results show that, at low Reynolds conditions, the flux ϕ at the duct exhibits distinct regimes for different λ intervals.
Modelling debris flows down general channels
Directory of Open Access Journals (Sweden)
S. P. Pudasaini
2005-01-01
Full Text Available This paper is an extension of the single-phase cohesionless dry granular avalanche model over curved and twisted channels proposed by Pudasaini and Hutter (2003. It is a generalisation of the Savage and Hutter (1989, 1991 equations based on simple channel topography to a two-phase fluid-solid mixture of debris material. Important terms emerging from the correct treatment of the kinematic and dynamic boundary condition, and the variable basal topography are systematically taken into account. For vanishing fluid contribution and torsion-free channel topography our new model equations exactly degenerate to the previous Savage-Hutter model equations while such a degeneration was not possible by the Iverson and Denlinger (2001 model, which, in fact, also aimed to extend the Savage and Hutter model. The model equations of this paper have been rigorously derived; they include the effects of the curvature and torsion of the topography, generally for arbitrarily curved and twisted channels of variable channel width. The equations are put into a standard conservative form of partial differential equations. From these one can easily infer the importance and influence of the pore-fluid-pressure distribution in debris flow dynamics. The solid-phase is modelled by applying a Coulomb dry friction law whereas the fluid phase is assumed to be an incompressible Newtonian fluid. Input parameters of the equations are the internal and bed friction angles of the solid particles, the viscosity and volume fraction of the fluid, the total mixture density and the pore pressure distribution of the fluid at the bed. Given the bed topography and initial geometry and the initial velocity profile of the debris mixture, the model equations are able to describe the dynamics of the depth profile and bed parallel depth-averaged velocity distribution from the initial position to the final deposit. A shock capturing, total variation diminishing numerical scheme is implemented to
Flow of foam through a convergent channel.
Dollet, Benjamin; Bocher, Claire
2015-11-01
We study experimentally the flow of a foam confined as a bubble monolayer between two plates through a convergent channel. We quantify the velocity, the distribution and orientation of plastic events, and the elastic stress, using image analysis. We use two different soap solutions: a sodium dodecyl sulfate (SDS) solution, with a negligible wall friction between the bubbles and the confining plates, and a mixture containing a fatty acid, giving a large wall friction. We show that for SDS solutions, the velocity profile obeys a self-similar form which results from the superposition of plastic events, and the elastic deformation is uniform. For the other solution, the velocity field differs and the elastic deformation increases towards the exit of the channel. We discuss and quantify the role of wall friction on the velocity profile, the elastic deformation, and the rate of plastic events.
Stability of stratified two-phase flows in horizontal channels
Barmak, Ilya; Ullmann, Amos; Brauner, Neima; Vitoshkin, Helen
2016-01-01
Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems the stratified flow with smooth interface is stable only in confined zone of relatively lo...
Stable Riprap Size for Open Channel Flows
1988-03-01
accomplish these objectives by- studying the stability and resistance to flow of riprap having grada - tion, thickness, and shape similar to that used for...Incipient motion could not be used in this study because it would not allow determination of the effects of riprap grada - tion or thickness. 3.4 TEST...104 Table 4.15 Analysis of Dorena Dam Prototype Data IV:2H Side Slope, Straight Channel Right Esti- /2 or Grada - mated Depth V 1/2 Sta- Left V Over
Vortex statistics in turbulent channel flows
Elsas, José Hugo; Augusto Moriconi, Luca Roberto
2016-11-01
In order to address the role of coherent structures in wall bounded turbulence, we study the statistics of morphological and kinematic properties of vortices, such as circulation, radius and height distributions. To accomplish that, we introduce a novel vortex identification method named as "vorticity curvature criterion" which is based on the local properties of the vorticity field. We furthermore employ a background subtraction procedure to remove shearing background effects expected to be present in the topology of the streamwise/wall-normal plane flow configurations. We discuss, through a comparative study of performance with the usual swirling strength criterion, and extending the previous analyses to the detection of coherent structures in the spanwise/wall normal planes, isotropization issues for the paradigmatic case of numerical turbulent channel flows. We acknowledge the funding from CNPq, CAPES and Faperj.
Effect of bubble deformability on the vertical channel bubbly flow
Dabiri, Sadegh; Lu, Jiacai; Tryggvason, Gretar
2012-01-01
This article describes the fluid dynamics video: "Effect of bubble deformability on the vertical channel bubbly flow". The effect of bubble deformability on the flow rate of bubbly upflow in a turbulent vertical channel is examined using direct numerical simulations. A series of simulations with bubbles of decreasing deformability reveals a sharp transition from a flow with deformable bubbles uniformly distributed in the middle of the channel to a flow with nearly spherical bubbles with a wal...
The additivity problem and constrained quantum channels
Holevo, A. S.
2005-06-01
We give formulations of the famous additivity conjecture for several important quantities characterizing quantum channel and prove their global equivalence to the additivity of the classical capacity of a channel under input constrains (like mean energy constrain).
Effects of Parallel Channel Interactions, Steam Flow, Liquid Subcool ...
African Journals Online (AJOL)
Tests were performed to examine the effects of parallel channel interactions, steam flow, liquid subcool and channel heat addition on the delivery of liquid from the upper plenum into the channels and lower plenum of Boiling Water Nuclear Power Reactors during reflood transients. Early liquid delivery into the channels, ...
Experiments on Unsteady Seperating Flow in an Open Channel
Koppel, T.
1981-01-01
Experiments on unsteady separating flow past a sudden expansion in an open channel are described. To simulate tidal flow the flow rate in the approach channel varied as a half-sine with time. Different visualization techniques to obtain an insight into the behaviour of the separating vortex in time
Characteristics of two-phase flows in large diameter channels
Energy Technology Data Exchange (ETDEWEB)
Schlegel, J.P., E-mail: schlegelj@mst.edu [Department of Mining and Nuclear Engineering, Missouri University of Science and Technology, 301 W 14th St., Rolla, MO 65401 (United States); Hibiki, T.; Ishii, M. [School of Nuclear Engineering, Purdue University, 400 Central Dr., West Lafayette, IN 47907 (United States)
2016-12-15
Two-phase flows in large diameter channels have a great deal of importance in a wide variety of industrial applications. Nuclear systems, petroleum refineries, and chemical processes make extensive use of larger systems. Flows in such channels have very different properties from flows in smaller channels which are typically used in experimental research. In this paper, the various differences between flows in large and small channels are highlighted using the results of previous experimental and analytical research. This review is followed by a review of recent experiments in and model development for flows in large diameter channels performed by the authors. The topics of these research efforts range from void fraction and interfacial area concentration measurement to flow regime identification and modeling, drift-flux modeling for high void fraction conditions, and evaluation of interfacial area transport models for large diameter channels.
Optimization of Meridional Flow Channel Design of Pump Impeller
Miyauchi Sunao; Horiguchi Hironori; Fukutomi Jun-ichirou; Takahashi Akihiro
2004-01-01
The meridional flow channel design of a pump impeller affects its performance. However, since so many design parameters exist, a new design method is proposed in which a meridional and blade-to-blade flow channel is designed by the parallel use of the circulation distribution provided by the designer. Thus, an optimization method was used to design an axis-symmetrical meridional flow channel from the circulation distribution. In addition, the inverse design method proposed by Zangeneh et al. ...
Parametric analysis of laminar pulsating flow in a rectangular channel
Blythman, Richard; Alimohammadi, Sajad; Persoons, Tim; Jeffers, Nick; Murray, Darina B.
2017-10-01
Pulsating flow has potential for enhanced cooling of future electronics and photonics systems. To better understand the mechanisms underlying any heat transfer enhancement, it is necessary to decouple the mechanical and thermal problems. The current work performs a parametric analysis of the flow hydrodynamics using particle image velocimetry (PIV) measurements, CFD simulations and analytical solutions, reorganised in terms of amplitude and phase values using complex notation. To the best of the authors' knowledge, the frequency-dependent behaviour of amplitude and phase of wall shear stress has not been studied in a two-dimensional channel. For laminar flow, the amplitudes are directly proportional to pressure. The amplitudes of various local and mean wall shear stress measures are augmented with frequency compared to steady flow, especially near the short walls and corners. The phases of wall shear stress differ at each wall at moderate frequencies - with the bulk-mean values at the short wall leading those at the long wall - and tend to π/4 in the limit of high frequency. The amplitudes of pressure gradient increase more significantly than wall shear stress magnitudes due to accelerative forces. The boundaries to the quasi-steady, intermediate and inertia-dominated regimes are estimated at Womersley number W o = 1.6 and 27.6 in a rectangular channel, based on the contribution of viscous and inertial terms.
Stationary flow solution for water levels in open channels
Opheusden, van J.H.J.; Molenaar, J.; Beltman, W.H.J.; Adriaanse, P.I.
2010-01-01
We study stationary flow in open discharge channels. A model is derived from basic principles, which is solved numerically for the water level and discharge as a function of position along the channel. The model describes the effect of external inflow from fields adjacent to the channel. Several
Hydraulic flow through a channel contraction: multiple steady states
Akers, B.; Bokhove, Onno
2008-01-01
We have investigated shallow water flows through a channel with a contraction by experimental and theoretical means. The horizontal channel consists of a sluice gate and an upstream channel of constant width $b_0$ ending in a linear contraction of minimum width $b_c$. Experimentally, we observe
BİLGİL, Ahmet
2003-01-01
The determination of velocity distribution in open channel flows is crucial in many critical engineering problems such as channel design, calculation of energy losses and sedimentation. In this study, velocity distribution is experimentally investigated in a smooth rectangular open channel. Wall shear stresses are calculated using measured local velocities. Assuming logarithmic velocity distribution along perpendiculars to a wetted perimeter, dimensionless wall shear stresses K(I) =...
TWO PHASE FLOW SPLIT MODEL FOR PARALLEL CHANNELS
African Journals Online (AJOL)
Ifeanyichukwu Onwuka
Volumetric Flux. ϕ. Wall Heat Addition Rate Watts. N. Number of Channels with. Lower Plenum entry and Upper plenum exit. M. Number of Cross-flow paths. K .... Phase Split Equation. One way of obtaining the additional information is to define (N+M-l) phase relationships between the liquid and vapour flows at the channel ...
Development of a Linear Flow Channel Reactor for sulphur removal ...
African Journals Online (AJOL)
2013-09-23
Sep 23, 2013 ... in acid mine wastewater treatment operations ... bed reactor treating a synthetic acid mine water (2 000 mg∙ℓ−1 Na2SO4 solution) and the Liner Flow Channel Reactors (sur- face area 1.1 m2 and ... Keywords: floating sulphur biofilms, acid mine drainage, AMD passive treatment, linear flow channel reactor,.
Improving flow distribution in influent channels using computational fluid dynamics.
Park, No-Suk; Yoon, Sukmin; Jeong, Woochang; Lee, Seungjae
2016-10-01
Although the flow distribution in an influent channel where the inflow is split into each treatment process in a wastewater treatment plant greatly affects the efficiency of the process, and a weir is the typical structure for the flow distribution, to the authors' knowledge, there is a paucity of research on the flow distribution in an open channel with a weir. In this study, the influent channel of a real-scale wastewater treatment plant was used, installing a suppressed rectangular weir that has a horizontal crest to cross the full channel width. The flow distribution in the influent channel was analyzed using a validated computational fluid dynamics model to investigate (1) the comparison of single-phase and two-phase simulation, (2) the improved procedure of the prototype channel, and (3) the effect of the inflow rate on flow distribution. The results show that two-phase simulation is more reliable due to the description of the free-surface fluctuations. It should first be considered for improving flow distribution to prevent a short-circuit flow, and the difference in the kinetic energy with the inflow rate makes flow distribution trends different. The authors believe that this case study is helpful for improving flow distribution in an influent channel.
Energy Technology Data Exchange (ETDEWEB)
Klymenko, Oleksiy V.; Svir, Irina [Mathematical and Computer Modelling Laboratory, Kharkov National University of Radioelectronics, 14 Lenin Avenue, Kharkov 61166 (Ukraine); Oleinick, Alexander I. [Mathematical and Computer Modelling Laboratory, Kharkov National University of Radioelectronics, 14 Lenin Avenue, Kharkov 61166 (Ukraine); Departement de Chimie, Ecole Normale Superieure, UMR CNRS 8640 ' ' PASTEUR' ' , 24 rue Lhomond, 75231 Paris Cedex 05 (France); Amatore, Christian [Departement de Chimie, Ecole Normale Superieure, UMR CNRS 8640 ' ' PASTEUR' ' , 24 rue Lhomond, 75231 Paris Cedex 05 (France)
2007-12-20
We propose a theoretical method for reconstructing the shape of a hydrodynamic flow profile occurring locally within a rectangular microfluidic channel based on experimental currents measured at double microband electrodes embedded in one channel wall and operating in the generator-collector regime. The ranges of geometrical and flow parameters providing best conditions for the flow profile determination are indicated. The solution of convection-diffusion equation (direct problem) is achieved through the application of the specifically designed conformal mapping of spatial coordinates and an exponentially expanding time grid for obtaining accurate concentration and current distributions. The inverse problem (the problem of flow profile determination) is approached using a variational formulation whose solution is obtained by the Ritz's method. The method may be extended for any number of electrodes in the channel and/or different operating regimes of the system (e.g. generator-generator). (author)
Experimental study of natural circulation flow instability in rectangular channels
Energy Technology Data Exchange (ETDEWEB)
Zhou, Tao; Qi, Shi; Song, Mingqiang [North China Electric Power Univ., Beijing (China). School of Nuclear Science and Engineering; Passive Nuclear Safety Technology, Beijing (China). Beijing Key Lab.; Xiao, Zejun [Nuclear, Reactor Thermal Hydraulics Technology, Chengdu (China). CNNC Key Lab.
2017-05-15
Experiments of natural circulation flow instability were conducted in rectangular channels with 5 mm and 10 mm wide gaps. Results for different heating powers were obtained. The results showed that the flow will tend to be instable with the growing of heating power. The oscillation period of pressure D-value and volume flow are the same, but their phase positions are opposite. They both can be described by trigonometric functions. The existence of edge position and secondary flow will strengthen the disturbance of fluid flow in rectangle channels, which contributes to heat transfer. The disturbance of bubble and fluid will be strengthened, especially in the saturated boiling section, which make it possible for the mixing flow. The results also showed that the resistance in 5 mm channel is bigger than that in 10 mm channel, it is less likely to form stable natural circulation in the subcooled region.
Topology optimization of flow problems
DEFF Research Database (Denmark)
Gersborg, Allan Roulund
2007-01-01
to the development of the topology optimization method by studying different problem formulations related to topology optimization of fluid problems. In addition, the COMSOL software has been used as a post processing tool. Prior to design manufacturing this allows the engineer to quantify the performance...
Analysis and modelling of non-steady flow in pipe and channel networks
Jovic, Vinko
2013-01-01
Analysis and Modelling of Non-Steady Flow in Pipe and Channel Networks deals with flows in pipes and channel networks from the standpoints of hydraulics and modelling techniques and methods. These engineering problems occur in the course of the design and construction of hydroenergy plants, water-supply and other systems. In this book, the author presents his experience in solving these problems from the early 1970s to the present day. During this period new methods of solving hydraulic problems have evolved, due to the development of computers and numerical methods. This book
On complementary channels and the additivity problem
Holevo, A. S.
2005-01-01
We explore complementarity between output and environment of a quantum channel (or, more generally, CP map), making an observation that the output purity characteristics for complementary CP maps coincide. Hence, validity of the mutiplicativity/additivity conjecture for a class of CP maps implies its validity for complementary maps. The class of CP maps complementary to entanglement-breaking ones is described and is shown to contain diagonal CP maps as a proper subclass, resulting in new clas...
Advanced porous electrodes with flow channels for vanadium redox flow battery
Bhattarai, Arjun; Wai, Nyunt; Schweiss, Ruediger; Whitehead, Adam; Lim, Tuti M.; Hng, Huey Hoon
2017-02-01
Improving the overall energy efficiency by reducing pumping power and improving flow distribution of electrolyte, is a major challenge for developers of flow batteries. The use of suitable channels can improve flow distribution through the electrodes and reduce flow resistance, hence reducing the energy consumption of the pumps. Although several studies of vanadium redox flow battery have proposed the use of bipolar plates with flow channels, similar to fuel cell designs, this paper presents the use of flow channels in the porous electrode as an alternative approach. Four types of electrodes with channels: rectangular open channel, interdigitated open cut channel, interdigitated circular poked channel and cross poked circular channels, are studied and compared with a conventional electrode without channels. Our study shows that interdigitated open channels can improve the overall energy efficiency up to 2.7% due to improvement in flow distribution and pump power reduction while interdigitated poked channel can improve up to 2.5% due to improvement in flow distribution.
Design of Nano- and Microfibrous Channels for Fast Capillary Flow.
Shou, Dahua; Fan, Jintu
2017-12-17
The speed of capillary flow is a key bottleneck in improving the performance of nano- and microfluidic devices for various applications including microfluidic diagnostics, thermal management heat pipes, micro-molding devices, functional fabrics, and oil-water separators. Here we present a novel nano- or microfibrous hollow wedged channel (named as W-Channel) which can significantly speed up the capillary flow. The capillary flow in the initial 100 seconds in the nanofibrous W-Channel was shown to be 8 times faster than that in the single-layer strip of the same material when placed vertically and over 20 times faster when placed horizontally. The enhanced flow under gravity is attributed to the adaptive interplay of capillary pressure and flow resistance within the triangular hollow wedge between the fibrous layers. The W-Channel can be fabricated following a simple procedure using inexpensive materials such as electrospun nanofibers or microfibrous filter papers.
Extensional channel flow revisited: a dynamical systems perspective
Marques, Francisco; Meseguer, Alvaro; Mellibovsky, Fernando; Weidman, Patrick D.
2017-06-01
Extensional self-similar flows in a channel are explored numerically for arbitrary stretching-shrinking rates of the confining parallel walls. The present analysis embraces time integrations, and continuations of steady and periodic solutions unfolded in the parameter space. Previous studies focused on the analysis of branches of steady solutions for particular stretching-shrinking rates, although recent studies focused also on the dynamical aspects of the problems. We have adopted a dynamical systems perspective, analysing the instabilities and bifurcations the base state undergoes when increasing the Reynolds number. It has been found that the base state becomes unstable for small Reynolds numbers, and a transitional region including complex dynamics takes place at intermediate Reynolds numbers, depending on the wall acceleration values. The base flow instabilities are constitutive parts of different codimension-two bifurcations that control the dynamics in parameter space. For large Reynolds numbers, the restriction to self-similarity results in simple flows with no realistic behaviour, but the flows obtained in the transition region can be a valuable tool for the understanding of the dynamics of realistic Navier-Stokes solutions.
Very-large-scale coherent motions in open channel flows
Zhong, Qiang; Hussain, Fazle; Li, Dan-Xun
2016-11-01
Very-large-scale coherent structures (VLSSs) - whose characteristic length is of the order of 10 h (h is the water depth) - are found to exist in the log and outer layers near the bed of open channel flows. For decades researchers have speculated that large coherent structures may exist in open channel flows. However, conclusive evidence is still lacking. The present study employed pre-multiplied velocity power spectral and co-spectral analyses of time-resolved PIV data obtained in open channel flows. In all cases, two modes - large-scale structures (of the order of h) and VLSSs - dominate the log and outer layers of the turbulent boundary layer. More than half of TKE and 40% of the Reynolds shear stress in the log and outer layers are contributed by VLSSs. The strength difference of VLSSs between open and closed channel flows leads to pronounced redistribution of TKE near the free surface of open channel flows, which is a unique phenomenon that sets the open channel flows apart from other wall-bounded turbulent flows. Funded by China Postdoctoral Science Foundation (No.2015M580105), National Natural Science Foundation of China (No.51127006).
Flow boiling in microgap channels experiment, visualization and analysis
Alam, Tamanna; Jin, Li-Wen
2013-01-01
Flow Boiling in Microgap Channels: Experiment, Visualization and Analysis presents an up-to-date summary of the details of the confined to unconfined flow boiling transition criteria, flow boiling heat transfer and pressure drop characteristics, instability characteristics, two phase flow pattern and flow regime map and the parametric study of microgap dimension. Advantages of flow boiling in microgaps over microchannels are also highlighted. The objective of this Brief is to obtain a better fundamental understanding of the flow boiling processes, compare the performance between microgap and c
Flow Routing for Delineating Supraglacial Meltwater Channel Networks
Directory of Open Access Journals (Sweden)
Leonora King
2016-12-01
Full Text Available Growing interest in supraglacial channels, coupled with the increasing availability of high-resolution remotely sensed imagery of glacier surfaces, motivates the development and testing of new approaches to delineating surface meltwater channels. We utilized a high-resolution (2 m digital elevation model of parts of the western margin of the Greenland Ice Sheet (GrIS and retention of visually identified sinks (i.e., moulins to investigate the ability of a standard D8 flow routing algorithm to delineate supraglacial channels. We compared these delineated channels to manually digitized channels and to channels extracted from multispectral imagery. We delineated GrIS supraglacial channel networks in six high-elevation (above 1000 m and one low-elevation (below 1000 m catchments during and shortly after peak melt (July and August 2012, and investigated the effect of contributing area threshold on flow routing performance. We found that, although flow routing is sensitive to data quality and moulin identification, it can identify 75% to 99% of channels observed with multispectral analysis, as well as low-order, high-density channels (up to 15.7 km/km2 with a 0.01 km2 contributing area threshold in greater detail than multispectral methods. Additionally, we found that flow routing can delineate supraglacial channel networks on rough ice surfaces with widespread crevassing. Our results suggest that supraglacial channel density is sufficiently high during peak melt that low contributing area thresholds can be employed with little risk of overestimating the channel network extent.
Computation of gradually varied flow in compound open channel ...
Indian Academy of Sciences (India)
In this method, the energy and continuity equations are solved for steady, gradually varied flow by the Newton–Raphson method and the proposed methodology is applied to tree-type and looped-channel networks. An algorithm is presented to determine multiple critical depths in a compound channel. Modifications in ...
Experimental studies on the flow through soft tubes and channels
Indian Academy of Sciences (India)
Keywords. Laminar-turbulent transition; soft tubes/channels; hydrodynamic stability; transition; turbulence; internal flows. Abstract. Experiments conducted in channels/tubes with height/diameter less than 1 mm with soft walls made of polymer gels show that the transition Reynolds number could be significantly lower than ...
Flow Oriented Channel Assignment for Multi-radio Wireless Mesh Networks
Directory of Open Access Journals (Sweden)
Niu Zhisheng
2010-01-01
Full Text Available We investigate channel assignment for a multichannel wireless mesh network backbone, where each router is equipped with multiple interfaces. Of particular interest is the development of channel assignment heuristics for multiple flows. We present an optimization formulation and then propose two iterative flow oriented heuristics for the conflict-free and interference-aware cases, respectively. To maximize the aggregate useful end-to-end flow rates, both algorithms identify and resolve congestion at instantaneous bottleneck link in each iteration. Then the link rate is optimally allocated among contending flows that share this link by solving a linear programming (LP problem. A thorough performance evaluation is undertaken as a function of the number of channels and interfaces/node and the number of contending flows. The performance of our algorithm is shown to be significantly superior to best known algorithm in its class in multichannel limited radio scenarios.
Numerical Investigation of Developing Velocity Distributions in Open Channel Flows
Directory of Open Access Journals (Sweden)
Usman Ghani
2014-04-01
Full Text Available The velocity profiles in open channel flows start developing after entering into the channel for quite some length. All types of laboratory experiments for open channel flows are carried out in the fully developed flow regions which exist at some length downstream the inlet. In this research work an attempt has been made to investigate the impact of roughness and slope of the channel bed on the length required for establishment of fully developed flow in an open channel. A range of different roughness values along with various slopes were considered for this purpose. It was observed that an increase in roughness results in reduction of development length; and development length reduces drastically when roughness reaches to the range normally encountered in open channel flows with emergent vegetation or natural river flows. However, it was observed that the change of slope did not have any noticeable effect on development length. This work suggests that CFD (Computational Fluid Dynamics technique can be used for getting a reliable development length before performing an experimental work
Stability of stratified two-phase flows in inclined channels
Barmak, Ilya; Ullmann, Amos; Brauner, Neima
2016-01-01
Linear stability of stratified gas-liquid and liquid-liquid plane-parallel flows in inclined channels is studied with respect to all wavenumber perturbations. The main objective is to predict parameter regions in which stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in inclined flows, so that the stability analysis has to be carried out for each branch separately. Special attention is paid to the multiple solution regions to reveal the feasibility of non-unique stable stratified configurations in inclined channels. The stability boundaries of each branch of steady state solutions are presented on the flow pattern map and are accompanied by critical wavenumbers and spatial profiles of the most unstable perturbations. Instabilities of different nature are visualized by streamlines of the neutrally stable perturbed flows, consisting of the critical perturbation superimposed on the base flow. The present analysis confirms the existence of ...
Statistics of polymer extensions in turbulent channel flow.
Bagheri, Faranggis; Mitra, Dhrubaditya; Perlekar, Prasad; Brandt, Luca
2012-11-01
We present direct numerical simulations of turbulent channel flow with passive Lagrangian polymers. To understand the polymer behavior we investigate the behavior of infinitesimal line elements and calculate the probability distribution function (PDF) of finite-time Lyapunov exponents and from them the corresponding Cramer's function for the channel flow. We study the statistics of polymer elongation for both the Oldroyd-B model (for Weissenberg number Wi1 (FENE model) the polymer are significantly more stretched near the wall than at the center of the channel where the flow is closer to homogenous isotropic turbulence. Furthermore near the wall the polymers show a strong tendency to orient along the streamwise direction of the flow, but near the center line the statistics of orientation of the polymers is consistent with analogous results obtained recently in homogeneous and isotropic flows.
Modeling fluid flow in open channel with circular cross‐section ...
African Journals Online (AJOL)
Flow in a closed conduit is regarded as open channel flow, if it has a free surface. This study considers unsteady non]uniform open channel flow in a closed conduit with circular cross]section. We investigate the effects of the flow depth, the cross section area of flow, channel radius, slope of the channel, roughness coefficient ...
Estimation of flow direction in meandering compound channels
Liu, Xingnian; Zhou, Qin; Huang, Sheng; Guo, Yakun; Liu, Chao
2018-01-01
The flow in the main channel of a meandering compound channel does not occur in the ridge direction because of the effect of the upstream floodplain flows. This study proposes a model for estimating the flow direction in the depth-averaged two-dimensional domain (depth-averaged flow angles) between the entrance and the apex sections. Detailed velocity measurements were performed in the region between the meander entrance section and apex section in a large-scale meandering compound channel. The vertical size of the secondary current cell is highly related to the depth-averaged flow angle; thus, the means of the local flow angles above the secondary current cell and within the cell are separately discussed. The experimental measurements indicate that the mean local flow angle above the cell is equal to the section angle, whereas the mean local flow angle within the cell is equal to zero. The proposed model is validated using published data from five sources. Good agreement is obtained between the predictions and measurements, indicating that the proposed model can accurately estimate the depth-averaged flow direction in the meandering compound channels. Finally, the limitations and application ranges of the model are discussed.
Chemical reaction and heat source effects on MHD oscillatory flow in an irregular channel
Directory of Open Access Journals (Sweden)
P.V. Satya Narayana
2016-12-01
Full Text Available This paper investigates the effect of heat and mass transfer on MHD oscillatory flow in an asymmetric wavy channel with chemical reaction and heat source. The unsteadiness in the flow is due to an oscillatory pressure gradient across the ends of the channel. A magnetic field of uniform strength is applied in the direction perpendicular to the channel. However, the induced magnetic field is neglected due to the assumption of small magnetic Reynolds number. The temperature difference of the channel is also assumed high enough to induce heat transfer due to radiation. The governing equations are solved analytically by regular perturbation method. The analytical results are evaluated numerically and then are presented graphically to discuss the effects of different parameters entering into the problem. It is observed that the heat transport of a system is more increased in oscillatory flow than in ordinary conduction.
Flow resistance in open channels with fixed movable bed
Simoes, Francisco J.
2010-01-01
In spite of an increasingly large body of research by many investigators, accurate quantitative prediction of open channel flow resistance remains a challenge. In general, the relations between the elements influencing resistance (turbulence, boundary roughness, and channel shape features, such as discrete obstacles, bars, channel curvature, recirculation areas, secondary circulation, etc.) and mean flow variables are complex and poorly understood. This has resulted in numerous approaches to compute friction using many and diverse variables and equally diverse prescriptions for their use. In this paper, a new resistance law for surface (grain) resistance, the resistance due to the flow viscous effects on the channel boundary roughness elements, is presented for the cases of flow in the transition (5 friction losses in channels and natural rivers with plane beds, regardless of sediment transport conditions. This work is useful to hydraulic engineers involved with the derivation of depth-discharge relations in open channel flow and with the estimation of sediment transport rates for the case of bedload transport.
TWO PHASE FLOW SPLIT MODEL FOR PARALLEL CHANNELS
African Journals Online (AJOL)
Ifeanyichukwu Onwuka
transients, up to ten parallel flow paths, simple and complicated geometries, including the boilers of fossil steam generators and nuclear power plants. A test calculation has been made with a simplified three- channel system subjected to a two-phase flow transient, and the results have been very encouraging. NOTATION.
Two Phase Flow Split Model for Parallel Channels | Iloeje | Nigerian ...
African Journals Online (AJOL)
The model and code are capable of handling single and two phase flows, steady states and transients, up to ten parallel flow paths, simple and complicated geometries, including the boilers of fossil steam generators and nuclear power plants. A test calculation has been made with a simplified three-channel system ...
Unsteady hydromagnetic Couette flow within a porous channel with ...
African Journals Online (AJOL)
Unsteady hydromagnetic Couette flow of a viscous, incompressible and electrically conducting fluid between two infinitely long parallel porous plates, taking Hall current into account, in the presence of a transverse magnetic field is studied. Fluid flow within the channel is induced due to impulsive movement of the lower ...
Single phase channel flow forced convection heat transfer
Energy Technology Data Exchange (ETDEWEB)
Hartnett, J.P.
1999-04-01
A review of the current knowledge of single phase forced convection channel flow of liquids (Pr > 5) is presented. Two basic channel geometries are considered, the circular tube and the rectangular duct. Both laminar flow and turbulent flow are covered. The review begins with a brief overview of the heat transfer behavior of Newtonian fluids followed by a more detailed presentation of the behavior of purely viscous and viscoelastic Non-Newtonian fluids. Recent developments dealing with aqueous solutions of high molecular weight polymers and aqueous solutions of surfactants are discussed. The review concludes by citing a number of challenging research opportunities.
Flow instability and vortex street in eccentric annular channels
Choueiri, George; Tavoularis, Stavros
2013-11-01
Flow development in an eccentric annular channel with a diameter ratio of 0.5 has been investigated using flow visualization, two-component laser Doppler velocimetry and planar and stereoscopic particle image velocimetry. The eccentricity e was varied between 0.3 and 0.9 and the Reynolds number was 1000 flow instability and the generation of a quasi-periodic vortex street, which manifested itself by strong cross-flows across the gap and an increase in axial velocity in the gap region, but also affected the flow in the entire channel. The vortex strength was highest for e ~ 0 . 7 and the Strouhal number of the cross-flow oscillations (based on bulk velocity and core diameter) increased with increasing Re, reaching an asymptote near 0.12 for Re >= 10000 . Supported by NSERC and AECL.
Inverse feasibility problems of the inverse maximum flow problems
Indian Academy of Sciences (India)
A strongly polynomial time algorithm to solve the inverse maximum flow problem under l1 norm (denoted ... IMF can not be solved using weakly polynomial algorithms (although sometimes they can be preferred) because ..... in the network ˜G. We shall sort descending the arcs of ˜G by their capacities˜c1. After sorting, the.
Simulations of peristaltic slip-flow of hydromagnetic bio-fluid in a curved channel
Directory of Open Access Journals (Sweden)
N. Ali
2016-02-01
Full Text Available The influence of slip and magnetic field on transport characteristics of a bio-fluid are analyzed in a curved channel. The problem is modeled in curvilinear coordinate system under the assumption that the wavelength of the peristaltic wave is larger in magnitude compared to the width of the channel. The resulting nonlinear boundary value problem (BVP is solved using an implicit finite difference technique (FDT. The flow velocity, pressure rise per wavelength and stream function are illustrated through graphs for various values of rheological and geometrical parameters of the problem. The study reveals that a thin boundary layer exists at the channel wall for strong magnetic field. Moreover, small values of Weissenberg number counteract the curvature and make the velocity profile symmetric. It is also observed that pressure rise per wavelength in pumping region increases (decreases by increasing magnetic field, Weissenberg number and curvature of the channel (slip parameter.
Thermal Drawdown-Induced Flow Channeling in Fractured Geothermal Reservoirs
Energy Technology Data Exchange (ETDEWEB)
Fu, Pengcheng; Hao, Yue; Walsh, Stuart D. C.; Carrigan, Charles R.
2015-06-30
We investigate the flow-channeling phenomenon caused by thermal drawdown in fractured geothermal reservoirs. A discrete fracture network-based, fully coupled thermal–hydrological–mechanical simulator is used to study the interactions between fluid flow, temperature change, and the associated rock deformation. The responses of a number of randomly generated 2D fracture networks that represent a variety of reservoir characteristics are simulated with various injection-production well distances. We find that flow channeling, namely flow concentration in cooled zones, is the inevitable fate of all the scenarios evaluated. We also identify a secondary geomechanical mechanism caused by the anisotropy in thermal stress that counteracts the primary mechanism of flow channeling. This new mechanism tends, to some extent, to result in a more diffuse flow distribution, although it is generally not strong enough to completely reverse flow channeling. We find that fracture intensity substantially affects the overall hydraulic impedance of the reservoir but increasing fracture intensity generally does not improve heat production performance. Increasing the injection-production well separation appears to be an effective means to prolong the production life of a reservoir.
Radiative peristaltic flow of magneto nanofluid in a porous channel with thermal radiation
Directory of Open Access Journals (Sweden)
T. Hayat
Full Text Available Peristaltic flow of MHD nano fluid in a porous channel with velocity and thermal slip conditions is examined. Nanomaterial is comprised with water and copper/silver. Thermal radiation is present. The relevant problems have been solved for the velocity, temperature, pressure rise, frictional force and heat transfer rate. Physical impact of parameters in this study is analyzed.
Radiative peristaltic flow of magneto nanofluid in a porous channel with thermal radiation
Hayat, T.; Rani, Saima; Alsaedi, A.; Rafiq, M.
Peristaltic flow of MHD nano fluid in a porous channel with velocity and thermal slip conditions is examined. Nanomaterial is comprised with water and copper/silver. Thermal radiation is present. The relevant problems have been solved for the velocity, temperature, pressure rise, frictional force and heat transfer rate. Physical impact of parameters in this study is analyzed.
Thin-film flow in helically wound rectangular channels with small torsion
Stokes, Y. M.; Duffy, B. R.; Wilson, S. K.; Tronnolone, H.
2013-08-01
Laminar gravity-driven thin-film flow down a helically wound channel of rectangular cross-section with small torsion in which the fluid depth is small is considered. Neglecting the entrance and exit regions we obtain the steady-state solution that is independent of position along the axis of the channel, so that the flow, which comprises a primary flow in the direction of the axis of the channel and a secondary flow in the cross-sectional plane, depends only on position in the two-dimensional cross-section of the channel. A thin-film approximation yields explicit expressions for the fluid velocity and pressure in terms of the free-surface shape, the latter satisfying a nonlinear ordinary differential equation that has a simple exact solution in the special case of a channel of rectangular cross-section. The predictions of the thin-film model are shown to be in good agreement with much more computationally intensive solutions of the small-helix-torsion Navier-Stokes equations. The present work has particular relevance to spiral particle separators used in the mineral-processing industry. The validity of an assumption commonly used in modelling flow in spiral separators, namely, that the flow in the outer region of the separator cross-section is described by a free vortex, is shown to depend on the problem parameters.
Numerical solution of incompressible flow through branched channels
Czech Academy of Sciences Publication Activity Database
Louda, Petr; Kozel, K.; Příhoda, Jaromír; Beneš, L.; Kopáček, T.
2011-01-01
Roč. 46, č. 1 (2011), s. 318-324 ISSN 0045-7930 R&D Projects: GA ČR GA103/09/0977; GA ČR GAP101/10/1230 Institutional research plan: CEZ:AV0Z20760514 Keywords : channel flow * branched channel * EARSM turbulence model Subject RIV: BK - Fluid Dynamics Impact factor: 1.810, year: 2011 http://www.sciencedirect.com/science/article/pii/S0045793010003506
Separation of Particles in Swirling Flow in Coaxial Channel
Directory of Open Access Journals (Sweden)
Vasilevsky Michail
2016-01-01
Full Text Available Cyclones are widely used devices to separate a dispersed phase (e.g. particles or droplets from a continuous phase. The separation of particles in coaxial channels with different length is considered in paper. In this study we show that as coaxial channels length grows, the efficiency increases. In addition we demonstrate that as a gap between cylinder components is reduced, the aerosol spray efficiency is reduced also in turbulent flow.
Use of finite volume radiation for predicting the Knudsen minimum in 2D channel flow
Energy Technology Data Exchange (ETDEWEB)
Malhotra, Chetan P. [TCS Innovation Labs - TRDDC, 54 Hadapsar Industrial Estate, Pune 411013 (India); Mahajan, Roop L. [ICTAS, College of Engineering, Virginia Polytechnic Institute, VA 24061 (United States)
2014-12-09
In an earlier paper we employed an analogy between surface-to-surface radiation and free-molecular flow to model Knudsen flow through tubes and onto planes. In the current paper we extend the analogy between thermal radiation and molecular flow to model the flow of a gas in a 2D channel across all regimes of rarefaction. To accomplish this, we break down the problem of gaseous flow into three sub-problems (self-diffusion, mass-motion and generation of pressure gradient) and use the finite volume method for modeling radiation through participating media to model the transport in each sub-problem as a radiation problem. We first model molecular self-diffusion in the stationary gas by modeling the transport of the molecular number density through the gas starting from the analytical asymptote for free-molecular flow to the kinetic theory limit of gaseous self-diffusion. We then model the transport of momentum through the gas at unit pressure gradient to predict Poiseuille flow and slip flow in the 2D gas. Lastly, we predict the generation of pressure gradient within the gas due to molecular collisions by modeling the transport of the forces generated due to collisions per unit volume of gas. We then proceed to combine the three radiation problems to predict flow of the gas over the entire Knudsen number regime from free-molecular to transition to continuum flow and successfully capture the Knudsen minimum at Kn ∼ 1.
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.
Directory of Open Access Journals (Sweden)
Munawwar Ali Abbas
2016-03-01
Full Text Available Entropy generation during peristaltic flow of nanofluids in a non-uniform two dimensional channel with compliant walls has been studied. The mathematical modelling of the governing flow problem is obtained under the approximation of long wavelength and zero Reynolds number (creeping flow regime. The resulting non-linear partial differential equations are solved with the help of a perturbation method. The analytic and numerical results of different parameters are demonstrated mathematically and graphically. The present analysis provides a theoretical model to estimate the characteristics of several Newtonian and non-Newtonian fluid flows, such as peristaltic transport of blood.
Tutorial on Feedback Control of Flows, Part I: Stabilization of Fluid Flows in Channels and Pipes
Directory of Open Access Journals (Sweden)
Ole M. Aamo
2002-07-01
Full Text Available The field of flow control has picked up pace over the past decade or so, on the promise of real-time distributed control on turbulent scales being realizable in the near future. This promise is due to the micromachining technology that emerged in the 1980s and developed at an amazing speed through the 1990s. In lab experiments, so called micro-electro-mechanical systems (MEMS that incorporate the entire detection-decision-actuation process on a single chip, have been batch processed in large numbers and assembled into flexible skins for gluing onto body-fluid interfaces for drag reduction purposes. Control of fluid flows span a wide variety of specialities. In Part I of this tutorial, we focus on the problem of reducing drag in channel and pipe flows by stabilizing the parabolic equilibrium profile using boundary feedback control. The control strategics used for this problem include classical control, based on the Nyquist criteria, and various optimal control techniques (H2, H-Infinity, as well as applications of Lyapunov stability theory.
Open-channel integrating-type flow meter
Koopman, K.C.
1971-01-01
A relatively inexpensive meter for measuring cumulative flow in open channels with a rated control,. called a "totalizer", was developed. It translates the nonlinear function of gage height to flow by use of a cam and a float. A variable resistance element in an electronic circuit is controlled by the float so that the electron flow in the circuit corresponds to the flow of water. The flow of electricity causes electroplating of an electrode with silver. The amount of silver deposited is proportionate to the flow of water. The total flow of water is determined by removing the silver from the electrode at a fixed rate with ·an electronic device and recording the time for removal with a counter. The circuit is designed so that the ,resultant reading on the counter is in acre-feet of water.
Public channel cryptography: chaos synchronization and Hilbert's tenth problem.
Kanter, Ido; Kopelowitz, Evi; Kinzel, Wolfgang
2008-08-22
The synchronization process of two mutually delayed coupled deterministic chaotic maps is demonstrated both analytically and numerically. The synchronization is preserved when the mutually transmitted signals are concealed by two commutative private filters, a convolution of the truncated time-delayed output signals or some powers of the delayed output signals. The task of a passive attacker is mapped onto Hilbert's tenth problem, solving a set of nonlinear Diophantine equations, which was proven to be in the class of NP-complete problems [problems that are both NP (verifiable in nondeterministic polynomial time) and NP-hard (any NP problem can be translated into this problem)]. This bridge between nonlinear dynamics and NP-complete problems opens a horizon for new types of secure public-channel protocols.
Numerical simulations of heat transfer in plane channel flow
Gharbi, Najla El; Benzaoui, Ahmed
2010-01-01
Reynolds-averaged Navier-Stokes (RANS) turbulence models (such as k-{\\epsilon} models) are still widely used for engineering applications because of their relatively simplicity and robustness. In fully developed plane channel flow (i.e. the flow between two infinitely large plates), even if available models and near-wall treatments provide adequate mean flow velocities, they fail to predict suitable turbulent kinetic energy "TKE" profiles near walls. TKE is involved in determination of eddy viscosity/diffusivity and could therefore provide inaccurate concentrations and temperatures. In order to improve TKE a User Define Function "UDF" based on an analytical profile for TKE was developed and implemented in Fluent. Mean streamwise velocity and turbulent kinetic energy "TKE" profiles were compared to DNS data for friction Reynolds number $Re_{\\tau}$ = 150. Simulation results for TKE show accurate profiles. Simulation results for horizontal heated channel flows obtained with Fluent are presented. Numerical result...
NUMERICAL MODELING OF GENERALIZED NEWTONIAN FLOWS IN CHANNELS
Kozel, Karel
2012-01-01
This paper is concerned with numerical solution of generalized Newtonian flow in the channel geometry. This flow is described by the system of generalized Navier-Stokes equations. The system of equations consists of continuity and momentum equations. Viscosity in the momentum equations is not constant and is prescribed by a function depending on the shear rate. Numerical solution is based on the artificial compressibility method. Using this method allows us to solve hyperbolic-parabolic syste...
Dynamics of prolate ellipsoidal particles in a turbulent channel flow
Mortensen, P.H.; Andersson, H.I.; Gillissen, J.J.J.; Boersma, B.J.
2008-01-01
The dynamical behavior of tiny elongated particles in a directly simulated turbulent flow field is investigated. The ellipsoidal particles are affected both by inertia and hydrodynamic forces and torques. The time evolution of the particle orientation and translational and rotational motions in a statistically steady channel flow is obtained for six different particle classes. The focus is on the influence of particle aspect ratio ? and the particle response time on the particle dynamics, i.e...
Prediction of concentrated flow width in ephemeral gully channels
Nachtergaele, J.; Poesen, J.; Sidorchuk, A.; Torri, D.
2002-07-01
Empirical prediction equations of the form W = aQb have been reported for rills and rivers, but not for ephemeral gullies. In this study six experimental data sets are used to establish a relationship between channel width (W, m) and flow discharge (Q, m3 s-1) for ephemeral gullies formed on cropland. The resulting regression equation (W = 2·51 Q0·412; R2 = 0·72; n = 67) predicts observed channel width reasonably well. Owing to logistic limitations related to the respective experimental set ups, only relatively small runoff discharges (i.e. Q channel width was attributed to a calculated peak runoff discharge on sealed cropland, the application field of the regression equation was extended towards larger discharges (i.e. 5 × 10channels revealed that the discharge exponent (distribution over the wetted perimeter between rills, gullies and rivers, (ii) a decrease in probability of a channel formed in soil material with uniform erosion resistance from rills over gullies to rivers and (iii) a decrease in average surface slope from rills over gullies to rivers.channel width equation for concentrated flow on cropland. For the frozen soils the equation
Compressible material flow in cylindrical channel with variable cross section
Directory of Open Access Journals (Sweden)
Pryanishnikova Elena
2017-01-01
Full Text Available In the mathematical model of the flow of compressible material the effect of friction and the slip velocity of the material at the side boundary surfaces are considered. The dependence of the slip velocity on the average velocity at the entrance of the channel is built.
LES of droplet-laden non-isothermal channel flow
Michalek, W.R.; Liew, R.; Kuerten, Johannes G.M.; Zeegers, J.C.H.
In this paper subgrid models for LES of droplet-laden non-isothermal channel flow are tested and improved for three Reynolds numbers based on friction velocity, Reτ of 150, 395, and 950 with the aim to develop a simulation method for LES of a droplet-laden Ranque-Hilsch vortex tube. A new subgrid
Transport of suspended particles in turbulent open channel flows
Breugem, W.A.
2012-01-01
Two experiments are performed in order to investigate suspended sediment transport in a turbulent open channel flow. The first experiment used particle image velocimetry (PIV) to measure the fluid velocity with a high spatial resolution, while particle tracking velocimetry (PTV) was used to measure
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
Port-Hamiltonian discretization for open channel flows
Pasumarthy, R.; Ambati, V.R.; Schaft, A.J. van der
A finite-dimensional Port-Hamiltonian formulation for the presented. A numerical scheme based on this formulation is shallow water equations. The scheme is verified against conservation of mass and energy to the discrete level. dynamics of smooth open channel flows is developed for both the linear
Theory of viscous flow in curved shallow channels
De Vriend, H.J.
1972-01-01
The axisymmetrical, viscous flow in curved channels is considered in the case where the hydraulic radius of the cross-section is small with respect to the average radius of curvature of the bend. First Ananyan's theory on this subject is reconsidered, using a regular perturbation method. The results
Channel flow analysis. [velocity distribution throughout blade flow field
Katsanis, T.
1973-01-01
The design of a proper blade profile requires calculation of the blade row flow field in order to determine the velocities on the blade surfaces. An analysis theory is presented for several methods used for this calculation and associated computer programs that were developed are discussed.
Wood flow problems in the Swedish forestry
Energy Technology Data Exchange (ETDEWEB)
Carlsson, Dick [Forestry Research Inst. of Sweden, Uppsala (Sweden); Roennqvist, M. [Linkoeping Univ. (Sweden). Dept. of Mathematics
1998-12-31
In this paper we give an overview of the wood-flow in Sweden including a description of organization and planning. Based on that, we will describe a number of applications or problem areas in the wood-flow chain that are currently considered by the Swedish forest companies to be important and potential in order to improve overall operations. We have focused on applications which are short term planning or operative planning. We do not give any final results as much of the development is currently ongoing or is still in a planning phase. Instead we describe what kind of models and decision support systems that could be applied in order to improve co-operation within and integration of the wood-flow chain 13 refs, 20 figs, 1 tab
Blood flow analysis with considering nanofluid effects in vertical channel
Noreen, S.; Rashidi, M. M.; Qasim, M.
2017-06-01
Manipulation of heat convection of copper particles in blood has been considered peristaltically. Two-phase flow model is used in a channel with insulating walls. Flow analysis has been approved by assuming small Reynold number and infinite length of wave. Coupled equations are solved. Numerical solution are computed for the pressure gradient, axial velocity function and temperature. Influence of attention-grabbing parameters on flow entities has been analyzed. This study can be considered as mathematical representation to the vibrance of physiological systems/tissues/organs provided with medicine.
Granular flow over inclined channels with linear contraction
Tunuguntla, D R; Thornton, A R; Bokhove, O
2015-01-01
We consider dry granular flow down an inclined chute with a localised contraction theoretically and numerically. The flow regimes are predicted through a novel extended one-dimensional hydraulic theory. A discrete particle method validated empirical constitutive law is used to close this one-dimensional asymptotic model. The one-dimensional model is verified by solving the two-dimensional shallow granular equations through discontinuous Galerkin finite element method (DGFEM). For supercritical flows, the one-dimensional asymptotic theory surprisingly holds although the two-dimensional oblique granular jumps largely vary across the converging channel.
Flow Instability in Channel Flow with a Streamwise-periodic Array of Circular Cylinders
Lee, Kyongjun; Yoon, Dong-Hyeog; Yang, Kyung-Soo
2011-11-01
A parametric study has been carried out to elucidate the characteristics of flow instability in laminar channel flow with a streamwise-periodic array of circular cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to a significant change in flow instability. There exist two kinds of instability; flow undergoes a primary instability (Hopf bifurcation) at a low Reynolds number, and the resulting time-periodic two-dimensional flow subsequently becomes unstable to three-dimensional disturbances at a higher Reynolds number (secondary instability). We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent time-periodic 2D flow, including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinders and the channel wall. We also present a Floquet stability analysis on the time-periodic 2D flows to identify the onset of the secondary instability leading to 3D flow. This work was supported by UVRC, Korea.
Red cell membrane elasticity as determined by flow channel technique.
Chien, S; Sung, L A; Lee, M M; Skalak, R
1992-01-01
The elasticity of red cell membrane was determined in a rectangular flow channel under controlled shear flow. The relation between shear stress and cell extension ratio (lambda) has been analyzed with the use of Evans' two-dimensional model. The deformed cell shapes observed experimentally agreed well with the model with lambda up to 1.4. The best correlation was found at lambda = 1.2. The analysis suggests a nonlinear extensional membrane modulus in the low stress range encountered in the flow channel. In terms of an appropriate strain parameter, the elastic modulus is shown to rise toward the level encountered in micropipette aspiration experiments. The implications of the present findings in modeling of cell mechanics and in cell hemolysis are discussed.
Algebraic disturbances and their consequences in rotating channel flow transition
Jose, Sharath; Pier, Benoît; Govindarajan, Rama
2016-01-01
It is now established that subcritical mechanisms play a crucial role in the transition to turbulence of non-rotating plane shear flows. The role of these mechanisms in rotating channel flow is examined here in the linear and nonlinear stages. Distinct patterns of behaviour are found: the transient growth leading to nonlinearity at low rotation rates $Ro$, a highly chaotic intermediate $Ro$ regime, a localised weak chaos at higher $Ro$, and complete stabilization of transient disturbances at very high $Ro$. At very low $Ro$, the transient growth amplitudes are close to those for non-rotating flow, but Coriolis forces already assert themselves by producing distinct asymmetry about the channel centreline. Nonlinear processes are then triggered, in a streak-breakdown mode of transition. The high $Ro$ regimes do not show these signatures, here the leading eigenmode emerges as dominant in the early stages. Elongated structures plastered close to one wall are seen at higher rotation rates. Rotation is shown to redu...
Mangold, Nicolas; Howard, Alan
2013-04-01
Outflow channels are broad fluvial landforms formed by catastrophic flows with typical braided pattern. A controversy exists about their origin as aqueous flows because recent works have observed volcanic processes creating similar landforms, for example on Mercury. One caveat of the aqueous flows hypothesis is the lack of deltaic deposits that should be associated with deposition of transported material. Postflow filling can hide these deltas subsequently, but this should not be the case for 100% of outflow activity. We show from a newly found series of outflow that some outflow channels can display features typical of aqueous deposits. A connected series of outflow channels in the Ismenius Lacus quadrangle are identified for the first time and characterized using High Resolution Stereo Camera images of Mars Express and Context camera images of Mars Reconnaissance Orbiter. These channels, which stretch over >400 km south to north and join the northern plains, were identified from braided channels, scour/groove marks, poorly sinuous valleys and depositional landforms. Discharge rates were estimated to 0.1 to 5 x 106 m3 s-1 from analysis of Mars Observer Laser Altimeter topographic data. Pathways of channels segments were extracted from topography showing a unique source at a breached crater rim, suggesting overflow from ponded depressions. A series of delta fans are observed inside depressions along the channel pathways. The presence of these deltas formed in former transient bodies of water is a compelling argument for formation of this outflow channel system by fluvial flows. The similarity of these flows with other outflow channels on Mars proves that volcanically-related outflows cannot explain all channels observed on Mars. In addition, this study also shows that catastrophic floods are able to create fan deltas in transient lakes, a distinct context than usually involved for such landforms.
Heat Transfer to MHD Oscillatory Viscoelastic Flow in a Channel Filled with Porous Medium
Directory of Open Access Journals (Sweden)
Rita Choudhury
2012-01-01
Full Text Available The combined effect of a transverse magnetic field and radiative heat transfer on unsteady flow of a conducting optically thin viscoelastic fluid through a channel filled with saturated porous medium and nonuniform walls temperature has been discussed. It is assumed that the fluid has small electrical conductivity and the electromagnetic force produced is very small. Closed-form analytical solutions are constructed for the problem. The effects of the radiation and the magnetic field parameters on velocity profile and shear stress for different values of the viscoelastic parameter with the combination of the other flow parameters are illustrated graphically, and physical aspects of the problem are discussed.
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.)
Effect of Flow Channel Shape on Performance in Reverse Electrodialysis
Energy Technology Data Exchange (ETDEWEB)
Kwon, Kilsung [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Kim, Deok Han; Kim, Daejoong [Sogang Univ., Seoul (Korea, Republic of)
2017-05-15
Reverse electrodialysis (RED), which generates electrical energy from the difference in concentration of two solutions, has been actively studied owing to its high potential and the increased interest in renewable energy resulting from the Paris Agreement on climate change. For RED commercialization, its power density needs to be maximized, and therefore various methods have been discussed. In this paper, the power density was measured using various flow shapes based on the aspect ratio, opening ratio, and number of distribution channels. We found that the power density is enhanced with a decrease in the aspect ratio and an increase in the opening ratio and number of distribution channels.
Molecular dynamics simulations of oscillatory flows in microfluidic channels
DEFF Research Database (Denmark)
Hansen, J.S.; Ottesen, Johnny T.
2006-01-01
In this paper we apply the direct non-equilibrium molecular dynamics technique to oscillatory flows of fluids in microscopic channels. Initially, we show that the microscopic simulations resemble the macroscopic predictions based on the Navier–Stokes equation very well for large channel width, high...... density and low temperature. Further simulations for high temperature and low density show that the non-slip boundary condition traditionally used in the macroscopic equation is greatly compromised when the fluid–wall interactions are the same as the fluid–fluid interactions. Simulations of a system...
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.
Ke, Xinyou; Prahl, Joseph M; Savinell, Robert F
2016-01-01
A simple analytical model of a layered system comprised of a single passage of a serpentine flow channel and a parallel underlying porous electrode (or porous layer) is proposed. This analytical model is derived from Navier-Stokes motion in the flow channel and Darcy-Brinkman model in the porous layer. The continuities of flow velocity and normal stress are applied at the interface between the flow channel and the porous layer. The effects of the inlet volumetric flow rate, thickness of the flow channel and thickness of a typical carbon fiber paper porous layer on the volumetric flow rate within this porous layer are studied. The maximum current density based on the electrolyte volumetric flow rate is predicted, and found to be consistent with reported numerical simulation. It is found that, for a mean inlet flow velocity of 33.3 cm s-1, the analytical maximum current density is estimated to be 377 mA cm-2, which compares favorably with experimental result reported by others of ~400 mA cm-2.
LES of droplet-laden non-isothermal channel flow
Michałek, W. R.; Liew, R.; Kuerten, J. G. M.; Zeegers, J. C. H.
2011-12-01
In this paper subgrid models for LES of droplet-laden non-isothermal channel flow are tested and improved for three Reynolds numbers based on friction velocity, Reτ of 150, 395, and 950 with the aim to develop a simulation method for LES of a droplet-laden Ranque-Hilsch vortex tube. A new subgrid model combining the beneficial properties of the dynamic eddy-viscosity model and the approximate deconvolution model is proposed. Furthermore, the subgrid model in the droplet equations based on approximate deconvolution is found to perform well also in non-isothermal channel flow. At the highest Reynolds number in the test the dynamic model yields results with a similar accuracy as the approximate deconvolution model.
LES of droplet-laden non-isothermal channel flow
Energy Technology Data Exchange (ETDEWEB)
Michalek, W R; Kuerten, J G M [Department of Mechanical Engineering, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Liew, R; Zeegers, J C H, E-mail: w.michalek@tue.nl [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands)
2011-12-22
In this paper subgrid models for LES of droplet-laden non-isothermal channel flow are tested and improved for three Reynolds numbers based on friction velocity, Re{sub {tau}} of 150, 395, and 950 with the aim to develop a simulation method for LES of a droplet-laden Ranque-Hilsch vortex tube. A new subgrid model combining the beneficial properties of the dynamic eddy-viscosity model and the approximate deconvolution model is proposed. Furthermore, the subgrid model in the droplet equations based on approximate deconvolution is found to perform well also in non-isothermal channel flow. At the highest Reynolds number in the test the dynamic model yields results with a similar accuracy as the approximate deconvolution model.
Doppler-Based Flow Rate Sensing in Microfluidic Channels
Directory of Open Access Journals (Sweden)
Liron Stern
2014-09-01
Full Text Available We design, fabricate and experimentally demonstrate a novel generic method to detect flow rates and precise changes of flow velocity in microfluidic devices. Using our method we can measure flow rates of ~2 mm/s with a resolution of 0.08 mm/s. The operation principle is based on the Doppler shifting of light diffracted from a self-generated periodic array of bubbles within the channel and using self-heterodyne detection to analyze the diffracted light. As such, the device is appealing for variety of “lab on chip” bio-applications where a simple and accurate speed measurement is needed, e.g., for flow-cytometry and cell sorting.
An improved near-wall treatment for turbulent channel flows
El Gharbi, Najla; Absi, Rafik; Benzaoui, Ahmed; Bennacer, Rachid
2011-01-01
The success of predictions of wall-bounded turbulent flows requires an accurate description of the flow in the near-wall region. This article presents a comparative study between different near-wall treatments and presents an improved method. The study is applied to fully developed plane channel flow (i.e. the flow between two infinitely large plates). Simulations were performed using Fluent. Near-wall treatments available in Fluent were tested: standard wall functions, non-equilibrium wall function and enhanced wall treatment. A user defined function (UDF), based on an analytical profile for the turbulent kinetic energy (Absi, R., 2008. Analytical solutions for the modeled k-equation. ASME Journal of Applied Mechanics, 75 (4), 044501), is developed and implemented. Predicted turbulent kinetic energy profiles are presented and validated by DNS data.
Analytical solutions and numerical modeling for a dam-break problem in inclined channels
Pelinovsky, Efim; Didenkulova, Ira; Didenkulov, Oleg; Rodin, Artem
2016-04-01
Here we obtain different analytical solutions of the shallow-water equations for inviscid nonlinear waves in inclined channels. (i) The first solution describes Riemann wave moving up or down alone the channel slope. It requires the initial fluid flow, which often accompanies waves generated by landslides. This solution is valid for a finite time before the wave breaks. (ii) The second solution generalizes the classical dam-break problem for the case of a dam located in the inclined channel. In this case the cross-section of the channel influences the speed of wave propagation inside the channel, and therefore changes wave dynamics inside the channel compare to the plane beach. (iii) The third solution describes the intermediate stage of the wave front dynamics for a dam of a large height. This solution is derived with the use of generalized Carrier-Greenspan approach developed early by Didenkulova & Pelinovsky (2011) and Rybkin et al (2014). Some of the analytical solutions are tested with the means of numerical modeling. The numerical modeling is carried out using the CLAWPACK software based on nonlinear shallow water equations. Application of the described solutions to possible laboratory experiments is discussed.
Electro-osmotically driven MHD flow and heat transfer in micro-channel
Shit, G. C.; Mondal, A.; Sinha, A.; Kundu, P. K.
2016-05-01
A theoretical analysis is presented for electro-osmotic flow (EOF) of blood in a hydrophobic micro-channel with externally applied magnetic field. The lumen of micro-channels is assumed to be porous medium in addition to the consideration of permeability of the channel walls. The effects of slip velocity and thermal-slip are taken into consideration. The governing equations in the electrical double layer (EDL) together with the Poisson-Boltzmann equation and the body force exerted by the applied potential are furthermore considered. The flow is governed by the non-Newtonian viscoelastic fluid model. These equations along with the thermal energy equation are approximated by assuming that the channel height is much greater than the thickness of electrical double layer consisting the stern and diffusive layers. The problem is solved analytically and the computed results have presented graphically for various values of the dimensionless parameters. The results presented here have significant impact on the therapeutic treatment in hyperthermia as well as in controlling blood flow and heat transfer in micro-channels.
Scrutiny of underdeveloped nanofluid MHD flow and heat conduction in a channel with porous walls
Directory of Open Access Journals (Sweden)
M. Fakour
2014-11-01
Full Text Available In this paper, laminar fluid flow and heat transfer in channel with permeable walls in the presence of a transverse magnetic field is investigated. Least square method (LSM for computing approximate solutions of nonlinear differential equations governing the problem. We have tried to show reliability and performance of the present method compared with the numerical method (Runge–Kutta fourth-rate to solve this problem. The influence of the four dimensionless numbers: the Hartmann number, Reynolds number, Prandtl number and Eckert number on non-dimensional velocity and temperature profiles are considered. The results show analytical present method is very close to numerically method. In general, increasing the Reynolds and Hartman number is reduces the nanofluid flow velocity in the channel and the maximum amount of temperature increase and increasing the Prandtl and Eckert number will increase the maximum amount of theta.
Processes of Turbulent Liquid Flows in Pipelines and Channels
Directory of Open Access Journals (Sweden)
R. I. Yesman
2011-01-01
Full Text Available The paper proposes a methodology for an analysis and calculation of processes pertaining to turbulent liquid flows in pipes and channels. Various modes of liquid motion in pipelines of thermal power devices and equipment have been considered in the paper.The presented dependences can be used while making practical calculations of losses due to friction in case of transportation of various energy carriers.
Development of a Linear Flow Channel Reactor for sulphur removal ...
African Journals Online (AJOL)
2013-09-23
Sep 23, 2013 ... in acid mine wastewater treatment operations. JB Molwantwa1 and PD ... bed reactor treating a synthetic acid mine water (2 000 mg∙ℓ−1 Na2SO4 solution) and the Liner Flow Channel Reactors (sur- face area 1.1 m2 and 2.2 ... structures were reported for tannery wastewater evaporation ponds (Rose et al., ...
Fluid-Structure Interaction of Channel Driven Cavity Flow
2016-06-01
study the fluid- structure interaction and provide benchmark data for validation of numerical fluid-structure interaction models. The channel driven...driven cavity flow in order to study the fluid-structure interaction and provide benchmark data for validation of numerical fluid-structure interaction...Finally, I would like to thank Mom and Dad for ensuring I received the best education possible while I lived at home. xiv THIS PAGE INTENTIONALLY
Freezing in turbulent flow inside tubes and channels
Weigand, Bernhard; Beer, Hans
1993-01-01
A simple and quite flexible numerical model is presented to predict the steady state ice-layer formation inside a cooled two dimensional channel or a tube containing a turbulent flow. The effects of arbitrary entrance velocity distributions upon the shape of the ice-layers are examined. The presented numerical scheme is verified by comparing the predicted ice-layers with measurements and generally good agreement was found.
Laboratorial studies on the seepage impact in open-channel flow turbulence
Herrera Granados, Oscar; Kostecki, Stanislaw
2011-12-01
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.
Polar cap flow channel events: spontaneous and driven responses
Directory of Open Access Journals (Sweden)
P. E. Sandholt
2010-11-01
Full Text Available We present two case studies of specific flow channel events appearing at the dusk and/or dawn polar cap boundary during passage at Earth of interplanetary (IP coronal mass ejections (ICMEs on 10 January and 25 July 2004. The channels of enhanced (>1 km/s antisunward convection are documented by SuperDARN radars and dawn-dusk crossings of the polar cap by the DMSP F13 satellite. The relationship with Birkeland currents (C1–C2 located poleward of the traditional R1–R2 currents is demonstrated. The convection events are manifest in ground magnetic deflections obtained from the IMAGE (International Monitor for Auroral Geomagnetic Effects Svalbard chain of ground magnetometer stations located within 71–76° MLAT. By combining the ionospheric convection data and the ground magnetograms we are able to study the temporal behaviour of the convection events. In the two ICME case studies the convection events belong to two different categories, i.e., directly driven and spontaneous events. In the 10 January case two sharp southward turnings of the ICME magnetic field excited corresponding convection events as detected by IMAGE and SuperDARN. We use this case to determine the ground magnetic signature of enhanced flow channel events (the NH-dusk/By<0 variant. In the 25 July case a several-hour-long interval of steady southwest ICME field (Bz<0; By<0 gave rise to a long series of spontaneous convection events as detected by IMAGE when the ground stations swept through the 12:00–18:00 MLT sector. From the ground-satellite conjunction on 25 July we infer the pulsed nature of the polar cap ionospheric flow channel events in this case. The typical duration of these convection enhancements in the polar cap is 10 min.
Towards faster solution of large power flow problems
Idema, R.; Papaefthymiou, G.; Lahaye, D.J.P.; Vuik, C.; Van der Sluis, L.
2012-01-01
Current and future developments in the power system industry demand fast power flow solvers for larger power flow problems. The established methods are no longer viable for such problems, as they are not scalable in the problem size. In this paper, the use of Newton-Krylov power flow methods is
Ke, Xinyou; Alexander, J Iwan D; Savinell, Robert F
2016-01-01
In this work, a two-dimensional mathematical model is developed to study the flow patterns and volumetric flow penetrations in the flow channel over the porous electrode layered system in vanadium flow battery with serpentine flow field design. The flow distributions at the interface between the flow channel and porous electrode are examined. It is found that the non-linear pressure distributions can distinguish the interface flow distributions under the ideal plug flow and ideal parabolic flow inlet boundary conditions. However, the volumetric flow penetration within the porous electrode beneath the flow channel through the integration of interface flow velocity reveals that this value is identical under both ideal plug flow and ideal parabolic flow inlet boundary conditions. The volumetric flow penetrations under the advection effects of flow channel and landing/rib are estimated. The maximum current density achieved in the flow battery can be predicted based on the 100% amount of electrolyte flow reactant ...
The role of dissipation and mixing in exchange flow through a contracting channel
Winters, Kraig B.; Seim, Harvey E.
2000-03-01
We investigate the transport of mass and momentum between layers in idealized exchange flow through a contracting channel. Lock-exchange initial value problems are run to approximately steady state using a three-dimensional, non-hydrostatic numerical model. The numerical model resolves the large-scale exchange flow and shear instabilities that form at the interface, parameterizing the effects of subgrid-scale turbulence. The closure scheme is based on an assumed steady, local balance of turbulent production and dissipation in a density-stratified fluid.
A Flow-Channel Analysis for the Mars Hopper
Energy Technology Data Exchange (ETDEWEB)
W. Spencer Cooley
2013-02-01
The Mars Hopper is an exploratory vehicle designed to fly on Mars using carbon dioxide from the Martian atmosphere as a rocket propellant. The propellent gasses are thermally heated while traversing a radioisotope ther- mal rocket (RTR) engine’s core. This core is comprised of a radioisotope surrounded by a heat capacitive material interspersed with tubes for the propellant to travel through. These tubes, or flow channels, can be manu- factured in various cross-sectional shapes such as a special four-point star or the traditional circle. Analytical heat transfer and computational fluid dynamics (CFD) anal- yses were performed using flow channels with either a circle or a star cross- sectional shape. The nominal total inlet pressure was specified at 2,805,000 Pa; and the outlet pressure was set to 2,785,000 Pa. The CO2 inlet tem- perature was 300 K; and the channel wall was 1200 K. The steady-state CFD simulations computed the smooth-walled star shape’s outlet temper- ature to be 959 K on the finest mesh. The smooth-walled circle’s outlet temperature was 902 K. A circle with a surface roughness specification at 0.01 mm gave 946 K and at 0.1 mm yielded 989 K. The The effects of a slightly varied inlet pressure were also examined. The analytical calculations were based on the mass flow rates computed in the CFD simulations and provided significantly higher outlet temperature results while displaying the same comparison trends. Research relating to the flow channel heat transfer studies was also done. Mathematical methods to geometrically match the cross-sectional areas of the circle and star, along with a square and equilateral triangle, were derived. A Wolfram Mathematica 8 module was programmed to analyze CFD results using Richardson Extrapolation and calculate the grid convergence index (GCI). A Mathematica notebook, also composed, computes and graphs the bulk mean temperature along a flow channel’s length while the user dynam- ically provides the input
Limiting photocurrent analysis of a wide channel photoelectrochemical flow reactor
Davis, Jonathan T.; Esposito, Daniel V.
2017-03-01
The development of efficient and scalable photoelectrochemical (PEC) reactors is of great importance for the eventual commercialization of solar fuels technology. In this study, we systematically explore the influence of convective mass transport and light intensity on the performance of a 3D-printed PEC flow cell reactor based on a wide channel, parallel plate geometry. Using this design, the limiting current density generated from the hydrogen evolution reaction at a p-Si metal-insulator-semiconductor (MIS) photocathode was investigated under varied reactant concentration, fluid velocity, and light intensity. Additionally, a simple model is introduced to predict the range of operating conditions (reactant concentration, light intensity, fluid velocity) for which the photocurrent generated in a parallel plate PEC flow cell is limited by light absorption or mass transport. This model can serve as a useful guide for the design and operation of wide-channel PEC flow reactors. The results of this study have important implications for PEC reactors operating in electrolytes with dilute reactant concentrations and/or under high light intensities where high fluid velocities are required in order to avoid operation in the mass transport-limited regime.
Scrutiny of mixed convection flow of a nanofluid in a vertical channel
Directory of Open Access Journals (Sweden)
M. Fakour
2014-11-01
Full Text Available The laminar fully developed nanofluid flow and heat transfer in a vertical channel are investigated. By means of a new set of similarity variables, the governing equations are reduced to a set of three coupled equations with an unknown constant, which are solved along with the corresponding boundary conditions and the mass flux conservation relation by the homotopy perturbation method (HPM. We have tried to show reliability and performance of the present method compared with the numerical method (Runge–Kutta fourth-rate to solve this problem. The effects of the Grashof number (Gr, Prandtl number (Pr and Reynolds number (Re on the nanofluid flows are then investigated successively. The effects of the Brownian motion parameter (Nb, the thermophoresis parameter (Nt, and the Lewis number (Le on the temperature and nanoparticle concentration distributions are discussed. The current analysis shows that the nanoparticles can improve the heat transfer characteristics significantly for this flow problem.
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....
Mathematical simulation of a twisted pseudoplastic fluid flow in a cylindrical channel
Matvienko, O. V.; Bazuev, V. P.; Yuzhanova, N. K.
2011-05-01
The results of investigations of a pseudoplastic fluid twisted flow in a cylindrical channel are presented. With increase in the shear stresses caused by the flow twisting, the effective viscosity decreases. As a result, in the axial part of the channel a zone of lower pressure is formed which, at smaller flow twisting, leads to the formation of the zone of backward flows.
Ke, Xinyou; Prahl, Joseph M.; Alexander, J. Iwan D.; Savinell, Robert F.
2016-01-01
In this work, a two-dimensional mathematical model is developed to study the flow patterns and volumetric flow penetrations in the flow channel over the porous electrode layered system in vanadium flow battery with serpentine flow field design. The flow distributions at the interface between the flow channel and porous electrode are examined. It is found that the non-linear pressure distributions can distinguish the interface flow distributions under the ideal plug flow and ideal parabolic fl...
Numerical investigation of particles turbulent dispersion in channel flow
Directory of Open Access Journals (Sweden)
Li Tian
2012-01-01
Full Text Available This paper investigates the performance of Reynolds-averaged Navier-Stokes model on dispersion of particles in wall turbulence. A direct numerical simulation of wall-bounded channel flow with particles suspensions was set as a benchmark. The standard k-ω model coupled with two different eddy interaction models was used in Reynolds-averaged Navier-Stokes model and compared to the direct numerical simulation. Detailed comparisons between direct numerical simulation and Reynolds-averaged Navier-Stokes model on particle distribution evolving over time were carried out.
Investigation on Effect of Flow Direction on Hydrodynamics for vertical Channel Bubbly Flow
Directory of Open Access Journals (Sweden)
M Pang
2016-12-01
Full Text Available In order to fully understand hydrodynamics of the bubbly flow laden with microbubbles, the effect of flow direction on the phase distribution and the liquid–phase turbulence modulation in a vertical channel flow laden with microbubbles was detailedly investigated with a developed numerical method, where the liquid–phase velocity field was solved by direct numerical simulations and the microbubble trajectories were tracked by Newtonian equations of motion. The present investigations show the flow direction has the key influence on the phase distribution and the liquid–phase turbulence modulation; for the bubbly upflow, the overwhelming majority of microbubbles accumulate near the channel wall, the phase distribution display approximately the double–peaked distribution patter, and the liquid–phase turbulence was suppressed; for the bubby downflow, however, the microbubbles are far away from the channel wall to move towards the channel centre, the phase distribution shows roughly the off–center–peaked distribution pattern, and the liquid–phase turbulence was enhanced.
Energy Technology Data Exchange (ETDEWEB)
Sanaye, S.; Dehghandokht, M. [Iran Univ. of Science and Technology, Tehran (Iran, Islamic Republic of). Dept. of Mechanical Engineering, Energy Systems Improvement Lab; Beigi, H.M.; Bahrami, S. [Sardsaz Khodro Co., Tehran (Iran, Islamic Republic of). Research and Development Div.
2010-07-01
The problem of ozone depletion was partly solved by replacing CFC refrigerant with HFC refrigerants. Since the risk of refrigerant leak in automotive air conditioning systems is much greater than that of common air conditioning systems and refrigerators, there is a need to develop new automotive air conditioning systems that consume less power and require less refrigerant. This paper presented and validated the thermal performance of a parallel flow multi-channel condenser developed by Sardsaz Khodro Company. The condenser is a brazed aluminium one with air in cross-flow; the refrigerant circulates inside multi-channel flat tubes composed of 7 parallel ports. The condenser is composed of 4 refrigerant passes and several small channel tubes. The air follows a single cross flow path across louvered fins. A computer program for performance analysis of parallel flow condensers widely used in mobile air conditioning systems, using an empirical equation for the heat transfer coefficient, was developed on the basis of pressure drop. The model was based on an effectiveness-NTU method. The simulated performance results for the condenser heat capacity, refrigerant pressure drop, subcooling at the outlet of condenser and condenser outlet air temperature were close to experimental data results from calorimeter tests. 5 refs., 11 figs.
Streamwise decay of localized states in channel flow
Zammert, Stefan
2016-01-01
Channel flow, the pressure driven flow between parallel plates, has exact coherent structures that show various degrees of localization. For states which are localized in streamwise direction but extended in spanwise direction, we show that they are exponentially localized, with decay constants that are different on the upstream and downstream side. We extend the analysis of Brand and Gibson, J. Fluid Mech. 750, R1 (2014), for stationary states to the case of advected structures that is needed here, and derive expressions for the decay in terms of eigenvalues and eigenfunctions of certain second order differential equations. The results are in very good agreement with observations on exact coherent structures of different transversal wave length.
MHD pressure driven flow of nanofluid in curved channel
Energy Technology Data Exchange (ETDEWEB)
Noreen, S. [Department of Mathematics, COMSATS Institute of Information Technology, Park Road, Chak Shehzad, Islamabad 44000 (Pakistan); Qasim, M., E-mail: mq_qau@yahoo.com [Department of Mathematics, COMSATS Institute of Information Technology, Park Road, Chak Shehzad, Islamabad 44000 (Pakistan); Khan, Z.H. [Department of Mathematics, University of Malakand, Dir (Lower), Khyber Pakhtunkhwa (Pakistan)
2015-11-01
The pressure driven peristaltic flow of nanofluid in a curved channel is investigated. The flow exploration demeanors the induced magnetic field. Long wavelength and low Reynolds number approach is followed. Numerical solutions are obtained by employing shooting method. The effects of substantial parameters have been portrayed and discussed on the temperature and mass distributions, stream function, magnetic force function, induced magnetic field and pressure rise per wavelength. - Highlights: • Symmetry in the profiles of u, ϕ and h{sub x} is disturbed because of curvature effects. • The magnitude of longitudinal velocity increases with curvature. • The qualitative behavior of Nt and Nb on γ and Ω is opposite. • Magnitude h{sub x} decreases with k.
influence of off-take angles on flow distribution at concave channel
African Journals Online (AJOL)
user
the walls of the channels are mostly not the effective boundaries of the flow region resulting to the occurrence of separation zone. Taylor [10] conducted the first comprehensive study on a dividing flow in open channel and suggested from the results obtained that for a given angle of intersection of the branch channel, it was.
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.
Atlas chamber, power flow channel, and diagnostic interface design
Energy Technology Data Exchange (ETDEWEB)
Wurden, G.A.; Davis, H.A.; Taylor, A.; Bowman, D.; Ballard, E.; Ney, S.; Scudder, D.; Trainor, J.
1997-09-01
The Atlas pulsed-power machine, presently being designed at Los Alamos, will deliver a pulse of {approximately} 45 MA, in 4--5 {micro}sec, with energies of up to 6 MJ (from a bank of 36 MJ maximum) to a load assembly, located in vacuum. Design considerations for the vacuum vessel, power flow channel from the vessel inward, are presented. In contrast to Sandia`s PBFA II-Z, where 20 MA currents and 2--2.5 MJ of energy are delivered to ({approximately} 15 mg) loads in {approximately} 100 nsec, the Atlas structures will have to be designed for longer timescales and higher energies to drive heavy lines ({approximately} 70 g). Design issues for the chamber include materials stresses, formation of (and protection from) debris and molten jets, impulse loading, and survivability and ease of replacement of internal structures. For the power flow channel designs, issues are minimizing inductance, preventing movement of conductors during and after firing, damage mitigation, reducing the cost of materials and installation, and electrical insulation. A key issue for damage mitigation is the radius within which total destruction of material objects occurs. Choices of vessel size, insulator materials, cost and ease of manufacturing, and mechanical stability issues are presently in the conceptual design phase. Typical access requirements for diagnostics (including radial and axial X-ray backlighting, flux loops, spectroscopy, interferometry, bolometry, etc.) are provided for in the design.
Flow visualization in a low-density plasma channel
Kimmel, R. L.; Hayes, J. R.; Estevadeordal, J.; Crafton, J. W.; Fonov, S. D.; Gogineni, S.
2010-04-01
A schlieren system and surface-stress-sensitive film system were developed for a plasma channel which posed unique challenges for flow visualization because of the combination of low air density and the presence of plasma discharges. Temperature-sensitive paint and direct-current discharge were also applied to flow visualization. Three pulsed schlieren light sources were evaluated. A light-emitting diode (LED), a xenon NanopulserTM and laser breakdown, were tested on identical flowfields. The LED provided excellent illumination, with pulses ranging from μs to continuous. The NanopulserTM provided excellent, short-duration images, although illumination varied from shot-to-shot. Laser-breakdown provided short-duration, incoherent illumination that was constant from pulse-to-pulse. The surface-stress-sensitive film was applied to surface flow visualization. A low-modulus elastomer doped with a luminescent dye was used to visualize the surface shear stress and pressure field in laminar shock boundary layer interactions. Intensity distributions from the dye were imaged to interrogate the surface pressure gradients. Displacement of surface markers provided shear information. Results showed the presence of Görtler vortices in the reattaching shear flow. Görtler vortices were also evident in temperature-sensitive paint images and in the plasma discharge glow. These vortices were evident in the intensity images from the elastomer, which could be related to the surface pressure gradient, but were not readily evident in surface shear measurements.
Multiphysical model of heterogenous flow moving along а channel of variable cross-section
Directory of Open Access Journals (Sweden)
М. А. Васильева
2017-10-01
Full Text Available The article deals with the problem aimed at solving the fundamental problems of developing effective methods and tools for designing, controlling and managing the stream of fluid flowing in variable-section pipelines intended for the production of pumping equipment, medical devices and used in such areas of industry as mining, chemical, food production, etc. Execution of simulation modelling of flow motion according to the scheme of twisted paddle static mixer allows to estimate the efficiency of mixing by calculating the trajectory and velocities of the suspended particles going through the mixer, and also to estimate the pressure drop on the hydraulic flow resistance. The model examines the mixing of solids dissolved in a liquid at room temperature. To visualize the process of distributing the mixture particles over the cross-section and analyzing the mixing efficiency, the Poincaréplot module of the COMSOL Multiphysics software environment was used. For the first time, a multi-physical stream of heterogeneous flow model has been developed that describes in detail the physical state of the fluid at all points of the considered section at the initial time, takes into account the design parameters of the channel (orientation, dimensions, material, etc., specifies the laws of variation of the parameters at the boundaries of the calculated section in conditions of the wave change in the internal section of the working chamber-channel of the inductive peristaltic pumping unit under the influence of the energy of the magnetic field.
Inverse optical imaging viewed as a backward channel communication problem
De Micheli, Enrico
2013-01-01
The inverse problem in optics, which is closely related to the classical question of the resolving power, is reconsidered as a communication channel problem. The main result is the evaluation of the maximum number $M_\\epsilon$ of $\\epsilon$-distinguishable messages ($\\epsilon$ being a bound on the noise of the image) which can be conveyed back from the image to reconstruct the object. We study the case of coherent illumination. By using the concept of Kolmogorov's $\\epsilon$-capacity, we obtain: $M_\\epsilon ~ 2^{S \\log(1/\\epsilon)} \\to \\infty$ as $\\epsilon \\to 0$, where S is the Shannon number. Moreover, we show that the $\\epsilon$-capacity in inverse optical imaging is nearly equal to the amount of information on the object which is contained in the image. We thus compare the results obtained through the classical information theory, which is based on the probability theory, with those derived from a form of topological information theory, based on Kolmogorov's $\\epsilon$-entropy and $\\epsilon$-capacity, whi...
Does the choice of the forcing term affect flow statistics in DNS of turbulent channel flow?
Quadrio, Maurizio; Hasegawa, Yosuke
2015-01-01
We seek possible statistical consequences of the way a forcing term is added to the Navier--Stokes equations in the Direct Numerical Simulation (DNS) of incompressible channel flow. Simulations driven by constant flow rate, constant pressure gradient and constant power input are used to build large databases, and in particular to store the complete temporal trace of the wall-shear stress for later analysis. As these approaches correspond to different dynamical systems, it can in principle be envisaged that these differences are reflect by certain statistics of the turbulent flow field. The instantaneous realizations of the flow in the various simulations are obviously different, but, as expected, the usual one-point, one-time statistics do not show any appreciable difference. However, the PDF for the fluctuations of the streamwise component of wall friction reveals that the simulation with constant flow rate presents lower probabilities for extreme events of large positive friction. The low probability value ...
Computer model for selective flow measuring structures in open channels
Hickey, M. J.
1980-02-01
Quantifying various pollutants in natural waterways has received increased emphasis with more stringent regulations issued by the Environmental Protection Agency (E.P.A.). Measuring natural stream flows presents a magnitude of problems, the most significant is the type of structure needed to measure the flows at the desired level of accuracy. A computer model designed to select a structure to best fit the engineer's needs is under development. This model, given the pertinent boundary conditions, will pinpoint the structure most suitable, if one exists. This selection process greatly facilitates the old selection process of trial and error.
Integral representation in the hodograph plane for compressible flow problems
DEFF Research Database (Denmark)
Hansen, Erik Bent; Hsiao, George C.
1999-01-01
The compressible flow equations are linear in the hodograph plane. This fact is exploited to derive a representation formula and to construct a fundamental solution for compressible, subsonic flow problems....
What Ion Flow along Ion Channels Can Tell us about Their Functional Activity
Directory of Open Access Journals (Sweden)
Lucia Becucci
2016-12-01
Full Text Available The functional activity of channel-forming peptides and proteins is most directly verified by monitoring the flow of physiologically relevant inorganic ions, such as Na+, K+ and Cl−, along the ion channels. Electrical current measurements across bilayer lipid membranes (BLMs interposed between two aqueous solutions have been widely employed to this end and are still extensively used. However, a major drawback of BLMs is their fragility, high sensitivity toward vibrations and mechanical shocks, and low resistance to electric fields. To overcome this problem, metal-supported tethered BLMs (tBLMs have been devised, where the BLM is anchored to the metal via a hydrophilic spacer that replaces and mimics the water phase on the metal side. However, only mercury-supported tBLMs can measure and regulate the flow of the above inorganic ions, thanks to mercury liquid state and high hydrogen overpotential. This review summarizes the main results achieved by BLMs incorporating voltage-gated channel-forming peptides, interpreting them on the basis of a kinetic mechanism of nucleation and growth. Hg-supported tBLMs are then described, and their potential for the investigation of voltage-gated and ohmic channels is illustrated by the use of different electrochemical techniques.
Sugihara-Seki, M
2001-01-01
The flow around adherent cells in a parallel-plate channel and that in a circular cylindrical tube are numerically analyzed, and their effects on the adherent cells are compared. The cells are modeled as rigid spherical particles and they are assumed to be attached to a wall of a 2D channel uniformly in a square array, or a wall of a circular tube regularly in a line along the tube axis. It is found that, when the size ratios of the particle-to-channel height and the particle-to-tube diameter are smaller than approximately 0.2, the distributions of the shear stress and the pressure exerted on the surface of an adherent particle as well as the drag force and torque acting on it compare favorably in the 2D channel flow and tube flow. As the size ratios increase from 0.2, the differences between the 2D channel and the tube increase drastically, especially when separation distances between neighboring particles are large.
Directory of Open Access Journals (Sweden)
Syed Tauseef Mohyud-Din
2015-12-01
Full Text Available This article is dedicated to analyzing the heat transfer in the flow of water-based nanofluids in a channel with non-parallel stretchable walls. The magnetohydrodynamic (MHD nature of the flow is considered. Equations governing the flow are transformed into a system of nonlinear ordinary differential equations. The said system is solved by employing two different techniques, the variational iteration method (VIM and the Runge-Kutta-Fehlberg method (RKF. The influence of the emerging parameters on the velocity and temperature profiles is highlighted with the help of graphs coupled with comprehensive discussions. A comparison with the already existing solutions is also made, which are the special cases of the current problem. It is observed that the temperature profile decreases with an increase in the nanoparticle volume fraction. Furthermore, a magnetic field can be used to control the possible separation caused by the backflows in the case of diverging channels. The effects of parameters on the skin friction coefficient and Nusselt number are also presented using graphical aid. The nanoparticle volume fraction helps to reduce the temperature of the channel and to enhance the rate of heat transfer at the wall.
Solving the minimum flow problem with interval bounds and flows
Indian Academy of Sciences (India)
The minimum cost ﬂow problem with interval data can be solved using two minimum cost ﬂow problems with crisp data. In this paper, the idea of Ghiyasvand was extended for solving the minimum ﬂow problem with interval-valued lower, upper bounds and ﬂows. This problem can be solved using two minimum ﬂow ...
Insights from depth-averaged numerical simulation of flow at bridge abutments in compound channels.
2011-07-01
Two-dimensional, depth-averaged flow models are used to study the distribution of flow around spill-through abutments situated on floodplains in compound channels and rectangular channels (flow on very wide floodplains may be treated as rectangular c...
More Than Flow: Revisiting the Theory of Four Channels of Flow
Directory of Open Access Journals (Sweden)
Ching-I Teng
2012-01-01
Full Text Available Flow (FCF theory has received considerable attention in recent decades. In addition to flow, FCF theory proposed three influential factors, that is, boredom, frustration, and apathy. While these factors have received relatively less attention than flow, Internet applications have grown exponentially, warranting a closer reexamination of the applicability of the FCF theory. Thus, this study tested the theory that high/low levels of skill and challenge lead to four channels of flow. The study sample included 253 online gamers who provided valid responses to an online survey. Analytical results support the FCF theory, although a few exceptions were noted. First, skill was insignificantly related to apathy, possibly because low-skill users can realize significant achievements to compensate for their apathy. Moreover, in contrast with the FCF theory, challenge was positively related to boredom, revealing that gamers become bored with difficult yet repetitive challenges. Two important findings suggest new directions for FCF theory.
Flow analysis in a return channel of a multi-stage centrifugal pump
Energy Technology Data Exchange (ETDEWEB)
Lee, Jung Hyun; Hur, Nahm Keon; Moshfeghi, Mohammad [Sogang University, Seoul (Korea, Republic of); Yoon, In Sik [Dooch Pump, Hwasung (Korea, Republic of)
2016-09-15
Flow recirculation is an unpleasant and even hazardous phenomenon that can cause mechanical damage in turbomachinery and has to be prevented during their operations. We numerically studied the effects of return channel blade curvature on reducing the recirculation of flow inside the return channel vanes of a multi-stage centrifugal pump. Computational fluid dynamics (CFD) analyses were performed for a wide range of volumetric flow rates. The standard k-ε turbulence model was adopted as the turbulence model, and the impeller rotation simulated employing the Multiple reference frames (MRF) method. First, a baseline model together with five different modified geometries for return channel was studied and compared using a two-stage pump framework. The results reveal that decreasing the curvature of the return channel blade makes smooth streamlines and eliminates the flow recirculation inside the return channels. As the second part, two return channels with the highest pump performance were selected to be used in the simulation of a multistage pump. The simulations of the multi-stage pump show that the flow inside the baseline return channel includes considerable areas of flow recirculation, while the modified return channels again have attached flow stream. It is concluded that the return channels with the smooth curvatures and outlet blade angles above 90° remove the flow recirculation inside the return channels, resulting in higher pump efficiencies.
Solute dispersion in open channel flow with bed absorption
Wang, Ping; Chen, G. Q.
2016-12-01
Reactive solute dispersion is of essential significance in various ecological and environmental applications. It is only qualitatively known that boundary absorption depletes pollutant around the boundary and reduces the concentration nearby. All the existing studies on this topic have been focused on the longitudinally distributed mean concentration, far from enough to fully characterize the transport process with tremendous cross-sectional concentration nonuniformity. This work presents an analytical study of the evolution of two-dimensional concentration distribution for solute dispersion in a laminar open channel flow with bed absorption. The fourth order Aris-Gill expansion proposed in our previous study (Wang and Chen, 2016b) is further extended for the case with bed absorption to cover the transitional effects of skewness and kurtosis. Results reveal the extremely nonuniform cross-sectional concentration distribution, and demonstrate that concentration at the bed instead of the mean should be used for reliable quantification of the absorption flux. The accurate two-dimensional concentration distribution presented in this study brings important environmental implications such as risk assessment associated with peak concentration position and duration of toxic pollutant cloud in open channel waters.
Directory of Open Access Journals (Sweden)
Islam S.M. Khalil
2016-06-01
Full Text Available Targeted therapy using magnetic microparticles and nanoparticles has the potential to mitigate the negative side-effects associated with conventional medical treatment. Major technological challenges still need to be addressed in order to translate these particles into in vivo applications. For example, magnetic particles need to be navigated controllably in vessels against flowing streams of body fluid. This paper describes the motion control of paramagnetic microparticles in the flowing streams of fluidic channels with time-varying flow rates (maximum flow is 35 ml.hr−1. This control is designed using a magnetic-based proportional-derivative (PD control system to compensate for the time-varying flow inside the channels (with width and depth of 2 mm and 1.5 mm, respectively. First, we achieve point-to-point motion control against and along flow rates of 4 ml.hr−1, 6 ml.hr−1, 17 ml.hr−1, and 35 ml.hr−1. The average speeds of single microparticle (with average diameter of 100 μm against flow rates of 6 ml.hr−1 and 30 ml.hr−1 are calculated to be 45 μm.s−1 and 15 μm.s−1, respectively. Second, we implement PD control with disturbance estimation and compensation. This control decreases the steady-state error by 50%, 70%, 73%, and 78% at flow rates of 4 ml.hr−1, 6 ml.hr−1, 17 ml.hr−1, and 35 ml.hr−1, respectively. Finally, we consider the problem of finding the optimal path (minimal kinetic energy between two points using calculus of variation, against the mentioned flow rates. Not only do we find that an optimal path between two collinear points with the direction of maximum flow (middle of the fluidic channel decreases the rise time of the microparticles, but we also decrease the input current that is supplied to the electromagnetic coils by minimizing the kinetic energy of the microparticles, compared to a PD control with disturbance compensation.
Lovette, J. P.; Duncan, J. M.; Vimal, S.; Band, L. E.
2015-12-01
Natural riparian areas play numerous roles in the maintenance and improvement of stream water quality. Both restoration of riparian areas and improvement of hydrologic connectivity to the stream are often key goals of river restoration projects. These management actions are designed to improve nutrient removal by slowing and treating overland flow delivered from uplands and by storing, treating, and slowly releasing streamwater from overbank inundation during flood events. A major question is how effective this storage of overbank flow is at treating streamwater based on the cumulative time stream discharge at a downstream location has spent in shallower, slower overbank flow. The North Carolina Floodplain Mapping Program maintains a detailed statewide Flood Risk Information System (FRIS) using HEC-RAS modeling, lidar, and detailed surveyed river cross-sections. FRIS provides extensive information regarding channel geometry on approximately 39,000 stream reaches (a slightly coarser spatial resolution than the NHD+v2 dataset) with tens of cross-sections for each reach. We use this FRIS data to calculate volume and discharge from floodplain riparian areas separately from in-channel flow during overbank events. Preliminary results suggest that a small percentage of total annual discharge interacts with the full floodplain extent along a stream reach due to the infrequency of overbank flow events. However, with the significantly different physical characteristics of the riparian area when compared to the channel itself, this overbank flow can provide unique services to water quality. Our project aims to use this information in conjunction with data from the USGS SPARROW program to target non-point source hotspots of Nitrogen and Phosphorus addition and removal. By better understanding the flow dynamics within riparian areas during high flow events, riparian restoration projects can be carried out with improved efficacy.
Relaminarisation of Re_{\\tau} = 100 channel flow with globally stabilising linear feedback control
Sharma, A S; McKeon, B J; Limebeer, D J N L; Koberg, W H; Sherwin, S J; 10.1063/1.3662449
2013-01-01
The problems of nonlinearity and high dimension have so far prevented a complete solution of the control of turbulent flow. Addressing the problem of nonlinearity, we propose a flow control strategy which ensures that the energy of any perturbation to the target profile decays monotonically. The controller's estimate of the flow state is similarly guaranteed to converge to the true value. We present a one-time off-line synthesis procedure, which generalises to accommodate more restrictive actuation and sensing arrangements, with conditions for existence for the controller given in this case. The control is tested in turbulent channel flow ($Re_\\tau=100$) using full-domain sensing and actuation on the wall-normal velocity. Concentrated at the point of maximum inflection in the mean profile, the control directly counters the supply of turbulence energy arising from the interaction of the wall-normal perturbations with the flow shear. It is found that the control is only required for the larger-scale motions, sp...
Mathematical modelling and its impact on open channel flow | Eyo ...
African Journals Online (AJOL)
Mathematical model for dredging (excavating) an open channel, namely, a river has been developed using the conditions for best hydraulic performances for the channel. Applying the model to a numerical example we determine new dimensions for the new open channel for two-channel sections, viz: the trapezoidal and ...
Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel.
Directory of Open Access Journals (Sweden)
Aaiza Gul
Full Text Available This study investigated heat transfer in magnetohydrodynamic (MHD mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe3O4 was selected as a conventional base fluid. In addition, non-magnetic (Al2O3 aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work.
Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel.
Gul, Aaiza; Khan, Ilyas; Shafie, Sharidan; Khalid, Asma; Khan, Arshad
2015-01-01
This study investigated heat transfer in magnetohydrodynamic (MHD) mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe3O4) was selected as a conventional base fluid. In addition, non-magnetic (Al2O3) aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work.
Dynamic evolution process of turbulent channel flow after opposition control
Ge, Mingwei; Tian, De; Yongqian, Liu
2017-02-01
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 and in the viscous sublayer. Project supported by the National Natural Science Foundation of China (Grant No. 11402088 and Grant No. 51376062) , State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources (Grant No. LAPS15005), and ‘the Fundamental Research Funds for the Central Universities’ (Grant No.2014MS33).
Directory of Open Access Journals (Sweden)
Duangthongsuk Weerapun
2017-01-01
Full Text Available This article presents an experimental investigation on the heat transfer performance and pressure drop characteristic of two types of nanofluids flowing through microchannel heat sink with multiple zigzag flow channel structures (MZMCHS. SiO2 nanoparticles dispersed in DI water with concentrations of 0.3 and 0.6 vol.% were used as working fluid. MZMCHS made from copper material with dimension of 28 × 33 mm. Hydraulic diameter of MZMCHs is designed at 1 mm, 7 number of flow channels and heat transfer area is about 1,238 mm2. Effects of particle concentration and flow rate on the thermal and hydraulic performances are determined and then compare with the common base fluid. The results indicated that the heat transfer coefficient of nanofluids was higher than that of the water and increased with increasing particle concentration as well as Reynolds number. For pressure drop, the particle concentrations have no significant effect on the pressure drop across the test section.
Komar, P. D.
1979-01-01
The hydraulics of channelized water flows on Mars and the resulting sediment transport rates are calculated, and similar computations are performed for such terrestrial analogs as the Mississippi River and the catastrophic Lake Missoula floods that formed the Channeled Scabland in eastern Washington State. The morphologies of deep-sea channels formed by catastrophic turbidity currents are compared with the Martian channels, many similarities are pointed out, and the hydraulics of the various flows are compared. The results indicate that the velocities, discharges, bottom shear stresses, and sediment-transport capacity of water flows along the Martian channels would be comparable to those of the oceanic turbidity currents and the Lake Missoula floods. It is suggested that the submarine canyons from which turbidity currents originate are the terrestrial counterparts to the chaotic-terrain areas or craters that serve as sources for many of the Martian channels.
Yambe, Kiyoyuki; Saito, Hidetoshi
2017-12-01
When the working gas of an atmospheric-pressure non-equilibrium (cold) plasma flows into free space, the diameter of the resulting flow channel changes continuously. The shape of the channel is observed through the light emitted by the working gas of the atmospheric-pressure plasma. When the plasma jet forms a conical shape, the diameter of the cylindrical shape, which approximates the conical shape, defines the diameter of the flow channel. When the working gas flows into the atmosphere from the inside of a quartz tube, the gas mixes with air. The molar ratio of the working gas and air is estimated from the corresponding volume ratio through the relationship between the diameter of the cylindrical plasma channel and the inner diameter of the quartz tube. The Reynolds number is calculated from the kinematic viscosity of the mixed gas and the molar ratio. The gas flow rates for the upper limit of laminar flow and the lower limit of turbulent flow are determined by the corresponding Reynolds numbers estimated from the molar ratio. It is confirmed that the plasma jet length and the internal plasma length associated with strong light emission increase with the increasing gas flow rate until the rate for the upper limit of laminar flow and the lower limit of turbulent flow, respectively. Thus, we are able to explain the increasing trend in the plasma lengths with the diameter of the flow channel and the molar ratio by using the cylindrical approximation.
Electro-osmotic flow of couple stress fluids in a micro-channel propagated by peristalsis
Tripathi, Dharmendra; Yadav, Ashu; Anwar Bég, O.
2017-04-01
A mathematical model is developed for electro-osmotic peristaltic pumping of a non-Newtonian liquid in a deformable micro-channel. Stokes' couple stress fluid model is employed to represent realistic working liquids. The Poisson-Boltzmann equation for electric potential distribution is implemented owing to the presence of an electrical double layer (EDL) in the micro-channel. Using long wavelength, lubrication theory and Debye-Huckel approximations, the linearized transformed dimensionless boundary value problem is solved analytically. The influence of electro-osmotic parameter (inversely proportional to Debye length), maximum electro-osmotic velocity (a function of external applied electrical field) and couple stress parameter on axial velocity, volumetric flow rate, pressure gradient, local wall shear stress and stream function distributions is evaluated in detail with the aid of graphs. The Newtonian fluid case is retrieved as a special case with vanishing couple stress effects. With increasing the couple stress parameter there is a significant increase in the axial pressure gradient whereas the core axial velocity is reduced. An increase in the electro-osmotic parameter both induces flow acceleration in the core region (around the channel centreline) and it also enhances the axial pressure gradient substantially. The study is relevant in the simulation of novel smart bio-inspired space pumps, chromatography and medical micro-scale devices.
Analytical solution of time periodic electroosmotic flows: analogies to Stokes' second problem.
Duttat, P; Beskok, A
2001-11-01
Analytical solutions of time periodic electroosmotic flows in two-dimensional straight channels are obtained as a function of a nondimensional parameter kappa, which is based on the electric double-layer (EDL) thickness, kinematic viscosity, and frequency of the externally applied electric field. A parametric study as a function of kappa reveals interesting physics, ranging from oscillatory "pluglike" flows to cases analogous to the oscillating flat plate in a semi-infinite flow domain (Stokes' second problem). The latter case differs from the Stokes' second solution within the EDL, since the flow is driven with an oscillatory electric field rather than an oscillating plate. The analogous case of plate oscillating with the Helmholtz-Smoluchowski velocity matches our analytical solution in the bulk flow region. This indicates that the instantaneous Helmholtz-Smoluchowski velocity is the appropriate electroosmotic slip condition even for high-frequency excitations. The velocity profiles for large kappa values show inflection points very near the walls with localized vorticity extrema that are stronger than the Stokes layers. This have the potential to result in low Reynolds number flow instabilities. It is also shown that, unlike the steady pure electroosmotic flows, the bulk flow region of time periodic electroosmotic flows are rotational when the diffusion length scales are comparable to and less than the half channel height.
Zamuraev, V. P.; Kalinina, A. P.
2017-10-01
This work concerns the process of deceleration of supersonic flow up to the transonic velocities in the channel. This process is connected with the problem of combustion organizing of fuels in the various ramjet engines. The influence of mode of energy supply and the type of channel geometry (axisymmetric or planar channel) is studied as well as the other factors. The similarity of gas dynamic structure formed under hydrogen burning and under pulse periodic energy supply is studied.
Combined free and forced convection flow in a rotating channel with ...
African Journals Online (AJOL)
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Seth, G.S. and Singh,M.K., 2008. Combined free and forced convection MHD flow in a rotating channel with perfectly conducting walls, Ind. J. Theo. Phys., Vol. 56, pp. 203. Seth, G.S. and Ansari, Md. S., 2009. Magnetohydrodynamic convective flow in a rotating channel with Hall effects, Int. J. Theor. Appl. Mech., Vol. 4, No.
Two-phase flow boiling in small channels: A brief review
Indian Academy of Sciences (India)
Boiling flows are encountered in a wide range of industrial applications such as boilers, core and steam generators in nuclear reactors, petroleum transportation, electronic cooling and various types of chemical reactors. Many of these applications involve boiling flows in conventional channels (channel size ≥ 3 mm).
influence of off-take angles on flow distribution at concave channel
African Journals Online (AJOL)
user
ABSTRACT. A physical model with meandering features was constructed and used to investigate the effect of off-take angles on the flow distribution at a concave channel bifurcation. Seven different off-take angles with varied main channel flow rates were used for the study. Predicting equations for the off-take discharge ...
Combined free and forced convection flow in a rotating channel with ...
African Journals Online (AJOL)
user
Math. Soc., BHU, Varanasi, India,. Vol. 12, pp. 47. Seth, G.S. and Singh,M.K., 2008. Combined free and forced convection MHD flow in a rotating channel with perfectly conducting walls, Ind. J. Theo. Phys., Vol. 56, pp. 203. Seth, G.S. and Ansari, Md. S., 2009. Magnetohydrodynamic convective flow in a rotating channel with ...
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
Fabrication of micromachined pipettes in a flow channel for single molecule handling of DNA
Rusu, C.R.; van 't Oever, Ronny; de Boer, Meint J.; Jansen, Henricus V.; Berenschot, Johan W.; Bennink, Martin L.; Kanger, Johannes S.; de Grooth, B.G.; Elwenspoek, Michael Curt; Greve, Jan; van den Berg, Albert; Brugger, J.P.
2000-01-01
We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap set-up (optical tweezers) to study mechanical and structural properties of λ-DNA molecules. The flow cell was realized using silicon
Rusu, C.R.; van 't Oever, Ronny; de Boer, Meint J.; Berenschot, Johan W.; Elwenspoek, Michael Curt; Jansen, Henricus V.; Bennink, Martin L.; Kanger, Johannes S.; de Grooth, B.G.; Greve, Jan; Brugger, J.P.; van den Berg, Albert; de Boer, M.; Mariella Jr., Raymond P.
2000-01-01
We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap set-up (optical tweezers) to study mechanical and structural properties of λ-DNA molecules. The flow cell was realized using silicon
Numerical modelling of thermal and fluid flow phenomena in the mould channel
Directory of Open Access Journals (Sweden)
L. Sowa
2007-12-01
Full Text Available In the paper, a mathematical and a numerical model of the solidification of a cylindrical slender shaped casting, which take into account the process of filling the mould cavity with molten metal, has been proposed. Pressure and velocity fields were obtained by solving the momentum equations and the continuity equation, while the thermal fields were obtained by solving the heat conduction equation containing the convection term. Next, the numerical analysis of the solidification process of metals alloy in a cylindrical mould channel has been made. In the model one takes into account interdependence the heat transfer and fluid flow phenomena. Coupling of the thermal and fluid flow phenomena has been taken into consideration by the changes of the fluidity function and thermophysical parameters of alloy with respect to the temperature. The influence of the pressure and the temperature of metal pouring on the solid phase growth kinetics were estimated. The problem has been solved by the finite element method.
3D Topology optimization of Stokes flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan; Dammann, Bernd
The present talk is concerned with the application of topology optimization to creeping flow problems in 3D. This research is driven by the fact that topology optimization has proven very successful as a tool in academic and industrial design problems. Success stories are reported from such diverse...... fields as solid mechanics and optics and is due to the method's flexibility in the (rough) parametrization of the design, see [1] and the reference therein for an overview. Borrvall and Petersson [2] is the seminal reference for topology optimization in fluid flow problems. They considered design...... of energy efficient devices for 2D Stokes flow. Creeping flow problems are described by the Stokes equations which model very viscous fluids at macro scales or ordinary fluids at very small scales. The latter gives the motivation for topology optimization problems based on the Stokes equations being a model...
Analysis Of The Effect Of Flow Channel Width On The Performance Of PEMFC
Directory of Open Access Journals (Sweden)
Elif Eker
2013-08-01
Full Text Available In this work, it was analysed the effect of different channel width on performance of PEM fuel cell. Current density were measured on the single cells of parallel flow fields that has 25 cm² active layer, using three different kinds of channel width. The cell width and the channel height remain constant.The results show that increasing the channel width while the cell width remains constant decreases the current density.
Energy Technology Data Exchange (ETDEWEB)
Chu, In-Cheol; Lee, Seung Jun; Youn, Young Jung; Park, Jong Kuk; Choi, Hae Seob; Euh, Dong Jin [KAERI, Daejeon (Korea, Republic of)
2015-05-15
CMFD (Computation Multi-Fluid Dynamics) tools have been being developed to simulate two-phase flow safety problems in nuclear reactor, including the precise prediction of local bubble parameters in subcooled boiling flow. However, a lot of complicated phenomena are encountered in the subcooled boiling flow such as bubble nucleation and departure, interfacial drag of bubbles, lateral migration of bubbles, bubble coalescence and break-up, and condensation of bubbles, and the constitutive models for these phenomena are not yet complete. As a result, it is a difficult task to predict the radial profile of bubble parameters and its propagation along the flow direction. Several experiments were performed to measure the local bubble parameters for the validation of the CMFD code analysis and improvement of the constitutive models of the subcooled boiling flow, and to enhance the fundamental understanding on the subcooled boiling flow. The information on the propagation of the local flow parameters along the flow direction was not provided because the measurements were conducted at the fixed elevation. In SUBO experiments, the radial profiles of local bubble parameters, liquid velocity and temperature were obtained for steam-water subcooled boiling flow in a vertical annulus. The local flow parameters were measured at six elevations along the flow direction. The pressure was in the range of 0.15 to 0.2 MPa. We have launched an experimental program to investigate quantify the local subcooled boiling flow structure under elevated pressure condition in order to provide high precision experimental data for thorough validation of up-to-date CMFD codes. In the present study, the first set of experimental data on the propagation of the radial profile of the bubble parameters was obtained for the subcooled boiling flow of R-134a in a pressurized vertical annulus channel. An experimental program was launched for an in-depth investigation of a subcooled boiling flow in an elevated
The Effects of the PEM Fuel Cell Performance with the Waved Flow Channels
Directory of Open Access Journals (Sweden)
Yue-Tzu Yang
2013-01-01
Full Text Available The objective of this study is to use a new style of waved flow channel instead of the plane surface channel in the proton exchange membrane fuel cell (PEMFC. The velocity, concentration, and electrical performance with the waved flow channel in PEMFC are investigated by numerical simulations. The results show that the waved channel arises when the transport benefits through the porous layer and improves the performance of the PEMFC. This is because the waved flow channel enhances the forced convection and causes the more reactant gas flow into the gas diffusion layer (GDL. The performance which was compared to a conventional straight gas flow channel increases significantly with the small gap size when it is smaller than 0.5 in the waved flow channel. The performance is decreased at the high and low velocities as the force convection mechanism is weakened and the reactant gas supply is insufficient. The pressure drop is increased as the gap size becomes smaller, and the wave number decreases. (gap size δ > 0.3 has a reasonable pressure drop. Consequently, compared to a conventional PEMFC, the waved flow channel improves approximately 30% of power density.
Experimental study on the effects of fixed boundaries in channelized free surface dry granular flows
Sarno, Luca; Carleo, Luigi; Nicolina Papa, Maria
2017-04-01
The dynamics of granular mixtures, involved in geophysical flows like avalanches and debris flows, is far from being completely understood. Several features of their motion, such as rheological stratification, non-local and boundary effects, still represent open problems. Experimental investigations at laboratory scale are an important tool that can provide insights about the dynamics of gravity driven granular flows. The measuring techniques should be non-invasive in order to measure undisturbed flows. In this work we present an experimental campaign devoted to the measurement of the velocity profiles of free surface steady granular flows in an open channel. To achieve this goal the flows were recorded by two cameras and velocity profiles were obtained by image analysis. The employed granular medium consists of acetal-polymeric beads with a mean diameter of 3mm and an estimated internal friction angle of 27°. All the experiments have been performed in a 2m-long plexiglas flume with a rectangular cross-section and a slope angle of 30°. The upper part of the channel was used as a reservoir where the material was loaded before each run and then let flow down through an adjustable gate. Several mass flow rates were investigated. Three different basal surfaces were employed so as to observe slip and non-slip boundary conditions: a smooth Bakelite surface, a roughened surface, obtained by gluing a layer of grains on the bed surface and a sandpaper surface with characteristic length of the roughness equal to 425 µm. The flume is equipped with two high-speed cameras, one placed aside the channel and the other one perpendicular to the channel bed, as to get both side-wall and free surface velocity profiles. The particle image velocimetry open-source code, PIVlab, is employed for estimating the flow velocities. All the free surface velocity profiles show an approximately parabolic shape with a maximum at the cross-section midpoint and a minimum at the side-walls, due to
Konopel'ko, N. A.; Shakhov, E. M.
2017-10-01
A kinetic equation (S-model) is used to solve the nonstationary problem of a monatomic rarefied gas flowing from a tank of infinite capacity into a vacuum through a long plane channel. Initially, the gas is at rest and is separated from the vacuum by a barrier. The temperature of the channel walls is kept constant. The flow is found to evolve to a steady state. The time required for reaching a steady state is examined depending on the channel length and the degree of gas rarefaction. The kinetic equation is solved numerically by applying a conservative explicit finite-difference scheme that is firstorder accurate in time and second-order accurate in space. An approximate law is proposed for the asymptotic behavior of the solution at long times when the evolution to a steady state becomes a diffusion process.
Energy Technology Data Exchange (ETDEWEB)
Desrayaud, G. [Universite de Picardie Jules Verne, INSSET, Lab. Modelisation et Simulation Multi Echelle, MSME FRE 3160 CNRS, 02 - Saint-Quentin (France); Lauriat, G. [Universite Paris-Est, Lab. Modelisation et Simulation Multi Echelle, MSME FRE 3160 CNRS, 77 - Marne-la-Vallee (France)
2009-11-15
The present numerical investigation is concerned with flow reversal phenomena for laminar, mixed convection of air in a vertical parallel-plate channel of finite length. Results are obtained for buoyancy-assisted flow in a symmetrically heated channel with uniform wall temperatures for various Grashof numbers and Reynolds numbers in the range 300 {<=} Re {<=} 1300. The effects of buoyancy forces on the flow pattern are investigated and the shapes of velocity and temperature profiles are discussed in detail. Flow reversals centred in the entrance of the channel are predicted. The strength of the cells decreases as the Reynolds number is increased, until they disappear. The regime of reversed flow is identified for high values of the Peclet number in a Pe-Gr/Re map. It is also shown that the channel length has no influence on the occurrence of the reversal flow provided that H/D {>=} 10. (authors)
Modeling Flow Pattern and Evolution of Meandering Channels with a Nonlinear Model
Directory of Open Access Journals (Sweden)
Leilei Gu
2016-09-01
Full Text Available Meander dynamics has been the focus of river engineering for decades; however, it remains a challenge for researchers to precisely replicate natural evolution processes of meandering channels with numerical models due to the high nonlinearity of the governing equations. The present study puts forward a nonlinear model to simulate the flow pattern and evolution of meandering channels. The proposed meander model adopts the nonlinear hydrodynamic submodel developed by Blanckaert and de Vriend, which accounts for the nonlinear interactions between secondary flow and main flow and therefore has no curvature restriction. With the computational flow field, the evolution process of the channel centerline is simulated using the Bank Erosion and Retreat Model (BERM developed by Chen and Duan. Verification against two laboratory flume experiments indicates the proposed meander model yields satisfactory agreement with the measured data. For comparison, the same experimental cases are also simulated with the linear version of the hydrodynamic submodel. Calculated results show that the flow pattern and meander evolution process predicted by the nonlinear and the linear models are similar for mildly curved channels, whereas they exhibit different characteristics when channel sinuosity becomes relatively high. It is indicated that the nonlinear interactions between main flow and secondary flow prevent the growth of the secondary flow and induce a more uniform transverse velocity profile in high-sinuosity channels, which slows down the evolution process of meandering channels.
Phase distribution of nitrogen-water two-phase flow in parallel micro channels
Zhou, Mi; Wang, Shuangfeng; Zhou, You
2017-04-01
The present work experimentally investigated the phase splitting characteristics of gas-liquid two-phase flow passing through a horizontal-oriented micro-channel device with three parallel micro-channels. The hydraulic diameters of the header and the branch channels were 0.6 and 0.4 mm, respectively. Five different liquids, including de-ionized water and sodium dodecyl sulfate (SDS) solution with different concentration were employed. Different from water, the surface tension of SDS solution applied in this work decreased with the increment of mass concentration. Through series of visual experiments, it was found that the added SDS surfactant could obviously facilitate the two-phase flow through the parallel micro channels while SDS solution with low concentration would lead to an inevitable blockage of partial outlet branches. Experimental results revealed that the two phase distribution characteristics depended highly on the inlet flow patterns and the outlet branch numbers. To be specific, at the inlet of slug flow, a large amount of gas preferred flowing into the middle branch channel while the first branch was filled with liquid. However, when the inlet flow pattern was shifted to annular flow, all of the gas passed through the second and the last branches, with a little proportion of liquid flowing into the first channel. By comparison with the experimental results obtained from a microchannel device with five parallel micro-T channels, uneven distribution of the two phase can be markedly noticed in our present work.
Topology optimization of 3D Stokes flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan
Topology optimization has been applied to a multitude of physical systems and is now a mature technology used in industrial practice, see [1] for an overview. Borrvall and Petersson [2] introduced topology optimization of Stokes flow problems which initiated works on extending topology optimization...... to different flow problems. However, this research has focused on 2D fluid modelling, which limits the practical impact of the computed designs. The explanation of the limitation is that the finite size domain used in topology optimization problems ensures that the velocity components couples, even for Stokes...... only. The motivation for considering topology optimization in 3D Stokes flow originates from micro fluidic systems. At small scales the Stokes equations are a reasonable mathematical model to use for the fluid behavior. Physically Stokes flow is an exotic inertia free flow, which in practice...
Topology Optimization of Large Scale Stokes Flow Problems
DEFF Research Database (Denmark)
Aage, Niels; Poulsen, Thomas Harpsøe; Gersborg-Hansen, Allan
2008-01-01
This note considers topology optimization of large scale 2D and 3D Stokes flow problems using parallel computations. We solve problems with up to 1.125.000 elements in 2D and 128.000 elements in 3D on a shared memory computer consisting of Sun UltraSparc IV CPUs.......This note considers topology optimization of large scale 2D and 3D Stokes flow problems using parallel computations. We solve problems with up to 1.125.000 elements in 2D and 128.000 elements in 3D on a shared memory computer consisting of Sun UltraSparc IV CPUs....
The Transitional Backward-Facing Step Flow in a Water Channel with Variable Expansion Geometry
Tihon, J. (Jaroslav); Pěnkavová, V. (Věra); Havlica, J. (Jaromír); Šimčík, M. (Miroslav)
2012-01-01
The backward-facing step flow is investigated experimentally and numerically at moderate Reynolds numbers. The different channel expansion ratios (ER = 1.4, 2, 2.5, and 4) and inlet flow conditions (steady and pulsatile) are applied with the aim to analyze the structure and stability of the flow behind the step. The electrodiffusion technique is used to measure the wall shear rate along the experimental water channel. The direction sensitive sensors detect the near-wall extent of different fl...
Heat transfer and surface flow visualization around a 180 deg turn in a rectangular channel
Energy Technology Data Exchange (ETDEWEB)
Astarita, G.; Cardone, G.; Carlomagno, G.M. [Univ. of Naples (Italy)
1995-12-31
The efficiency of gas turbine engines strongly depends on the gas entry temperature, the higher the latter, the more efficient is the turbine thermal cycle. Present advanced gas turbines operate at gas entry temperatures much higher than metal creeping temperatures and therefore require intensive cooling of their blades especially in the early stages. The aim of the present study is to obtain detailed measurements of the convective heat transfer coefficient nearby a 180deg sharp turn in a rectangular channel, and to prove that the use of infrared thermography may be appropriate to experimentally study this type of problem. A rectangular two-pass channel, which is 40 mm high and 200 mm wide, is tested for two different geometries of the tip of the partition wall: a square tip and semicircular one. To perform surface flow visualization and heat transfer measurements, the heated-thin-foil technique is used and results in terms of temperature maps and Nusselt number Nu distributions are obtained. Nu is computed by means of the local bulk temperature which is evaluated by making a one-dimensional energy balance along the channel. Reynolds number, based on average inlet velocity and hydraulic diameter of the channel is varied between 1.6 {times} 10{sup 4} and 6.4 {times} 10{sup 4}. By moving in the streamwise direction, at the beginning of the heated zone a rapid increase of the wall temperature is found due to the development of the thermal boundary layer. Two well distinguishable separation zones are found, one at the first outer corner of the channel and the other attached to the partition wall and just downstream of its tip. The influence of the geometry of the latter seems to be limited mainly to the position of the onset of the second separation zone. A third weak recirculation zone seems to appear in the vicinity of the second outer corner at the highest tested Reynolds number.
Some problems of hydrodynamics of two-phase flow mixtures in minichannels
Directory of Open Access Journals (Sweden)
Wengel Monika
2014-06-01
Full Text Available Gas-liquid two-phase flow in minichannels has been the subject of increased research interest in the past few years. Evaluation, however, of today’s state of the art regarding hydrodynamics of flow in minichannels shows significant differences between existing test results. In the literature there is no clear information regarding: defining the boundary between minichannels and conventional channels, labelling of flow patterns. The review of literature on the hydrodynamics of gas-liquid flow in minichannels shows that, despite the fact that many research works have been published, the problem of determining the effect of diameter of the minichannel on the hydrodynamics of the flow is still at an early stage. Therefore, the paperpresents the results of research concerning determination of flow regime map for the vertical upward flow in minichannels. The research is based on a comprehensive analysis of the literature data and on the research that has been carried out. Such approach to the mentioned above problems concerning key issues of the two-phase flow in minichannels allowed to determine ranges of occurrence of flow structures with a relatively high accuracy.
Directory of Open Access Journals (Sweden)
A. H. ELBATRAN
2015-07-01
Full Text Available Helical channels have a wide range of applications in petroleum engineering, nuclear, heat exchanger, chemical, mineral and polymer industries. They are used in the separation processes for fluids of different densities. The centrifugal force, free surface and geometrical effects of the helical channel make the flow pattern more complicated; hence it is very difficult to perform physical experiment to predict channel performance. Computational Fluid Dynamics (CFD can be suitable alternative for studying the flow pattern characteristics in helical channels. The different ranges of dimensional parameters, such as curvature and torsion, often cause various flow regimes in the helical channels. In this study, the effects of physical parameters such as curvature, torsion, Reynolds number, Froude number and Dean Number on the characteristics of the turbulent flow in helical rectangular channels have been investigated numerically, using a finite volume RANSE code Fluent of Ansys workbench 10.1 UTM licensed. The physical parameters were reported for range of curvature (δ of 0.16 to 0.51 and torsion (λ of 0.032 to 0.1 .The numerical results of this study showed that the decrease in the channel curvature and the increase in the channel torsion numbers led to the increase of the flow velocity inside the channel and the change in the shape of water free surface at given Dean, Reynolds and Froude numbers.
Vinatier, Fabrice; Belaud, Gilles; Combemale, David
2016-01-01
Vegetation characteristics providing spatial heterogeneity at the channel reach scale can produce complex flow patterns and the relationship between plant patterns morphology and flow resistance is still an open question (Nepf 2012). Unlike experiments in laboratory, measuring the vegetation characteristics related to flow resistance on open channel in situ is difficult. Thanks to its high resolution and light weight, scanner lasers allow now to collect in situ 3D vegetation characteristics. In this study we used a 1064 nm usual Terrestrial Laser Scanner (TLS) located 5 meters at nadir above a 8 meters long equipped channel in order to both i) characterize the vegetation structure heterogeneity within the channel form a single scan (blockage factor, canopy height) and ii) to measure the 2D water level all over the channel during steady flow within a few seconds scan. This latter measuring system was possible thanks to an additive dispersive product sprinkled at the water surface. Vegetation characteristics an...
Problems in rarefied flows and chemical kinetics
Zhang, Peng
In Part I, a theory on weakly rarefied, low Mach number flows with surface reactions based on small sticking coefficients was first formulated for a binary gas mixture with an irreversible surface reaction, and then extended to a multicomponent mixture with multi-step surface reactions for situation in which all chemically active species are small in concentration compared to a major inert species. Particular interest was placed on the interaction between the Knudsen layer and the surface reactions. Results show that the Knudsen layer modifies not only the incident flux of the molecules striking the surface, but also the temperature-sensitive sticking coefficients and consequently the surface reaction rates. The surface reactions in turn modify the flow structure in the Knudsen layer through the non-zero net flux at the surface. Rate expressions for the surface reactions based on sticking coefficients were derived, and slip boundary conditions for temperature and species concentration suitable for application were established. The widely-used Motz-Wise correction formula for the surface reaction rate was revised and the underlying assumptions leading to its derivation were shown to be incorrect. As an application of the theory, an activation energy asymptotic analysis with one-step overall reaction was performed for the stabilization and extinction of a premixed flame over a rotating disk at sufficiently low pressures, for its relevance in low-pressure CVD (chemical vapor deposition) operations in which the flow is weakly rarefied. Extinction criteria based on the critical Damkohler number were obtained through the S-curve concept, parametrically demonstrating the influence of the CVD operating conditions, such as the spin rate and temperature of the disk, on flame extinction. It is further shown that, while decreasing pressure and hence the reactivity of the mixture tends to extinguish the flame, the trend can be substantially weakened by taking into account of
MATHEMATICAL MODEL NON-ISOTHERMAL FLOW HIGHLY VISCOUS MEDIA CHANNELS MATRIX EXTRUDER
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A. S. Sidorenko
2015-01-01
Full Text Available We consider a one-dimensional steady flow of highly viscous medium in a cylindrical channel with Dissipation and dependence of the viscosity on the temperature. It is assumed that a relatively small intervals of temperature variation of the dynamic viscosity with a sufficient degree of accuracy can be assumed to be linear. The model was based on the equations of hydrodynamics and the heat transfer fluid. In the task channel wall temperature is assumed constant. An approximate solution of the problem, according to which the distribution of velocity, pressure and temperature is sought in the form of an expansion in powers of the dimensionless transverse coordinates. A special case, when the ratio of the velocity distribution, pressure and temperature is allowed to restrict the number of terms in the expansion as follows: for speed - the first 3 to the pressure - the first two for the temperature - the first 5. The expressions to determine the temperature profile of the medium in the channel and characterization dissipative heating. To simulate the process of heat transfer highly viscous media developed a program for personal electronic computers. The calculation was performed using experimental research data melt flow grain mixture of buckwheat and soybeans for the load speed of 0.08 mm / s. The method of computer simulation carried out checks on the adequacy of the solutions to the real process of heat transfer. Analysis of the results indicates that for small values of the length of the channel influence dissipation function appears mainly at the wall. By increasing the reduced length of this phenomenon applies to all section of the channel. At high temperature profile along the channel length is determined entirely by dissipation. In the case of heat transfer due to frictional heat only, the form of curves of temperature distribution is a consequence of the interaction effects of heating due to viscous shear effects cooling by conduction. The
Study of heat transfer and flow of nanofluid in permeable channel in the presence of magnetic field
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M. Fakour
2015-03-01
Full Text Available In this paper, laminar fluid flow and heat transfer in channel with permeable walls in the presence of a transverse magnetic field is investigated. Least square method (LSM for computing approximate solutions of nonlinear differential equations governing the problem. We have tried to show reliability and performance of the present method compared with the numerical method (Runge-Kutta fourth-rate to solve this problem. The influence of the four dimensionless numbers: the Hartmann number, Reynolds number, Prandtl number and Eckert number on non-dimensional velocity and temperature profiles are considered. The results show analytical present method is very close to numerically method. In general, increasing the Reynolds and Hartman number is reduces the nanofluid flow velocity in the channel and the maximum amount of temperature increase and increasing the Prandtl and Eckert number will increase the maximum amount of theta.
Evaluation of correlations of flow boiling heat transfer of R22 in horizontal channels.
Zhou, Zhanru; Fang, Xiande; Li, Dingkun
2013-01-01
The calculation of two-phase flow boiling heat transfer of R22 in channels is required in a variety of applications, such as chemical process cooling systems, refrigeration, and air conditioning. A number of correlations for flow boiling heat transfer in channels have been proposed. This work evaluates the existing correlations for flow boiling heat transfer coefficient with 1669 experimental data points of flow boiling heat transfer of R22 collected from 18 published papers. The top two correlations for R22 are those of Liu and Winterton (1991) and Fang (2013), with the mean absolute deviation of 32.7% and 32.8%, respectively. More studies should be carried out to develop better ones. Effects of channel dimension and vapor quality on heat transfer are analyzed, and the results provide valuable information for further research in the correlation of two-phase flow boiling heat transfer of R22 in channels.
Application of a simple space-time averaged porous media model to flow in densely vegetated channels
Hoffmann, M.R.
2004-01-01
Traditional flow modeling in open channels uses time-averaged turbulence models. These models are valid in clear fluid, but not if dense obstructions are present in the flow field. In this article we show that newly developed flow models can describe open channel flow as flow in a porous medium.
Topology Optimization in wave-propagation and flow problems
DEFF Research Database (Denmark)
Sigmund, Ole; Jensen, Jakob Søndergaard; Gersborg-Hansen, A.
2004-01-01
We discuss recent extensions of the topology optimization method to wave-propagation and flow problems. More specifically, we optimize material distribution in scalar wave propagation problems modelled by Helmholtz equation. Moreover, we investigate the influence of the inertia term on the optimal...
Topology optimization of 3D Stokes flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan; Sigmund, Ole; Bendsøe, Martin P.
The design of MEMS devices have benefitted from the topology optimization tool and complicated layout problems have been solved, see [1] for an overview. This research is aimed at micro fluidic devices known as micro-Total-Analysis-Systems (muTAS) where the main physical phenomena originate from...... optimization tool for micro fluidic design problems by considering design of energy efficient devices subjected to Stokes flow. Several researchers have elaborated on [2], however, this research has focused on 2D fluid modelling which limits the practical impact of the computed designs. This limitation...... is caused by the finite size domain used in topology optimization problems which ensures that the velocity components couples, even for Stokes flow [3]. Physically Stokes flow is an exotic inertia free flow, which in practice complicates mixing by passive devices. Passive mixing devices are relevant...
Complete energetic description of hydrokinetic turbine impact on flow channel dynamics
Brasseale, E.; Kawase, M.
2016-02-01
Energy budget analysis on tidal channels quantifies and demarcates the impacts of marine renewables on environmental fluid dynamics. Energy budget analysis assumes the change in total kinetic energy within a volume of fluid can be described by the work done by each force acting on the flow. In a numerically simulated channel, the balance between energy change and work done has been validated up to 5% error.The forces doing work on the flow include pressure, turbulent dissipation, and stress from the estuary floor. If hydrokinetic turbines are installed in an estuarine channel to convert tidal energy into usable power, the dynamics of the channel change. Turbines provide additional pressure work against the flow of the channel which will slow the current and lessen turbulent dissipation and bottom stress. These losses may negatively impact estuarine circulation, seafloor scour, and stratification.The environmental effects of turbine deployment have been quantified using a three dimensional, Reynolds-averaged, Navier-Stokes model of an idealized flow channel situated between the ocean and a large estuarine basin. The channel is five kilometers wide, twenty kilometers long and fifty meters deep, and resolved to a grid size of 10 meters by 10 meters by 1 meter. Tidal currents are simulated by an initial difference in sea surface height across the channel of 160 centimeters from the channel entrance to the channel exit. This creates a pressure gradient which drives flow through the channel. Tidal power turbines are represented as disks that force the channel in proportion to the strength of the current. Three tidal turbines twenty meters in diameters have been included in the model to simulate the impacts of a pilot scale test deployment.This study is the first to appreciate the energetic impact of marine renewables in a three dimensional model through the energy equation's constituent terms. This study provides groundwork for understanding and predicting the
Directory of Open Access Journals (Sweden)
Zengchao You
2017-03-01
Full Text Available The performance of a miniaturized channel for the separation of polymer and metal nanoparticles (NP using Asymmetrical Flow Field-Flow Fractionation (AF4 was investigated and compared with a conventional AF4 system. To develop standard separation methods, experimental parameters like cross flow, gradient profile and injection time were varied and optimized. Corresponding chromatographic parameters were calculated and compared. Our results indicate that the chromatographic resolution in the miniaturized channel is lower, whereas significantly shorter analyses time and less solvent consumption were obtained. Moreover, the limit of detection (LOD and limit of quantification (LOQ obtained from hyphenation with a UV-detector are obviously lower than in a conventional channel, which makes the miniaturized channel interesting for trace analysis.
Modeling lateral circulation and its influence on the along-channel flow in a branched estuary
Zhu, Lei; He, Qing; Shen, Jian
2017-12-01
A numerical modeling study of the influence of the lateral flow on the estuarine exchange flow was conducted in the north passage of the Changjiang estuary. The lateral flows show substantial variabilities within a flood-ebb tidal cycle. The strong lateral flow occurring during flood tide is caused primarily by the unique cross-shoal flow that induces a strong northward (looking upstream) barotropic force near the surface and advects saltier water toward the northern part of the channel, resulting in a southward baroclinic force caused by the lateral density gradient. Thus, a two-layer structure of lateral flows is produced during the flood tide. The lateral flows are vigorous near the flood slack and the magnitude can exceed that of the along-channel tidal flow during that period. The strong vertical shear of the lateral flows and the salinity gradient in lateral direction generate lateral tidal straining, which are out of phase with the along-channel tidal straining. Consequently, stratification is enhanced at the early stage of the ebb tide. In contrast, strong along-channel straining is apparent during the late ebb tide. The vertical mixing disrupts the vertical density gradient, thus suppressing stratification. The impact of lateral straining on stratification during spring tide is more pronounced than that of along-channel straining during late flood and early ebb tides. The momentum balance along the estuary suggests that lateral flow can augment the residual exchange flow. The advection of lateral flows brings low-energy water from the shoal to the deep channel during the flood tide, whereas the energetic water is moved to the shoal via lateral advection during the ebb tide. The impact of lateral flow on estuarine circulation of this multiple-channel estuary is different from single-channel estuary. A model simulation by blocking the cross-shoal flow shows that the magnitudes of lateral flows and tidal straining are reduced. Moreover, the reduced lateral
Dispersion of swimming algae in laminar and turbulent channel flows: theory and simulations
Croze, O A; Ahmed, M; Bees, M A; Brandt, L
2012-01-01
Algal swimming is often biased by environmental cues, e.g. gravitational and viscous torques drive cells towards downwelling fluid (gyrotaxis). In view of biotechnological applications, it is important to understand how such biased swimming affects cell dispersion in a flow. Here, we study the dispersion of gyrotactic swimming algae in laminar and turbulent channel flows. By direct numerical simulation (DNS) of cell motion within upwelling and downwelling channel flows, we evaluate time-dependent measures of dispersion for increasing values of the flow Peclet (Reynolds) numbers, Pe (Re). Furthermore, we derive an analytical `swimming Taylor-Aris dispersion' theory, using flow-dependent transport parameters given by existing microscopic models. In the laminar regime, DNS results and analytical predictions compare very well, providing the first confirmation that cells' response to flow is best described by the generalized-Taylor-dispersion microscopic model. We predict that cells drift along a channel faster th...
Effects of channel incision on base flow stream habitats and fishes
Shields, F. D.; Knight, S. S.; Cooper, C. M.
1994-01-01
Channel incision is a widespread phenomenon that results in stream and riparian habitat degradation. Fishes and physical habitat variables were sampled at base flow from three incised stream channels and one reference stream in northwest Mississippi, USA, to quantify incision effects on fish habitat and provide a basis for habitat rehabilitation planning and design. Incised channels were sampled in spring and autumn; the reference channel was sampled only in the autumn. Incised channel habitat quality was inferior to the reference channel despite the presence of structures designed to restore channel stability. Incised channels had physical habitat diversity levels similar to a nonincised reference channel, but contained fewer types of habitat. At base flow, incised channels were dominated by shallow, sandy habitats, moderate to high mean local Froude numbers, and had relatively little organic debris in their beds. In contrast, the reference stream had greater mean water depth, contained more woody debris, and provided more deep pool habitat. Fish assemblages in incised channels were composed of smaller fishes representing fewer species relative to the reference site. Fish species richness was directly proportional to the mean local Froude number, an indicator of the availability of pool habitat.
Experimental Investigation on the Effects of the Fixed Boundaries in Channelized Dry Granular Flows
Sarno, L.; Carleo, L.; Papa, M. N.; Villani, P.
2018-01-01
The dynamics of granular mixtures, involved in several geophysical phenomena like rock avalanches and debris flows, is far from being completely understood. Several features of their motion, such as non-local and boundary effects, still represent open problems. An extensive experimental study on free-surface channelized granular flows is here presented, where the effects of the fixed boundaries are systematically investigated. The entire experimental data set is obtained by using a homogenous acetal-polymeric granular material and three different basal surfaces, allowing different kinematic boundary conditions. Velocity profiles at both the sidewall and the free surface are obtained by using high-speed cameras and the open-source particle image velocimetry code, PIVlab. Significantly, different sidewall velocity profiles are observed by varying the basal roughness and the flow depth. Owing to sidewall friction and non-local effects, such profiles exhibit a clear rheological stratification for high enough flow depths and they can be well described by recurring to composite functions, variously formed of linear, Bagnold and exponential scalings. Moreover, it has been discovered that transitions from one velocity profile to another are also possible on the same basal surface by merely varying the flow depth. This shape transition is due partly to the sidewall resistances, the basal boundary condition and, in particular, the occurrence/inhibition of basal grain rolling. In most of the experiments, the normal-to-bed velocity profiles and the velocity measurements at the free surface strongly suggest the occurrence of a secondary circulating flow, made possible by a chiefly collisional regime beneath the free surface.
Rip currents and alongshore flows in single channels dredged in the surf zone
Moulton, Melissa; Elgar, Steve; Raubenheimer, Britt; Warner, John C.; Kumar, Nirnimesh
2017-05-01
To investigate the dynamics of flows near nonuniform bathymetry, single channels (on average 30 m wide and 1.5 m deep) were dredged across the surf zone at five different times, and the subsequent evolution of currents and morphology was observed for a range of wave and tidal conditions. In addition, circulation was simulated with the numerical modeling system COAWST, initialized with the observed incident waves and channel bathymetry, and with an extended set of wave conditions and channel geometries. The simulated flows are consistent with alongshore flows and rip-current circulation patterns observed in the surf zone. Near the offshore-directed flows that develop in the channel, the dominant terms in modeled momentum balances are wave-breaking accelerations, pressure gradients, advection, and the vortex force. The balances vary spatially, and are sensitive to wave conditions and the channel geometry. The observed and modeled maximum offshore-directed flow speeds are correlated with a parameter based on the alongshore gradient in breaking-wave-driven-setup across the nonuniform bathymetry (a function of wave height and angle, water depths in the channel and on the sandbar, and a breaking threshold) and the breaking-wave-driven alongshore flow speed. The offshore-directed flow speed increases with dissipation on the bar and reaches a maximum (when the surf zone is saturated) set by the vertical scale of the bathymetric variability.
Dual plane problems for creeping flow of power-law incompressible medium
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Dmitriy S. Petukhov
2016-09-01
Full Text Available In this paper, we consider the class of solutions for a creeping plane flow of incompressible medium with power-law rheology, which are written in the form of the product of arbitrary power of the radial coordinate by arbitrary function of the angular coordinate of the polar coordinate system covering the plane. This class of solutions represents the asymptotics of fields in the vicinity of singular points in the domain occupied by the examined medium. We have ascertained the duality of two problems for a plane with wedge-shaped notch, at which boundaries in one of the problems the vector components of the surface force vanish, while in the other—the vanishing components are the vector components of velocity, We have investigated the asymptotics and eigensolutions of the dual nonlinear eigenvalue problems in relation to the rheological exponent and opening angle of the notch for the branch associated with the eigenvalue of the Hutchinson–Rice–Rosengren problem learned from the problem of stress distribution over a notched plane for a power law medium. In the context of the dual problem we have determined the velocity distribution in the flow of power-law medium at the vertex of a rigid wedge, We have also found another two eigenvalues, one of which was determined by V. V. Sokolovsky for the problem of power-law fluid flow in a convergent channel.
Control works in debris-flow channels: influence on morphology and sediment transfer
Marchi, L.
2012-04-01
Extensive torrent control works, such as grade-control dams, debris basins, deflecting walls, etc. have been implemented in the European Alps since the last decades of 19th century. These structural measures, aimed at stabilizing channels and to control sediment transport, are also widespread in Japan and are increasingly present in other mountain regions. As debris flows are one of the most destructive processes in steep mountain channels, hydraulic works are often intended to attenuate debris-flow hazard. Multi-temporal aerial photos and historic records permit evaluating the long term effects of torrent control works on the morphological settings of the channels and the delivery of sediment. The experience arising from over one century of torrent control works in debris-flow channels of the Alps permits also to improve the management of steep headwater catchments. A basic issue in the management of debris-flow channels is the recognition of success versus failure of engineering control works. Successful debris-flow control works provide benchmarks for further implementations, whereas the failure in reducing debris-flow hazard may lead to refinements in planning and design of control works or to the choice of preferring non-structural measures for coping with debris flows. Data from historical archives on debris-flow occurrence and on the performance of control works are the basic sources of information for these analyses. Moreover, when dealing with hydraulic structures for debris-flow control, it should be reminded that the artificial morphology resulting from the construction of check dams provides only a temporary stability to the channel and adjacent banks. This stresses the importance of evaluating the state of conservation and the effectiveness of control works and implies the need for their careful and continuous maintenance. Inventories of hydraulic structures, coupled with detailed data on catchment and channel topography, sediment sources and supply
Analysing Gas-Liquid Flow in PEM Electrolyser Micro-Channels (Poster)
DEFF Research Database (Denmark)
Lafmejani, Saeed Sadeghi; Olesen, Anders Christian; Kær, Søren Knudsen
-sized channels (hydraulic diameter of 1 mm) of PEM water electrolysis. Precisely controlling all the parameters that affect the gas-liquid flow in a PEM water electrolysis cell is quite challenging, hence a simplified setup is constructed consisting of only a transparent channel with a sheet of titanium felt......One means of increasing the hydrogen yield to cost ratio of a PEM water electrolyser, is to increase the operating current density. However, at high current densities (higher than 1 A/cm2), management of heat and mass transfer in the anode current collector and channel becomes crucial and can lead...... to hot spots. Management of heat and fluid flow through the micro-channels play a great role in the capability of PEM water electrolysis when working at high current densities. Despite, many studies have been done on gas-liquid flows; still there is a lack of research on gas-liquid flows in micro...
Flow Patterns in an Open Channel Confluence with Increasingly Dominant Tributary Inflow
National Research Council Canada - National Science Library
Laurent Schindfessel; Stephan Creëlle; Tom De Mulder
2015-01-01
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...
Hardy, R. J.; Lane, S. N.; Ferguson, R. I.; Parsons, D. R.
2003-06-01
Recent developments in numerical algorithms have enabled the construction of three-dimensional models for the prediction of flows in open channels. These advances encompass improvements in both numerical solutions and the process representation required for an accurate system definition. However, to date, there is still little agreement on how to assess systematically and report the credibility of these simulations. This paper addresses this problem by adopting a Grid Convergence Index approach. The results indicate, for two simple hypothetical cases, a zero-degree confluence and a meander bend, that the numerical code can be verified to an acceptable numerical standard. However, it is shown that this does not mean that verification is complete, as the literature implies, as whilst the discretization resolution may be sufficient to verify one of the model variables it does not imply that every variable has converged. Furthermore, the scheme may still be insufficient to capture all the processes of interest that are operating within the chosen environment.
Analysis of Nonlinear Dispersion of a Pollutant Ejected by an External Source into a Channel Flow
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T. Chinyoka
2010-01-01
Full Text Available This paper focuses on the transient analysis of nonlinear dispersion of a pollutant ejected by an external source into a laminar flow of an incompressible fluid in a channel. The influence of density variation with pollutant concentration is approximated according to the Boussinesq approximation, and the nonlinear governing equations of momentum and pollutant concentration are obtained. The problem is solved numerically using a semi-implicit finite difference method. Solutions are presented in graphical form and given in terms of fluid velocity, pollutant concentration, skin friction, and wall mass transfer rate for various parametric values. The model can be a useful tool for understanding the polluting situations of an improper discharge incident and evaluating the effects of decontaminating measures for the water body.
A “poor man's approach” to topology optimization of cooling channels based on a Darcy flow model
DEFF Research Database (Denmark)
Zhao, Xi; Zhou, Mingdong; Sigmund, Ole
2018-01-01
A topology optimization methodology for optimizing cooling channels using an approximate but low-cost flow and heat transfer model is presented. The fluid flow is modeled using the Darcy model, which is a linear problem that can be solved very efficiently compared to the Navier–Stokes equations....... The obtained fluid velocity is subsequently used in a stabilized convection–diffusion heat transfer model to calculate the temperature distribution. The governing equations are cast in a monolithic form such that both the solid and fluid can be modeled using a single equation set. The material properties...
Non-stationary flow solution for water levels in open channels for TOXSWA
Opheusden, van J.H.J.; Molenaar, J.; Beltman, W.H.J.; Adriaanse, P.I.
2011-01-01
We study non-stationary flow in open discharge channels. A model is derived from basic principles, conservation of mass and momentum, which is solved numerically for the cross sectional area and discharge as a function of time and position along the channel. The model describes the effect of
INTERACTION OF LIQUID FLAT SCREENS WITH GAS FLOW RESTRICTED BY CHANNEL WALLS
Directory of Open Access Journals (Sweden)
S. T. Aksentiev
2005-01-01
Full Text Available The paper gives description of physical pattern of liquid screen interaction that are injected from the internal walls of a rectangular channel with gas flow. Criterion dependences for determination of intersection coordinates of external boundaries with longitudinal channel axis and factor of liquid screen head resistance.
Flow channel shape optimum design for hydroformed metal bipolar plate in PEM fuel cell
Energy Technology Data Exchange (ETDEWEB)
Peng, Linfa; Lai, Xinmin; Liu, Dong' an; Hu, Peng [State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, Shanghai 200240 (China); Ni, Jun [Department of Mechanical Engineering and Applied Mechanics, University of Michigan, Ann Arbor, MI 48109 (United States)
2008-03-15
Bipolar plate is one of the most important and costliest components of polymer electrolyte membrane (PEM) fuel cells. Micro-hydroforming is a promising process to reduce the manufacturing cost of PEM fuel cell bipolar plates made of metal sheets. As for hydroformed bipolar plates, the main defect is the rupture because of the thinning of metal sheet during the forming process. The flow channel section decides whether high quality hydroformed bipolar plates can be successively achieved or not. Meanwhile, it is also the key factor that is related with the reaction efficiency of the fuel cell stacks. In order to obtain the optimum flow channel section design prior the experimental campaign, some key geometric dimensions (channel depth, channel width, rib width and transition radius) of flow channel section, which are related with both reaction efficiency and formability, are extracted and parameterized as the design variables. By design of experiments (DOE) methods and an adoptive simulated annealing (ASA) optimization method, an optimization model of flow channel section design for hydroformed metal bipolar plate is proposed. Optimization results show that the optimum dimension values for channel depth, channel width, rib width and transition radius are 0.5, 1.0, 1. 6 and 0.5 mm, respectively with the highest reaction efficiency (79%) and the acceptable formability (1.0). Consequently, their use would lead to improved fuel cell efficiency for low cost hydroformed metal bipolar plates. (author)
Directory of Open Access Journals (Sweden)
K. Hanegan
2015-03-01
Full Text Available In this study, a Delft3D model of the Wax Lake Delta was developed to simulate flow and sediment flux through delta distributary channels. The model was calibrated for tidal constituents as well as velocity and sediment concentration across channel transects. The calibrated model was then used to simulate full spring–neap tidal cycles under constant low flow upstream boundary conditions, with grain size variation in suspended load represented using two sediment fractions. Flow and sediment flux results through distributary channel cross-sections were examined for spatial and temporal variability with the goal of characterizing the role of tides in sediment reworking and delta development. The Wax Lake Delta has prograded through channel extension, river mouth bar deposition, and channel bifurcation. Here we show that tidal modulation of currents influences suspended sand transport, and spatial acceleration through distributary channels at low tides is sufficient to suspend sand in distal reaches during lower flows. The basinward-increasing transport capacity in distributary channels indicates that erosive channel extension could be an important process, even during non-flood events.
A mathematical model of the flow and bed topography in curved channels
Olesen, K.W.
1985-01-01
A two-dimensional horizontal mathematical model of the flow and bed topography in alluvial channel bends is presented. The applicability of the model is restricted to channels of which the width-depth ratio is large, the Froude number is small, bed load is dominant and grain sorting effects are
Invariant form of the flow curve PEVG relative to hydraulic radius of the channel
Сівецький, Володимир Іванович; Рябінін, Дмитро Дмитрович; Сокольський, Олександр Леонідович; Волинець, Віталій Миколайович
2012-01-01
Hydraulic radius is used in hydraulics for estimation of resistance and calculation of nonround-form channels. The estimation of acceptability of use of hydraulic radius for calculation of non-Newtonian liquids flow in nonround-form channels and determination of their rheological characteristics was realized
Billah, Md. Mamun; Khan, Md Imran; Rahman, Mohammed Mizanur; Alam, Muntasir; Saha, Sumon; Hasan, Mohammad Nasim
2017-06-01
A numerical study of steady two dimensional mixed convention heat transfer phenomena in a rectangular channel with active flow modulation is carried out in this investigation. The flow in the channel is modulated via a rotating cylinder placed at the center of the channel. In this study the top wall of the channel is subjected to an isothermal low temperature while a discrete isoflux heater is positioned on the lower wall. The fluid flow under investigation is assumed to have a Prandtl number of 0.71 while the Reynolds No. and the Grashof No. are varied in wide range for four different situations such as: i) plain channel with no cylinder, ii) channel with stationary cylinder, iii) channel with clockwise rotating cylinder and iv) channel with counter clockwise rotating cylinder. The results obtained in this study are presented in terms of the distribution of streamlines, isotherms in the channel while the heat transfer process from the heat source is evaluated in terms of the local Nusselt number, average Nusselt number. The outcomes of this study also indicate that the results are strongly dependent on the type of configuration and direction of rotation of the cylinder and that the average Nusselt number value rises with an increase in Reynolds and Grashof numbers but the correlation between these parameters at higher values of Reynolds and Grashof numbers becomes weak.
Kefaloyianni, Eirini; Coetzee, William A.
2011-01-01
Endothelial cells (ECs) are constantly exposed to blood flow-induced shear forces in the vessels and this is a major determinant of endothelial function. Ion channels have a major role in endothelial function and in the control of vascular tone. We hypothesized that shear force is a general regulator of ion channel expression, which will have profound effects on endothelial function. We examined this hypothesis using large-scale quantitative real-time RT-PCR. Human coronary artery ECs were exposed to two levels of flow-induced shear stress for 24 h, while control cells were grown under static conditions. The expression of ion channel subunits was compared between control and flow-adapted cells. We used primers against 55 ion channel and exchanger subunits and were able to detect 54 subunits. Five dyn/cm2 of shear induced downregulation of 1 (NCX1) and upregulation of 18 subunits, including KCa2.2, KCa2.3, CX37, Kv1.5 and HCN2. Fifteen dyn/cm2 of shear stress induced the expression of 30 ion channel subunits, including KCa2.3, KCa2.2, CX37, Kir2.3 and KCa3.1. Our data demonstrate that substantial remodeling of endothelial ion channel subunit expression occurs with flow adaptation and suggest that altered ion channel expression may significantly contribute to vascular pathology associated with flow-induced alterations. PMID:21389733
Channel height and curvature effects on flow boiling from an electronic chip
Leland, J. E.; Chow, L. C.
1995-04-01
Forced convective boiling from a discrete heat source in a curved rectangular channel has been experimentally investigated. The flow area height and radius of curvature of the channel were varied to ascertain the effects of induced buoyancy and secondary flow. For comparison, results were also obtained for a similar heat source in a straight channel. Three configurations encompassing two radii of curvature, 28.6 and 56.4 mm, and three heights, 3.18, 5.56, and 6.35 mm, were studied. An additional channel height of 1.14 mm was investigated for the straight geometry only. Data were obtained for subcoolings of 5, 20, and 35 C and flow velocities of 1-7 m/s. For the straight geometry, critical heat flux (CHF) did not vary much for heights greater than 1.14 mm. The percent increase in curved channel CHF over straight channel CHF was highest for 5 C subcooling. This implies that buoyancy effects are most important when there is significant vapor generation. For a given subcooling and velocity, the radius of curvature had little effect. This implies that secondary flow has little effect under these conditions. A correlation is developed that describes the effects of buoyancy and secondary flow on CHF in the curved channel.
Directory of Open Access Journals (Sweden)
Matteo Pascotto
2013-01-01
Full Text Available The flow field inside a cooling channel for the trailing edge of gas turbine blades has been numerically investigated with the aim to highlight the effects of channel rotation and orientation. A commercial 3D RANS solver including a SST turbulence model has been used to compute the isothermal steady air flow inside both static and rotating passages. Simulations were performed at a Reynolds number equal to 20000, a rotation number (Ro of 0, 0.23, and 0.46, and channel orientations of γ=0∘, 22.5°, and 45°, extending previous results towards new engine-like working conditions. The numerical results have been carefully validated against experimental data obtained by the same authors for conditions γ=0∘ and Ro = 0, 0.23. Rotation effects are shown to alter significantly the flow field inside both inlet and trailing edge regions. These effects are attenuated by an increase of the channel orientation from γ=0∘ to 45°.
Finite analytic numerical solution of two-dimensional channel flow over a backward-facing step
Ho, K.-S.; Chen, C.-J.
1986-01-01
Laminar channel flow over a backward-facing step is investigated. The finite analytic (FA) method is used to obtain the numerical solution. The FA solutions predict the recirculation zone lengths and the recirculated mass flow rates for Reynolds numbers, Re, of 25, 50, 73, 125, 191 and 229 which correlate well with experimental measurements. The general flow patterns of the recirculation region flows for the Reynolds numbers considered in this study are similar to each other.
Simulation of pollutant transport in mobile water-flow channels in permafrost environment
Directory of Open Access Journals (Sweden)
E. I. Debolskaya
2013-01-01
Full Text Available A common problem for the Arctic region is pollution by persistent organic compounds and other substances that have accumulated over the years in these areas. With temperature increasing, these substances can get out of the snow, ice, permafrost in the human environment. With climate warming and permafrost degradation the risk of toxic substances from the burial sites of chemical and radioactive waste increases. The work is devoted to research the pollution propagation in the rivers flowing in the permafrost taking into account the possible deformations of the channels caused by the melting of the permafrost with increasing temperature of the river flow water. We also consider the distribution of pollutants released during erosion of the coastal slopes, caused thermal erosion. Numerical experiments confirmed the quantitative assessment obtained from the field observations of the erosion rate increases with increasing temperature. Study the impact of thermal and mechanical erosion of the distribution of impurities led to the conclusion that as a result of the formation of taliks uniform flow conditions are violated, resulting in a non-stationary distribution of impurities. The increase in the volume of the test section of the river due to the appearance of cavities in the coastal slope leads to an increase in impurity concentration. Analysis of the results of modeling the spread of contamination during thawing sources in the frozen shores, demonstrated the relationship in the process of distribution of impurities from the position of the source and allowed to give a preliminary quantitative assessment.
Razuvanov, N. G.; Poddubnyi, I. I.; Kostychev, P. V.
2017-11-01
The research of hydrodynamics and heat transfer at the liquid metal (LM) downward flow and upflow in a vertical duct of a rectangular cross section with a ratio of sides ∼1/3 in a coplanar magnetic field (MF) under conditions of bilateral symmetrical heating is performed. The problem simulates the LM flow in the heat exchange channels for cooling the liquid metal module of the blanket of the thermonuclear reactor (TNR) of the TOKAMAK type. The experiments were carried out on the basis of the mercury magnetohydrodynamic test-bed (MHD) Moscow Power Engineering Institute (MPEI) – Joint Institute for High Temperatures of the Russian Academy of Sciences (JIHT RAS). The probe measurement technique was used in the flow. Profiles of averaged velocity and averaged temperature, as well as profiles of temperature pulsations in the axial planes of the channel cross-section, are obtained; the distribution of the dimensionless wall temperature along the perimeter unfolding of the channel in the section and along the length of the channel. A significant effect of thermogravitational convection (TGC), which leads to unexpected effects, is found. At the downflow in a magnetic field, in some modes, low-frequency pulsations of anomalously high intensity occur.
The zonal satellite problem - II: Near-escape flow
Directory of Open Access Journals (Sweden)
Mioc V.
1998-01-01
Full Text Available The study of the zonal satellite problem is continued by tackling the situation r→∞. New equations of motion (for which the infinite distance is a singularity and the corresponding first integrals of energy and angular momentum are set up. The infinity singularity is blown up via McGehee-type transformations, and the infinity manifold is pasted on the phase space. The fictitious flow on this manifold is described. Then, resorting to the rotational symmetry of the problem and to the angular momentum integral, the near-escape local flow is depicted. The corresponding phase curves are interpreted as physical motions.
Interfacial wave behavior in oil-water channel flows: Prospects for a general understanding
Energy Technology Data Exchange (ETDEWEB)
McCready, M.J.; Uphold, D.D.; Gifford, K.A. [Univ. of Notre Dame, IN (United States)
1997-12-31
Oil-water pressure driven channel flow is examined as a model for general two-layer flows where interfacial disturbances are important. The goal is to develop sufficient understanding of this system so that the utility and limitations of linear and nonlinear theories can be known a priori. Experiments show that sometimes linear stability is useful at predicting the steady or dominant evolving waves. However in other situations there is no agreement between the linearly fastest growing wave and the spectral peak. An interesting preliminary result is that the bifurcation to interfacial waves is supercritical for all conditions that were studied for an oil-water channel flow, gas-liquid channel flow and two-liquid Couette flow. However, three different mechanisms are dominant for each of these three situations.
Flow dynamics and concentration polarisation in spacer-filled channels
DEFF Research Database (Denmark)
Lipnizki, Jens; Jonsson, Gunnar Eigil
2002-01-01
been shown that the mass transport along the membrane is not fully described by the Sherwood correlation, which describes a decreasing mass transfer with an increasing distance from the inlet. It was observed that in open channel without spacers, the slope of the Sherwood correlation is decreasing......The key to developing highly efficient spiral-wound modules is the improvement of the mass transfer mechanisms. In this study a study of the mass transfer has been carried out using a flat test cell with six permeate outlets and a rectangular feed channel. Using this experimental set-up, it has....... This phenomenon was also observed in spacer-filled channels. In this case the stripes on the surface depended on the spacer geometry. Furthermore, the experiments were used to calculate the energy consumption vs. the mass transfer coefficient for different spacers. This research can be used as a foundation...
Unidirectionally migrating deep-water channels: Architectural styles and flow processes
Gong, C.; Steel, R. J.; Wang, Y.; Xu, Q.
2014-12-01
3D seismic data are used to investigate flow processes and sedimentation in deep-water slope channels of an alternate type characterized by short and straight channel courses, a lack of levees, and absence of any coeval fans. The study allows a picture of unusual flow processes in submarine channels. The studied channels can be divided into two discrete segments: (1) Upper segments are characterized by low aspect ratio(W/T), little lateral offset (Lm), and low migration/aggradation ratios (Lm/Va). These upper segment channels build vertically-stacked channel-complex sets (CCSs), each of which is characterized by a facies transition from fine-grained sands in the lower part overlain by debris flow deposits and then shale drapes. Energetic sediment density flows triggered by fluid escape and/or strong wave action were well able to bypass sediment and to mask relatively weak bottom currents, yielding deep-water channels characterized by little lateral offset and dominantly aggradational stacking patterns. (2) Lower segments are characterized by higher W/T, wide lateral offset (Lm), and high Lm/Va. They consist of laterally-migrated CCSs, each of which consists of fine-grained reworked sands in the lower part overlain by debris flow deposits and, finally, shale drapes. Bottom currents restricted within the channels would have induced a tilt of the interface between turbidity currents and the overriding bottom currents (Wedderburn number > 1). This would have deflected turbidity currents downward and back toward the gentle channel bank, thus causing channel migration (the steep bank) by ~2° to 15°, and yielding a helical flow circulation composed of a high-velocity zone along the steep bank and a low-velocity zone along the gentle bank. This bottom current-induced helical flow circulation promoted deposition on the gentle bank, but it favored erosion on the steep banke, yielding deep-water channels exhibiting wide lateral offset and dominantly laterally
Artificial Bee Colony Algorithm for Solving Optimal Power Flow Problem
Directory of Open Access Journals (Sweden)
Luong Le Dinh
2013-01-01
Full Text Available This paper proposes an artificial bee colony (ABC algorithm for solving optimal power flow (OPF problem. The objective of the OPF problem is to minimize total cost of thermal units while satisfying the unit and system constraints such as generator capacity limits, power balance, line flow limits, bus voltages limits, and transformer tap settings limits. The ABC algorithm is an optimization method inspired from the foraging behavior of honey bees. The proposed algorithm has been tested on the IEEE 30-bus, 57-bus, and 118-bus systems. The numerical results have indicated that the proposed algorithm can find high quality solution for the problem in a fast manner via the result comparisons with other methods in the literature. Therefore, the proposed ABC algorithm can be a favorable method for solving the OPF problem.
Optimal secondary energy growth in a plane channel flow
Cossu, Carlo; Chevalier, M.; Henningson, D.S.
2007-01-01
International audience; The optimal growth of perturbations to transiently growing streaks is studied in Poiseuille flow. Basic flows are generated by direct numerical simulation giving "primary" optimal spanwise periodic vortices of finite amplitude as the initial condition. They evolve into finite amplitude primary transiently growing streaks. Linear "secondary" optimal energy growth supported by these primary flows are computed using an adjoint technique which takes into full account the u...
Fine-grained linings of leveed channels facilitate runout of granular flows
Kokelaar, B.P.; Graham, R. L.; Gray, J.M.N.T.; Vallance, James W.
2014-01-01
Catastrophic dense granular flows, such as occur in rock avalanches, debris flows and pyroclastic flows, move as fully shearing mixtures that have approximately 60 vol.% solids and tend to segregate to form coarse-grained fronts and leveed channels. Levees restrict spreading of unconfined flows and form as coarse particles that become concentrated in the top of the flow are transported to the front and then advect to the sides in the flow head. Channels from which most material has drained away down slope are commonly lined with fine-grained deposit, widely thought to remain from the tail of the waning flow. We show how segregation in experimental dense flows of carborundum or sand (300–425 μm) mixed with spherical fine ballotini (150–250 μm), on rough slopes of 27–29°, produces fine-grained channel linings that are deposited with the levees, into which they grade laterally. Maximum runout distance is attained with mixtures containing 30–40% sand, just sufficient to segregate and form levees that are adequately robust to restrict the spreading attributable to the low-friction fines. Resin impregnation and serial sectioning of deliberately arrested experimental flows shows how fines-lined levees form from the flow head; the flows create their own stable ‘conduit’ entirely from the front, which in a geophysical context can play an important mechanistic role in facilitating runout. The flow self-organization ensures that low-friction fines at the base of the segregated channel flow shear over fine-grained substrate in the channel, thus reducing frictional energy losses. We propose that in pyroclastic flows and debris flows, which have considerable mobility attributable to pore-fluid pressures, such fine-grained flow-contact zones form similarly and not only reduce frictional energy losses but also reduce flow–substrate permeability so as to enhance pore-fluid pressure retention. Thus the granular flow self-organization that produces fine
Optimal Results and Numerical Simulations for Flow Shop Scheduling Problems
Directory of Open Access Journals (Sweden)
Tao Ren
2012-01-01
Full Text Available This paper considers the m-machine flow shop problem with two objectives: makespan with release dates and total quadratic completion time, respectively. For Fm|rj|Cmax, we prove the asymptotic optimality for any dense scheduling when the problem scale is large enough. For Fm‖ΣCj2, improvement strategy with local search is presented to promote the performance of the classical SPT heuristic. At the end of the paper, simulations show the effectiveness of the improvement strategy.
Flow Structure and Channel Change in a Chute Cutoff along a Large Meandering River
Rhoads, B. L.; Best, J.; Johnson, K.; Engel, F. L.
2009-12-01
Meander cutoffs, which develop when flow cuts across the narrow neck of a bend, are common features along actively migrating meandering rivers. Despite the importance of cutoffs in the dynamics of river meandering and floodplain sedimentation, few, if any, studies have documented in detail the fluvial processes involved in the development of a meander cutoff. This paper examines the morphodynamics of a chute cutoff along the Wabash River, Illinois-Indiana, immediately following initiation of the cutoff. The original cutoff channel formed across the neck of Mackey Bend, a meander loop immediately upstream of the confluence with the Ohio River, during a major flood in June 2008. The formation of the cutoff channel likely involved migration of a headcut from the downstream side to the upstream side of the meander neck along the path of a floodplain slough. A key focus of the investigation has been to document flow structure at the upstream and downstream ends of the cutoff channel so that patterns of flow can be related to morphological change. Three separate measurement campaigns using an acoustic doppler current profiler (ADCP) and single-beam echosounder were conducted between January and May 2009 to determine 3D flow structure and bed morphology during events with different discharges and flow stages. In addition, channel dimensions were surveyed using a dGPS system in September 2008 and in August 2009. Results indicate that the cutoff channel has widened dramatically over a one-year period, increasing its width by as much as 100 percent. Curvature of flow into the entrance of the cutoff channel from the Wabash River generates strong helical motion that advects momentum toward the outer bank, resulting in high velocities near the bank toe and ongoing bank retreat through slab failures. This flow pattern, accentuated by dramatic widening of the cutoff channel, has resulted in deposition along the inner bank and development of a large bar platform at this location
Urban stormwater runoff: a new class of environmental flow problem.
Walsh, Christopher J; Fletcher, Tim D; Burns, Matthew J
2012-01-01
Environmental flow assessment frameworks have begun to consider changes to flow regimes resulting from land-use change. Urban stormwater runoff, which degrades streams through altered volume, pattern and quality of flow, presents a problem that challenges dominant approaches to stormwater and water resource management, and to environmental flow assessment. We used evidence of ecological response to different stormwater drainage systems to develop methods for input to environmental flow assessment. We identified the nature of hydrologic change resulting from conventional urban stormwater runoff, and the mechanisms by which such hydrologic change is prevented in streams where ecological condition has been protected. We also quantified the increase in total volume resulting from urban stormwater runoff, by comparing annual streamflow volumes from undeveloped catchments with the volumes that would run off impervious surfaces under the same rainfall regimes. In catchments with as little as 5-10% total imperviousness, conventional stormwater drainage, associated with poor in-stream ecological condition, reduces contributions to baseflows and increases the frequency and magnitude of storm flows, but in similarly impervious catchments in which streams retain good ecological condition, informal drainage to forested hillslopes, without a direct piped discharge to the stream, results in little such hydrologic change. In urbanized catchments, dispersed urban stormwater retention measures can potentially protect urban stream ecosystems by mimicking the hydrologic effects of informal drainage, if sufficient water is harvested and kept out of the stream, and if discharged water is treated to a suitable quality. Urban stormwater is a new class of environmental flow problem: one that requires reduction of a large excess volume of water to maintain riverine ecological integrity. It is the best type of problem, because solving it provides an opportunity to solve other problems such
Urban stormwater runoff: a new class of environmental flow problem.
Directory of Open Access Journals (Sweden)
Christopher J Walsh
Full Text Available Environmental flow assessment frameworks have begun to consider changes to flow regimes resulting from land-use change. Urban stormwater runoff, which degrades streams through altered volume, pattern and quality of flow, presents a problem that challenges dominant approaches to stormwater and water resource management, and to environmental flow assessment. We used evidence of ecological response to different stormwater drainage systems to develop methods for input to environmental flow assessment. We identified the nature of hydrologic change resulting from conventional urban stormwater runoff, and the mechanisms by which such hydrologic change is prevented in streams where ecological condition has been protected. We also quantified the increase in total volume resulting from urban stormwater runoff, by comparing annual streamflow volumes from undeveloped catchments with the volumes that would run off impervious surfaces under the same rainfall regimes. In catchments with as little as 5-10% total imperviousness, conventional stormwater drainage, associated with poor in-stream ecological condition, reduces contributions to baseflows and increases the frequency and magnitude of storm flows, but in similarly impervious catchments in which streams retain good ecological condition, informal drainage to forested hillslopes, without a direct piped discharge to the stream, results in little such hydrologic change. In urbanized catchments, dispersed urban stormwater retention measures can potentially protect urban stream ecosystems by mimicking the hydrologic effects of informal drainage, if sufficient water is harvested and kept out of the stream, and if discharged water is treated to a suitable quality. Urban stormwater is a new class of environmental flow problem: one that requires reduction of a large excess volume of water to maintain riverine ecological integrity. It is the best type of problem, because solving it provides an opportunity to solve
Urban Stormwater Runoff: A New Class of Environmental Flow Problem
Walsh, Christopher J.; Fletcher, Tim D.; Burns, Matthew J.
2012-01-01
Environmental flow assessment frameworks have begun to consider changes to flow regimes resulting from land-use change. Urban stormwater runoff, which degrades streams through altered volume, pattern and quality of flow, presents a problem that challenges dominant approaches to stormwater and water resource management, and to environmental flow assessment. We used evidence of ecological response to different stormwater drainage systems to develop methods for input to environmental flow assessment. We identified the nature of hydrologic change resulting from conventional urban stormwater runoff, and the mechanisms by which such hydrologic change is prevented in streams where ecological condition has been protected. We also quantified the increase in total volume resulting from urban stormwater runoff, by comparing annual streamflow volumes from undeveloped catchments with the volumes that would run off impervious surfaces under the same rainfall regimes. In catchments with as little as 5–10% total imperviousness, conventional stormwater drainage, associated with poor in-stream ecological condition, reduces contributions to baseflows and increases the frequency and magnitude of storm flows, but in similarly impervious catchments in which streams retain good ecological condition, informal drainage to forested hillslopes, without a direct piped discharge to the stream, results in little such hydrologic change. In urbanized catchments, dispersed urban stormwater retention measures can potentially protect urban stream ecosystems by mimicking the hydrologic effects of informal drainage, if sufficient water is harvested and kept out of the stream, and if discharged water is treated to a suitable quality. Urban stormwater is a new class of environmental flow problem: one that requires reduction of a large excess volume of water to maintain riverine ecological integrity. It is the best type of problem, because solving it provides an opportunity to solve other problems such
Directory of Open Access Journals (Sweden)
A. Sami Bataineh
2016-09-01
Full Text Available In this paper, we present an approximate solution method for the problem of magnetohydrodynamic (MHD flow and heat transfer of a second grade fluid in a channel with a porous wall. The method is based on the Bernstein polynomials with their operational matrices and collocation method. Under some regularity conditions, upper bounds of the absolute errors are given. We apply the residual correction procedure which may estimate the absolute error to the problem. We may estimate the absolute error by using a procedure depends on the sequence of the approximate solutions. For some certain cases, we apply the method to the problem in the numerical examples. Moreover, we test the impact of changing the flow parameters numerically. The results are consistent with the results of Runge-Kutta fourth order method and homotopy analysis method.
A three-dimensional dynamical model for channeled lava flow with nonlinear rheology
Filippucci, Marilena; Tallarico, Andrea; Dragoni, Michele
2010-05-01
Recent laboratory studies on the rheology of lava samples from different volcanic areas have highlighted that the apparent viscosity depends on a power of the strain rate. Several authors agree in attributing this dependence to the crystal content of the sample and to temperature. Starting from these results, in this paper we studied the effect of a power law rheology on a gravity-driven lava flow. The equation of motion is nonlinear in the diffusion term, and an analytical solution does not seem to be possible. The finite-volume method has been applied to solve numerically the equation governing the fully developed laminar flow of a power law non-Newtonian fluid in an inclined rectangular channel. The convergence, the stability, and the order of approximation were tested for the Newtonian rheology case, comparing the numerical solution with the available analytical solution. Results indicate that the assumption on the rheology, whether linear or nonlinear, strongly affects the velocity and/or the thickness of the lava channel both for channels with fixed geometry and for channels with constant flow rate. Results on channels with fixed geometry are confirmed by some simulations for real lava channels. Finally, the study of the Reynolds number indicates that gravity-driven lava channel flows are always in laminar regime, except for strongly nonlinear pseudoplastic fluids with low fluid consistency and at high slopes.
Analytical methods for heat transfer and fluid flow problems
Weigand, Bernhard
2015-01-01
This book describes useful analytical methods by applying them to real-world problems rather than solving the usual over-simplified classroom problems. The book demonstrates the applicability of analytical methods even for complex problems and guides the reader to a more intuitive understanding of approaches and solutions. Although the solution of Partial Differential Equations by numerical methods is the standard practice in industries, analytical methods are still important for the critical assessment of results derived from advanced computer simulations and the improvement of the underlying numerical techniques. Literature devoted to analytical methods, however, often focuses on theoretical and mathematical aspects and is therefore useless to most engineers. Analytical Methods for Heat Transfer and Fluid Flow Problems addresses engineers and engineering students. The second edition has been updated, the chapters on non-linear problems and on axial heat conduction problems were extended. And worked out exam...
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.
A new scripting library for modeling flow and transport in fractured rock with channel networks
Dessirier, Benoît; Tsang, Chin-Fu; Niemi, Auli
2018-02-01
Deep crystalline bedrock formations are targeted to host spent nuclear fuel owing to their overall low permeability. They are however highly heterogeneous and only a few preferential paths pertaining to a small set of dominant rock fractures usually carry most of the flow or mass fluxes, a behavior known as channeling that needs to be accounted for in the performance assessment of repositories. Channel network models have been developed and used to investigate the effect of channeling. They are usually simpler than discrete fracture networks based on rock fracture mappings and rely on idealized full or sparsely populated lattices of channels. This study reexamines the fundamental parameter structure required to describe a channel network in terms of groundwater flow and solute transport, leading to an extended description suitable for unstructured arbitrary networks of channels. An implementation of this formalism in a Python scripting library is presented and released along with this article. A new algebraic multigrid preconditioner delivers a significant speedup in the flow solution step compared to previous channel network codes. 3D visualization is readily available for verification and interpretation of the results by exporting the results to an open and free dedicated software. The new code is applied to three example cases to verify its results on full uncorrelated lattices of channels, sparsely populated percolation lattices and to exemplify the use of unstructured networks to accommodate knowledge on local rock fractures.
Mathematical Flow Determination in Open Channel by Method of ...
African Journals Online (AJOL)
The distance steps used in this method need not be equal, and may be chosen in such a manner as to deal with each channel geometry and spatial distribution of lateral inflows. Studies so far show that there are minimal differences in accuracy between the direct and iterative formulation of method. Journal of the Nigerian ...
Mixed convective magnetohydrodynamic flow in a vertical channel filled with nanofluids
Directory of Open Access Journals (Sweden)
S. Das
2015-06-01
Full Text Available The fully developed mixed convection flow in a vertical channel filled with nanofluids in the presence of a uniform transverse magnetic field has been studied. Closed form solutions for the fluid temperature, velocity and induced magnetic field are obtained for both the buoyancy-aided and -opposed flows. Three different water-based nanofluids containing copper, aluminium oxide and titanium dioxide are taken into consideration. Effects of the pertinent parameters on the nanofluid temperature, velocity, and induced magnetic field as well as the shear stress and the rate of heat transfer at the channel wall are shown in figures and tables followed by a quantitative discussion. It is found that the magnetic field tends to enhance the nanofluid velocity in the channel. The induced magnetic field vanishes in the cental region of the channel. The critical Rayleigh number at onset of instability of flow is strongly dependent on the volume fraction of nanoparticles and the magnetic field.
Darcy Flow in a Wavy Channel Filled with a Porous Medium
Energy Technology Data Exchange (ETDEWEB)
Gray, Donald D; Ogretim, Egemen; Bromhal, Grant S
2013-05-17
Flow in channels bounded by wavy or corrugated walls is of interest in both technological and geological contexts. This paper presents an analytical solution for the steady Darcy flow of an incompressible fluid through a homogeneous, isotropic porous medium filling a channel bounded by symmetric wavy walls. This packed channel may represent an idealized packed fracture, a situation which is of interest as a potential pathway for the leakage of carbon dioxide from a geological sequestration site. The channel walls change from parallel planes, to small amplitude sine waves, to large amplitude nonsinusoidal waves as certain parameters are increased. The direction of gravity is arbitrary. A plot of piezometric head against distance in the direction of mean flow changes from a straight line for parallel planes to a series of steeply sloping sections in the reaches of small aperture alternating with nearly constant sections in the large aperture bulges. Expressions are given for the stream function, specific discharge, piezometric head, and pressure.
Computation of gradually varied flow in compound open channel ...
Indian Academy of Sciences (India)
becomes questionable due to differences in the hydraulic and geometric characteris- tics of the main ... continuity and energy equations can be written in terms of flow depths and flow rates for all the reaches ... 2. Methodology. The following form of the energy equation can be applied between the two ends of a reach to.
Turbulent oscillating channel flow subjected to a wind stress
Kramer, W.; Clercx, H.J.H.; Armenio, V.
2008-01-01
The Westerschelde estuary in the Netherlands is characterized by a strong tidal driven flow with typical velocities in the range of 0.2 to 1 m/s. In addition to the tides the wind (5 m/s) exerts a stress at the free surface driving the upper fluid layers. To investigate this flow we performed
Modelling of Unsteady Flow in Compound Channels | Tuitoek ...
African Journals Online (AJOL)
A model based on the St. Venant equations of flow with incorporation of terms to account for the momentum transfer phenomenon, was developed to route unsteady flow in compound ... The resulting equations called CCDG 1-D model were solved by the characteristic-dissipative-Galerkin (CDG) finite element method.
AN EVOLUTIONARY ALGORITHM FOR CHANNEL ASSIGNMENT PROBLEM IN WIRELESS MOBILE NETWORKS
Directory of Open Access Journals (Sweden)
Yee Shin Chia
2012-12-01
Full Text Available The channel assignment problem in wireless mobile network is the assignment of appropriate frequency spectrum to incoming calls while maintaining a satisfactory level of electromagnetic compatibility (EMC constraints. An effective channel assignment strategy is important due to the limited capacity of frequency spectrum in wireless mobile network. Most of the existing channel assignment strategies are based on deterministic methods. In this paper, an adaptive genetic algorithm (GA based channel assignment strategy is introduced for resource management and to reduce the effect of EMC interferences. The most significant advantage of the proposed optimization method is its capability to handle both the reassignment of channels for existing calls as well as the allocation of channel to a new incoming call in an adaptive process to maximize the utility of the limited resources. It is capable to adapt the population size to the number of eligible channels for a particular cell upon new call arrivals to achieve reasonable convergence speed. The MATLAB simulation on a 49-cells network model for both uniform and nonuniform call traffic distributions showed that the proposed channel optimization method can always achieve a lower average new incoming call blocking probability compared to the deterministic based channel assignment strategy.
Oscillating flow and separation of species in rectangular channels
Energy Technology Data Exchange (ETDEWEB)
Hacioglu, A., E-mail: ahacioglu@ufl.edu; Narayanan, R., E-mail: ranga@ufl.edu [Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611 (United States)
2016-07-15
The mass transfer and separation of species in a tube using oscillatory flows are strongly affected by the fluid flow profiles in the tube. It has been well established that oscillatory motion in a one-dimensional flow configuration leads to a single tuning dimensionless frequency, where optimum separation may be effected. In this work, the effect on species separation by two-dimensional laminar flow arising in a rectangular cross section is studied and a surprising result is that a second tuning frequency may occur at lower dimensionless oscillation frequencies. The physics reveals that this new optimum disappears when the aspect ratio is either very large or close to unity. These observations are related to the flow profiles at different aspect ratios.
Jansen, John D.; Nanson, Gerald C.
2010-12-01
Water and sediment flux interactions are examined in Magela Creek, an alluvial (anabranching) sand bed river in the northern Australian tropics. Dense riparian vegetation stabilizes the channels and floodplains thereby preventing erosional instability at flow depths up to 6.2 times bankfull and discharges up to 15 times bankfull. Narrow anabranching channels characterize >92% of the alluvial reach and transport bed load more efficiently than short reaches of wide single-channels, yet overall 29 ± 12% of the bed load is sequestered and the average vertical accretion rate is 0.41 ± 0.17 mm yr-1 along the 12 km study reach. The most effective discharge for transporting sediment (40-45 m3 s-1) is consistent at all 5 stations (10 channels) examined and is equivalent to the channel-forming discharge. It has an average recurrence interval of 1.01 years, occurs for an exceptionally long portion (13-15%) of the annual flow duration, and averages a remarkable 2.1 times bankfull. The high flow efficiency (i.e., bed load transport rate to stream power ratio) of the anabranches is facilitated by low width/depth channels with banks reinforced by vegetation. Colonnades of bank top trees confine high-velocity flows overbed (i.e., over the channel bed) at stages well above bankfull. At even larger overbank flows, momentum exchange between the channels and forested floodplains restrains overbed velocities, in some cases causing them to decline, thereby limiting erosion. Magela Creek exhibits a complicated set of planform, cross-sectional and vegetative adjustments that boost overbed velocities and enhance bed load yield in multiple channels while restraining velocities and erosion at the largest discharges.
Large-eddy simulation of a mildly curved open-channel flow
Van Balen, W.; Uijttewaal, W.S.J.; Blanckaert, K.
2009-01-01
After validation with experimental data, large-eddy simulation (LES) is used to study in detail the open-channel flow through a curved flume. Based on the LES results, the present paper addresses four issues. Firstly, features of the complex bicellular pattern of the secondary flow, occurring in
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
On debris flows, river networks, and the spatial structure of channel morphology.
P.E. Bigelow; L.E. Benda; D.J. Miller; K.M. Burnett
2007-01-01
In this paper, we examine the influence of debris-flow deposits and fans on channels and habitat characteristics in small to intermediate-size watersheds in the Oregon Coast Range. We evaluate: (1) the proportion of stream length bordered by debris fans and the spacing between fans, (2) the recurrence interval of debris flows in unmanaged watersheds, (3) the proportion...
On Howard's conjecture in heterogeneous shear flow problem
Indian Academy of Sciences (India)
M. Senthilkumar (Newgen Imaging) 1461 1996 Oct 15 13:05:22
the basic heterogeneity distribution function, are negligible as compared to the first-order terms in gβ. 2. Mathematical formulation of the problem. The basic equations governing the linear instability in a Boussinesq inviscid parallel shear flow which is confined between two rigid horizontal boundaries is given by. 451 ...
Topology optimization of mass distribution problems in Stokes flow
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan; Berggren, Martin; Dammann, Bernd
We consider topology optimization of mass distribution problems in 2D and 3D Stokes flow with the aim of designing devices that meet target outflow rates. For the purpose of validation, the designs have been post processed using the image processing tools available in FEMLAB. In turn, this has en...
Reduced-Complexity Semidefinite Relaxations of Optimal Power Flow Problems
DEFF Research Database (Denmark)
Andersen, Martin Skovgaard; Hansson, Anders; Vandenberghe, Lieven
2014-01-01
We propose a new method for generating semidefinite relaxations of optimal power flow problems. The method is based on chordal conversion techniques: by dropping some equality constraints in the conversion, we obtain semidefinite relaxations that are computationally cheaper, but potentially weaker...
Nonmodal instability of a stratified plane-channel suspension flow with fine particles.
Boronin, Sergei A; Osiptsov, Alexander N
2016-03-01
We consider the nonmodal instability and transient growth of small disturbances in a plane-channel suspension flow with a nonuniform concentration profile of fine noncolloidal particles accumulated in two localized layers, symmetric about the channel axis. A single-velocity model of an effective Newtonian fluid with a finite particle volume fraction is employed. It is established that fine particles distributed nonuniformly in the main flow significantly modify the growth rate of the first mode in a wide range of governing parameters. The most pronounced destabilizing effect is produced by the particles localized in the vicinity of the walls. A parametric study of the so-called optimal disturbances showed that they are streaks elongated in the flow direction, similar to the optimal disturbances in the flow devoid of particles. The transverse wave number of the optimal disturbances depends strongly on the location of the particle layers. Even when the particle mass concentration (averaged over the channel cross section) is small (of the order of a percent) and the particles are localized in the middle between the walls and the channel axis, the energy of the optimal disturbances is by several orders of magnitude larger than in dusty-gas and pure-fluid flows. When the particle layers are located in the vicinity of the walls or the channel axis, the nonmodal instability mechanism is less pronounced, as compared to the flow devoid of particles.
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.
Direct simulation Monte Carlo method for gas flows in micro-channels with bends with added curvature
Directory of Open Access Journals (Sweden)
Tisovský Tomáš
2017-01-01
Full Text Available Gas flows in micro-channels are simulated using an open source Direct Simulation Monte Carlo (DSMC code dsmcFOAM for general application to rarefied gas flow written within the framework of the open source C++ toolbox called OpenFOAM. Aim of this paper is to investigate the flow in micro-channel with bend with added curvature. Results are compared with flows in channel without added curvature and equivalent straight channel. Effects of micro-channel bend was already thoroughly investigated by White et al. Geometry proposed by White is also used here for refference.
MHD oscillatory flow through a porous channel saturated with porous medium
Directory of Open Access Journals (Sweden)
J.A. Falade
2017-03-01
Full Text Available In this paper, we investigate the effect of suction/injection on the unsteady oscillatory flow through a vertical channel with non-uniform wall temperature. The fluid is subjected to a transverse magnetic field and the velocity slip at the lower plate is taken into consideration. Exact solutions of the dimensionless equations governing the fluid flow are obtained and the effects of the flow parameters on temperature, velocity profiles, skin friction and rate of heat transfer are discussed and shown graphically. It is interesting to note that skin friction increases on both channel plates as injection increases on the heated plate.
Jan, Chyan-Deng
2014-01-01
Gradually-varied flow (GVF) is a steady non-uniform flow in an open channel with gradual changes in its water surface elevation. The evaluation of GVF profiles under a specific flow discharge is very important in hydraulic engineering. This book proposes a novel approach to analytically solve the GVF profiles by using the direct integration and Gaussian hypergeometric function. Both normal-depth- and critical-depth-based dimensionless GVF profiles are presented. The novel approach has laid the foundation to compute at one sweep the GVF profiles in a series of sustaining and adverse channels, w
Directory of Open Access Journals (Sweden)
Yoshitaka Shirasaki
2013-01-01
Full Text Available An integrated channel selector system employing thermoreversible gelation of a polymer was developed. Here, we show a system with 3×3 arrayed microchannels having nine crossing points. Infrared laser irradiation was used to form gel areas at several crossing points in arranging a flow path from the inlet to one of the nine outlets passing through certain junctions and channels. The multipoint irradiation by the infrared laser was realized using a personal-computer-controlled digital mirror device. The system was demonstrated to be able to direct flow to all nine outlets. Finally, we achieved to produce flexible paths for flowing particles including side trips.
Daniel J. Miller; Kelly M. Burnett
2008-01-01
Debris flows are important geomorphic agents in mountainous terrains that shape channel environments and add a dynamic element to sediment supply and channel disturbance. Identification of channels susceptible to debris-flow inputs of sediment and organic debris, and quantification of the likelihood and magnitude of those inputs, are key tasks for characterizing...
Flow of Helium-4 in One-dimensional Channel
Harris, Clayton R.; Banavar, Samhita; Kim, Duk Y.; Chan, Moses H. W.; Bischof, Jesse; Badding, John V.; Hayes, John; Sazio, Pier
2014-03-01
Superfluidity breaks down in the one-dimensional limit. However, other experiments have demonstrated superfluid flow through pores on the order of nanometers. Here we report on studying liquid helium flow through a single-hole glass capillary with internal diameters ranging from 80 to 150 nm. We observed a significant flow rate increase below the lambda transition temperature. The estimated critical velocities at low temperatures are approximately 10 m/s, which belongs to the highest group of measured critical velocities. Experimental study at Penn State is supported by NSF Grants No. DMR 1103159.
Sakimoto, S. E. H.
2016-12-01
Planetary volcanism has redefined what is considered volcanism. "Magma" now may be considered to be anything from the molten rock familiar at terrestrial volcanoes to cryovolcanic ammonia-water mixes erupted on an outer solar system moon. However, even with unfamiliar compositions and source mechanisms, we find familiar landforms such as volcanic channels, lakes, flows, and domes and thus a multitude of possibilities for modeling. As on Earth, these landforms lend themselves to analysis for estimating storage, eruption and/or flow rates. This has potential pitfalls, as extension of the simplified analytic models we often use for terrestrial features into unfamiliar parameter space might yield misleading results. Our most commonly used tools for estimating flow and cooling have tended to lag significantly behind state-of-the-art; the easiest methods to use are neither realistic or accurate, but the more realistic and accurate computational methods are not simple to use. Since the latter computational tools tend to be both expensive and require a significant learning curve, there is a need for a user-friendly approach that still takes advantage of their accuracy. One method is use of the computational package for generation of a server-based tool that allows less computationally inclined users to get accurate results over their range of input parameters for a given problem geometry. A second method is to use the computational package for the generation of a polynomial empirical solution for each class of flow geometry that can be fairly easily solved by anyone with a spreadsheet. In this study, we demonstrate both approaches for several channel flow and lava lake geometries with terrestrial and extraterrestrial examples and compare their results. Specifically, we model cooling rectangular channel flow with a yield strength material, with applications to Mauna Loa, Kilauea, Venus, and Mars. This approach also shows promise with model applications to lava lakes, magma
Carling, Paul; Kleinhans, Maarten; Leyland, Julian; Besozzi, Louison; Duranton, Pierre; Trieu, Hai; Teske, Roy
2014-01-01
Understanding of flow resistance of forested floodplains is essential for floodplain flow routing and floodplain reforestation projects. Although the flow resistance of grass-lined channels is well-known, flow retention due to flow-blocking by trees is poorly understood. Flow behaviour through
Simulation of the solidification in a channel of a water-cooled glass flow
Directory of Open Access Journals (Sweden)
G. E. Ovando Chacon
2014-12-01
Full Text Available A computer simulation study of a laminar steady-state glass flow that exits from a channel cooled with water is reported. The simulations are carried out in a two-dimensional, Cartesian channel with a backward-facing step for three different angles of the step and different glass outflow velocities. We studied the interaction of the fluid dynamics, phase change and thermal behavior of the glass flow due to the heat that transfers to the cooling water through the wall of the channel. The temperature, streamline, phase change and pressure fields are obtained and analyzed for the glass flow. Moreover, the temperature increments of the cooling water are characterized. It is shown that, by reducing the glass outflow velocity, the solidification is enhanced; meanwhile, an increase of the step angle also improves the solidification of the glass flow.
Rabbi, Khan Md.; Rakib, Tawfiqur; Das, Sourav; Mojumder, Satyajit; Saha, Sourav
2016-07-01
This paper demonstrates magneto-hydrodynamic (MHD) mixed convection flow through a channel with a rectangular obstacle at the entrance region using non-Newtonian power law fluid. The obstacle is kept at uniformly high temperature whereas the inlet and top wall of the channel are maintained at a temperature lower than obstacle temperature. Poiseuille flow is implemented as the inlet velocity boundary condition. Grid independency test and code validation are performed to justify the computational accuracy before solving the present problem. Galerkin weighted residual method has been appointed to solve the continuity, momentum and energy equations. The problem has been solved for wide range of pertinent parameters like Richardson number (Ri = 0.1 - 10) at a constant Reynolds number (Re = 100), Hartmann number (Ha = 0 - 100), power index (n = 0.6 - 1.6). The flow and thermal field have been thoroughly discussed through streamline and isothermal lines respectively. The heat transfer performance of the given study has been illustrated by average Nusselt number plots. It is observed that increment of Hartmann number (Ha) tends to decrease the heat transfer rate up to a critical value (Ha = 20) and then let increase the heat transfer performance. Thus maximum heat transfer rate has been recorded for higher Hartmann number and Rayleigh number in case of pseudo-plastic (n = 0.6) non-Newtonian fluid flow.
Flow patterns in an open channel confluence with increasingly dominant tributary inflow
Laurent Schindfessel; Stéphan Creëlle; Tom De Mulder
2015-01-01
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 discharg...
Dynamics of flow behind backward-facing step in a narrow channel
Directory of Open Access Journals (Sweden)
Uruba V.
2013-04-01
Full Text Available The results and their analysis from experiments obtained by TR-PIV are presented on the model of backward-facing step in a narrow channel. The recirculation zone is studied in details. Mean structures are evaluated from fluctuating velocity fields. Then dynamics of the flow is characterized with help of POD (BOD technique. Substantial differences in high energy dynamical structures behaviour within the back-flow region and further downstream behind the flow reattachment have been found.
Dynamics of flow behind backward-facing step in a narrow channel
Uruba, V.
2013-04-01
The results and their analysis from experiments obtained by TR-PIV are presented on the model of backward-facing step in a narrow channel. The recirculation zone is studied in details. Mean structures are evaluated from fluctuating velocity fields. Then dynamics of the flow is characterized with help of POD (BOD) technique. Substantial differences in high energy dynamical structures behaviour within the back-flow region and further downstream behind the flow reattachment have been found.
Active and hibernating turbulence in minimal channel flow of Newtonian and polymeric fluids
Xi, Li
2010-01-01
Turbulent channel flow of drag-reducing polymer solutions is simulated in minimal flow geometries. Even in the Newtonian limit, we find intervals of "hibernating" turbulence that display many features of the universal maximum drag reduction (MDR) asymptote observed in polymer solutions: weak streamwise vortices, nearly nonexistent streamwise variations and a mean velocity gradient that quantitatively matches experiments. As viscoelasticity increases, the frequency of these intervals also increases, while the intervals themselves are unchanged, leading to flows that increasingly resemble MDR.
The LES of the channel flow in a non aligned system of coordinates
Germano, Massimo; Abbà, Antonella
2010-11-01
The plane channel flow continues to be a very important test case for the verification and the validation of LES. In the channel flow test there is a privileged direction, usually one reference axis is oriented along the stream and the size of the computational box is increased in the streamwise direction in order to capture correctly the dominant turbulent structures and to produce a fully developed flow. All that is peculiar of this particular test, and in this paper we will investigate the sensitivity of the channel test to the particular alignment of the coordinate system with the mean flow. In a non aligned system of coordinates there is no privileged direction, there are two components of the forcing term, the mean pressure gradient, and the homogeneities of the Reynolds stresses are destroyed. In our paper we simulate the channel flow in a rotated system of coordinates, and we compare the results with the stream aligned data. We think that this test could evidence the flexibility of different LES codes and LES subgrid models to simulate the turbulent flow and to capture the correct statistical values in non aligned conditions. The first preliminary results are slightly contradictory: the resolved Reynolds stresses seem degraded while the mean flow is better predicted. The dynamic anisotropic subgrid model of Abbà, Cercignani and Valdettaro seems well fitted to represent correctly the large scales in non aligned conditions.
A Rotary Flow Channel for Shear Stress Sensor Calibration
Zuckerwar, Allan J.; Scott, Michael A.
2004-01-01
A proposed shear sensor calibrator consists of a rotating wheel with the sensor mounted tangential to the rim and positioned in close proximity to the rim. The shear stress generated by the flow at the sensor position is simply tau(sub omega) = (mu)r(omega)/h, where mu is the viscosity of the ambient gas, r the wheel radius, omega the angular velocity of the wheel, and h the width of the gap between the wheel rim and the sensor. With numerical values of mu = 31 (mu)Pa s (neon at room temperature), r = 0.5 m, omega = 754 /s (7200 rpm), and h = 50.8 m, a shear stress of tau(sub omega) = 231 Pa can be generated. An analysis based on one-dimensional flow, with the flow velocity having only an angular component as a function of the axial and radial coordinates, yields corrections to the above simple formula for the curvature of the wheel, flatness of the sensor, and finite width of the wheel. It is assumed that the sensor mount contains a trough (sidewalls) to render a velocity release boundary condition at the edges of the rim. The Taylor number under maximum flow conditions is found to be 62.3, sufficiently low to obviate flow instability. The fact that the parameters entering into the evaluation of the shear stress can be measured to high accuracy with well-defined uncertainties makes the proposed calibrator suitable for a physical standard for shear stress calibration.
Energy Technology Data Exchange (ETDEWEB)
Hong, Sungdeok; Kim, C. S.; Kim, M. H.; Kim, Y. W. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Seo, D. U.; Park, G. C. [Seoul National Univ., Seoul (Korea, Republic of)
2014-05-15
The Korea Atomic Energy Research Institute (KAERI) has developed a hybrid-design decomposer to withstand severe operating conditions. Hong and Seo have been studying a two-dimensional numerical analysis for a catalyst channel line-up with a 3mm ball shaped catalyst. They compared their CFD results to many widespread correlations developed for porous media such as those by Carman, Ergun, and Zhavoronkov as well as Susskind and Becker and Reichelt including a pebble-bed nuclear reactor design correlation. They concluded that the validation should be accomplished by the experiments for a catalyst channel simulating the channel of the PHE. In this paper, we discuss the pressure drop experiments on a flow channel filled with ball shaped catalysts. The test section simulates a single channel of the PHE secondary side plate-fin channel. The experimental results compared well with the known pressure drop correlations and a numerical analysis, respectively. We discussed an experimental validation of a pressure drop correlations and 2D CFD analysis on a flow channel filled with catalysts in the channel. The results of the pressure drop measurements are compared with the results obtained using well-known empirical correlations and 2D CFD analysis. From the comparison results, the validity of all the correlations and 2D numerical analysis is not satisfactory. There are two kind of reasons are presumed. While the general packed channel has radially infinite and complete circular cross section, the catalyst channel has radially finite with a very narrow width and irregular wavy cross section. Another reason is presumed to be because the inordinate large void fraction in the catalyst channel which is beyond the application range on void fraction in the empirical correlations.
Transient Taylor-Aris dispersion for time-dependent flows in straight channels
DEFF Research Database (Denmark)
Vedel, Søren; Bruus, Henrik
2012-01-01
Taylor–Aris dispersion, the shear-induced enhancement of solute diffusion in the flow direction of the solvent, has been studied intensely in the past half century for the case of steady flow and single-frequency pulsating flows. Here, combining Aris’s method of moments with Dirac’s bra–ket forma......Taylor–Aris dispersion, the shear-induced enhancement of solute diffusion in the flow direction of the solvent, has been studied intensely in the past half century for the case of steady flow and single-frequency pulsating flows. Here, combining Aris’s method of moments with Dirac’s bra......–ket formalism, we derive an expression for the effective solute diffusivity valid for transient Taylor–Aris dispersion in any given time-dependent, multi-frequency solvent flow through straight channels. Our theory shows that the solute dispersion may be greatly enhanced by the time-dependent parts of the flow...
Combined effect of free and forced convection on MHD flow in a rotating porous channel
Directory of Open Access Journals (Sweden)
D. R. V. Prasada Rao
1982-01-01
Full Text Available This paper gives a steady linear theory of the combined effect of the free and forced convection in rotating hydromagnetic viscous fluid flows in a porous channel under the action of a uniform magnetic field. The flow is governed by the Grashof number G, the Hartmann number H, the Ekman number E, and the suction Reynolds number S. The solutions for the velocity field, temperature distribution, magnetic field, mass rate of flow and the shear stresses on the channel boundaries are obtained using a perturbation method with the small parameter S. The nature of the associated boundary layers is investigated for various values of the governing flow parameters. The velocity, the temperature, and the shear stresses are discussed numerically by drawing profiles with reference to the variations in the flow parameters.
A note on critical flow section in collector channels
Indian Academy of Sciences (India)
Springer Verlag Heidelberg #4 2048 1996 Dec 15 10:16:45
received no attention so far. The aim of the present study is to report a methodology for generalized solution of critical flow section in collector ..... Churchill S W 1977 Friction factor equation spans all fluid regimes. Chem. Eng. 84: 91–92. Conte S D, de Boor C 1987 Elementary numerical analysis: an algorithmic approach ( ...
Turbulence characteristics of open channel flow over non ...
Indian Academy of Sciences (India)
The effect of the non-equilibrium mobile dunes on the flow characteristics and turbulence is examined by computing turbulent intensities, turbulent kinetic energy and Reynolds shear stresses using time averaged and time–space averaged velocity measurements. The magnitudes of transverse velocities are approximately ...
Experimental studies on the flow through soft tubes and channels
Indian Academy of Sciences (India)
V Kumaran either an increase in the transition Reynolds number, or due to turbulence attenuation. In the case .... Schlichting modes in the flow past a rigid surface and which are destabilised by increased dissipation in the ..... normal wall displacements, whereas in reality the gel will experience both tangential and normal.
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
Wellmeyer, Jessica L.; Slattery, Michael C.; Phillips, Jonathan D.
2005-07-01
As human population worldwide has grown, so has interest in harnessing and manipulating the flow of water for the benefit of humans. The Trinity River of eastern Texas is one such watershed greatly impacted by engineering and urbanization. Draining the Dallas-Fort Worth metroplex, just under 30 reservoirs are in operation in the basin, regulating flow while containing public supplies, supporting recreation, and providing flood control. Lake Livingston is the lowest, as well as largest, reservoir in the basin, a mere 95 km above the Trinity's outlet near Galveston Bay. This study seeks to describe and quantify channel activity and flow regime, identifying effects of the 1968 closure of Livingston dam. Using historic daily and peak discharge data from USGS gauging stations, flow duration curves are constructed, identifying pre- and post-dam flow conditions. A digital historic photo archive was also constructed using six sets of aerial photographs spanning from 1938 to 1995, and three measures of channel activity applied using a GIS. Results show no changes in high flow conditions following impoundment, while low flows are elevated. However, the entire post-dam period is characterized by significantly higher rainfall, which may be obscuring the full impact of flow regulation. Channel activity rates do not indicate a more stabilized planform following dam closure; rather they suggest that the Trinity River is adjusting itself to the stress of Livingston dam in a slow, gradual process that may not be apparent in a modern time scale.
A mathematical model of the flow and bed topography in curved channels
Olesen, K.W.
1985-01-01
A two-dimensional horizontal mathematical model of the flow and bed topography in alluvial channel bends is presented. The applicability of the model is restricted to channels of which the width-depth ratio is large, the Froude number is small, bed load is dominant and grain sorting effects are negligible. First order analyses of the mathematical model, using both steady and unsteady perturbations, are carried out, and an integration procedure based on a CSFT finite difference approximation o...
Cooling of a channeled lava flow with non-Newtonian rheology: crust formation and surface radiance
Directory of Open Access Journals (Sweden)
Stefano Santini
2011-12-01
Full Text Available We present here the results from dynamical and thermal models that describe a channeled lava flow as it cools by radiation. In particular, the effects of power-law rheology and of the presence of bends in the flow are considered, as well as the formation of surface crust and lava tubes. On the basis of the thermal models, we analyze the assumptions implicit in the currently used formulae for evaluation of lava flow rates from satellite thermal imagery. Assuming a steady flow down an inclined rectangular channel, we solve numerically the equation of motion by the finite-volume method and a classical iterative solution. Our results show that the use of power-law rheology results in relevant differences in the average velocity and volume flow rate with respect to Newtonian rheology. Crust formation is strongly influenced by power-law rheology; in particular, the growth rate and the velocity profile inside the channel are strongly modified. In addition, channel curvature affects the flow dynamics and surface morphology. The size and shape of surface solid plates are controlled by competition between the shear stress and the crust yield strength: the degree of crust cover of the channel is studied as a function of the curvature. Simple formulae are currently used to relate the lava flow rate to the energy radiated by the lava flow as inferred from satellite thermal imagery. Such formulae are based on a specific model, and consequently, their validity is subject to the model assumptions. An analysis of these assumptions reveals that the current use of such formulae is not consistent with the model.
Loy, G. E.; Furbish, D. J.; Covey, A.
2010-12-01
Landsliding of the White Bluffs along the Columbia River in Washington State has constricted the width of the river on one side of Locke Island, a two-kilometer long island positioned in the middle of the channel. Associated changes in flow are thought to be causing relatively rapid erosion of Locke Island on the constricted side. This island is of cultural significance to Native American tribes of south-central Washington, so there are social as well as scientific reasons to understand how the alteration of stream channel processes resulting from the landsliding might be influencing observed erosion rates. Simple hydrodynamic calculations suggest that the constriction on one side of the island creates an upstream backwater effect. As a consequence a cross-stream pressure gradient upstream of the island results in steering of flow around the island into the unobstructed thread. This diversion of water decreases the discharge through the constriction. Therefore, flow velocities within the constriction are not necessarily expected to be higher than those in the unobstructed thread, contrary to initial reports suggesting that higher velocities within the constriction are the main cause of erosion. We set up streamtable experiments with lapse rate imaging to illustrate the backwater effects of the channel constriction and the associated cross-stream steering of flow around a model island. Our experiments are scaled by channel roughness and slope rather than geometrically, as the main focus is to understand the mechanical behavior of flow in this type of island-landslide system. In addition, we studied the stream velocities and flow steering as well as the magnitude of the backwater effect in both the constricted and unobstructed channels using tracer particles in the time-lapse images. These experimental data are compared with calculated upstream backwater distances determined from the known water-surface slope, flow depth, total discharge, and bed roughness
Large woody debris and flow resistance in step-pool channels, Cascade Range, Washington
Curran, Janet H.; Wohl, Ellen E.
2003-01-01
Total flow resistance, measured as Darcy-Weisbach f, in 20 step-pool channels with large woody debris (LWD) in Washington, ranged from 5 to 380 during summer low flows. Step risers in the study streams consist of either (1) large and relatively immobile woody debris, bedrock, or roots that form fixed, or “forced,” steps, or (2) smaller and relatively mobile wood or clasts, or a mixture of both, arranged across the channel by the stream. Flow resistance in step-pool channels may be partitioned into grain, form, and spill resistance. Grain resistance is calculated as a function of particle size, and form resistance is calculated as large woody debris drag. Combined, grain and form resistance account for less than 10% of the total flow resistance. We initially assumed that the substantial remaining portion is spill resistance attributable to steps. However, measured step characteristics could not explain between-reach variations in flow resistance. This suggests that other factors may be significant; the coefficient of variation of the hydraulic radius explained 43% of the variation in friction factors between streams, for example. Large woody debris generates form resistance on step treads and spill resistance at step risers. Because the form resistance of step-pool channels is relatively minor compared to spill resistance and because wood in steps accentuates spill resistance by increasing step height, we suggest that wood in step risers influences channel hydraulics more than wood elsewhere in the channel. Hence, the distribution and function, not just abundance, of large woody debris is critical in steep, step-pool channels.
Modeling water droplet condensation and evaporation in DNS of turbulent channel flow
Russo, E.; Kuerten, J. G. M.; van der Geld, C. W. M.; Geurts, B. J.
2011-12-01
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 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.
The zonal satellite problem - I: Near-collision flow
Directory of Open Access Journals (Sweden)
Mioc V.
1998-01-01
Full Text Available The force field described by a potential function of the form U = Σn k=1 ak/rk (r = distance between particles, ak = real parameters models various concrete situations belonging to astronomy, physics, mechanics, astrodynamics, etc. The two-body problem is being tackled in such a field. The motion equations and the first integrals of energy and angular momentum are established. The McGehee-type coordinates are used to blow up the collision singularity and to paste the resulting manifold on the phase space. The flow on the collision manifold is depicted. Then, using the rotational symmetry of the problem and the angular momentum integral, the local flow near collision is described and interpreted in terms of physical motion.
Two-phase Flow Characteristics in a Gas-Flow Channel of Polymer Electrolyte Membrane Fuel Cells
Cho, Sung Chan
Fuel cells, converting chemical energy of fuels directly into electricity, have become an integral part of alternative energy and energy efficiency. They provide a power source of high energy-conversion efficiency and zero emission, meeting the critical demands of a rapidly growing society. The proton exchange membrane (PEM) fuel cells, also called polymer electrolyte fuel cells (PEFCs), are the major type of fuel cells for transportation, portable and small-scale stationary applications. They provide high-power capability, work quietly at low temperatures, produce only water byproduct and no emission, and can be compactly assembled, making them one of the leading candidates for the next generation of power sources. Water management is one of the key issues in PEM fuel cells: appropriate humidification is critical for the ionic conductivity of membrane while excessive water causes flooding and consequently reduces cell performance. For efficient liquid water removal from gas flow channels of PEM fuel cells, in-depth understanding on droplet dynamics and two-phase flow characteristics is required. In this dissertation, theoretical analysis, numerical simulation, and experimental testing with visualization are carried out to understand the two-phase flow characteristics in PEM fuel cell channels. Two aspects of two-phase phenomena will be targeted: one is the droplet dynamics at the GDL surface; the other is the two-phase flow phenomena in gas flow channels. In the former, forces over a droplet, droplet deformation, and detachment are studied. Analytical solutions of droplet deformation and droplet detachment velocity are obtained. Both experiments and numerical simulation are conducted to validate analytical results. The effects of contact angle, channel geometry, superficial air velocity, properties of gas phase fluids are examined and criteria for the detachment velocity are derived to relate the Reynolds number to the Weber number. In the latter, two-phase flow
Tree-ring records of variation in flow and channel geometry
Merigliano, M.F.; Friedman, J. M.; Scott, M. L.
2013-01-01
We review the use of tree rings to date flood disturbance, channel change, and sediment deposition, with an emphasis on rivers in semi-arid landscapes in the western United States. As watershed area decreases and aridity increases, large floods have a more pronounced and sustained effect on channel width and location, resulting in forest area-age distributions that are farther from a steady-state exponential relation. Furthermore, forests along three major snowmelt rivers in the northern Rocky Mountains, USA, have smaller than expected areas of young trees, suggesting that high flows and channel migration have decreased since the late 1800s.
Elasto-inertial particle focusing under the viscoelastic flow of DNA solution in a square channel.
Kim, Bookun; Kim, Ju Min
2016-03-01
Particle focusing is an essential step in a wide range of applications such as cell counting and sorting. Recently, viscoelastic particle focusing, which exploits the spatially non-uniform viscoelastic properties of a polymer solution under Poiseuille flow, has attracted much attention because the particles are focused along the channel centerline without any external force. Lateral particle migration in polymer solutions in square channels has been studied due to its practical importance in lab-on-a-chip applications. However, there are still many questions about how the rheological properties of the medium alter the equilibrium particle positions and about the flow rate ranges for particle focusing. In this study, we investigated lateral particle migration in a viscoelastic flow of DNA solution in a square microchannel. The elastic property is relevant due to the long relaxation time of a DNA molecule, even when the DNA concentration is extremely low. Further, the shear viscosity of the solution is essentially constant irrespective of shear rate. Our current results demonstrate that the particles migrate toward the channel centerline and the four corners of a square channel in the dilute DNA solution when the inertia is negligible (elasticity-dominant flow). As the flow rate increases, the multiple equilibrium particle positions are reduced to a single file along the channel centerline, due to the elasto-inertial particle focusing mechanism. The current results support that elasto-inertial particle focusing mechanism is a universal phenomenon in a viscoelastic fluid with constant shear viscosity (Boger fluid). Also, the effective flow rate ranges for three-dimensional particle focusing in the DNA solution were significantly higher and wider than those for the previous synthetic polymer solution case, which facilitates high throughput analysis of particulate systems. In addition, we demonstrated that the DNA solution can be applied to focus a wide range of
Effect of the Aligned Flow Obstacles on Downward-Facing CHF in an Inclined Rectangular Channel
Energy Technology Data Exchange (ETDEWEB)
Jeong, Ui ju; Son, Hong Hyun; Seo, Gwang Hyeok; Jeun, Gyoo Dong; Kim, Sung Joong [Hanyang, Seoul (Korea, Republic of)
2016-05-15
The cooling channel consists of the inclined (10 .deg. ) portion of the downward facing heating channel and vertical portion of the heating channel. Features unique to flow boiling with the downward-facing heater surface in the inclined cooling channel where the studs are installed have drawn a considerable attention. That's because prior studies on boiling crisis indicate the orientation of the heated wall can exert substantial influence on CHF. Especially, the concentration of the vapor near the downward facing heater surface makes this region susceptible to premature boiling crisis when compared to vertical or upward-facing heated wall. Also, the installed studs could cause a partial flow blockage, and distort the flow streamline. Due to the distortion, stagnation points may occur in the cooling channel, promoting the concentration of the vapor near the heated wall. Then, the locally degraded heat transfer around the points may result in the formation of vapor pocket. The primary objective of this study is to make available experimental data on the CHF values varying the shape of studs and to improve understanding of the mechanism of flow boiling crisis associated with the aligned flow obstructions by means of visual experimental study. This study presents experimental data for subcooled flow boiling of water at atmospheric pressure and low mass flux conditions. The major outcomes from this investigation can be summarized as follows: (1) The CHF value from bare test section is -320kW/m{sup 2} , significantly lower than the values from the existing correlations even considering the uncertainty in the experiments. (2) The CHF value is remarkably decreased as columnar structures are installed in the channel. It is confirmed that formation and extinction of local dryout occurs repeatedly just behind the first stud at heat flux of -160 kW/m{sup 2}.
The transverse dynamics of flow in a tidal channel within a greater strait
Khosravi, Maziar; Siadatmousavi, Seyed Mostafa; Vennell, Ross; Chegini, Vahid
2017-12-01
Vessel-mounted ADCP measurements were conducted to describe the transverse structure of flow between the two headland tips in Khuran Channel, south of Iran (26° 45' N), where the highest tidal velocities in spring tides were 1.8 m/s. Current profiles were obtained using a 614.4 kHz TRDI WorkHorse Broadband ADCP over nine repetitions of three cross-channel transects during one semidiurnal tidal cycle. The 2.2-km-long transects ran north/south across the channel. A least-square fit to semidiurnal, quarter-diurnal, and sixth diurnal harmonics was used to separate the tidal signals from the observed flow. Spatial gradients showed that the greatest lateral shears and convergences were found over the northern channel and near the northern headland tip due to very sharp bathymetric changes in this area. Contrary to the historical assumption, the across-channel momentum balance in the Khuran Channel was ageostrophic. The current study represents one of the few examples reported where the lateral friction influences the across-channel momentum balance.
Flow-shop scheduling problem under uncertainties: Review and trends
Directory of Open Access Journals (Sweden)
Eliana María González-Neira
2017-03-01
Full Text Available Among the different tasks in production logistics, job scheduling is one of the most important at the operational decision-making level to enable organizations to achieve competiveness. Scheduling consists in the allocation of limited resources to activities over time in order to achieve one or more optimization objectives. Flow-shop (FS scheduling problems encompass the sequencing processes in environments in which the activities or operations are performed in a serial flow. This type of configuration includes assembly lines and the chemical, electronic, food, and metallurgical industries, among others. Scheduling has been mostly investigated for the deterministic cases, in which all parameters are known in advance and do not vary over time. Nevertheless, in real-world situations, events are frequently subject to uncertainties that can affect the decision-making process. Thus, it is important to study scheduling and sequencing activities under uncertainties since they can cause infeasibilities and disturbances. The purpose of this paper is to provide a general overview of the FS scheduling problem under uncertainties and its role in production logistics and to draw up opportunities for further research. To this end, 100 papers about FS and flexible flow-shop scheduling problems published from 2001 to October 2016 were analyzed and classified. Trends in the reviewed literature are presented and finally some research opportunities in the field are proposed.
Relative Effects of Asymmetry and Wall Slip on the Stability of Plane Channel Flow
Directory of Open Access Journals (Sweden)
Sukhendu Ghosh
2017-12-01
Full Text Available The effect of wall velocity slip on the stability of a pressure-driven two-dimensional asymmetric channel flow is examined by considering Navier slip condition on the channel walls. The two-parameter families of mean velocity profiles are considered to approximate the underlying asymmetric basic flow. Competing effects of skewness and maximum velocity on the stability of the flow are explored for a range of model parameters. The Orr–Sommerfeld system of the asymmetric flow is solved using a Chebyshev spectral collocation method for both symmetric and non-symmetric type slip boundary conditions. Numerical results indicate that moderate asymmetry in the basic flow has a significant role on the stability of the Poiseuille-kind parallel/nearly parallel flows. Wall slip shows a passive control on the instability of the asymmetric flow by increasing or decreasing the critical Reynolds number and the set of unstable wave numbers. The stabilizing/destabilizing effect of slip velocity on the flow instability is weak or strong depending on the presence of velocity slip at the upper or lower wall. Velocity slip has a profound grip on the flow behaviour by changing the shear rate inside the perturbed flow.
Self-sustained processes in the logarithmic layer of turbulent channel flows
Hwang, Yongyun; Cossu, Carlo
2011-06-01
It has recently been shown that large-scale and very-large-scale motions can self-sustain in turbulent channel flows even in the absence of input from motions at smaller scales. Here we show that also motions at intermediate scales, mainly located in the logarithmic layer, survive when motions at smaller scales are artificially quenched. These elementary self-sustained motions involve the bursting and regeneration of sinuous streaks. This is a further indication that a full range of autonomous self-sustained processes exists in turbulent channel flows with scales ranging from those of the buffer layer streaks to those of the large scale motions in the outer layer.
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 perforated ribs, the slit height is 20% of the rib height, and the open-area ratio is 16%. We discuss the flow in terms of mean velocity, streamlines, vorticity, turbulence intensity, and Reynolds shear stress. We find that the recirculation bubbles after the perforated ribs are significantly smaller than...
Spatiotemporal Dynamic of Two-dimensional core annular flow in square channel
Latrache, N.; Nsom, B.; Decruppe, J.-P.
2013-04-01
In this work, we study the spatiotemporal dynamics of a two-dimensional core-annular flow (CAF) in a square channel of an oil/water system. The flow rate of oil is fixed at Qo=0.19 l/s and the flow rate of water Qw is varied from 0.20 l/s to 0.46 l/s. For large values of Qw (typically Qw>0.23l/s), the CAF is unstable, and it becomes stable for low values of Qw (typically Qwflow rate Qw. Theses characteristics are used to explain the pressure drop as function of the water flow rate.
A revised correlation based on heat transfer model of slug flow in mini/micro-channels
Li, Xuejiao; Jia, Li; Yin, Liaofei; An, Zhoujian
2017-07-01
As flow boiling in mini/micro-channel, slug flow was corresponding to the optimal heat transfer ability owing to the evaporation of thin liquid film. Based on the heat transfer mechanism of liquid film evaporation, a simplified heat transfer model of slug flow was proposed. Li-Wu heat transfer correlation (Int J Heat Mass Transf 53(9): 1778-1787, 2010) was revised by introducing evaporation parameter, C e . With the evaporation parameter, C e , the revised correlation predicted the slug flow database with MAE (Mean Absolute Error) 25.14%, which improved the prediction accuracy remarkably.
Simulation of 3-D Nonequilibrium Seeded Air Flow in the NASA-Ames MHD Channel
Gupta, Sumeet; Tannehill, John C.; Mehta, Unmeel B.
2004-01-01
The 3-D nonequilibrium seeded air flow in the NASA-Ames experimental MHD channel has been numerically simulated. The channel contains a nozzle section, a center section, and an accelerator section where magnetic and electric fields can be imposed on the flow. In recent tests, velocity increases of up to 40% have been achieved in the accelerator section. The flow in the channel is numerically computed us ing a 3-D parabolized Navier-Stokes (PNS) algorithm that has been developed to efficiently compute MHD flows in the low magnetic Reynolds number regime: The MHD effects are modeled by introducing source terms into the PNS equations which can then be solved in a very efficient manner. The algorithm has been extended in the present study to account for nonequilibrium seeded air flows. The electrical conductivity of the flow is determined using the program of Park. The new algorithm has been used to compute two test cases that match the experimental conditions. In both cases, magnetic and electric fields are applied to the seeded flow. The computed results are in good agreement with the experimental data.
The equilibrium alluvial river under variable flow and its channel-forming discharge
Blom, Astrid; Arkesteijn, Liselot; Chavarrías, Víctor; Viparelli, Enrica
2017-10-01
When the water discharge, sediment supply, and base level vary around stable values, an alluvial river evolves toward a mean equilibrium or graded state with small fluctuations around this mean state (i.e., a dynamic or statistical equilibrium state). Here we present analytical relations describing the mean equilibrium geometry of an alluvial river under variable flow by linking channel slope, width, and bed surface texture. The solution holds in river normal flow zones (or outside both the hydrograph boundary layer and the backwater zone) and accounts for grain size selective transport and particle abrasion. We consider the variable flow rate as a series of continuously changing yet steady water discharges (here termed an alternating steady discharge). The analysis also provides a solution to the channel-forming water discharge, which is here defined as the steady water discharge that, given the mean sediment supply, provides the same equilibrium channel slope as the natural long-term hydrograph. The channel-forming water discharge for the gravel load is larger than the one associated with the sand load. The analysis illustrates how the load is distributed over the range of water discharge in the river normal flow zone, which we term the "normal flow load distribution". The fact that the distribution of the (imposed) sediment supply spatially adapts to this normal flow load distribution is the origin of the hydrograph boundary layer. The results quantify the findings by Wolman and Miller (1960) regarding the relevance of both magnitude and frequency of the flow rate with respect to channel geometry.
The physics of stripe patterns in turbulent channel flow determined by DNS results
Kiš, P; Herwig, H
2015-01-01
The turbulent flow in an infinitely extended plane channel is analysed by solving the Navier-Stokes equations with a DNS approach. Solutions are obtained in a numerical solution domain of finite size in the streamwise as well as in the lateral direction setting periodic boundary conditions in both directions. Their impact on large scale structures in the turbulent flow field is analysed carefully in order to avoid their suppression. When this is done appropriately well known stripe patterns in these flows can be observed and analysed especially with respect to their relative motion compared to the mean flow velocity. Various details of this stripe pattern dominated velocity field are shown. Also global parameters like the friction factor in the flow field and the Nusselt number in the temperature field are determined based on the statistics of the flow and temperature data in a very large time period that guarantees fully developed turbulent flow and heat transfer.
Gas-liquid two-phase flows in rectangular polymer micro-channels
Kim, Namwon; Evans, Estelle T.; Park, Daniel S.; Soper, Steven A.; Murphy, Michael C.; Nikitopoulos, Dimitris E.
2011-08-01
This study addresses gas-liquid two-phase flows in polymer (PMMA) micro-channels with non-molecularly smooth and poorly wetting walls (typical contact angle of 65°) unlike previous studies conducted on highly wetting molecularly smooth materials (e.g., glass/silicon). Four fundamentally different topological flow regimes (Capillary Bubbly, Segmented, Annular, Dry) were identified along with two transitory ones (Segmented/Annular, Annular/Dry) and regime boundaries were identified from the two different test chips. The regime transition boundaries were influenced by the geometry of the two-phase injection, the aspect ratio of the test micro-channels, and potentially the chip material as evidenced from comparisons with the results of previous studies. Three principal Segmented flow sub-regimes (1, 2, and 3) were identified on the basis of quantified topological characteristics, each closely correlated with two-phase flow pressure drop trends. Irregularity of the Segmented regimes and related influencing factors were addressed and discussed. The average bubble length associated with the Segmented flows scaled approximately with a power law of the liquid volumetric flow ratio, which depends on aspect ratio, liquid superficial velocity, and the injection system. A simplified semi-empirical geometric model of gas bubble and liquid plug volumes provided good estimates of liquid plug length for most of the segmented regime cases and for all test-channel aspect ratios. The two-phase flow pressure drop was measured for the square test channels. Each Segmented flow sub-regime was associated with different trends in the pressure drop scaled by the viscous scale. These trends were explained in terms of the quantified flow topology (measured gas bubble and liquid plug lengths) and the number of bubble/plug pairs. Significant quantitative differences were found between the two-phase pressure drop in the polymer micro-channels of this study and those obtained from previous glass
Stability of non-parallel flow in a channel
Directory of Open Access Journals (Sweden)
Philip G. Drazin
1991-05-01
Full Text Available This is a review of several generalizations of Hiemenz's classic solution for steady two-dimensional flow of a uniform incompressible viscous fluid near a stagnation point on a bluff body. These generalizations are diverse exact solutions, steady and unsteady, two- and three-dimensional, of the Navier-Stokes equations. The solutions exhibit many types of instability and bifurcation. There are turning points, trans critical bifurcations, pitchfork bifurcations, Hopf bifurcations and Takens-Bogdanov bifurcations. The solutions also take the period-doubling and Ruelle-Takens routes to chaos.
Kim, Ki Hun; Moon, Myeong Hee
2011-11-15
A chip-type design asymmetrical flow field-flow fractionation (AF4) channel has been developed for high-speed separation of proteins and top-down proteomic analysis using online coupled electrospray ionization mass spectrometry (ESI-MS). The new miniaturized AF4 channel was assembled by stacking multilayer thin stainless steel (SS, 1.5 mm each) plates embedded with an SS frit in such a way that the total thickness of the channel assembly was about 6 mm. The efficiency of the miniaturized AF4 channel at different channel lengths was examined with the separation of protein standards by adjusting flow rates in which an identical effective channel flow rate or an identical void time can be maintained at different channels. Detection limit, overloading effect, reproducibility, and influence of channel membrane materials on separation efficiency were investigated. Desalting and purification of proteins achieved during the AF4 operation by the action of an exiting crossflow and the use of aqueous mass-spectrometry-compatible (MS-compatible) buffer were advantageous for online coupling of the chip-type AF4 with ESI-MS. The direct coupling of AF4 and ESI-MS capabilities was demonstrated for the high-speed separation and identification of carbonic anhydrase (29 kDa) and transferrin (78 kDa) by full scan MS and for the first top-down identification of proteins with AF4-ESI-MS-MS using collision-induced fragmentation (CID). The presence of intact dimers (156 kDa) of transferrin was confirmed by AF4-ESI-MS via size separation of the dimers from monomers, followed by multiply charged ion spectral analysis of the dimers and molecular mass determinations. It was also found from these experiments that AF4-ESI-MS analysis of transferrin exhibited an increased signal-to-noise ratio compared to that of direct ESI-MS analysis due to online purification of the protein sample and size separation of dimers with AF4.
Fleming, K K; Longmire, E K; Hubel, A
2007-10-01
Cells are routinely cryopreserved in dimethyl sulfoxide (DMSO), a cryoprotective agent, for medical applications. Infusion of a DMSO-laden cell suspension results in adverse patient reactions, but current DMSO extraction processes result in significant cell losses. A diffusion-based numerical model was employed to characterize DMSO extraction in fully developed channel flow containing a wash stream flowing parallel to a DMSO-laden cell suspension. DMSO was allowed to diffuse across cell membranes as well as across the channel depth. A variety of cases were considered with the ultimate goal of characterizing the optimal geometry and flow conditions to process clinical volumes of cell suspension in a reasonable time (2-3 ml/min). The results were dependent on four dimensionless parameters: depth fraction of the DMSO-laden stream, Peclet number, cell volume fraction in the DMSO-laden stream, and cell membrane permeability parameter. Smaller depth fractions led to faster DMSO extraction but channel widths that were not practical. Higher Peclet numbers led to longer channels but smaller widths. For the Peclet values and channel depths considered (>or=500 microm) and appropriate permeability values, diffusion across cell membranes was significantly faster than diffusion across the channel depth. Cell volume fraction influenced the cross-stream diffusion of DMSO by limiting the fluid volume fraction available in the contaminant stream but did not play a significant role in channel geometry or operating requirements. The model was validated against preliminary experiments in which DMSO was extracted from suspensions of B-lymphoblast cells. The model results suggest that a channel device with practical dimensions can remove a sufficient level of contaminant within a mesoscale volume of cells in the required time.
Sobolev, A. F.; Yakovets, M. A.
2017-11-01
Exact solutions to problems of the propagation of acoustic modes in lined channels with an impedance jump in the presence of a uniform flow are constructed. Two problems that can be solved by the Wiener- Hopf method—the propagation of acoustic modes in an infinite cylindrical channel with a transverse impedance jump and the propagation of acoustic modes in a rectangular channel with an impedance jump on one of its walls—are considered. On the channel walls, the Ingard-Myers boundary conditions are imposed and, as an additional boundary condition in the vicinity of the junction of the linings, the condition expressing the finiteness of the acoustic energy. Analytical expressions for the amplitudes of the transmitted and reflected fields are obtained.
A particle swarm algorithm for the optimal power flow problem
Energy Technology Data Exchange (ETDEWEB)
Mantawy, A.H. [King Fahd Univ. of Petroleum and Minerals, Dhahran (Saudi Arabia). Dept. of Electrical Engineering; Al-Ghamdi, M.S. [Saudi Aramco, Dhahran (Saudi Arabia). Consulting Services Dept.
2006-07-01
Deregulated and open access electric utilities are faced with the challenge of optimizing the operation of their generation and transmission systems. This paper addressed the Optimal Power Flow (OPF) problem which is a generalized formulation of the economic dispatch problem involving voltage and other operating constraints. A typical OPF problem seeks a dispatch of active power (P) and/or reactive power (Q) by adjusting the appropriate control variables, so that a specific objective in operating a power system network is optimized. The OPF problem in electrical power systems is considered as a static non-linear and a non-convex optimization problem with both continuous and discrete control variables. In this work, the particle swam algorithm was used to solve the optimal power flow problem. The active power losses and generation fuel cost were minimized and compared using the IEEE 30-bus system. System operating constraints, including constraints dictated by the electrical network were satisfied. The proposed algorithm offered many advantages, such as flexibility in adding or deleting any system constraints and objective functions. It calculated the optimum generation pattern as well as all control variables in order to minimize the specified objective function and satisfy the system constraints. The control variables included: active power generation except the slack bus; all PV-bus voltages; all transformer load tap changers; and, the setting of all switched reactors or static VAR components. The flexibility of the algorithm allows operators and control engineers to relieve any overload or voltage violation of any component in the system during normal operation and in emergency situations. Additional objective functions and constraints can be readily added to the developed software package. 14 refs., 3 tabs.
Measurements of Shear Lift Force on a Bubble in Channel Flow in Microgravity
Nahra, Henry K.; Motil, Brian J.; Skor, Mark
2003-01-01
Under microgravity conditions, the shear lift force acting on bubbles, droplets or solid particles in multiphase flows becomes important because under normal gravity, this hydrodynamic force is masked by buoyancy. This force plays an important role in furnishing the detachment process of bubbles in a setting where a bubble suspension is needed in microgravity. In this work, measurements of the shear lift force acting on a bubble in channel flow are performed. The shear lift force is deduced from the bubble kinematics using scaling and then compared with predictions from models in literature that address different asymptotic and numerical solutions. Basic trajectory calculations are then performed and the results are compared with experimental data of position of the bubble in the channel. A direct comparison of the lateral velocity of the bubbles is also made with the lateral velocity prediction from investigators, whose work addressed the shear lift on a sphere in different two-dimensional shear flows including Poiseuille flow.
Heat Transfer Characteristics of the Supercritical CO{sub 2} Flowing in a Vertical Annular Channel
Energy Technology Data Exchange (ETDEWEB)
Yoo, Tae Ho; Bae, Yoon Yeong; Kim, Hwan Yeol [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2010-05-15
Heat transfer test facility, SPHINX(Supercritical Pressure Heat transfer Investigation for NeXt generation), has been operated at KAERI for an investigation of the thermal-hydraulic characteristics of supercritical CO{sub 2} at several test sections with a different geometry. The loop uses CO{sub 2} because it has much lower critical pressure and temperature than those of water. Experimental study of heat transfer to supercritical CO{sub 2} in a vertical annular channel with and hydraulic diameter of 4.5 mm has been performed. CO{sub 2} flows downward through the annular channel simulating the downward-flowing coolant in a multi-pass reactor or water rod moderator in a single pass reactor. The heat transfer characteristics in a downward flow were analyzed and compared with the upward flow test results performed previously with the same test section at KAERI
Krank, Benjamin; Fehn, Niklas; Wall, Wolfgang A.; Kronbichler, Martin
2017-11-01
We present an efficient discontinuous Galerkin scheme for simulation of the incompressible Navier-Stokes equations including laminar and turbulent flow. We consider a semi-explicit high-order velocity-correction method for time integration as well as nodal equal-order discretizations for velocity and pressure. The non-linear convective term is treated explicitly while a linear system is solved for the pressure Poisson equation and the viscous term. The key feature of our solver is a consistent penalty term reducing the local divergence error in order to overcome recently reported instabilities in spatially under-resolved high-Reynolds-number flows as well as small time steps. This penalty method is similar to the grad-div stabilization widely used in continuous finite elements. We further review and compare our method to several other techniques recently proposed in literature to stabilize the method for such flow configurations. The solver is specifically designed for large-scale computations through matrix-free linear solvers including efficient preconditioning strategies and tensor-product elements, which have allowed us to scale this code up to 34.4 billion degrees of freedom and 147,456 CPU cores. We validate our code and demonstrate optimal convergence rates with laminar flows present in a vortex problem and flow past a cylinder and show applicability of our solver to direct numerical simulation as well as implicit large-eddy simulation of turbulent channel flow at Reτ = 180 as well as 590.
Ng, Chiu-On; Sun, Rui
2017-10-01
A semi-analytical model is presented for pressure-driven flow through a channel, where local pressure loss is incurred at a sudden change in the boundary condition: from no-slip to partial-slip. Assuming low-Reynolds-number incompressible flow and periodic stick-slip wall patterning, the problems for parallel-plate and circular channels are solved using the methods of eigenfunction expansion and point match. The present study aims to examine in detail how the flow will evolve, on passing through the cross section at which the change in the slip condition occurs, from a no-slip parabolic profile to a less sheared profile with a boundary slip. The present problem is germane to, among other applications, flow through a channel bounded by superhydrophobic surfaces, which intrinsically comprise an array of no-slip and partial-slip segments. Results are presented to show that the sudden change in the boundary condition will result in additional resistance to the flow. Near the point on the wall where a slip change occurs is a region of steep pressure gradient and intensive vorticity. The acceleration of near-wall fluid particles in combination with the no-slip boundary condition leads to a very steep velocity gradient at the wall, thereby a sharp increase in the wall shear stress, shortly before the fluid enters the channel with a slippery wall. Results are also presented to show the development of flow in the entrance region in the slippery channel. The additional pressure loss can be represented by a dimensionless loss parameter, which is a pure function of the slip length for channels much longer than the entrance length.
Versatile control of multiphase laminar flow for in-channel microfabrication.
Gao, Yunxiang; Chen, Liwei
2008-10-01
We have improved the multiphase laminar flow based in-channel fabrication method to overcome diffusion-induced broadening. A sheathing phase with protecting molecules confines metal wire deposition and allows for flexible control of the location, width, and uniformity of deposited metal wires. Two-layered T-junctions are introduced to form vertically stacked multiphase laminar flow. Combining these techniques, we fabricate quadrupole silver electrodes on the four sidewalls of rectangular polydimethylsiloxane (PDMS) microchannels that are 3 cm in length.
JO, DAESEONG; OMAR S. AL-YAHIA; RAGA'I M. ALTAMIMI; PARK, JONGHARK; CHAE, HEETAEK
2014-01-01
Heat transfer characteristics in a narrow rectangular channel are experimentally investigated for upward and downward flows. The experimental data obtained are compared with existing data and predictions by many correlations. Based on the observations, there are differences from others: (1) there are no different heat transfer characteristics between upward and downward flows, (2) most of the existing correlations under-estimate heat transfer characteristics, and (3) existing correlations do ...
Sensitivity of the scale partition for variational multiscale large-eddy simulation of channel flow
Holmen, J; Hughes, T.J.R; Oberai, A.A.; Wells, G. N.
2004-01-01
The variational multiscale method has been shown to perform well for large-eddy simulation (LES) of turbulent flows. The method relies upon a partition of the resolved velocity field into large- and small-scale components. The subgrid model then acts only on the small scales of motion, unlike conventional LES models which act on all scales of motion. For homogeneous isotropic turbulence and turbulent channel flows, the multiscale model can outperform conventional LES formulations. An issue in...
DEFF Research Database (Denmark)
Carroll, Nick J.; Jensen, Kaare Hartvig; Parsa, Shima
2014-01-01
We present a simple, noninvasive method for simultaneous measurement of flow velocity and inference of liquid viscosity in a microfluidic channel. We track the dynamics of a sharp front of photobleached fluorescent dye using a confocal microscope and measure the intensity at a single point...... theological properties of the liquid. This technique provides a simple method for simultaneous elucidation of flow velocity and liquid viscosity in microchannels....
Debris-flow runout predictions based on the average channel slope (ACS)
Prochaska, A.B.; Santi, P.M.; Higgins, J.D.; Cannon, S.H.
2008-01-01
Prediction of the runout distance of a debris flow is an important element in the delineation of potentially hazardous areas on alluvial fans and for the siting of mitigation structures. Existing runout estimation methods rely on input parameters that are often difficult to estimate, including volume, velocity, and frictional factors. In order to provide a simple method for preliminary estimates of debris-flow runout distances, we developed a model that provides runout predictions based on the average channel slope (ACS model) for non-volcanic debris flows that emanate from confined channels and deposit on well-defined alluvial fans. This model was developed from 20 debris-flow events in the western United States and British Columbia. Based on a runout estimation method developed for snow avalanches, this model predicts debris-flow runout as an angle of reach from a fixed point in the drainage channel to the end of the runout zone. The best fixed point was found to be the mid-point elevation of the drainage channel, measured from the apex of the alluvial fan to the top of the drainage basin. Predicted runout lengths were more consistent than those obtained from existing angle-of-reach estimation methods. Results of the model compared well with those of laboratory flume tests performed using the same range of channel slopes. The robustness of this model was tested by applying it to three debris-flow events not used in its development: predicted runout ranged from 82 to 131% of the actual runout for these three events. Prediction interval multipliers were also developed so that the user may calculate predicted runout within specified confidence limits. ?? 2008 Elsevier B.V. All rights reserved.
Analytical solution to problems of hydraulic jump in horizontal triangular channels
Directory of Open Access Journals (Sweden)
I.M.H. Rashwan
2013-09-01
Full Text Available A hydraulic jump is formed in a channel whenever supercritical flow changes to subcritical flow in a short distance. It can be used in triangular ditch irrigation to raise the downstream water surface. The basic elements and characteristics of the hydraulic jump are provided to aid designers in selecting more practical basins. In the present study, the slope side, discharge and the energy loss in hydraulic jump in horizontal triangular section are known whereas one has to obtain the sequent depths. The specific force and specific energy equations in a horizontal triangular open channel are made dimensionless, writing it for the sequent depths as a function of discharge and head loss. The proposed modes for hydraulic jump elements are of high accuracy and applicable to a wide range of discharge intensity values and initial conditions without any limitations for the assumptions under consideration.
Bucs, Szilard
2015-09-25
Micro-scale flow distribution in spacer-filled flow channels of spiral-wound membrane modules was determined with a particle image velocimetry system (PIV), aiming to elucidate the flow behaviour in spacer-filled flow channels. Two-dimensional water velocity fields were measured in a flow cell (representing the feed spacer-filled flow channel of a spiral wound reverse osmosis membrane module without permeate production) at several planes throughout the channel height. At linear flow velocities (volumetric flow rate per cross-section of the flow channel considering the channel porosity, also described as crossflow velocities) used in practice (0.074 and 0.163 m∙s-1) the recorded flow was laminar with only slight unsteadiness in the upper velocity limit. At higher linear flow velocity (0.3 m∙s-1) the flow was observed to be unsteady and with recirculation zones. Measurements made at different locations in the flow cell exhibited very similar flow patterns within all feed spacer mesh elements, thus revealing the same hydrodynamic conditions along the length of the flow channel. Three-dimensional (3-D) computational fluid dynamics simulations were performed using the same geometries and flow parameters as the experiments, based on steady laminar flow assumption. The numerical results were in good agreement (0.85-0.95 Bray-Curtis similarity) with the measured flow fields at linear velocities of 0.074 and 0.163 m∙s-1, thus supporting the use of model-based studies in the optimization of feed spacer geometries and operational conditions of spiral wound membrane systems.
Extended lubrication theory: improved estimates of flow in channels with variable geometry.
Tavakol, Behrouz; Froehlicher, Guillaume; Holmes, Douglas P; Stone, Howard A
2017-10-01
Lubrication theory is broadly applicable to the flow characterization of thin fluid films and the motion of particles near surfaces. We offer an extension to lubrication theory by starting with Stokes equations and considering higher-order terms in a systematic perturbation expansion to describe the fluid flow in a channel with features of a modest aspect ratio. Experimental results qualitatively confirm the higher-order analytical solutions, while numerical results are in very good agreement with the higher-order analytical results. We show that the extended lubrication theory is a robust tool for an accurate estimate of pressure drop in channels with shape changes on the order of the channel height, accounting for both smooth and sharp changes in geometry.
A stable and convergent scheme for viscoelastic flow in contraction channels
Energy Technology Data Exchange (ETDEWEB)
Trebotich, David; Colella, Phillip; Miller, Gregory
2004-02-15
We present a new algorithm to simulate unsteady viscoelastic flows in abrupt contraction channels. In our approach we split the viscoelastic terms of the Oldroyd-B constitutive equation using Duhamel's formula and discretize the resulting PDEs using a semi-implicit finite difference method based on a Lax-Wendroff method for hyperbolic terms. In particular, we leave a small residual elastic term in the viscous limit by design to make the hyperbolic piece well-posed. A projection method is used to impose the incompressibility constraint. We are able to compute the full range of elastic flows in an abrupt contraction channel--from the viscous limit to the elastic limit--in a stable and convergent manner for elastic Mach numbers less than one. We demonstrate the method for unsteady Oldroyd-B and Maxwell fluids in planar contraction channels.
Mathematical modeling of fluid flow in complex multi-channel structures
Shashkin, V. Y.
2017-10-01
The work is focused on a numerical hydraulic model, which allows one to simulate fluid flow in a complex, arbitrarily configured multi-channel system with a capability of automatic visualization of its structure. The main elements of a system are channels which are united in the system by means of a particular set of coupling elements (local resistance, knots). The processes models in channels are based on the equation of continuity, momentum conservation. The system structure is made by forming matrices of regional and internal boundary conditions according to the developed algorithm. By the model the algorithm is created, on the basis of which the application program is developed. The application program enables one to determine parameters of a steady state of fluid flow in the complex multichannel structures. The calculation structure is shown.
An Integrative Model of Excitation Driven Fluid Flow in a 2D Uterine Channel
Maggio, Charles; Fauci, Lisa; Chrispell, John
2009-11-01
We present a model of intra-uterine fluid flow in a sagittal cross-section of the uterus by inducing peristalsis in a 2D channel. This is an integrative multiscale computational model that takes as input fluid viscosity, passive tissue properties of the uterine channel and a prescribed wave of membrane depolarization. This voltage pulse is coupled to a model of calcium dynamics inside a uterine smooth muscle cell, which in turn drives a kinetic model of myosin phosphorylation governing contractile muscle forces. Using the immersed boundary method, these muscle forces are communicated to a fluid domain to simulate the contractions which occur in a human uterus. An analysis of the effects of model parameters on the flow properties and emergent geometry of the peristaltic channel will be presented.
Numerical investigation of turbulent flow and heat transfer in channel with ribs
DEFF Research Database (Denmark)
Myllerup, Lisbeth; Larsen, Poul Scheel
1999-01-01
The performance of three different low-Reynolds number turbulence models has been explored for the benchmark test of fully developed (periodic) flow in a ribbed plane channel. Results are presented for two values of the Reynolds number (based on mean velocity and hydraulic diameter), Re = 37...
Two-phase flow boiling in small channels: A brief review
Indian Academy of Sciences (India)
Steam generators. Evaporators. Refrigerators. Condensers. Refrigerator. Electronic micro chips. Compact heat exchangers. Compact evaporators. Cooling devices. Figure 1. (a) Schematic representation of gaps identified in literature on channel size. (b) Pictorial view of industrial equipments where two-phase flow is shown ...
Discrete element study of liquid-solid slurry flows through constricted channels
Abbas, M.E.; van der Hoef, Martin Anton; Bokhove, Onno; Kuipers, J.A.M.
2010-01-01
Discrete element model is used to simulate the flow of liquid-granule mixtures in an inclined channel containing a linear contraction. All the relevant particle/particle and particle/fluid interactions are included in the numerical model. The presence of the contraction induces different steady
Stationary bottom generated velocity fluctuations in one-dimensional open channel flow
de Jong, B.
1994-01-01
Statistical characteristics are calculated for stationary velocity fluctuations in a one-dimensional open channel flow with a given vertical velocity profile and with one-dimensional irregular bottom waves, characterized by a spectral density function. The calculations are based on an approximate
Temporal Correlations in Vortex Channel Flow Studied Using High-Resolution Hall Probes.
James, S.; Field, S. B.; Shtrikman, H.; Hong, K.; Reich, D. H.
1998-03-01
The dynamics of vortices near the depinning transition can be quite complex, with vortices moving via channel-like flow configurations in a manner which is not fully understood. We have investigated this system using single and multiple GaAs heterojunction Hall probes fixed to a current-carrying Nb strip. A single 1μm fixed probe reveals that the (time-averaged) flux beneath it changes in a discrete fashion at evidently random times. The flux may remain at a particular value for up to several seconds before changing, during which time millions of vortices pass under the probe. This suggests that the vortices flow along very long-lived channels which occasionally rearrange themselves, perhaps due to thermal activation of pinned vortices. An extension of the investigation using a linear array of 16 Hall probes arranged perpendicular to the vortex flow will further reveal spatial and temporal correlations in this channel flow. The array consists of a 1μm-wide bar along which adjoin 16 pairs of 1μm-wide voltage leads at 1μm intervals. A 16 channel digital lockin technique has been developed to record the data.
Collision frequency and radial distribution function in particle-laden turbulent channel flow
Kuerten, Johannes G.M.; Vreman, A.W.
2016-01-01
We performed Eulerian–Lagrangian direct numerical simulation of particle-laden channel flow at a frictional Reynolds number of 950. A fully parallelized deterministic particle collision algorithm is applied for elastic collisions between two particles and particles and the walls. A total number of
Mixed convection flow and heat transfer in a vertical wavy channel ...
African Journals Online (AJOL)
Mixed convection flow and heat transfer in a vertical wavy channel containing porous and fluid layer with traveling thermal waves. ... Results for a wide range of governing parameters such as Grashof number, viscosity ratio, width ratio, conductivity ratio, and traveling thermal temperature are plotted for different values of ...
Combined free and forced convection flow in a rotating channel with ...
African Journals Online (AJOL)
Combined free and forced convection flow of a viscous incompressible electrically conducting fluid in a rotating channel is studied. Analytical solution for the velocity and induced magnetic field is obtained in closed form. Asymptotic behavior of the solution for the velocity and induced magnetic field is analyzed for large ...
Statistics of spatial derivatives of velocity and pressure in turbulent channel flow
Vreman, A.W.; Kuerten, Johannes G.M.
Statistical profiles of the first- and second-order spatial derivatives of velocity and pressure are reported for turbulent channel flow at Re τ = 590. The statistics were extracted from a high-resolution direct numerical simulation. To quantify the anisotropic behavior of fine-scale structures, the
Boundary Layer Fluid Flow in a Channel with Heat Source, Soret ...
African Journals Online (AJOL)
The boundary layer fluid flow in a channel with heat source, soret effects and slip condition was studied. The governing equations were solved using perturbation technique. The effects of different parameters such Prandtl number Pr , Hartmann number M, Schmidt number Sc, suction parameter ƒÜ , soret number Sr and the ...
Effects of Parallel Channel Interactions on Two-Phase Flow Split in ...
African Journals Online (AJOL)
The tests would aid the development of a realistic transient computer model for tracking the distribution of two-phase flows into the multiple parallel channels of a Nuclear Reactor, during Loss of Coolant Accidents (LOCA), and were performed at the General Electric Nuclear Energy Division Laboratory, California. The test ...
VOF modelling of gas–liquid flow in PEM water electrolysis cell micro-channels
DEFF Research Database (Denmark)
Lafmejani, Saeed Sadeghi; Olesen, Anders Christian; Kær, Søren Knudsen
2017-01-01
In this study, the gaseliquid flow through an interdigitated anode flow field of a PEM water electrolysis cell (PEMEC) is analysed using a three-dimensional, transient, computational fluid dynamics (CFD) model. To account for two-phase flow, the volume of fluid (VOF) method in ANSYS Fluent 17.2 i...... that comprises multiphase flow in porous media and micro-channel, electro-chemistry in catalyst layers, ion transport in membrane, hydrogen evolution, etc. The model can aid in the study of gaseliquid flow and its impact on the performance of a PEMEC........2 is used. The modelled geometry consists of the anode channels and the anode transport layer (ATL). To reduce the complexity of the phenomena governing PEMEC operation, the dependence upon electro-chemistry is disregarded. Instead, a fixed source of the gas is applied at the interface between the ATL......In this study, the gaseliquid flow through an interdigitated anode flow field of a PEM water electrolysis cell (PEMEC) is analysed using a three-dimensional, transient, computational fluid dynamics (CFD) model. To account for two-phase flow, the volume of fluid (VOF) method in ANSYS Fluent 17...
Energy Technology Data Exchange (ETDEWEB)
Garg, P. [Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee 247 667 (India); Picardo, J. R.; Pushpavanam, S., E-mail: spush@iitm.ac.in [Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai 600 036 (India)
2014-07-15
In this work, we investigate the fully developed flow field of two vertically stratified fluids (one phase flowing above the other) in a curved channel of rectangular cross section. The domain perturbation technique is applied to obtain an analytical solution in the asymptotic limit of low Reynolds numbers and small curvature ratios (the ratio of the width of the channel to its radius of curvature). The accuracy of this solution is verified by comparison with numerical simulations of the nonlinear equations. The flow is characterized by helical vortices within each fluid, which are driven by centrifugal forces. The number of vortices and their direction of circulation varies with the parameters of the system (the volume fraction, viscosity ratio, and Reynolds numbers). We identify nine distinct flow patterns and organize the parameter space into corresponding flow regimes. We show that the fully developed interface between the fluids is not horizontal, in general, but is deformed by normal stresses associated with the circulatory flow. The results are especially significant for flows in microchannels, where the Reynolds numbers are small. The mathematical results in this paper include an analytical solution to two coupled biharmonic partial differential equations; these equations arise in two-phase, two-dimensional Stokes flows.
Segregation by size difference in binary suspensions of fluid droplets in channel flow.
Makino, Masato; Sugihara-Seki, Masako
2013-01-01
In channel flow of multicomponent suspensions, segregation behavior of suspended components perpendicular to the flow direction is often observed, which is considered to be caused by the differential properties of the lateral migration depending on their shape, size, flexibility, and other characteristics. In the present study, we investigate the effect of size differences between suspended components on the segregation behavior, by a two-dimensional numerical simulation for binary dispersed suspensions of fluid droplets of two different sizes subjected to a plane Poiseuille channel flow. The small and large droplets are assumed to have equal surface tensions and equal viscosity ratios of internal to external fluids. The time evolutions of the lateral positions of large and small droplets relative to the channel centerline were computed by changing the area fraction of the small droplets in a mixture with a constant total area fraction. The large droplets are found to migrate closer to the channel centerline and the small droplets are found to migrate closer to the channel wall compared to the corresponding lateral positions in mono-dispersed suspensions at the same area fractions, although the mean lateral positions of the large and small droplets in mono-dispersed suspension are comparable. This segregation behavior as well as the margination of small droplets are enhanced when the size difference between large and small droplets is increased and the area fraction of large droplets is increased. These results may arise from higher tendencies for the large droplets to approach the channel centerline compared to the small droplets, which consequently expel small droplets from the central region toward the channel walls.
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.
Effect of ribbed and smooth coolant cross-flow channel on film cooling
Energy Technology Data Exchange (ETDEWEB)
Peng, Wei; Sun, Xiaokai [Institute of Nuclear and New Energy Technology, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Tsinghua University, Beijing 100084 (China); Jiang, Peixue, E-mail: jiangpx@tsinghua.edu.cn [Key Laboratory for Thermal Science and Power Engineering of Ministry of Educations, Department of Thermal Engineering, Tsinghua University, Beijing 100084 (China); Wang, Jie [Institute of Nuclear and New Energy Technology, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Tsinghua University, Beijing 100084 (China)
2017-05-15
Highlights: • Little different for plenum model and the cross-flow model at M = 0.5. • Crossflow model is much better than plenum model at M = 1.0, especially with ribs. • Coolant flow channel with V-shaped ribs has the best adiabatic film cooling. • Film cooling with the plenum model is better at M = 0.5 than at M = 1.0. • Crossflow model is better at M = 0.5 near film hole and at M = 1.0 for downstream. - Abstract: The influence of ribbed and unribbed coolant cross-flow channel on film cooling was investigated with the coolant supply being either a plenum-coolant feed or a coolant cross-flow feed. Validation experiments were conducted with comparison to numerical results using different RANS turbulence models showed that the RNG k–ε turbulence model and the RSM model gave closer predictions to the experimental data than the other RANS models. The results indicate that at a low blowing ratio of M = 0.5, the coolant supply channel structure has little effect on the film cooling. However, at a high blowing ratio of M = 1.0, the adiabatic wall film cooling effectiveness is significantly lower with the plenum feed than with the cross-flow feed, especially for the cases with ribs. The film cooling with the plenum model is better at M = 0.5 than at M = 1.0. The film cooling with the cross-flow model is better at a blowing ratio of M = 0.5 in the near hole region, while further downstream, it is better at M = 1.0. The results also show that the coolant cross-flow channel with V-shaped ribs has the best adiabatic film cooling effectiveness.
Shadowgraph, Schlieren and interferometry in a 2D cavitating channel flow
Mauger, Cyril; Méès, Loïc; Michard, Marc; Azouzi, Alexandre; Valette, Stéphane
2012-12-01
Cavitation plays an important role in fuel atomization mechanisms, but the physics of cavitation and its impact on spray formation and injector efficiency are not well documented yet. Experimental investigations are required to support the development and the validation of numerical models and the design of tomorrow's injectors, in the context of pollutant and fuel consumption reduction. The complexity of modern injectors and the extreme conditions of injection do not facilitate experimental investigations. In this paper, experiments are conducted in a simplified geometry. The model nozzle consists of a transparent 2D micro-channel supplied with a test oil (ISO 4113). Three different optical techniques are proposed to investigate the channel flow, with the pressure drop between upstream and downstream chambers as a parameter. A shadowgraph-like imaging technique allows the observation of cavitation inception and vapor cavities development throughout the channel. The technique also reveals the presence of density gradients (pressure or temperature) in the channel flow. However, this additional information is balanced by difficulties in image interpretation, which are discussed in the paper. In addition, a combination of Schlieren technique and interferometric imaging is used to measure the density fields inside the channel. The three techniques results are carefully analyzed and confronted. These results reveal a wealth of information on the flow, with pressure waves generated by bubble collapses, turbulence in the wake of vapor cavities and bubble survival in flow regions of high pressure. Our results also show that cavitation inception is located in the shear layers between the recirculation zones and the main flow, relatively far from the inlet corner, where the pressure is minimum in average. To explain this behavior, we propose a scenario of cavitation inception based on the occurrence and the growing of instabilities in the shear layers.
Shadowgraph, Schlieren and interferometry in a 2D cavitating channel flow
Energy Technology Data Exchange (ETDEWEB)
Mauger, Cyril; Mees, Loic; Michard, Marc; Azouzi, Alexandre [Universite Claude Bernard Lyon 1, Laboratoire de Mecanique des Fluides et d' Acoustique (LMFA), CNRS UMR5509, Ecole Centrale de Lyon, INSA de Lyon, Ecully (France); Valette, Stephane [Ecole Nationale d' Ingenieurs de Saint Etienne, Laboratoire de Tribologie et Dynamique des Systemes (LTDS), CNRS UMR5513, Ecole Centrale de Lyon, Saint-Etienne (France)
2012-12-15
Cavitation plays an important role in fuel atomization mechanisms, but the physics of cavitation and its impact on spray formation and injector efficiency are not well documented yet. Experimental investigations are required to support the development and the validation of numerical models and the design of tomorrow's injectors, in the context of pollutant and fuel consumption reduction. The complexity of modern injectors and the extreme conditions of injection do not facilitate experimental investigations. In this paper, experiments are conducted in a simplified geometry. The model nozzle consists of a transparent 2D micro-channel supplied with a test oil (ISO 4113). Three different optical techniques are proposed to investigate the channel flow, with the pressure drop between upstream and downstream chambers as a parameter. A shadowgraph-like imaging technique allows the observation of cavitation inception and vapor cavities development throughout the channel. The technique also reveals the presence of density gradients (pressure or temperature) in the channel flow. However, this additional information is balanced by difficulties in image interpretation, which are discussed in the paper. In addition, a combination of Schlieren technique and interferometric imaging is used to measure the density fields inside the channel. The three techniques results are carefully analyzed and confronted. These results reveal a wealth of information on the flow, with pressure waves generated by bubble collapses, turbulence in the wake of vapor cavities and bubble survival in flow regions of high pressure. Our results also show that cavitation inception is located in the shear layers between the recirculation zones and the main flow, relatively far from the inlet corner, where the pressure is minimum in average. To explain this behavior, we propose a scenario of cavitation inception based on the occurrence and the growing of instabilities in the shear layers. (orig.)
Application guide for AFINCH (Analysis of Flows in Networks of Channels) described by NHDPlus
Holtschlag, David J.
2009-01-01
AFINCH (Analysis of Flows in Networks of CHannels) is a computer application that can be used to generate a time series of monthly flows at stream segments (flowlines) and water yields for catchments defined in the National Hydrography Dataset Plus (NHDPlus) value-added attribute system. AFINCH provides a basis for integrating monthly flow data from streamgages, water-use data, monthly climatic data, and land-cover characteristics to estimate natural monthly water yields from catchments by user-defined regression equations. Images of monthly water yields for active streamgages are generated in AFINCH and provide a basis for detecting anomalies in water yields, which may be associated with undocumented flow diversions or augmentations. Water yields are multiplied by the drainage areas of the corresponding catchments to estimate monthly flows. Flows from catchments are accumulated downstream through the streamflow network described by the stream segments. For stream segments where streamgages are active, ratios of measured to accumulated flows are computed. These ratios are applied to upstream water yields to proportionally adjust estimated flows to match measured flows. Flow is conserved through the NHDPlus network. A time series of monthly flows can be generated for stream segments that average about 1-mile long, or monthly water yields from catchments that average about 1 square mile. Estimated monthly flows can be displayed within AFINCH, examined for nonstationarity, and tested for monotonic trends. Monthly flows also can be used to estimate flow-duration characteristics at stream segments. AFINCH generates output files of monthly flows and water yields that are compatible with ArcMap, a geographical information system analysis and display environment. Chloropleth maps of monthly water yield and flow can be generated and analyzed within ArcMap by joining NHDPlus data structures with AFINCH output. Matlab code for the AFINCH application is presented.
Effect of Water Flows on Ship Traffic in Narrow Water Channels Based on Cellular Automata
Directory of Open Access Journals (Sweden)
Hu Hongtao
2017-11-01
Full Text Available In narrow water channels, ship traffic may be affected by water flows and ship interactions. Studying their effects can help maritime authorities to establish appropriate management strategies. In this study, a two-lane cellular automation model is proposed. Further, the behavior of ship traffic is analyzed by setting different water flow velocities and considering ship interactions. Numerical experiment results show that the ship traffic density-flux relation is significantly different from the results obtained by classical models. Furthermore, due to ship interactions, the ship lane-change rate is influenced by the water flow to a certain degree.
Spatiotemporal Dynamic of Two-dimensional core annular flow in square channel
Nsom B.; Latrache N.; Decruppe J-P.
2013-01-01
In this work, we study the spatiotemporal dynamics of a two-dimensional core-annular flow (CAF) in a square channel of an oil/water system. The flow rate of oil is fixed at Qo=0.19 l/s and the flow rate of water Qw is varied from 0.20 l/s to 0.46 l/s. For large values of Qw (typically Qw>0.23l/s), the CAF is unstable, and it becomes stable for low values of Qw (typically Qw
Modelling of capillary-driven flow for closed paper-based microfluidic channels
Songok, Joel; Toivakka, Martti
2017-06-01
Paper-based microfluidics is an emerging field focused on creating inexpensive devices, with simple fabrication methods for applications in various fields including healthcare, environmental monitoring and veterinary medicine. Understanding the flow of liquid is important in achieving consistent operation of the devices. This paper proposes capillary models to predict flow in paper-based microfluidic channels, which include a flow accelerating hydrophobic top cover. The models, which consider both non-absorbing and absorbing substrates, are in good agreement with the experimental results.
Water flow algorithm decision support tool for travelling salesman problem
Kamarudin, Anis Aklima; Othman, Zulaiha Ali; Sarim, Hafiz Mohd
2016-08-01
This paper discuss about the role of Decision Support Tool in Travelling Salesman Problem (TSP) for helping the researchers who doing research in same area will get the better result from the proposed algorithm. A study has been conducted and Rapid Application Development (RAD) model has been use as a methodology which includes requirement planning, user design, construction and cutover. Water Flow Algorithm (WFA) with initialization technique improvement is used as the proposed algorithm in this study for evaluating effectiveness against TSP cases. For DST evaluation will go through usability testing conducted on system use, quality of information, quality of interface and overall satisfaction. Evaluation is needed for determine whether this tool can assists user in making a decision to solve TSP problems with the proposed algorithm or not. Some statistical result shown the ability of this tool in term of helping researchers to conduct the experiments on the WFA with improvements TSP initialization.
Reducing spin-up time for simulations of turbulent channel flow
Nelson, K. S.; Fringer, O. B.
2017-10-01
Spin-up of turbulent channel flow forced with a constant mean pressure gradient is prolonged because the flow accelerates due to an imbalance between the driving pressure gradient and total bottom stress. To this end, a method ensuring a time invariant volume-averaged streamwise velocity during spin-up is presented and compared to simulations forced with a mean pressure gradient for both linear and logarithmic initial velocity profiles. The comparisons are made for open-channel flow with a friction Reynolds number Reτ of 500. Additional simulations with Reτ ranging from 1 to 400 are also run to confirm validity of the method for a range of Reynolds numbers. While the method eliminates spin-up time related to approaching the target volume-averaged velocity, spin-up time is still required for the flow to transition to turbulence and reach statistical equilibrium. Therefore, the time evolution of turbulence in response to different initial velocity profiles and random perturbations is investigated. Simulations initialized with linear velocity profiles trigger turbulence and reach statistical equilibrium sooner than those initialized with logarithmic profiles given the same initial perturbations, a manifestation of the increased shear created by linear profiles. The results suggest that, combined with appropriate initial conditions, ensuring a time invariant volume-averaged streamwise velocity can reduce the computational time associated with spin-up of turbulent open-channel flows by at least a factor of five.
Rusu, C.R.; van 't Oever, Ronny; de Boer, Meint J.; Jansen, Henricus V.; Berenschot, Johan W.; Bennink, Martin L.; Kanger, Johannes S.; de Grooth, B.G.; Elwenspoek, Michael Curt; Greve, Jan; Brugger, J.P.; van den Berg, Albert
We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap setup (optical tweezers) to study mechanical and structural properties of λ-DNA molecules. The flow cell was realized using silicon
Directory of Open Access Journals (Sweden)
Chigozie Israel-Cookey
2010-09-01
Full Text Available This paper investigates effects of thermal radiation and magnetic field on hydromagnetic Couette flow of a highly viscous fluid with temperature-dependent viscosity and thermal conductivity at constant pressure through a porous channel. The influence of the channel permeability is also assessed. The relevant governing partial differential equations have been transformed to non-linear coupled ordinary differential equations by virtue of the steady nature of the flow and are solved numerically using a marching finite difference scheme to give approximate solutions for the velocity and temperature profiles. We highlight the effects of Nahme numbers, magnetic field, radiation and permeability parameters on both profiles. The results obtained are used to give graphical illustrations of the distribution of the flow variables and are discussed.
Directory of Open Access Journals (Sweden)
DAESEONG JO
2014-04-01
Full Text Available Heat transfer characteristics in a narrow rectangular channel are experimentally investigated for upward and downward flows. The experimental data obtained are compared with existing data and predictions by many correlations. Based on the observations, there are differences from others: (1 there are no different heat transfer characteristics between upward and downward flows, (2 most of the existing correlations under-estimate heat transfer characteristics, and (3 existing correlations do not predict the high heat transfer in the entrance region for a wide range of Re. In addition, there are a few heat transfer correlations applicable to narrow rectangular channels. Therefore, a new set of correlations is proposed with and without consideration of the entrance region. Without consideration of the entrance region, heat transfer characteristics are expressed as a function of Re and Pr for turbulent flows, and as a function of Gz for laminar flows. The correlation proposed for turbulent and laminar flows has errors of ±18.25 and ±13.62%, respectively. With consideration of the entrance region, the heat transfer characteristics are expressed as a function of Re, Pr, and z* for both laminar and turbulent flows. The correlation for turbulent and laminar flows has errors of ±19.5 and ±22.0%, respectively.
Czuba, Jonathan A.; Oberg, Kevin; Best, Jim; Parsons, Daniel R.
2009-01-01
In the Great Lakes of North America, the St. Clair River is the major outlet of Lake Huron and conveys water to Lake St. Clair which then flows to Lake Erie. One major topic of interest is morphological change in the St. Clair River and its impact on water levels in the Upper Great Lakes and connecting channel flows. A combined multibeam echosounder (MBES) bathymetric survey and acoustic Doppler current profiler (ADCP) flow survey of the outlet of Lake Huron and the Upper St. Clair River was conducted July 21 – 25, 2008. This paper presents how channel morphology and shipwrecks affect the flow in the Upper St. Clair River. The river is most constricted at the Blue Water Bridge near Port Huron, Michigan, with water velocities over 2 ms-1 for a flow of 5,200 m3s-1. Downstream of this constriction, the river flows around a bend and expands creating a large recirculation zone along the left bank due to flow separation. This recirculation zone reduces the effective channel width, and thus increases flow velocities to over 2 ms-1 in this region. The surveys reveal several shipwrecks on the bed of the St. Clair River, which possess distinct wakes in their flow velocity downstream of the wrecks. The constriction and expansion of the channel, combined with forcing of the flow by bed topography, initiates channel-scale secondary flow, creating streamwise vortices that maintain coherence downstream over a distance of several channel widths.
Spatiotemporal Dynamic of Two-dimensional core annular flow in square channel
Directory of Open Access Journals (Sweden)
Nsom B.
2013-04-01
Full Text Available In this work, we study the spatiotemporal dynamics of a two-dimensional core-annular flow (CAF in a square channel of an oil/water system. The flow rate of oil is fixed at Qo=0.19 l/s and the flow rate of water Qw is varied from 0.20 l/s to 0.46 l/s. For large values of Qw (typically Qw>0.23l/s, the CAF is unstable, and it becomes stable for low values of Qw (typically Qw<0.23l/s. The spatiotemporal diagram technique is used to determine the characteristics of the water-oil interface, namely the entry length, height, parallel length, frequency, wavenumber, phase velocity, amplitude and spatial growth rate of wave amplitudeas function of the water flow rate Qw. Theses characteristics are used to explain the pressure drop as function of the water flow rate.
Termini, D.
2009-04-01
Natural rivers are characterized by a strong hydraulic and geomorphic complexity. Many studies conducted in this field (Malthus and Mumby, 2003; Muhar, 1996) show that the accurate estimation both of the river morphological changes and of local hydraulic characteristics of flow (i.e. the local flow velocities and water depths) is necessary for the restoration and protection of biodiversity. Vegetation is a key factor to analyze the interrelated system of flow, sediment transport, and morphodynamic in rivers (Tsujimoto, 1999; Maione et al., 2000). On one hand, some kind of species of vegetation affect the habitat conditions, being crucial to the maintenance of biodiversity (Larkum et al, 2004); on the other hand, effects of vegetation on flow velocity are significant and are of crucial importance for stabilizing sediments and reducing erosion along the channel. In particular, it has been generally agreed that vegetation increases flow resistance and modifies sediment transport and deposition (Tsujimoto et al., 1996; Yen 2002). The analysis of the hydrodynamic conditions in vegetated channels is complex because vegetation is flexible in varying degrees and it oscillates in the flow changing position. Furthermore, because of temporal changing of roughness due to natural vegetative growth, the response of vegetation to the flow can change in time. In this paper the flow over real flexible vegetation is experimentally studied. A 2D-ADV (Acoustic Doppler Velocimeter) is used to measure the local flow velocities, for different vegetation concentrations and varying the discharge and the flume slope. The influence of both vegetation concentration and depth/vegetation height ratio on the measured velocity profiles is analyzed. The comparison between the velocity distribution and the turbulence intensity distribution is also presented. The spectral analysis is operated in order to verify the formation of turbulence structures inside the vegetated layer and the flow conveyance
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.
Studying laminar flows of power-law fluids in the annular channel with eccentricity
Zhigarev, V. A.; Neverov, A. L.; Guzei, D. V.; Pryazhnikov, M. I.
2017-09-01
The paper deals with numerical and experimental investigation of non-Newtonian flow of modeling drilling fluids in the annular channel. The Reynolds number was ranged from 100 to 1500. The parameters of the power-law model of drilling fluids were varied within the following ranges: n = 0.43-0.49, K = 0.22-0.89. The eccentricity was changed from 0 to 1. We have measured pressure drop in the annular channel and compared calculations with experimental data, achieving good agreement between calculations and experiment.
Hayat, T.; Iqbal, Rija; Tanveer, Anum; Alsaedi, A.
2016-06-01
This paper looks at the influences of magnetohydrodynamics (MHD) and thermal radiation on peristaltic transport of a pseudoplastic nanofluid in a tapered asymmetric channel. The tapered channel walls satisfy convective boundary conditions. The governing equations for the balance of mass, momentum, temperature and volume fraction for pseudoplastic nanofluid are first formulated and then utilized for long wavelength and small Reynolds number considerations. Effects of involved parameters on the flow characteristics have been plotted and examined. It is observed that the heat transfer Biot number shows a dual behavior on the temperature of nanofluid particles whereas the mass transfer Biot number with its increasing values enhances the fluid temperature.
Xing, F.; Meselhe, E. A.; Allison, M. A.; Weathers, H. D.
2017-09-01
Two- and three-dimensional Delft3D Flow and Morphology models were constructed for the lower Song Hau distributary channel of the Mekong River in Vietnam to provide insights into the hydrodynamics and sand transport of the channel system. The models were calibrated and validated with data for observed water level, water discharge, velocity, and suspended-sand concentration during the high- and low-flow seasons of 2014 and 2015. The water and sand budgets of the Dinh An and Tran De channels, the two sub-distributaries of the lower Song Hau channel, were calculated, showing that 73% of the fluvial water discharge and 90% of suspended sand were transported through the Dinh An channel, while the rest was transported through the Tran De channel in the high-flow season. In the low-flow season, the total fluvial water discharge was river channels during low-flow season was not observed in field studies. The different behaviors between models and field observations might be caused by the absence of baroclinic effects in the model set up. The Dinh An channel was found to be dominated by ebb tide, in favor of transporting water and sediment to the ocean, and the Tran De channel was dominated by flood tide. In the high-flow season, the residual currents were directed toward the ocean for both the Dinh An and Tran De channels. In the low-flow season, the magnitude of the residual currents decreased in the river channels. Under these conditions, the residual-current direction changed to be ambiguous in the Tran De channel, but remained seaward in the Dinh An channel. The low fluvial discharge combined with strong tides under very low-flow conditions can probably generate a net clockwise water circulation between the Dinh An and Tran De channels, which transports water from the ocean to the river through the Tran De channel, then back into the ocean through the Dinh An channel. The clockwise circulation pattern is likely to influence the channel evolution and impact saltwater
Boundary conditions for gas flow problems from anisotropic scattering kernels
To, Quy-Dong; Vu, Van-Huyen; Lauriat, Guy; Léonard, Céline
2015-10-01
The paper presents an interface model for gas flowing through a channel constituted of anisotropic wall surfaces. Using anisotropic scattering kernels and Chapman Enskog phase density, the boundary conditions (BCs) for velocity, temperature, and discontinuities including velocity slip and temperature jump at the wall are obtained. Two scattering kernels, Dadzie and Méolans (DM) kernel, and generalized anisotropic Cercignani-Lampis (ACL) are examined in the present paper, yielding simple BCs at the wall fluid interface. With these two kernels, we rigorously recover the analytical expression for orientation dependent slip shown in our previous works [Pham et al., Phys. Rev. E 86, 051201 (2012) and To et al., J. Heat Transfer 137, 091002 (2015)] which is in good agreement with molecular dynamics simulation results. More important, our models include both thermal transpiration effect and new equations for the temperature jump. While the same expression depending on the two tangential accommodation coefficients is obtained for slip velocity, the DM and ACL temperature equations are significantly different. The derived BC equations associated with these two kernels are of interest for the gas simulations since they are able to capture the direction dependent slip behavior of anisotropic interfaces.
Two-dimensional cavity flow in an infinitely long channel with non-zero vorticity
Cheng, Jianfeng; Du, Lili; Zhang, Qin
2017-10-01
The main object of this paper is to investigate the well-posedness theory of the incompressible inviscid cavity flow in an infinitely long channel. The flow is governed by two-dimensional incompressible, steady Euler system. The main results read that given a mass flux and a constant vorticity in the inlet of the channel, firstly, we establish the existence and the uniqueness of the incompressible cavity flow in an infinitely long symmetric channel, which contains a smooth free surface detaching at the boundary point of the obstacle. Secondly, some fundamental properties, such as the asymptotic behaviors of the cavity flow and the free boundary in the upstream and downstream, and the positivity of the horizontal velocity, are also obtained. Finally, we show that there does not exist a finite cavity or a cusped cavity in the infinitely long nozzle, which gives a positive answer to the conjecture by H. Villat in 1913 on the non-existence of a symmetric finite cusped cavity behind an obstacle.
Sensitivity of the scale partition for variational multiscale large-eddy simulation of channel flow
Holmen, Jens; Hughes, Thomas J. R.; Oberai, Assad A.; Wells, Garth N.
2004-03-01
The variational multiscale method has been shown to perform well for large-eddy simulation (LES) of turbulent flows. The method relies upon a partition of the resolved velocity field into large- and small-scale components. The subgrid model then acts only on the small scales of motion, unlike conventional LES models which act on all scales of motion. For homogeneous isotropic turbulence and turbulent channel flows, the multiscale model can outperform conventional LES formulations. An issue in the multiscale method for LES is choice of scale partition and sensitivity of the computed results to it. This is the topic of this investigation. The multiscale formulation for channel flows is briefly reviewed. Then, through the definition of an error measure relative to direct numerical simulation (DNS) results, the sensitivity of the method to the partition between large- and small-scale motions is examined. The error in channel flow simulations, relative to DNS results, is computed for various partitions between large- and small-scale spaces, and conclusions drawn from the results.
Validity of classical scaling laws in laminar channel flow with periodic spacer-like obstacles
Rohlfs, Wilko; Lienhard, John H.
2015-11-01
Laminar channel flows with periodic obstacles occur in different technical applications involving heat and mass transfer. They are present in membrane technologies such as electro-dialysis or spirally wound membrane modules. For process design, classical scaling laws of heat and mass transfer are typically used. The laws scale the transfer (Sherwood) number, Sh , to the hydrodynamic Reynolds, Re , the fluid specific Schmidt number, Sc , and to some dimensionless geometric parameters, G, in a classical form like Sh = CReα ScβGγ . However, the validity of those classical scaling laws is limited to the region where the concentration boundary layer develops as it is well known that the transfer numbers approach a constant (Reynolds and Schmidt independent) value in the developed region of a laminar channel flow. This study examines numerically the validity of the scaling laws if the channel flow is interrupted periodically by cylindrical obstacles of different size and separation distance. In the developed region, a Schmidt and Reynolds number dependency is found and associated to wall-normal flow induced by the obstacles, for which this dependency varies with obstacle size and separation distance. Funding for WR was provided by the German Academic Exchange Service DAAD.
Skin-friction Drag Reduction in Turbulent Channel Flow with Idealized Superhydrophobic Walls
Ratsegari, Amirreza; Akhavan, Rayhaneh
2013-11-01
Skin-friction drag reduction by super-hydrophobic (SH) surfaces was investigated using Lattice Boltzmann DNS in turbulent channel flow with SH longitudinal microgrooves on both walls. The liquid/gas interfaces in the SH microgrooves were modeled as flat, shear-free surfaces. Drag reductions (DR) ranging from 5 % to 47 % were observed for microgrooves of size 4 base flow wall units. It is shown that in both laminar and turbulent flow, DR scales as DR =Us /Ub + ɛ . In laminar flow, where DR is purely due to surface slip, ɛ = 0 . In turbulent flow, ɛ remains negligible when the slip length is smaller than the thickness of the viscous sublayer. For DR > 40 % , where the effect of surface slip can be felt in the buffer layer, ɛ attains a small non-zero value. Analysis of turbulence statistics and turbulence kinetic energy budgets confirms that outside of a layer of size approximately one slip length from the walls, the turbulence dynamics proceeds as in regular channel flow with no-slip walls.
Frolov, Roman V; Weckström, Matti
2016-01-01
Cellular signaling in both excitable and nonexcitable cells involves several classes of ion channels. Some of them are of minor importance, with very specialized roles in physiology, but here we concentrate on three major channel classes: TRP (transient receptor potential channels), voltage-gated sodium channels (Nav), and voltage-gated calcium channels (Cav). Here, we first propose a conceptual framework binding together all three classes of ion channels, a "flow-of-excitation model" that takes into account the inputs mediated by TRP and other similar channels, the outputs invariably provided by Cav channels, and the regenerative transmission of signals in the neural networks, for which Nav channels are responsible. We use this framework to examine the function, structure, and pharmacology of these channel classes both at cellular and also at whole-body physiological level. Building on that basis we go through the pathologies arising from the direct or indirect malfunction of the channels, utilizing ion channel defects, the channelopathies. The pharmacological interventions affecting these channels are numerous. Part of those are well-established treatments, like treatment of hypertension or some forms of epilepsy, but many other are deeply problematic due to poor drug specificity, ion channel diversity, and widespread expression of the channels in tissues other than those actually targeted. © 2016 Elsevier Inc. All rights reserved.
Weislogel, Mark M.; Wollman, Andrew P.; Jenson, Ryan M.; Geile, John T.; Tucker, John F.; Wiles, Brentley M.; Trattner, Andy L.; DeVoe, Claire; Sharp, Lauren M.; Canfield, Peter J.;
2015-01-01
It would be signicantly easier to design fluid systems for spacecraft if the fluid phases behaved similarly to those on earth. In this research an open 15:8 degree wedge-sectioned channel is employed to separate bubbles from a two-phase flow in a microgravity environment. The bubbles appear to rise in the channel and coalesce with the free surface in much the same way as would bubbles in a terrestrial environment, only the combined effects of surface tension, wetting, and conduit geometry replace the role of buoyancy. The host liquid is drawn along the channel by a pump and noncondensible gas bubbles are injected into it near the channel vertex at the channel inlet. Control parameters include bubble volume, bubble frequency, liquid volumetric flow rate, and channel length. The asymmetrically confined bubbles are driven in the cross-flow direction by capillary forces until they at least become inscribed within the section or until they come in contact with the free surface, whereupon they usually coalesce and leave the flow. The merging of bubbles enhances, but does not guarantee, the latter. The experiments are performed aboard the International Space Station as a subset of the Capillary Channel Flow experiments. The flight hardware is commanded remotely and continuously from ground stations during the tests and an extensive array of experiments is conducted identifying numerous bubble flow regimes and regime transitions depending on the ratio and magnitude of the gas and liquid volumetric flow rates. The breadth of the publicly available experiments is conveyed herein primarily by narrative and by regime maps, where transitions are approximated by simple expressions immediately useful for the purposes of design and deeper analysis.
The coefficientof hydraulic friction of laminar open flows in smooth channels
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Borovkov Valeriy Stepanovich
2015-05-01
Full Text Available The article examines the dependence of the hydraulic friction coefficient of open laminar uniform streams on the relative width of channels with smooth bottom. The article presents the functional dependence that describes the hydraulic resistance in open channels with smooth bottoms.The experiments were carried out in a rectangular tray (6000×100×200. Aqueous solutions of glycerol were used as working fluids. The superficial tension and liquid density for the used liquids changed a little. The article declares that the coefficient of hydraulic friction λ in the zone of the laminar flow depends on the relative width of the channels with smooth bottom. In the article it is also shown that the Charny formula satisfactorily agrees with the theoretical formula and with the experimental data.
Energy Technology Data Exchange (ETDEWEB)
Hayat, T. [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia); Iqbal, Rija [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Tanveer, Anum, E-mail: qau14@yahoo.com [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Alsaedi, A. [Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)
2016-06-15
This paper looks at the influences of magnetohydrodynamics (MHD) and thermal radiation on peristaltic transport of a pseudoplastic nanofluid in a tapered asymmetric channel. The tapered channel walls satisfy convective boundary conditions. The governing equations for the balance of mass, momentum, temperature and volume fraction for pseudoplastic nanofluid are first formulated and then utilized for long wavelength and small Reynolds number considerations. Effects of involved parameters on the flow characteristics have been plotted and examined. It is observed that the heat transfer Biot number shows a dual behavior on the temperature of nanofluid particles whereas the mass transfer Biot number with its increasing values enhances the fluid temperature. - Highlights: • Mathematical model for peristalsis of pseudoplastic nanofluid is formulated. • Analysis has been made in a tapered asymmetric channel. • Magnetohydrodynamic aspects have been outlined. • Influence of thermal radiation is investigated. • Convective conditions for both heat and mass transfer are present.
DEFF Research Database (Denmark)
Olesen, Anders Christian; Kær, Søren Knudsen
2014-01-01
of liquid water towards the catalytic layer of the electrode. As opposed to the more common serpentine and parallel channels, interdigitated channels force liquid water through the porous gas diffusion layer (GDL) of the electrode. This improves the supply of water, however it increases pressure losses......In this work a macroscopic, steady-state, three-dimensional, computational fluid dynamics model of the anode of a high-pressure polymer electrolyte membrane electrolysis cell (PEMEC) is presented. The developed model is used for studying the effect of employing an interdigitated, planar......-circular cell design on the distribution of water in the anode. In the electrolysis of water using PEMEC the anode is fed by demineralized water. Throughout the anode, oxygen is produced and a two-phase flow develops. Interdigitated channels assist in avoiding that gaseous oxygen obstructs the transport...
Effects of porosity and mixed convection on MHD two phase fluid flow in an inclined channel.
Hasnain, Jafar; Abbas, Zaheer; Sajid, Muhammad
2015-01-01
The present study deals with the flow and heat transfer analysis of two immiscible fluids in an inclined channel embedded in a porous medium. The channel is divided in two phases such that a third grade fluid occupies the phase I and a viscous fluid occupies the phase II. Both viscous and third grade fluids are electrically conducting. A constant magnetic field is imposed perpendicular to the channel walls. The mathematical model is developed by using Darcy's and modified Darcy's laws for viscous and third grade fluids respectively. The transformed ordinary differential equations are solved numerically using a shooting method. The obtained results are presented graphically and influence of emerging parameters is discussed in detail.
Wasklewicz, T.; Scheinert, C.
2016-01-01
Channel change has been a constant theme throughout William L. Graf's research career. Graf's work has examined channel changes in the context of natural environmental fluctuations, but more often has focused on quantifying channel change in the context of anthropogenic modifications. Here, we consider how channelization of a debris flows along a bajada has perpetuated and sustained the development of 'telescoping' alluvial fan. Two-dimensional debris-flow modeling shows the importance of the deeply entrenched channelized flow in the development of a telescoping alluvial fan. GIS analyses of repeat (five different debris flows), high-resolution (5 cm) digital elevation models (DEMs) generated from repeat terrestrial laser scanning (TLS) data elucidate sediment and topographic dynamics of the new telescoping portion of the alluvial fan (the embryonic fan). Flow constriction from channelization helps to perpetuate debris-flow runout and to maintain the embryonic fan and telescoping nature of the alluvial fan complex. Embryonic fan development, in response to five debris flows, proceeds with a major portion of the flows depositing on the southern portion of the embryonic fan. The third through the fifth debris flows also begin to shift some deposition to the northern portion of the embryonic. The transfer of sediment from a higher portion of the embryonic fan to a lower portion continues currently on the embryonic fan. While channelized flow has been shown to be critical to the maintenance of the telescoping fan, the flow constriction has led to higher than background levels of sediment deposition in Chalk Creek, a tributary of the Arkansas River. A majority of the sediment from each debris flow is incorporated into Chalk Creek as opposed to being stored on the embryonic fan.
The numerical solution of compressible fluid flow problems
Emmons, Howard W
1944-01-01
Numerical methods have been developed for obtaining the steady, adiabatic flow field of a frictionless, perfect gas about arbitrary two-dimensional bodies. The solutions include the subsonic velocity regions, the supersonic velocity regions, and the transition compression shocks, if required. Furthermore, the rotational motion and entropy changes following shocks are taken into account. Extensive use is made of the relaxation method. In this report the details of the methods of solution are emphasized so as to permit others to solve similar problems. Solutions already obtained are mentioned only by way of illustrating the possibilities of the methods described. The methods can be applied directly to wind tunnel and free air tests of arbitrary airfoil shapes at subsonic, sonic, and supersonic speeds.
Salama, Amgad
2014-08-25
Numerical simulation of flow and heat transfer in two adjacent channels is conducted with one of the channels partially blocked. This system simulates typical channels of a material testing reactor. The blockage is assumed due to the buckling of one of the channel plates inward along its width. The blockage ratio considered in this work is defined as the ratio between the cross-sectional area of the blocked and the unblocked channel. In this work, we consider a blockage ratio of approximately 40%. However, the blockage is different along the width of the channel, ranging from 0% at the end of the channel to 90% in the middle. The channel walls are sandwiching volumetric heat sources that vary spatially as chopped cosine functions. Interesting patterns are highlighted and investigated. The reduction in the flow area of one channel results in the flow redistributing among the two channels according to the changes in their hydraulic conductivities. The results of the numerical simulations show that the maximum wall temperature in the blocked channel is well below the boiling temperature at the operating pressure.
On the Modeling of an Open Channel MEMS Based Capacitive Flow Sensor
Directory of Open Access Journals (Sweden)
Vafaghi Maryam
2008-11-01
Full Text Available In this paper an open channel MEMS capacitive flow sensor has been designed based on a microplate deflection measuring. Proposed flow sensor consists with two separate units, one for sensing the static fluid pressure and the other for sensing the fluid static and dynamic pressure. The governing equation whose solution holds the answer to all our questions about the sensor’s characteristics is a nonlinear elasto-electrostatic equation. Sensor’s static response and mechanical behavior of the sensing elements in a channel have been simulated numerically by using of Step by Step Linearization Method. The sensor stability has been examined and the stable region of the sensor has been studied. The effect of fluid velocity and static pressure on stability limit of the sensor has been investigated and the effect of bias voltage on sensor sensitivity has been studied.
Influence of internal channel geometry of gas turbine blade on flow structure and heat transfer
Szwaba, Ryszard; Kaczynski, Piotr; Telega, Janusz; Doerffer, Piotr
2017-12-01
This paper presents the study of the influence of channel geometry on the flow structure and heat transfer, and also their correlations on all the walls of a radial cooling passage model of a gas turbine blade. The investigations focus on the heat transfer and aerodynamic measurements in the channel, which is an accurate representation of the configuration used in aeroengines. Correlations for the heat transfer coefficient and the pressure drop used in the design of internal cooling passages are often developed from simplified models. It is important to note that real engine passages do not have perfect rectangular cross sections, but include a corner fillets, ribs with fillet radii and a special orientation. Therefore, this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which has very realistic features.
On the theoretical velocity distribution and flow resistance in natural channels
Moramarco, Tommaso; Dingman, S. Lawrence
2017-12-01
The velocity distribution in natural channels is of considerable interest for streamflow measurements to obtain information on discharge and flow resistance. This study focuses on the comparison of theoretical velocity distributions based on 1) entropy theory, and 2) the two-parameter power law. The analysis identifies the correlation between the parameters of the distributions and defines their dependence on the geometric and hydraulic characteristics of the channel. Specifically, we investigate how the parameters are related to the flow resistance in terms of Manning roughness, shear velocity and water surface slope, and several formulae showing their relationships are proposed. Velocity measurements carried out in the past 20 years at Ponte Nuovo gauged section along the Tiber River, central Italy, are the basis for the analysis.
MHD copper-water nanofluid flow and heat transfer through convergent-divergent channel
Energy Technology Data Exchange (ETDEWEB)
Azimi, Mohammadreza; Riazi, Rouzbeh [Faculty of New Sciences and TechnologiesUniversity of Tehran, Tehran (Iran, Islamic Republic of)
2016-10-15
This work is focused on the analytical solution of a nanofluid consisting of pure water with copper nanoparticle steady flow through convergent-divergent channel. The velocity and temperature distributions are determined by a novel method called Reconstruction of variational iteration method (RVIM). The effects of angle of the channel, Reynolds and Hartmann numbers on the nanofluid flow are then investigated. The influences of solid volume fraction and Eckert number upon the temperature distribution are discussed. Based on the achieved results, Nusselt number enhances with increment of solid volume fraction of nanoparticles, Reynolds and Eckert numbers. Also the fourth order Runge-Kutta method, which is one of the most relevant numerical techniques, is used to investigate the validity and accuracy of RVIM and good agreement is observed between the solutions obtained from RVIM and some known numerical results.
The technology of heat transfer enhancement in channels by means of flow pulsations
Directory of Open Access Journals (Sweden)
Tsynaeva Anna
2016-01-01
Full Text Available The rate and efficiency of curing of concrete can boost when used intense heat. The work is dedicated to the development and research of technologies of intensification of heat transfer in channels by pulsations. The study was conducted by means of numerical methods based on mass and momentum conservation equations (Navier-Stokes with software Code Saturne. Verification of implemented methods and software was performed. The research of heat transfer enhancement for semicircle-shaped channel exposed to low-frequency pulsations was performed. The pulsation frequency of the flow during the study was in a range of 0…10 Hz. A significant (up to 4 times increase of turbulent kinetic energy with implementing pulsations was detected. Flow pulsations with frequency of 10 Hz results in 1.21 times increase of heat transfer coefficient.
Experimental study on influence of boundary on location of maximum velocity in open channel flows
Directory of Open Access Journals (Sweden)
Jing Yan
2011-06-01
Full Text Available The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.
The impact of plasma induced flow on the boundary layer in a narrow channel
Directory of Open Access Journals (Sweden)
Procházka P.
2015-01-01
Full Text Available The induced flow generated by dielectric barrier discharge (DBD actuator working in steady and unsteady regime will be used to modify properties of naturally developed boundary layer (BL in short and long rectangular perspex channel which is connected to the blow-down wind tunnel. The actuator is placed in spanwise configuration and the inlet velocities will range between 5 and 20 m•s-1. Previously, mean flow field and statistical quantities were subjugated to investigation. In this paper, there will be presented dynamical features of the BL. Oscillation pattern decomposition (OPD of influenced flow field and frequency analysis will be presented. These results should be taken into account regarding to use in the flow around a bluff body.
Exact coherent states and connections to turbulent dynamics in minimal channel flow
Park, Jae Sung
2015-01-01
Several new families of nonlinear three-dimensional travelling wave solutions to the Navier-Stokes equation, also known as exact coherent states, are computed for Newtonian plane Poiseuille flow. The symmetries and streak/vortex structures are reported and their possible connections to critical layer dynamics examined. While some of the solutions clearly display fluctuations that are localized around the critical layer (the surface on which the streamwise velocity matches the wave speed of the solution), for others this connection is not as clear. Dynamical trajectories along unstable directions of the solutions are computed. Over certain ranges of Reynolds number, two solution families are shown to lie on the basin boundary between laminar and turbulent flow. Direct comparison of nonlinear travelling wave solutions to turbulent flow in the same channel is presented. The state-space dynamics of the turbulent flow are organized around one of the newly-identified travelling wave families, and in particular the ...
Interfacial friction factors for air-water co-current stratified flow in inclined channels
Energy Technology Data Exchange (ETDEWEB)
Choi, Ki Yong; No, Hee Cheon [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)
1997-12-31
The interfacial shear stress is experimentally investigated for co-current air-water stratified flow in inclined rectangular channels having a length of 1854mm, width of 120 mm and height of 40mm at almost atmospheric pressure. Experiments are carried out in several inclinations from 0 deg up to 10 deg. The local film thickness and the wave height are measured at three locations, i.e., L/H = 8,23, and 40. According to the inclination angle, the experimental data are categorized into two groups; nearly horizontal data group (0 deg {<=} {theta} {<=} 0.7 deg), and inclined channel data group (0.7 deg {<=} {theta} {<=} 10 deg ). Experimental observations for nearly horizontal data group show that the flow is not fully developed due to the water level gradient and the hydraulic jump within the channel. For the inclined channel data group, a dimensionless wave height, {Delta}h/h, is empirically correlated in terms of Re{sub G} and h/H. A modified root-mean-square wave height is proposed to consider the effects of the interfacial and wave propagation velocities. It is found that an equivalent roughness has a linear relationship with the modified root-mean-square wave height and its relationship is independent of the inclination. 10 refs., 6 figs., 1 tab. (Author)
Radu, Andrea I.
2012-04-01
A two-dimensional mathematical model coupling fluid dynamics, salt and substrate transport and biofilm development in time was used to investigate the effects of cross-flow velocity and substrate availability on biofouling in reverse osmosis (RO)/nanofiltration (NF) feed channels. Simulations performed in channels with or without spacer filaments describe how higher liquid velocities lead to less overall biomass amount in the channel by increasing the shear stress. In all studied cases at constant feed flow rate, biomass accumulation in the channel reached a steady state. Replicate simulation runs prove that the stochastic biomass attachment model does not affect the stationary biomass level achieved and has only a slight influence on the dynamics of biomass accumulation. Biofilm removal strategies based on velocity variations are evaluated. Numerical results indicate that sudden velocity increase could lead to biomass sloughing, followed however by biomass re-growth when returning to initial operating conditions. Simulations show particularities of substrate availability in membrane devices used for water treatment, e.g., the accumulation of rejected substrates at the membrane surface due to concentration polarization. Interestingly, with an increased biofilm thickness, the overall substrate consumption rate dominates over accumulation due to substrate concentration polarization, eventually leading to decreased substrate concentrations in the biofilm compared to bulk liquid. © 2012 Elsevier B.V.
Magnetohydrodynamic Peristaltic Flow of a Pseudoplastic Fluid in a Curved Channel
Noreen, Saima; Hayat, Tasawar; Alsaedi, Ahmed
2013-05-01
A mathematical model is developed to examine the effects of an induced magnetic field on the peristaltic flow in a curved channel. The non-Newtonian pseudoplastic fluid model is used to depict the combined elastic and viscous properties. The analysis has been carried out in the wave frame of reference, long wavelength and low Reynolds scheme are implemented. A series solution is obtained through perturbation analysis. Results for stream function, pressure gradient, magnetic force function, induced magnetic field, and current density are constructed. The effects of significant parameters on the flow quantities are sketched and discussed.
Hassan, A R; Maritz, R
2016-01-01
In this paper, the analysis of a reactive hydromagnetic Poiseuille fluid flow under different chemical kinetics through a channel in the presence of a heat source is carried out. An exothermic reaction is assumed while the concentration of the material is neglected. The Adomian decomposition method together with Pade approximation technique are used to obtain the solutions of the governing nonlinear non-dimensional differential equations. Effects of various physical parameters on the velocity and temperature fields of the fluid flow are investigated. The entropy generation analysis, irreversibility distribution ratio, Bejan number and the conditions for thermal criticality for different chemical kinetics are also presented.
Long-Range Nonlocal Flow of Vortices in Narrow Superconducting Channels
Grigorieva, I. V.; Geim, A. K.; Dubonos, S. V.; Novoselov, K. S.; Vodolazov, D. Y.; Peeters, F. M.; Kes, P. H.; Hesselberth, M.
2004-06-01
We report a new nonlocal effect in vortex matter, where an electric current confined to a small region of a long and sufficiently narrow superconducting wire causes vortex flow at distances hundreds of intervortex separations away. The observed remote traffic of vortices is attributed to a very efficient transfer of a local strain through the one-dimensional vortex lattice (VL), even in the presence of disorder. We also observe mesoscopic fluctuations in the nonlocal vortex flow, which arise due to “traffic jams” when vortex arrangements do not match a local geometry of a superconducting channel.
Numerical simulation of peristaltic flow of a Carreau nanofluid in an asymmetric channel
Directory of Open Access Journals (Sweden)
Noreen Sher Akbar
2014-03-01
Full Text Available In this article, we studied MHD peristaltic flow of a Carreau nanofluid in an asymmetric channel. The flow development is carried out in a wave frame of reference moving with velocity of the wave c1. The governing nonlinear partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations using similarity transformations and then tackled numerically using the fourth and fifth order Runge–Kutta–Fehlberg. Numerical results are obtained for dimensionless velocity, stream function, pressure rise, temperature and nanoparticle volume fraction. It is found that the pressure rise increases with increase in Hartmann Number and thermophoresis parameter.
Gomez, T; Flutet, V; Sagaut, P
2009-03-01
An exact relationship for the local skin friction is derived for the compressible turbulent wall-bounded flow (channel, pipe, flat plate). This expression is an extension of the compressible case of that derived by Fukagata [Phys. Fluids 14, L73 (2002)] in the case of incompressible wall-bounded flows. This decomposition shows that the skin friction can be interpreted as the contribution of four physical processes, i.e., laminar, turbulent, compressible, and a fourth coming from the interaction between turbulence and compressibility. Compressible numerical simulations show that, even at Mach number M=2 , the main contribution comes from the turbulence, i.e., the Reynolds stress term.
Directory of Open Access Journals (Sweden)
Matoušek Václav
2015-12-01
Full Text Available Gravity-driven open-channel flows carrying coarse sediment over an erodible granular deposit are studied. Results of laboratory experiments with artificial sediments in a rectangular tilting flume are described and analyzed. Besides integral quantities such as flow rate of mixture, transport concentration of sediment and hydraulic gradient, the experiments include measurements of the one-dimensional velocity distribution across the flow. A vertical profile of the longitudinal component of local velocity is measured across the vertical axis of symmetry of a flume cross section using three independent measuring methods. Due to strong flow stratification, the velocity profile covers regions of very different local concentrations of sediment from virtually zero concentration to the maximum concentration of bed packing. The layered character of the flow results in a velocity distribution which tends to be different in the transport layer above the bed and in the sediment-free region between the top of the transport layer and the water surface. Velocity profiles and integral flow quantities are analyzed with the aim of evaluating the layered structure of the flow and identifying interfaces in the flow with a developed transport layer above the upper plane bed.
Directory of Open Access Journals (Sweden)
K. V. Litvinov
2016-01-01
Full Text Available In this paper, we analyzed the flat non-isothermal stationary flow of abnormally viscous fluid in the channels with asymmetric boundary conditions and an unknown output boundary. The geometry of the channels in which the problem is considered, is such regions, that at the transition to bipolar a system of coordinates map into rectangles. This greatly simplifies the boundary conditions, since it is possible to use an orthogonal grid and boundary conditions are given in its nodes. Fields of this type are often found in applications. The boundary conditions are set as follows: the liquid sticks to the boundaries of the channels, which rotate at different speeds and have different radius and temperature; moreover, temperature at the entrance to deformation is known, while on the boundary with the surface the material has the surface temperature; the pressure on the enter and exit of the region becomes zero. The rheological model only takes into account the anomaly of viscosity. The material is not compressible. This process can be described by a system consisting of continuity equations, the equations of conservation of momentum and an energy equation: ∇
Secondary flows in the cooling channels of the high-performance light-water reactor
Energy Technology Data Exchange (ETDEWEB)
Laurien, E.; Wintterle, Th. [Stuttgart Univ., Institute for Nuclear Technolgy and Energy Systems (IKE) (Germany)
2007-07-01
The new design of a High-Performance Light-Water Reactor (HPLWR) involves a three-pass core with an evaporator region, where the compressed water is heated above the pseudo-critical temperature, and two superheater regions. Due to the strong dependency of the supercritical water density on the temperature significant mass transfer between neighboring cooling channels is expected if the temperature is unevenly distributed across the fuel element. An inter-channel flow is then superimposed to the secondary flow vortices induced by the non-isotropy of turbulence. In order to gain insight into the resulting flow patterns as well as into temperature and density distributions within the various subchannels of the fuel element CFD (Computational Fluid Dynamics) calculations for the 1/8 fuel element are performed. For simplicity adiabatic boundary conditions at the moderator box and the fuel element box are assumed. Our investigation confirms earlier results obtained by subchannel analysis that the axial mass flux is significantly reduced in the corner subchannel of this fuel element resulting in a net mass flux towards the neighboring subchannels. Our results provide a first estimation of the magnitude of the secondary flows in the pseudo-critical region of a supercritical light-water reactor. Furthermore, it is demonstrated that CFD is an efficient tool for investigations of flow patterns within nuclear reactor fuel elements. (authors)
Double-diffusive two-fluid flow in a slippery channel: A linear stability analysis
Ghosh, Sukhendu; Usha, R.; Sahu, Kirti Chandra
2014-12-01
The effect of velocity slip at the walls on the linear stability characteristics of two-fluid three-layer channel flow (the equivalent core-annular configuration in case of pipe) is investigated in the presence of double diffusive (DD) phenomenon. The fluids are miscible and consist of two solute species having different rates of diffusion. The fluids are assumed to be of the same density, but varying viscosity, which depends on the concentration of the solute species. It is found that the flow stabilizes when the less viscous fluid is present in the region adjacent to the slippery channel walls in the single-component (SC) system but becomes unstable at low Reynolds numbers in the presence of DD effect. As the mixed region of the fluids moves towards the channel walls, a new unstable mode (DD mode), distinct from the Tollman Schlichting (TS) mode, arises at Reynolds numbers smaller than the critical Reynolds number for the TS mode. We also found that this mode becomes more prominent when the mixed layer overlaps with the critical layer. It is shown that the slip parameter has nonmonotonic effect on the stability characteristics in this system. Through energy budget analysis, the dual role of slip is explained. The effect of slip is influenced by the location of mixed layer, the log-mobility ratio of the faster diffusing scalar, diffusivity, and the ratio of diffusion coefficients of the two species. Increasing the value of the slip parameter delays the first occurrence of the DD-mode. It is possible to achieve stabilization or destabilization by controlling the various physical parameters in the flow system. In the present study, we suggest an effective and realistic way to control three-layer miscible channel flow with viscosity stratification.
Effects of poiseuille flows on swimming of magnetic helical robots in circular channels
Acemoğlu, Alperen; Acemoglu, Alperen; Yeşilyurt, Serhat; Yesilyurt, Serhat
2015-01-01
This study reports experimental and numerical model results on swimming of microswimmers inside circular channels. Designed to mimic the swimming behavior of biological organisms at low Reynolds number flows, a number of microswimmers are manufactured utilizing a 3D printer and consist of a helical tail and a body that encapsulates a small magnet. The swimming motion results from the synchronized rotation of the artificial swimmer with the rotating magnetic field induced by three electromagne...
SPH modelling of depth‐limited turbulent open channel flows over rough boundaries
Kazemi, Ehsan; Nichols, Andrew; Tait, Simon
2016-01-01
Summary A numerical model based on the smoothed particle hydrodynamics method is developed to simulate depth‐limited turbulent open channel flows over hydraulically rough beds. The 2D Lagrangian form of the Navier–Stokes equations is solved, in which a drag‐based formulation is used based on an effective roughness zone near the bed to account for the roughness effect of bed spheres and an improved sub‐particle‐scale model is applied to account for the effect of turbulence. The sub‐particle‐scale model is constructed based on the mixing‐length assumption rather than the standard Smagorinsky approach to compute the eddy‐viscosity. A robust in/out‐flow boundary technique is also proposed to achieve stable uniform flow conditions at the inlet and outlet boundaries where the flow characteristics are unknown. The model is applied to simulate uniform open channel flows over a rough bed composed of regular spheres and validated by experimental velocity data. To investigate the influence of the bed roughness on different flow conditions, data from 12 experimental tests with different bed slopes and uniform water depths are simulated, and a good agreement has been observed between the model and experimental results of the streamwise velocity and turbulent shear stress. This shows that both the roughness effect and flow turbulence should be addressed in order to simulate the correct mechanisms of turbulent flow over a rough bed boundary and that the presented smoothed particle hydrodynamics model accomplishes this successfully. © 2016 The Authors International Journal for Numerical Methods in Fluids Published by John Wiley & Sons Ltd PMID:28066121
SPH modelling of depth-limited turbulent open channel flows over rough boundaries.
Kazemi, Ehsan; Nichols, Andrew; Tait, Simon; Shao, Songdong
2017-01-10
A numerical model based on the smoothed particle hydrodynamics method is developed to simulate depth-limited turbulent open channel flows over hydraulically rough beds. The 2D Lagrangian form of the Navier-Stokes equations is solved, in which a drag-based formulation is used based on an effective roughness zone near the bed to account for the roughness effect of bed spheres and an improved sub-particle-scale model is applied to account for the effect of turbulence. The sub-particle-scale model is constructed based on the mixing-length assumption rather than the standard Smagorinsky approach to compute the eddy-viscosity. A robust in/out-flow boundary technique is also proposed to achieve stable uniform flow conditions at the inlet and outlet boundaries where the flow characteristics are unknown. The model is applied to simulate uniform open channel flows over a rough bed composed of regular spheres and validated by experimental velocity data. To investigate the influence of the bed roughness on different flow conditions, data from 12 experimental tests with different bed slopes and uniform water depths are simulated, and a good agreement has been observed between the model and experimental results of the streamwise velocity and turbulent shear stress. This shows that both the roughness effect and flow turbulence should be addressed in order to simulate the correct mechanisms of turbulent flow over a rough bed boundary and that the presented smoothed particle hydrodynamics model accomplishes this successfully. © 2016 The Authors International Journal for Numerical Methods in Fluids Published by John Wiley & Sons Ltd.
DEFF Research Database (Denmark)
Hilgers, Rob H P; Janssen, Ger M J; Fazzi, Gregorio E
2010-01-01
remodeling. In rats, mesenteric arteries were exposed to increased [+90%, high flow (HF)] or reduced blood flow [-90%, low flow (LF)] and analyzed 24 h later. There were no detectable changes in arterial structure or in expression level of endothelial nitric-oxide synthase, SK3, or IK1. Arterial relaxing......We tested the hypothesis that changes in arterial blood flow modify the function of endothelial Ca2+-activated K+ channels [calcium-activated K+ channel (K(Ca)), small-conductance calcium-activated K+ channel (SK3), and intermediate calcium-activated K+ channel (IK1)] before arterial structural...... arteries, the balance between the NO/prostanoid versus EDHF response was unaltered. However, the contribution of IK1 to the EDHF response was enhanced, as indicated by a larger effect of TRAM-34 and a larger residual NS309-induced relaxation in the presence of UCL 1684. Reduction of blood flow selectively...
Suppression of the secondary flow in a suction channel of a large centrifugal pump
Torii, D.; Nagahara, T.; Okihara, T.
2013-12-01
The suction channel configuration of a large centrifugal pump with a 90-degree bend was studied in detail to suppress the secondary flow at the impeller inlet for improving suction performance. Design of experiments (DOE) and computational fluid dynamics (CFD) were used to evaluate the sensitivity of several primary design parameters of the suction channel. A DOE is a powerful tool to clarify the sensitivity of objective functions to design parameters with a minimum of trials. An L9 orthogonal array was adopted in this study and nine suction channels were designed, through which the flow was predicted by steady state calculation. The results indicate that a smaller bend radius with a longer straight nozzle, distributed between the bend and the impeller, suppresses the secondary flow at the impeller inlet. An optimum ratio of the cross sectional areas at the bend inlet and outlet was also confirmed in relationship to the contraction rate of the downstream straight nozzle. These findings were obtained by CFD and verified by experiments. The results will aid the design of large centrifugal pumps with better suction performance and higher reliability.
Directory of Open Access Journals (Sweden)
Sahin Ahmed
2014-12-01
Full Text Available This study focuses analytically on the oscillatory hydromagnetic flow of a viscous, incompressible, electrically-conducting, non-Newtonian fluid in an inclined, rotating channel with non-conducting walls, incorporating couple stress effects. The model is then non-dimensionalized with appropriate variables and shown to be controlled by the inverse Ekman number (K2 = 1/Ek, the hydromagnetic body force parameter (M, channel inclination (α, Grashof number (Gr, Prandtl number (Pr, oscillation frequency (ω and time variable (ωT. Analytical solutions are derived using complex variables. Excellent agreement is obtained between both previous and present work. The influence of the governing parameters on the primary velocity, secondary velocity, temperature (θ, primary and secondary flow discharges per unit depth in the channel, and frictional shear stresses due to primary and secondary flow, is studied graphically and using tables. Applications of the study arise in the simulation of the manufacture of electrically-conducting polymeric liquids and hydromagnetic energy systems exploiting rheological working fluids.
Channelization and avalanche dynamics of sediments in a fracture driven by fluid flow
Kudrolli, Arshad; Clotet, Xavier
2015-11-01
We investigate the evolution of porosity in a sediment bed induced by fluid flow which is important to understanding the structure of aquifers, dam-breaks, and extraction and sequestration of hydrocarbons in the subsurface. We demonstrate that a porous medium composed of granular matter in a thin model fracture becomes heterogeneous and develops channels due to growth of fluid flow coupled with increase in porosity. Erosion is observed to progress through stick-slip events with larger avalanches following longer wait times. Self-clogging is also observed where eroded particles collectively redeposit and jam within the channels, which are then stable to higher fluid fluxes. We model the spatial distribution of the flow within the medium using measured maps of the porosity and Darcy's law, and show that the channels grow on average at points where the perpendicular component of the fluid flux at the interface is the greatest. Adding a stochastic component to the model for the local erosion and deposition thresholds, we find the statistical features of the spatial development of heterogeneity to be consistent with those observed in the experiments. This material is based upon work supported by DOE Office of Science and Office of Basic Energy Sciences program under DE-FG02-13ER16401
Hill, Craig; Kozarek, Jessica; Sotiropoulos, Fotis; Guala, Michele
2016-02-01
An investigation into the interactions between a model axial-flow hydrokinetic turbine (rotor diameter, dT = 0.15 m) and the complex hydrodynamics and sediment transport processes within a meandering channel was carried out in the Outdoor StreamLab research facility at the University of Minnesota St. Anthony Falls Laboratory. This field-scale meandering stream with bulk flow and sediment discharge control provided a location for high spatiotemporally resolved measurements of bed and water surface elevations around the model turbine. The device was installed within an asymmetric, erodible channel cross section under migrating bed form and fixed outer bank conditions. A comparative analysis between velocity and topographic measurements, with and without the turbine installed, highlights the local and nonlocal features of the turbine-induced scour and deposition patterns. In particular, it shows how the cross-section geometry changes, how the bed form characteristics are altered, and how the mean flow field is distorted both upstream and downstream of the turbine. We further compare and discuss how current energy conversion deployments in meander regions would result in different interactions between the turbine operation and the local and nonlocal bathymetry compared to straight channels.
Visualization of pre-set vortices in boundary layer flow over wavy surface in rectangular channel
Budiman, Alexander Christantho
2014-12-04
Abstract: Smoke-wire flow visualization is used to study the development of pre-set counter-rotating streamwise vortices in boundary layer flow over a wavy surface in a rectangular channel. The formation of the vortices is indicated by the vortical structures on the cross-sectional plane normal to the wavy surface. To obtain uniform spanwise vortex wavelength which will result in uniform vortex size, two types of spanwise disturbances were used: a series of perturbation wires placed prior and normal to the leading edge of the wavy surface, and a jagged pattern in the form of uniform triangles cut at the leading edge. These perturbation wires and jagged pattern induce low-velocity streaks that result in the formation of counter-rotating streamwise vortices that evolve downstream to form the mushroom-like structures on the cross-sectional plane of the flow. The evolution of the most amplified disturbances can be attributed to the formation of these mushroom-like structures. It is also shown that the size of the mushroom-like structures depends on the channel entrance geometry, Reynolds number, and the channel gap.Graphical Abstract: [Figure not available: see fulltext.
Two Proposed Algorithms for Re-Entrant Flow Shop Problem
Abe, Kazumi; Ida, Kenichi
In a re-entrant flow shop scheduling problem we proposed some algorithms to get a better TAT (turn around time) with a genetic search method. One is an operation which searches for a solution that shifts the start timing in limited areas of each lot. Another is an operation which searches for a solution that shifts left and chooses the machine which starts fastest. Some algorithms are effective on the benchmark including those proposed by Taji et al. In the first step, it is easiest to choose the probabilistic problem by local search. The second step is to search for the solution that shifts the start timing in limited areas of each lot, makes the Gantt chart, chooses the machine and gets the results. The third step is to search for the solution that again shifts left, makes the Gantt chart, chooses the machine and gets the results. The proposed algorithms are more valid than local search methods by Taji et al, such as swap, move, swap-2 neighborhood and FIFO (first in first out). The first algorithm has produced the best result in an experimental test when interval time was short. The second algorithm produced the best result of all solutions. The results have shown that the proposed algorithms are effective for interval time cut and get better TAT than previous methods.
Fabrication of Mesoscale Channel by Scanning Micro Electrochemical Flow Cell (SMEFC
Directory of Open Access Journals (Sweden)
Cheng Guo
2017-05-01
Full Text Available A unique micro electrochemical machining (ECM method based on a scanning micro electrochemical flow cell (SMEFC, in which the electrolyte is confined beneath the tool electrode instead of spreading on the workpiece surface, has been developed and its feasibility for fabricating mesoscale channels has been investigated. The effects of the surface conditions, the applied current, the feed rate, the concentration of the electrolyte and several geometrical parameters on the machining performance have been investigated through a series of experiments. The cross-sectional profile of the channels, the roughness of the channel bottom, the width and depth of the channel, the microstructures on the machined surface and the morphologies of the moving droplet have been analyzed and compared under different machining conditions. Furthermore, experiments with different overlaps of the electrolyte droplet traces have also been conducted, in which the SMEFC acts as a “milling tool”. The influences of the electrode offset distance (EOD, the current and the feed rate on the machining performance have also been examined through the comparison of the corresponding cross-sectional profiles and microstructures. The results indicate that, in addition to machining individual channels, the SMEFC system is also capable of generating shallow cavities with a suitable superimposed motion of the tool electrode.
Ion channel pharmacology under flow: automation via well-plate microfluidics.
Spencer, C Ian; Li, Nianzhen; Chen, Qin; Johnson, Juliette; Nevill, Tanner; Kammonen, Juha; Ionescu-Zanetti, Cristian
2012-08-01
Automated patch clamping addresses the need for high-throughput screening of chemical entities that alter ion channel function. As a result, there is considerable utility in the pharmaceutical screening arena for novel platforms that can produce relevant data both rapidly and consistently. Here we present results that were obtained with an innovative microfluidic automated patch clamp system utilizing a well-plate that eliminates the necessity of internal robotic liquid handling. Continuous recording from cell ensembles, rapid solution switching, and a bench-top footprint enable a number of assay formats previously inaccessible to automated systems. An electro-pneumatic interface was employed to drive the laminar flow of solutions in a microfluidic network that delivered cells in suspension to ensemble recording sites. Whole-cell voltage clamp was applied to linear arrays of 20 cells in parallel utilizing a 64-channel voltage clamp amplifier. A number of unique assays requiring sequential compound applications separated by a second or less, such as rapid determination of the agonist EC(50) for a ligand-gated ion channel or the kinetics of desensitization recovery, are enabled by the system. In addition, the system was validated via electrophysiological characterizations of both voltage-gated and ligand-gated ion channel targets: hK(V)2.1 and human Ether-à-go-go-related gene potassium channels, hNa(V)1.7 and 1.8 sodium channels, and (α1) hGABA(A) and (α1) human nicotinic acetylcholine receptor receptors. Our results show that the voltage dependence, kinetics, and interactions of these channels with pharmacological agents were matched to reference data. The results from these IonFlux™ experiments demonstrate that the system provides high-throughput automated electrophysiology with enhanced reliability and consistency, in a user-friendly format.
Cossu, Remo
Physical experiments are used to investigate the influence of the Coriolis forces on flow structures in channelized turbidity currents, and their implication for the evolution of straight and sinuous submarine channels. Initial tests were used to determine whether or not saline density currents are a good surrogate for particle-laden currents. Results imply that this assumption is valid when turbidity currents are weakly-depositional and have similar velocity and turbulence structures to saline density currents. Second, the controls of Coriolis forces on flow structures in straight channel sections are compared with two mathematical models: Ekman boundary layer dynamics and the theory of Komar [1969]. Ekman boundary layer dynamics prove to be a more suitable description of flow structures in rotating turbidity currents and should be used to derive flow parameters from submarine channels systems that are subjected to Coriolis forces. The significance of Coriolis forces for submarine channel systems were determined by evaluating the dimensionless Rossby number RoW. The Rossby number is defined as the ratio of the flow velocity, U, of a turbidity current to the channel width, W, and the rotation rate of the Earth represented by the Coriolis parameter, f. Coriolis forces are very significant for channel systems with RoW ≤. O(1) . Third, the effect of Coriolis forces on the internal flow structure in sinuous submarine channels is considered. Since previous studies have only considered pressure gradient and centrifugal forces, the Coriolis force provides a crucial contribution to the lateral momentum balance in channel bends. In a curved channel, both the Rossby number RoW and the ratio of the channel curvature radius R to the channel width W, determine whether Coriolis forces affect the internal flow structure. The results demonstrate that Coriolis forces can cause a significant shift of the density interface and the downstream velocity core of channelized turbidity
Flow structures in submarine channels affected by Coriolis forces: Experimental observations
Cossu, R.; Wells, M. G.
2011-12-01
In this talk we will show how Coriolis forces can control the flow dynamics of turbidity currents flowing in sinuous channels at high latitudes. We describe how the internal velocity structure changes with latitude, based on observations from rotating laboratory experiments. When these results are combined with existing conceptual facies and depositional models we can now describe the changes in sedimentation patterns that are observed at different latitudes. The experiments were conducted in a sinuous channel model placed in a tank that was rotated at various rates (reflected by the Coriolis parameters f) ranging from f = 0 (at the equator) to ± 0.5 rad s-1 (at higher latitudes). The dependence of the density interface of gravity currents on rotation is shown in Figure 1a. At the equator the interface slopes up to the outer bend due to the centrifugal forces. In the Northern Hemisphere (NH) the tilt of the interface increases as now the Coriolis forces reinforce the centrifugal acceleration. In contrast, in the Southern Hemisphere (SH) the current ramps up to the inner bend and Coriolis forces dominate over centrifugal forces. Figure 1b shows the corresponding position of the downstream velocity core in the bend apex. At the equator the core is predominantly close to the centerline, whilst in the NH the core is deflected to the inner bend and in the SH the velocity core is shifted to the outer bank. Based upon our experimental results, we hypothesize that Coriolis forces can affect the velocity structure and sedimentation regime. Lateral accretion packages (LAPs) are built only on one side in the channel and finer sediments will be deposited mainly on the levee bank to which the high velocity core is deflected. The Rossby number RoW = U/fW (where U is the mean downstream velocity and W the channel width) can be used to determine the influence of Coriolis forces. In channel systems at high-latitudes (with RoW 1 implying that Coriolis forces are negligible. LAPs
Kinematics and statistics of dense, slow granular flow through vertical channels
Ananda, K. S.; Moka, Sudheshna; Nott, Prabhu R.
We have investigated the flow of dry granular materials through vertical channels in the regime of dense slow flow using video imaging of the particles adjacent to a transparent wall. Using an image processing technique based on particle tracking velocimetry, the video movies were analysed to obtain the velocities of individual particles. Experiments were conducted in two- and three-dimensional channels. In the latter, glass beads and mustard seeds were used as model granular materials, and their translational velocities were measured. In the former, aluminium disks with a dark diametral stripe were used and their translational velocities and spin were measured. Experiments in the three-dimensional channels were conducted for a range of the channel width W, and for smooth and rough sidewalls. As in earlier studies, we find that shearing takes place predominantly in thin layers adjacent to the walls, while the rest of the material appears to move as a plug. However, there are large velocity fluctuations even in the plug, where the macroscopic deformation rate is negligibly small. The thickness of the shear layer, scaled by the particle diameter dp, increases weakly with W/dp. The experimental data for the velocity field are in good agreement with the Cosserat plasticity model proposed recently. We also measured the mean spin of the particles in the two-dimensional channel, and its deviation from half the vorticity. There is a clear, measurable deviation, which too is in qualitative agreement with the Cosserat plasticity model. The statistics of particle velocity and spin fluctuations in the two-dimensional channel were analysed by determining their probability distribution function, and their spatial and temporal correlation. They were all found to be broadly similar to previous observations for three-dimensional channels, but some differences are evident. The spatial correlation of the velocity fluctuations are much stronger in the two-dimensional channel, implying
National Research Council Canada - National Science Library
SUDO, Yukio; USUI, Tohru; KAMINAGA, Masanori
1991-01-01
Counter-current-flow limitation (CCFL) experiments were carried out for both vertical rectangular channels and vertical circular tubes varying in size and in configuration of their cross sections to clarify CCFL characteristics...
Energy Technology Data Exchange (ETDEWEB)
Duan, Y. [Department of Mechanical Engineering, University of Sheffield, Sheffield S1 3JD (United Kingdom); School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester M13 9PL (United Kingdom); He, S., E-mail: s.he@sheffield.ac.uk [Department of Mechanical Engineering, University of Sheffield, Sheffield S1 3JD (United Kingdom)
2017-02-15
Highlights: • Buoyancy may greatly redistribute the flow in a non-uniform channel. • Flow structures in the narrow gap are greatly changed when buoyancy is strong. • Large flow structures exist in wider gap, which is enhanced when heat is strong. • Buoyancy reduces mixing factor caused by large flow structures in narrow gap. - Abstract: It has been a long time since the ‘abnormal’ turbulent intensity distribution and high inter-sub-channel mixing rates were observed in the vicinity of the narrow gaps formed by the fuel rods in nuclear reactors. The extraordinary flow behaviour was first described as periodic flow structures by Hooper and Rehme (1984). Since then, the existences of large flow structures were demonstrated by many researchers in various non-uniform flow channels. It has been proved by many authors that the Strouhal number of the flow structure in the isothermal flow is dependent on the size of the narrow gap, not the Reynolds number once it is sufficiently large. This paper reports a numerical investigation on the effect of buoyancy on the large flow structures. A buoyancy-aided flow in a tightly-packed rod-bundle-like channel is modelled using large eddy simulation (LES) together with the Boussinesq approximation. The behaviour of the large flow structures in the gaps of the flow passage are studied using instantaneous flow fields, spectrum analysis and correlation analysis. It is found that the non-uniform buoyancy force in the cross section of the flow channel may greatly redistribute the velocity field once the overall buoyancy force is sufficiently strong, and consequently modify the large flow structures. The temporal and axial spatial scales of the large flow structures are influenced by buoyancy in a way similar to that turbulence is influenced. These scales reduce when the flow is laminarised, but start increasing in the turbulence regeneration region. The spanwise scale of the flow structures in the narrow gap remains more or
Directory of Open Access Journals (Sweden)
Hassan Safi Ahmed
2010-03-01
Full Text Available This paper presents the results of an experimental study on the influences of floodplain impermeable groynes on flow structure, velocity, and water depth around the groyne(s. A wooden symmetrical compound channel was used. Groyne models with three different groyne relative lengths, 0.5, 0.75, and 1.0, were used on one floodplain with single and series arrangements. Analysis of the experimental results using the measured flow velocity and water depth values showed that flow structure, velocity, and water depth mainly depend on groyne relative length and the relative distance between series groynes. The flow velocity at the main channel centerline increased by about 40%, 60%, and 85%, and in other parts on the horizontal plane at the floodplain mid-water depth by about 75%, 125%, and 175% of its original value in cases of one-side floodplain groyne(s with relative lengths of 0.5, 0.75, and 1.0, respectively. The effective distance between two groynes in series arrangement ranges from 3 to 4 times the groyne length. Using an impermeable groyne with a large relative length in river floodplains increases the generation of eddy and roller zones downstream of the groyne, leading to more scouring and deposition. To avoid that, the groyne relative length must be kept below half the floodplain width.
Chen, Hsieh; Alexander-Katz, Alfredo
2014-03-01
Using hydrodynamic simulations, we demonstrate that confined colloidal suspensions can greatly enhance the unfolding of collapsed single polymers in flow. When colloids come in direct contact with the polymers due to the flow, the collapsed chains become flattened or elongated on the surface of the colloids, increasing the probability of forming large chain protrusions that the flow can pull out to unfold the polymers. This phenomenon may be suppressed if the colloid size is commensurate with the confining channels, where the colloids form well-defined banding structures. Here, we analyze the colloid banding structures in detail and their relation to the chain unfolding. We find that for colloid volume fractions up to 30%, the confined colloids form simple cubic (sc), hexagonal (hex), or a mixture of sc + hex structures. By directly changing the heights of the confining channels, we show that the collapsed polymers unfold the most in the mixed sc + hex structures. The diffuse (not well-defined) bands in the mixed sc + hex structures provide the highest collision probability for the colloids and the polymers, thus enhancing unfolding the most. Without colloidal suspensions, we show that the confining channels alone do not have an observable effect on the unfolding of collapsed polymers. The well-defined colloid bands also suppress the unfolding of noncollapsed polymers. In fact, the average size for noncollapsed chains is even smaller in the well-defined bands than in a channel without any colloids. The appearance of well-defined bands in this case also indicates that lift forces experienced by the polymers in confinement are negligible compared to those exerted by the colloidal band structures. Our results may be important for understanding the dynamics of mixed colloid polymer solutions.
Heat transfer regimes for a flow of water at supercritcal conditions in vertical channels
Deev, V. I.; Kharitonov, V. S.; Churkin, A. N.; Baisov, A. M.
2017-11-01
Heat transfer regimes observed in experiments with water at supercritical conditions flowing in vertical channels of various cross-sections (such as round pipes, annulus, or rod bundles) are analyzed. In accordance with the established practice, the normal and the deteriorated heat transfer regimes were singled out as the basic regimes specific for heat carriers with highly variable properties. At the same time, it has been established that most published experimental data on supercritical pressure water heat transfer along the length of test sections demonstrate combined (or transient) heat transfer regimes. The features can be presented as a superposition of characteristics of the above-mentioned basic regimes. The combined regimes are not stable in certain ranges of water flow conditions in which sudden transitions between the basic regimes can occur. A system of similarity criteria governing heat transfer rate in the vicinity of the critical point is examined. As applicable to cores of water-cooled reactors, due to a small hydraulic diameter of cooling channels, buoyancy forces acting in these channels are negligible as compared with the inertia effects caused by thermal acceleration of the flow and viscous force. This concept yields two integrated criteria whose use in the correction factors for the basic heat transfer equation, which we proposed previously for the normal regimes, adequately (with an error of 20-25%) describes the specific of the heat transfer coefficient in the normal, deteriorated, and combined regimes. A system of equations is proposed for design calculation of heat transfer in channels of nuclear reactors cooled with supercritical pressure water.
Mitigating cold flow problems of biodiesel: Strategies with additives
Mohanan, Athira
The present thesis explores the cold flow properties of biodiesel and the effect of vegetable oil derived compounds on the crystallization path as well as the mechanisms at play at different stages and length scales. Model systems including triacylglycerol (TAG) oils and their derivatives, and a polymer were tested with biodiesel. The goal was to acquire the fundamental knowledge that would help design cold flow improver (CFI) additives that would address effectively and simultaneously the flow problems of biodiesel, particularly the cloud point (CP) and pour point (PP). The compounds were revealed to be fundamentally vegetable oil crystallization modifiers (VOCM) and the polymer was confirmed to be a pour point depressant (PPD). The results obtained with the VOCMs indicate that two cis-unsaturated moieties combined with a trans-/saturated fatty acid is a critical structural architecture for depressing the crystallization onset by a mechanism wherein while the straight chain promotes a first packing with the linear saturated FAMEs, the kinked moieties prevent further crystallization. The study of model binary systems made of a VOCM and a saturated FAME with DSC, XRD and PLM provided a complete phase diagram including the thermal transformation lines, crystal structure and microstructure that impact the phase composition along the different crystallization stages, and elicited the competing effects of molecular mass, chain length mismatch and isomerism. The liquid-solid boundary is discussed in light of a simple thermodynamic model based on the Hildebrand equation and pair interactions. In order to test for synergies, the PP and CP of a biodiesel (Soy1500) supplemented with several VOCM and PLMA binary cocktails were measured using a specially designed method inspired by ASTM standards. The results were impressive, the combination of additives depressed CP and PP better than any single additive. The PLM and DSC results suggest that the cocktail additives are most
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Taymaz Imdat
2015-01-01
Full Text Available The Lattice Boltzmann Method is applied to computationally investigate the laminar flow and heat transfer of an incompressible fluid with constant material properties in a two-dimensional channel with a built-in bluff body. In this study, a triangular prism is taken as the bluff body. Not only the momentum transport, but also the energy transport is modeled by the Lattice Boltzmann Method. A uniform lattice structure with a single time relaxation rule is used. For obtaining a higher flexibility on the computational grid, interpolation methods are applied, where the information is transferred from the lattice structure to the computational grid by Lagrange interpolation. The flow is investigated for different Reynolds numbers, while keeping the Prandtl number at the constant value of 0.7. The results show how the presence of a triangular prism effects the flow and heat transfer patterns for the steady-state and unsteady-periodic flow regimes. As an assessment of the accuracy of the developed Lattice Boltzmann code, the results are compared with those obtained by a commercial Computational Fluid Dynamics code. It is observed that the present Lattice Boltzmann code delivers results that are of similar accuracy to the well-established Computational Fluid Dynamics code, with much smaller computational time for the prediction of the unsteady phenomena.
Plasma flow channels with ULF waves observed by Cluster and Double Star
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M. Volwerk
2005-11-01
Full Text Available On 14 August 2004 a large-scale magnetic structure was observed by Double Star TC-1 in the southern lobe and by Cluster in the northern lobe of the magnetotail. The structure has the signature of a (localized dipolarization, decreasing Bx accompanied by an increasing Bz and a strong earthward flow. The propagation direction of this structure, however, seems to be more in the dawnward direction than earthward. The structure is accompanied by ULF waves with a period of ~5 min, which are simultaneously observed by the ground magnetometer station DIK, at the magnetic footpoints of the spacecraft. We interprete these waves as modes driven by the plasma flow and propagating in the flow channel.
Plasma flow channels with ULF waves observed by Cluster and Double Star
Directory of Open Access Journals (Sweden)
M. Volwerk
2005-11-01
Full Text Available On 14 August 2004 a large-scale magnetic structure was observed by Double Star TC-1 in the southern lobe and by Cluster in the northern lobe of the magnetotail. The structure has the signature of a (localized dipolarization, decreasing B_{x} accompanied by an increasing B_{z} and a strong earthward flow. The propagation direction of this structure, however, seems to be more in the dawnward direction than earthward. The structure is accompanied by ULF waves with a period of ~5 min, which are simultaneously observed by the ground magnetometer station DIK, at the magnetic footpoints of the spacecraft. We interprete these waves as modes driven by the plasma flow and propagating in the flow channel.
Directory of Open Access Journals (Sweden)
Fengming Wang
2012-12-01
Full Text Available The flow and heat transfer characteristics inside a rectangular channel embedded with pin fins were numerically and experimentally investigated. Several differently shaped pin fins (i.e., circular, elliptical, and drop-shaped with the same cross-sectional areas were compared in a staggered arrangement. The Reynolds number based on the obstructed section hydraulic diameter (defined as the ratio of the total wetted surface area to the open duct volume available for flow was varied from 4800 to 8200. The more streamlined drop-shaped pin fins were better at delaying or suppressing separation of the flow passing through them, which decreased the aerodynamic penalty compared to circular pin fins. The heat transfer enhancement of the drop-shaped pin fins was less than that of the circular pin fins. In terms of specific performance parameters, drop-shaped pin fins are a promising alternative configuration to circular pin fins.
Second law analysis for hydromagnetic couple stress fluid flow through a porous channel
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S.O. Kareem
2016-06-01
Full Text Available In this work, the combined effects of magnetic field and ohmic heating on the entropy generation rate in the flow of couple stress fluid through a porous channel are investigated. The equations governing the fluid flow are formulated, non-dimensionalised and solved using a rapidly convergent semi-analytical Adomian decomposition method (ADM. The result of the computation shows a significant dependence of fluid’s thermophysical parameters on Joule’s dissipation as well as decline in the rate of change of fluid momentum due to the interplay between Lorentz and viscous forces. Moreover, the rate of entropy generation in the flow system drops as the magnitude of the magnetic field increases.
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J.C. Umavathi
2014-01-01
Full Text Available Fully developed laminar mixed convection in a corrugated vertical channel filled with two immiscible viscous fluids has been investigated. By using a perturbation technique, the coupled nonlinear equations governing the flow and heat transfer are solved. The fluids are assumed to have different viscosities and thermal conductivities. Separate solutions are matched at the interface using suitable matching conditions. The velocity, the temperature, the Nusselt number and the shear stress are analyzed for variations of the governing parameters such as Grashof number, viscosity ratio, width ratio, conductivity ratio, frequency parameter, traveling thermal temperature and are shown graphically. It is found that the Grashof number, viscosity ratio, width ratio and conductivity ratio enhance the velocity parallel to the flow direction and reduce the velocity perpendicular to the flow direction.
Studies on two-phase ionic liquid-aqueous flows in small channels of various sizes
Tsaoulidis, Dimitrios; Chinaud, Maxime; Li, Qi; Angeli, Panagiota; University College London Team
2014-11-01
Two-phase flows in intensified small-scale systems find increasing applications in (bio)chemical analysis and synthesis, fuel cells, polymerisation, and separation processes (solvent extraction). Ionic liquids are emerging as a useful chemical in different areas of interest because of their unique properties such as negligible volatility and flammability, and good thermal and radiation stability. In this work, the hydrodynamic characteristics during plug flow have been investigated in detail. Experiments were carried out in Teflon channels of different sizes, i.e. 0.5, 1, and 2 mm internal diameter using two-phase systems relevant to spent nuclear fuel reprocessing, i.e. TBP/ionic liquid (30%, v/v)-nitric acid solutions. Important mixing characteristics and circulation patterns within the aqueous plugs have been studied by means of Particle Image Velocimetry (PIV). Finally, the mechanism of plug flow formation and the resulting plug size were investigated using Computational Fluid Dynamic (CFD).
Numerical simulation of MHD pulsatile flow of a biofluid in a channel
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Kashif Ali
2015-08-01
Full Text Available The purpose of this paper is to numerically study the interaction of an external magnetic field with the flow of a biofluid through a Darcy-Forchhmeir porous channel, due to an oscillatory pressure gradient, in the presence of wall transpiration as well as chemical reaction considerations. We have noticed that if the Reynolds number of the wall transpiration flow is increased, the average (or maximum velocity of the main flow direction is raised. Similar effect has also been observed for the rheological parameter and the Darcy parameter, whereas an opposite trend has been noted for both the Forchheimer quadratic drag parameter and the magnetic parameter. Further, an increase in the Reynolds number results in straightening the concentration profile, thus making it an almost linear function of the dimensionless spatial variable.
Electric modelling and image analysis of channel flow in bipolar plates
Energy Technology Data Exchange (ETDEWEB)
Martin, D.; Gonzalez, L.; Garcia-Alegre, M.C.; Guinea, D. [Instituto de Automatica Industrial, Consejo Superior de Investigaciones Cientificas, 28500 Arganda, Madrid (Spain); Guinea, D.M.; Moreno, B. [Instituto de Ceramica y Vidrio, Consejo Superior de Investigaciones Cientificas, Kelsen 5, 28049 Madrid (Spain)
2007-07-15
Bipolar plates are an essential part of Polymer Electrolyte Membrane Fuel Cells (PEMFC) and are related to fluid conduction. The topology of a bipolar plate is critical to the homogeneous distribution of the feeding gases over the accessible zone of the electrode. An electric model that simulates flow in bipolar plates and permits the optimisation of gas feeding in PEMFCs is proposed. As a first approach, an analogy is made between the gas pressure P and an electric voltage U in a circuit and a gas flow F and an electric current I. The fluidic resistance in a bipolar plate channel is thus R=P/F and is equivalent to the electric resistance R=U/I in a branch of a circuit. Computer image processing techniques allow the validation of the present flow estimation approach based on electrical variables. Separate plates were developed to experimentally implement a complete parallel bipolar topology. (author)
Lyulin, Y. V.; Rezanova, E. V.
2017-11-01
Heat- and mass transfer processes in a two-layer system of the liquid and gas are studied with respect to evaporation at interface. The stationary convective flows of two immiscible viscous incompressible fluids filling an infinite channel and being under action of the transverse gravitation field are studied analytically. Mathematical modeling of the flows is carried out with the help of the Navier-Stokes equations in Boussinesq approximation. The Dufour and Soret effects are taken into consideration in the gas-vapor phase. In the two-dimensional case the exact solutions of special type are constructed under condition of a given specific gas flow rate. Comparison of the analytical results with results of the physical experiments with the “liquid-gas” system like “ethanol-air” are presented.
Falconi, C. J.; Lehrenfeld, C.; Marschall, H.; Meyer, C.; Abiev, R.; Bothe, D.; Reusken, A.; Schlüter, M.; Wörner, M.
2016-01-01
The vertically upward Taylor flow in a small square channel (side length 2 mm) is one of the guiding measures within the priority program "Transport Processes at Fluidic Interfaces" (SPP 1506) of the German Research Foundation (DFG). This paper presents the results of coordinated experiments and three-dimensional numerical simulations (with three different academic computer codes) for typical local flow parameters (bubble shape, thickness of the liquid film, and velocity profiles) in different cutting planes (lateral and diagonal) for a specific co-current Taylor flow. For most quantities, the differences between the three simulation results and also between the numerical and experimental results are below a few percent. The experimental and computational results consistently show interesting three-dimensional flow effects in the rear part of the liquid film. There, a local back flow of liquid occurs in the fixed frame of reference which leads to a temporary reversal of the direction of the wall shear stress during the passage of a Taylor bubble. Notably, the axial positions of the region with local backflow and those of the minimum vertical velocity differ in the lateral and the diagonal liquid films. By a thorough analysis of the fully resolved simulation results, this previously unknown phenomenon is explained in detail and, moreover, approximate criteria for its occurrence in practical applications are given. It is the different magnitude of the velocity in the lateral film and in the corner region which leads to azimuthal pressure differences in the lateral and diagonal liquid films and causes a slight deviation of the bubble from the rotational symmetry. This deviation is opposite in the front and rear parts of the bubble and has the mentioned significant effects on the local flow field in the rear part of the liquid film.
Fully-resolved prolate spheroids in turbulent channel flows: A lattice Boltzmann study
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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.
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Billaux, D.; Long, J.C.S.; Peterson, J.E. Jr.
1990-03-01
A model for channelized flow in three-dimensional, random networks of fractures has been developed. In this model, the fractures are disc-shaped discontinuities in an impermeable matrix. Within each fracture, flow occurs only in a network of random channels. The channels in each fracture can be generated independently with random distributions of length, conductivity, and orientation in the fracture plane. Boundary conditions are specified on the sides of a flow region,'' and at the intersections of the channels with interior holes'' specified by the user to simulate boreholes or drifts. This code is part of a set of programs used to generate two-dimensional or three-dimensional random fracture networks, plot them, compute flow through them and analyze the results. 8 refs., 13 figs.
Hydromagnetic Blood Flow of Sisko Fluid in a Non-uniform Channel Induced by Peristaltic Wave
Zeeshan, A.; Bhatti, M. M.; Akbar, N. S.; Sajjad, Y.
2017-07-01
In this paper, a smooth repetitive oscillating wave traveling down the elastic walls of a non-uniform two-dimensional channels is considered. It is assumed that the fluid is electrically conducting and a uniform magnetic field is perpendicular to flow. The Sisko fluid is grease thick non-Newtonian fluid can be considered equivalent to blood. Taking long wavelength and low Reynolds number, the equations are reduced. The analytical solution of the emerging non-linear differential equation is obtained by employing Homotopy Perturbation Method (HPM). The outcomes for dimensionless flow rate and dimensionless pressure rise have been computed numerically with respect to sundry concerning parameters amplitude ratio ϕ, Hartmann number M, and Sisko fluid parameter b 1. The behaviors for pressure rise and average friction have been discussed in details and displayed graphically. Numerical and graphical comparison of Newtonian and non-Newtonian has also been evaluated for velocity and pressure rise. It is observed that the magnitude of pressure rise is maximum in the middle of the channel whereas for higher values of fluid parameter it increases. Further, it is also found that the velocity profile shows converse behavior along the walls of the channel against multiple values of fluid parameter.
Two-Phase Pressure Drop of a Refrigerant Flowing Vertically Downward in a Mini-channel
Miyata, Kazushi; Enoki, Koji; Mori, Hideo; Hamamoto, Yoshinori
Experiments were performed on two-phase pressure drop of a refrigerant R-410A flowing vertically downward in small copper circular tubes with 0.5-2.0 mm I.D., and small copper rectangular and triangular tubes with 1.04 and 0.88 mm inner hydraulic equivalent diameter, respectively, for the development of a high-performance heat exchanger using small tubes or multi-port extruded tubes for air conditioning systems.Pressure drops were measured and flow patterns were observed in the range of mass flux from 30 to 400 kg/(m2s)and quality from 0.1 to 0.9 at the saturation temperature of 10 °C. Characteristics of measured pressure drops were examined for different flow channel geometries. In high quality region or relatively high mass flux condition, the frictional pressure drop was reproduced well by the Lockhart-Martinelli correlation used together with a new correlation for Chisholm's parameter C as a function of hydraulic equivalent diameter. In low mass flux and low quality region, the frictional pressure drop was also reproduced well by multiplying the Chisholm two-phase multiplier factor by modified coefficient. In addition, flow pattern was observed with 0.5 and 2.0 mm I.D circular glass tubes. Slug flow and annular flow patterns were observed at lower and higher quality, respectively.
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.
Vertical velocity distribution in open-channel flow with rigid vegetation.
Zhu, Changjun; Hao, Wenlong; Chang, Xiangping
2014-01-01
In order to experimentally investigate the effects of rigid vegetation on the characteristics of flow, the vegetations were modeled by rigid cylindrical rod. Flow field is measured under the conditions of submerged rigid rod in flume with single layer and double layer vegetations. Experiments were performed for various spacings of the rigid rods. The vegetation models were aligned with the approaching flow in a rectangular channel. Vertical distributions of time-averaged velocity at various streamwise distances were evaluated using an acoustic Doppler velocimeter (ADV). The results indicate that, in submerged conditions, it is difficult to described velocity distribution along the entire depth using unified function. The characteristic of vertical distribution of longitudinal velocity is the presence of inflection. Under the inflection, the line is convex and groove above inflection. The interaction of high and low momentum fluids causes the flow to fold and creates strong vortices within each mixing layer. Understanding the flow phenomena in the area surrounding the tall vegetation, especially in the downstream region, is very important when modeling or studying the riparian environment. ADV measures of rigid vegetation distribution of the flow velocity field can give people a new understanding.
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Sidra Aman
2017-01-01
Full Text Available Applications of carbon nanotubes, single walls carbon nanotubes (SWCNTs and multiple walls carbon nanotubes (MWCNTs in thermal engineering have recently attracted significant attention. However, most of the studies on CNTs are either experimental or numerical and the lack of analytical studies limits further developments in CNTs research particularly in channel flows. In this work, an analytical investigation is performed on heat transfer analysis of SWCNTs and MWCNTs for mixed convection Poiseuille flow of a Casson fluid along a vertical channel. These CNTs are suspended in three different types of base fluids (Water, Kerosene and engine Oil. Xue [Phys. B Condens. Matter 368, 302–307 (2005] model has been used for effective thermal conductivity of CNTs. A uniform magnetic field is applied in a transverse direction to the flow as magnetic field induces enhancement in the thermal conductivity of nanofluid. The problem is modelled by using the constitutive equations of Casson fluid in order to characterize the non-Newtonian fluid behavior. Using appropriate non-dimensional variables, the governing equations are transformed into the non-dimensional form, and the perturbation method is utilized to solve the governing equations with some physical conditions. Velocity and temperature solutions are obtained and discussed graphically. Expressions for skin friction and Nusselt number are also evaluated in tabular form. Effects of different parameters such as Casson parameter, radiation parameter and volume fraction are observed on the velocity and temperature profiles. It is found that velocity is reduced under influence of the exterior magnetic field. The temperature of single wall CNTs is found greater than MWCNTs for all the three base fluids. Increase in volume fraction leads to a decrease in velocity of the fluid as the nanofluid become more viscous by adding CNTs.
Aman, Sidra; Khan, Ilyas; Ismail, Zulkhibri; Salleh, Mohd Zuki; Alshomrani, Ali Saleh; Alghamdi, Metib Said
2017-01-01
Applications of carbon nanotubes, single walls carbon nanotubes (SWCNTs) and multiple walls carbon nanotubes (MWCNTs) in thermal engineering have recently attracted significant attention. However, most of the studies on CNTs are either experimental or numerical and the lack of analytical studies limits further developments in CNTs research particularly in channel flows. In this work, an analytical investigation is performed on heat transfer analysis of SWCNTs and MWCNTs for mixed convection Poiseuille flow of a Casson fluid along a vertical channel. These CNTs are suspended in three different types of base fluids (Water, Kerosene and engine Oil). Xue [Phys. B Condens. Matter 368, 302-307 (2005)] model has been used for effective thermal conductivity of CNTs. A uniform magnetic field is applied in a transverse direction to the flow as magnetic field induces enhancement in the thermal conductivity of nanofluid. The problem is modelled by using the constitutive equations of Casson fluid in order to characterize the non-Newtonian fluid behavior. Using appropriate non-dimensional variables, the governing equations are transformed into the non-dimensional form, and the perturbation method is utilized to solve the governing equations with some physical conditions. Velocity and temperature solutions are obtained and discussed graphically. Expressions for skin friction and Nusselt number are also evaluated in tabular form. Effects of different parameters such as Casson parameter, radiation parameter and volume fraction are observed on the velocity and temperature profiles. It is found that velocity is reduced under influence of the exterior magnetic field. The temperature of single wall CNTs is found greater than MWCNTs for all the three base fluids. Increase in volume fraction leads to a decrease in velocity of the fluid as the nanofluid become more viscous by adding CNTs.
Rules Placement Problem in OpenFlow Networks: a Survey
Nguyen, Xuan Nam; Saucez, Damien; Barakat, Chadi; Turletti, Thierry
2016-01-01
International audience; Software-Defined Networking (SDN) abstracts low- level network functionalities to simplify network management and reduce costs. The OpenFlow protocol implements the SDN concept by abstracting network communications as flows to be processed by network elements. In OpenFlow, the high-level policies are translated into network primitives called rules that are distributed over the network. While the abstraction offered by OpenFlow allows to potentially implement any policy...
Energy Technology Data Exchange (ETDEWEB)
Han, Kun Yeun; Park, Jae Hong; Lee, Eul Rae [Kyungpook National University, Taegu (Korea, Republic of)
1997-02-28
Petrov-Galerkin finite element model for analyzing dynamic wave equation is applied to gradually and rapidly varied unsteady flow. The model is verified by applying to hydraulic jump, nonlinear disturbance propagation in frictionless horizontal channel and dam-break analysis. It shows stable and accurate results compared with analytical solutions for various cases. The model is applied to a surge propagation in a frictionless horizontal channel. Three-dimensional water surface profiles show that the computed result converges to the analytical one with sharp discontinuity. The model is also applied to the Taehwa River to analyze unsteady flood wave propagation. The computed results have good agreements with those of DWOPER model in terms of discharge and stage hydrographs. (author). 19 refs., 22 figs.
Developing Buoyancy Driven Flow of a Nanofluid in a Vertical Channel Subject to Heat Flux
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Nirmal C. Sacheti
2014-01-01
Full Text Available The developing natural convective flow of a nanofluid in an infinite vertical channel with impermeable bounding walls has been investigated. It is assumed that the nanofluid is dominated by two specific slip mechanisms and that the channel walls are subject to constant heat flux and isothermal temperature, respectively. The governing nonlinear partial differential equations coupling different transport processes have been solved numerically. The variations of velocity, temperature, and nanoparticles concentration have been discussed in relation to a number of physical parameters. It is seen that the approach to the steady-state profiles of velocity and temperature in the present work is different from the ones reported in a previous study corresponding to isothermal wall conditions.
A new method of simulating fiber suspensions and applications to channel Flows
Yang, Wei
2012-06-01
A successive iteration method is proposed to numerically simulate fiber suspensions. The computational field is discretized with the collocated finite volume method, and an ergodic hypothesis is adopted to greatly accelerate the solution to the Fokker - Planck equation. The method is employed in channel flows with different fiber volume fractions and aspect ratios, and its effectiveness is proved. The numerical results show that the existence of fibers significantly changes the pressure distribution, and the fiber aspect ratio has a greater effect on the velocity profile than on the volume faction. At the center of the channel, the velocity increases along the streamwise direction, while the velocity near the wall decreases slightly. The uncoupling and coupling solutions of the additional stress of the fiber suspensions are quite different. © 2012 Chinese Physical Society and IOP Publishing Ltd.
Theory to predict particle migration and margination in the pressure-driven channel flow of blood
Qi, Qin M.; Shaqfeh, Eric S. G.
2017-09-01
The inhomogeneous concentration distribution of erythrocytes and platelets in microchannel flows particularly in directions normal to the mean flow plays a significant role in hemostasis, drug delivery, and microfluidic applications. In this paper, we develop a coarse-grained theory to predict these distributions in pressure-driven channel flow at zero Reynolds number and compare them to experiments and simulations. We demonstrate that the balance between the deformability-induced lift force and the shear-induced diffusion created by hydrodynamic interactions in the suspension results in both a peak concentration of red blood cells at the channel center and a cell-free or Fahraeus-Lindqvist layer near the walls. On the other hand, the absence of a lift force and the strong red blood cell-platelet interactions result in an excess concentration of platelets in the cell-free layer. We demonstrate a strong role of hematocrit (i.e., erythrocyte volume fraction) in determining the cell-free layer thickness and the degree of platelet margination. We also demonstrate that the capillary number of the erythrocytes, based on the membrane shear modulus, plays a relatively insignificant role in the regimes that we have studied. Our theory serves as a good and simple alternative to large-scale computer simulations of the cross-stream transport processes in these mixtures.
Kornet, Kacper
2014-01-01
We put forward a new type of spectral method for the direct numerical simulation of flows where anisotropy or very fine boundary layers are present. The mean idea is to take advantage of the fact that such structures are dissipative and that their presence should reduce the number of degrees of freedom of the flow, when paradoxically, their fine resolution incurs extra computational cost in most current methods. The principle of this method is to use a functional basis with elements that already include these fine structure so as to avoid these extra costs. This leads us to develop an algorithm to implement a spectral method for arbitrary functional bases, and in particular, non-orthogonal ones. We construct a basic implementation of this algorithm to simulate Magnetohydrodynamic (MHD) channel flows with an externally imposed, transverse magnetic field, where very thin boundary layers are known to develop along the channel walls. In this case, the sought functional basis can be built out of the eigenfunctions...
Canuto, V. M.; Hartke, G. J.; Battaglia, A.; Chasnov, J.; Albrecht, G. F.
1988-01-01
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 stongly on the structure of the turbulence spectrun 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.
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 laminar flow in a sudden expansion obstacled channel
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Mushatet Khudheyer S.
2015-01-01
Full Text Available In the present work, a numerical study has been conducted to investigate the flow heat transfer through an obstacled sudden expansion channel. Rectangular adiabatic obstacles mounted behind the expansion region on the upper and lower wall of the channel used. The effects of obstacles length, obstacles thickness and number of obstacles on flow and thermal fields for different Reynolds number and expansion ratio examined. Three values of expansion ratio (ER equal to 1.5, 1.75 and 2 were used. The choice of values of Reynolds number takes in consideration the symmetry state. The governing equations of continuity, momentum and energy discretized by using the finite difference formulation and the resulting algebraic equations solved by using Gauss-Seidle iteration method. The obtained results show that the obstacles have a considerable effect on dynamics of the flow and enhancement of heat transfer. In addition, it is found that the heat transfer is enhanced more as the obstacles thickness increases and this trend is decreased as the obstacles length increases.
The interaction between fluid flow and ultra-hydrophobic surface in mini channel
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Jasikova Darina
2017-01-01
Full Text Available Interaction of liquid with ultra-hydrophobic surface is accompanied by creation of layer of air. The effect of the air film has a potential of use in industry in many applications. The quality of the surface is influenced by matrix roughness, the character of physical or chemical cover. There was developed a method for analysis of the liquid flow and the air film using the lighting in volume, visualization with CCD camera and long distance microscope, and optical filters. There were prepared four stainless steel samples of inner channel of dimensions (80 × 8 × 8 mm and initial surface roughness Ra 0.33, Ra 1.0, Ra 2.0, and Ra 2.2. The inner channel was treated with plasma and commercial hydrophobic coating Greblon (WEILBURGER Coatings GmbH. There was realized study focused on the liquid flow velocity profile close to the air film. There are present results for laminar, transient and turbulent flows. The study also estimated the air film thickness depending on the Re number. The knowledge of the air film behaviour helps applied suitable degree of processing and cover for the target application.
Garcia-Ybarra, Pedro L.; Pinelli, Alfredo
2006-08-01
The transport of a passive scalar within a turbulent plane channel flow has been theoretically analyzed by assuming that the Schmidt number Sc, associated to the molecular diffusivity of the passive scalar, is a large parameter. Throughout most of the channel cross-section the mean passive scalar density is constant, but adjacent to the walls a thin boundary layer develops embedded in the viscous sublayer, with a relative thickness of order Sc. In this narrow region a passive scalar profile arises due to the non-vanishing flux normal to the wall. This profile is parameter independent (universal) and leads to a constant flux of passive scalar that results from the addition of both the molecular diffusion flux and the turbulent transport one. The Sc-asymptotic matching of this profile with the constant core value provides an analytical expression for the wall-normal flux that depends on the fluid dynamics of the carrier flow. By using a DNS code to solve the external turbulent flow, the analytical expression has been quantified and compared with empirical expressions based on experimental data, showing excellent agreement. To cite this article: P.L. Garcia-Ybarra, A. Pinelli, C. R. Mecanique 334 (2006).
Modeling and simulation of PEM fuel cell's flow channels using CFD techniques
Energy Technology Data Exchange (ETDEWEB)
Cunha, Edgar F.; Andrade, Alexandre B.; Robalinho, Eric; Bejarano, Martha L.M.; Linardi, Marcelo [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)]. E-mails: efcunha@ipen.br; abodart@ipen.br; eric@ipen.br; mmora@ipen.br; mlinardi@ipen.br; Cekinski, Efraim [Instituto de Pesquisas Tecnologicas (IPT-SP), Sao Paulo, SP (Brazil)]. E-mail: cekinski@ipt.br
2007-07-01
Fuel cells are one of the most important devices to obtain electrical energy from hydrogen. The Proton Exchange Membrane Fuel Cell (PEMFC) consists of two important parts: the Membrane Electrode Assembly (MEA), where the reactions occur, and the flow field plates. The plates have many functions in a fuel cell: distribute reactant gases (hydrogen and air or oxygen), conduct electrical current, remove heat and water from the electrodes and make the cell robust. The cost of the bipolar plates corresponds up to 45% of the total stack costs. The Computational Fluid Dynamic (CFD) is a very useful tool to simulate hydrogen and oxygen gases flow channels, to reduce the costs of bipolar plates production and to optimize mass transport. Two types of flow channels were studied. The first type was a commercial plate by ELECTROCELL and the other was entirely projected at Programa de Celula a Combustivel (IPEN/CNEN-SP) and the experimental data were compared with modelling results. Optimum values for each set of variables were obtained and the models verification was carried out in order to show the feasibility of this technique to improve fuel cell efficiency. (author)
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M. Ali Abbas
2016-03-01
Full Text Available In this present analysis, three dimensional peristaltic flow of hyperbolic tangent fluid in a non-uniform channel has been investigated. We have considered that the pressure is uniform over the whole cross section and the interial effects have been neglected. For this purpose we consider laminar flow under the assumptions of long wavelength (λ→∞ and creeping flow (Re→0 approximations. The attained highly nonlinear equations are solved with the help of Homotopy perturbation method. The influence of various physical parameters of interest is demonstrated graphically for wall tension, mass characterization, damping nature of the wall, wall rigidity, wall elastance, aspect ratio and the Weissenberg number. In this present investigation we found that the magnitude of the velocity is maximum in the center of the channel whereas it is minimum near the walls. Stream lines are also drawn to discuss the trapping mechanism for all the physical parameters. Comparison has also been presented between Newtonian and non-Newtonian fluid.
Lacina, Karel; Vondál, Jiří; Skládal, Petr
2012-05-21
Four-channel flow-through electrochemical cell working in thin-layer regime was designed, fabricated and characterized experimentally and in computational fluid dynamics (CFD) simulations. The new principle of operation allows reproducible splitting of a stream of liquid into multiple flow channels. Systems comprising of 2-, 3-, 4- and 8-channels were tested. The proper function of the cell is given by the ratio of the cross-sections of the fluidic element collecting chamber and the particular flow paths among which the liquid is distributed. Suitable flow rates providing uniform liquid distribution were evaluated and the results were compared to CFD modeling. The flow-through cells designed according to the proposed principle can be simply incorporated in automated routine analysis as only one inlet and one common outlet are required. Copyright © 2012 Elsevier B.V. All rights reserved.
Pinos, Thomas Arthur Richard
Flame propagation through a channel equipped with obstacles was studied experimentally. Two types of obstacle geometries were investigated, i.e., wall-mounted cross-flow cylinders and fence-type obstacles mounted on the top and bottom channel surfaces. The motivation for this research is its applications to both high-speed propulsion and industrial explosion safety. The effect of obstacle distribution and blockage ratio on flame acceleration was investigated in a 2.54cm x 7.6cm "narrow" channel with wall-mounted cross-flow cylindrical obstacles. The cylinders were arranged in a "staggered" or "inline" pattern, with blockage ratios of 0.5 and 0.67. Schlieren images were used to study the flame shape and its leading edge velocity for a range of fuel-air mixtures compositions. It was determined that initial flame propagation occurs faster in higher blockage ratios due to the higher frequency perturbation to the flow. Flame acceleration led to different quasi-steady flame and detonation propagation regimes. In general, higher final steady flame velocities were reached in the lower blockage ratios, and detonation limits were found to be influenced by the geometry. The influence of channel width on flame acceleration was also determined using fence-type obstacles with a single blockage ratio. Experiments were performed in a 2.54cm x 7.6cm and 7.6cm x 7.6cm channel. Schlieren images were again used to study the flame shape and to obtain leading edge velocity. The flame tip was found to have a parabolic profile across the channel width for the narrower channel and flatter profile in the wider channel. It was determined that the channel width has a weak effect on the flame velocity down the channel length. As such, flame acceleration was initially only slightly more pronounced in the narrow channel before the reverse became true later in the wide channel.
Thermal measurements and flow visualization of heat convection in a tilted channel
Tisserand, Jean-Christophe; Creyssels, Mathieu; Riedinger, Xavier; Castaing, Bernard; Chillà, Francesca
2010-05-01
Convection is the most important heat transport mechanism. We can find it not only in many natural situations such as stars, planet's atmosphere but also in half-natural situations such as industrial plants. Furthermore, the Rayleigh-Benard system, in which a fluid is cooled from above and heated from below, is one of the most studied systems in thermal convection. Nevertheless, in this configuration, the neighborhood of the plates controls the heat transfer. Therefore, we have to make a system in which the flow forgets the cold and the hot plate. We have built a vertical long channel which links two chambers : the hot one at the lower end and the cold one at the upper end. Moreover, this channel, which is hanged to a structure, can be tilted from an angle of 0 degree to 90 degrees. The experimental facility used for this purpose is a square channel with an inner area of 5*5 cm² m and with a height of 20 cm. The cell is filled with water and is heated at the bottom by Joule effect. At the top, the temperature is regulated by a thermal bath and the mean temperature of the bulk is 25°C . It is worth noticing that this configuration could correspond to heat pipes (without phase transformation) used in thermalisation systems or could model a vertical access pit of an underground carry. In this paper, we want to highlight how the thermal convection in the bulk of the channel is. In the first part, the paper will be focused on the visualization of the flow into the channel thanks to particle image velocimetry (PIV) technique. We look at the mean velocity field (transverse and axial components) , the fluctuations of the mean velocity field and the shear Reynolds stress. Besides, we analyze how the influence of the power supply and the dependance of the tilt angle are. At last, we will interpret the PIV measurements in terms of turbulent viscosity and effective heat conduction and we will deduce from the PIV measurements the axial mean profile of temperature. Then, in a
Vanapalli, Siva; Suteria, Naureen; Nekouei, Mehdi
2017-11-01
We report a technique referred to as ``microfluidic bypass manometry'' for measurement of pressure drop versus flow rate (ΔP-Q) relations in a parallelized manner. It involves introducing co-flowing laminar streams into a microfluidic network that contains a series of loops, where each loop contains a test geometry and a bypass channel as a flow rate sensing element. To demonstrate the technique, we measure ΔP-Q relations simultaneously for forty test geometries ranging from linear to contraction-expansion to serpentine to pillar-laden microchannels. The measured Newtonian flow resistance of these different geometries is in excellent agreement with CFD simulations. To expand the capabilities of the method, we measured ΔP-Q relations for similar-sized oil droplets trapped in microcavities where the cavity geometry spans from prisms of 3 - 10 sides to cylinders. We find in all cases, ΔP-Q relation is nonlinear and the flow resistance is sensitive to drop confinement and weakly dependent on cavity geometry. We anticipate that microfluidic bypass manometry may find broad application in several areas including design of lab-on-chip devices, laminar drag reduction, rheology of complex fluids and mechanics of deformable particles.
Characteristics of slug flow in narrow rectangular channels under vertical condition
Wang, Yang; Yan, Changqi; Sun, Licheng; Xing, Dianchuan; Yan, Chaoxing; Tian, Daogui
2013-07-01
Gas-liquid slug flow is widely encountered in many practical industrial applications. A detailed understanding of the hydrodynamics of gas slug has important significance for modeling of the slug flow. Non-intrusive flow visualization using a high speed video camera system is applied to study characteristics of slug flow in a vertical narrow rectangular channel (3.25×40 mm2). Ideal Taylor bubbles are hardly observed, and most of the gas slugs are deformed, much more seriously at high liquid superficial velocity. The liquid film thicknesses of left and right narrow sides surrounding gas slug are divergent and wavy, but it has weak effect on liquid film velocity. The gas and liquid velocity as well as the length of gas slug have significant effect on the separating liquid film thickness. The separating liquid film velocity is decreased with the increase of gas superficial velocity at low liquid velocity, and increased with the increase of liquid superficial velocity. The film stops descending and the gas superficial velocity has no significant effect on liquid film separating velocity at high liquid velocity (jL≥1.204 m/s), and it is mainly determined by the liquid flow rate. The shape of slug nose has a significant effect on its velocity, while the effect of its length is very weak. The Ishii&Jones-Zuber drift flux correlation could predict slug velocity well, except at low liquid superficial velocity by reason of that the calculated drift velocity is less than experimental values.
Computational Investigation of Flow Fields and Erosion in a Dimpled Channel
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M. H. Alhajeri
2009-12-01
Full Text Available A numerical prediction of flow in a dimpled channel is reported. The flow regimes considered cover a wide range of Reynolds numbers, which range from 380 to 99000 and which are equivalent to a range of inlet velocities from very low (0.072 m/s to very high (60 m/s. In this study, calculations were made using the standard k-e model with standard wall function. The drag coefficient, skin friction drag, pressure drag, and pressure distribution around a dimple were investigated. As the velocity increased, the drag coefficient decreased until the velocity exceeded 45 m/s, after which it increased. Furthermore, the pressure drag and skin friction drag depend on the velocity. Particles with a density of 2440 kg/m3 and a diameter of 100 microns were tracked through the domain to estimate the frequency, velocity, and angle of impact of the particles and to estimate the resulting erosion rate. It was found that the maximum erosion rate occurred between 40 and 65 degrees from the leading edge of the dimple. Furthermore, a computational study of the flow fields of three dimples in an in-line arrangement is presented. This study showed that similar flow behaviours exist between the first and second dimples and that the flow behaviours are identical between the second and third cylindrical dimples.
Development of a Flow Injection Based High Frequency Dual Channel Quartz Crystal Microbalance
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Jinxing Liang
2017-05-01
Full Text Available When the quartz crystal microbalance (QCM is used in liquid for adsorption or desorption monitoring based bio- or chemical sensing applications, the frequency shift is not only determined by the surface mass change, but also by the change of liquid characteristics, such as density and viscosity, which are greatly affected by the liquid environmental temperature. A monolithic dual-channel QCM is designed and fabricated by arranging two QCM resonators on one single chip for cancelling the fluctuation induced by environmental factors. In actual applications, one QCM works as a specific sensor by modifying with functional membranes and the other acts as a reference, only measuring the liquid property. The dual-channel QCM is designed with an inverted-mesa structure, aiming to realize a high frequency miniaturized chip and suppress the frequency interference between the neighbored QCM resonators. The key problem of dual-channel QCMs is the interference between two channels, which is influenced by the distance of adjacent resonators. The diameter of the reference electrode has been designed into several values in order to find the optimal parameter. Experimental results demonstrated that the two QCMs could vibrate individually and the output frequency stability and drift can be greatly improved with the aid of the reference QCM.
Pryazhnikov, Maxim; Guzei, Dmitriy; Minakov, Andrey; Rodionova, Tatyana
2017-10-01
In this paper, the study of ferromagnetic nanoparticles behaviour in the constant magnetic field is carried out. For numerical simulation we have used Euler-Lagrange two-component approach. Using numerical simulation we have studied the growth of deposition of nanoparticles on the channel walls depending on the Reynolds number and the position of the magnet. The flow pattern, the concentration field and the trajectory of nanoparticles as a function of the Reynolds number were obtained. The good qualitative and quantitative agreement between numerical simulation and experiments was shown.
Radiative MHD compressible Couette flow in a parallel channel with a naturally permeable wall
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Vyas Paresh
2014-01-01
Full Text Available The paper pertains to investigations of thermal radiation effects on dissipative MHD Couette flow of a viscous compressible Newtonian heat- generating fluid in a parallel plate channel whose one wall is stationary and naturally permeable. Saffman’ slip condition is used at the clear fluid-porous interface. The fluid is considered to be optically thick and the radiative heat flux in the energy equation is assumed to follow Rossel and approximation. The momentum and energy equations have closed form solutions. The effects of various parameters on thermal regime are analyzed through graphs and tables.
Non-Newtonian fluid flow in an axisymmetric channel with porous wall
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M. Hosseini
2013-12-01
Full Text Available In the present article Optimal Homotopy Asymptotic Method (OHAM is used to obtain the solutions of momentum and heat transfer equations of non-Newtonian fluid flow in an axisymmetric channel with porous wall for turbine cooling applications. Numerical method is used for validity of this analytical method and excellent agreement is observed between the solutions obtained from OHAM and numerical results. Trusting to this validity, effects of some other parameters are discussed. The results show that Nusselt number increases with increase of Reynolds number, Prandtl number and power law index.
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.
LES of the channel flow in a non aligned system of coordinates
Energy Technology Data Exchange (ETDEWEB)
Abba, A [Dip. di Matematica ' F. Brioschi' , Politecnico di Milano, Via Bonardi 9, 20133 Milano (Italy); Rolfo, S [School of MACE, University of Manchester, Manchester M60 1QD (United Kingdom); Germano, M, E-mail: antonella.abba@polimi.it [Dip. di Ing. Aeronautica e Spaziale, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino (Italy)
2011-12-22
This work investigates the sensitivity of LES to a rotation of the usual stream-aligned system of coordinates in the case of channel flow at Re{sub {tau}} = 180. In the new reference system the principal axes are not necessarily aligned with the streamwise and the spanwise directions: consequently the mean pressure gradient has two different components. Two different codes and different SGS models have been tested in order to evaluate the sensitivity of the alignment of the grid with the mean stream and the coherent wall structures.
Aaiza, Gul; Khan, Ilyas; Shafie, Sharidan
2015-12-01
Energy transfer in mixed convection unsteady magnetohydrodynamic (MHD) flow of an incompressible nanofluid inside a channel filled with saturated porous medium is investigated. The channel with non-uniform walls temperature is taken in a vertical direction under the influence of a transverse magnetic field. Based on the physical boundary conditions, three different flow situations are discussed. The problem is modelled in terms of partial differential equations with physical boundary conditions. Four different shapes of nanoparticles of equal volume fraction are used in conventional base fluids, ethylene glycol (EG) (C 2 H 6 O 2 ) and water (H 2 O). Solutions for velocity and temperature are obtained discussed graphically in various plots. It is found that viscosity and thermal conductivity are the most prominent parameters responsible for different results of velocity and temperature. Due to higher viscosity and thermal conductivity, C 2 H 6 O 2 is regarded as better convectional base fluid compared to H 2 O.
Zamuraev, V. P.; Kalinina, A. P.
2017-10-01
The control action of the jet and the near-wall energy sources on the shock wave structure of supersonic flow in a channel to create a transonic region is studied. The stable mode of flow with the region characterized by transonic velocities arises. The results of calculations for flat and axisymmetric model are presented. Two formulations of the problem are considered. The first of them is based on the unsteady Euler equations and pulse-periodic energy sources, and the second one is based on the unsteady Navier-Stokes equations closed by k-ω SST turbulence model. The combustion of hydrogen, which is supplied from the holes in the channel walls is considered.
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Yang Liu
2016-08-01
Full Text Available This theoretical study investigates the nonlinear ionic current-voltage characteristics of nano-channels that have weakly overlapping electrical double layers. Numerical simulations as well as a 1-D mathematical model are developed to reveal that the electro-osmotic flow (EOF interplays with the concentration-polarization process and depletes the ion concentration inside the channels, thus significantly suppressing the channel conductance. The conductance may be restored at high electrical biases in the presence of recirculating vortices within the channels. As a result of the EOF-driven ion depletion, a limiting-conductance behavior is identified, which is intrinsically different from the classical limiting-current behavior.
On computations for thermal radiation in MHD channel flow with heat and mass transfer.
Hayat, T; Awais, M; Alsaedi, A; Safdar, Ambreen
2014-01-01
This study examines the simultaneous effects of heat and mass transfer on the three-dimensional boundary layer flow of viscous fluid between two infinite parallel plates. Magnetohydrodynamic (MHD) and thermal radiation effects are present. The governing problems are first modeled and then solved by homotopy analysis method (HAM). Influence of several embedded parameters on the velocity, concentration and temperature fields are described.
The Liner Shipping Fleet Repositioning Problem with Cargo Flows
DEFF Research Database (Denmark)
Tierney, Kevin; Jensen, Rune Møller
2012-01-01
to reposition vessels as cheaply as possible without disrupting the cargo flows of the network. The LSFRP is characterized by chains of interacting activities with a multi-commodity flow over paths defined by the activities chosen. Despite its great industrial importance, the LSFRP has received little attention...... in the literature. We introduce a novel mathematical model of the LSFRP with cargo flows based on a carefully constructed graph and evaluate it on real world data from our industrial collaborator....
Franz, Delbert D.; Melching, Charles S.
1997-01-01
The Full EQuations UTiLities (FEQUTL) model is a computer program for computation of tables that list the hydraulic characteristics of open channels and control structures as a function of upstream and downstream depths; these tables facilitate the simulation of unsteady flow in a stream system with the Full Equations (FEQ) model. Simulation of unsteady flow requires many iterations for each time period computed. Thus, computation of hydraulic characteristics during the simulations is impractical, and preparation of function tables and application of table look-up procedures facilitates simulation of unsteady flow. Three general types of function tables are computed: one-dimensional tables that relate hydraulic characteristics to upstream flow depth, two-dimensional tables that relate flow through control structures to upstream and downstream flow depth, and three-dimensional tables that relate flow through gated structures to upstream and downstream flow depth and gate setting. For open-channel reaches, six types of one-dimensional function tables contain different combinations of the top width of flow, area, first moment of area with respect to the water surface, conveyance, flux coefficients, and correction coefficients for channel curvilinearity. For hydraulic control structures, one type of one-dimensional function table contains relations between flow and upstream depth, and two types of two-dimensional function tables contain relations among flow and upstream and downstream flow depths. For hydraulic control structures with gates, a three-dimensional function table lists the system of two-dimensional tables that contain the relations among flow and upstream and downstream flow depths that correspond to different gate openings. Hydraulic control structures for which function tables containing flow relations are prepared in FEQUTL include expansions, contractions, bridges, culverts, embankments, weirs, closed conduits (circular, rectangular, and pipe
On the validity of the Navier-Stokes equations for nanoscale liquid flows: The role of channel size
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Chong Liu
2011-09-01
Full Text Available In this work, we investigate the validity of the Navier-Stokes (NS equations for nanoscale liquid flows through molecular dynamics simulations. We focus on the role of channel size by considering the fluid-wall interaction. Liquid flows between two planar parallel walls driven by an external force with channel size ranging from 2 to 80 nm are studied. The volumetric flux is computed and the dependence of the volumetric flux on the channel size is explained both qualitatively and quantitatively. It is found that the flow is sensitive to the fluid-wall binding energy and the classical fluid mechanics falls apart in small nanochannels. However, the wall effects become insignificant and the NS equations are valid when the channel size is larger than about 150 molecular diameters (∼ 50 nm.
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Celik Hasan
2015-01-01
Full Text Available Temperature and velocity fields in a vertical channel partially filled with porous medium under mixed convection heat transfer condition are obtained. The heat transfer equation and equation of motion for clear and porous layer regions are written and solved analytically. The nondimensionalization of the governing equations yields two Grashof numbers as Grc and Grd for clear and porous sections where Grd=Da.Grc. The dimensionless governing parameters for the problem are Grc (or Grd, Da, thermal conductivity ratio (i.e., K and thickness of porous layer. The temperature and velocity profiles for different values of Grc, Da, K and thickness of porous layer are plotted and their changes with the governing parameters are discussed. Moreover, the variation of pressure drop with the governing parameters is investigated. The decrease of porous layer thickness or thermal conductivity ratio increases the possibility of the downward flows. Thermal conductivity ratio plays important role on pressure drop, particularly for the channels with high values of Grc/Re.
Study on the Effect of Inlet Fluctuation on Cavitation in a Cone Flow Channel.
Hai, Liu; Shuping, Cao; Xiaohui, Luo
2015-05-01
A mathematical method was conducted to investigate the mechanism of formation of cavitation cloud, while the inlet stream contains a fluctuating flow. Based on the Rayleigh-Plesset equation and the static pressure distribution in a cone flow channel, parameters related to cavitation cloud are estimated, and the collapse pressure of the cavitation cloud is obtained by solving the equation of Mørch's model. Moreover, the effect of the amplitude and frequency of inlet fluctuation on cavitation is studied. Results revealed that the smaller the amplitude, the smaller the cloud and the lower the collapse pressure. And frequency of fluctuating stream was found to have a relative great effect on frequency of peak pressure but not so significant on peak collapse pressure and size of cloud. It is concluded that limiting the inlet fluctuation reduces the erosion and noise generated by cavitation collapse.
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M. K. Chaube
2015-01-01
Full Text Available A mathematical study on creeping flow of non-Newtonian fluids (power law model through a nonuniform peristaltic channel, in which amplitude is varying across axial displacement, is presented, with slip effects included. The governing equations are simplified by employing the long wavelength and low Reynolds number approximations. The expressions for axial velocity, stream function, pressure gradient, and pressure difference are obtained. Computational and numerical results for velocity profile, pressure gradient, and trapping under the effects of slip parameter, fluid behavior index, angle between the walls, and wave number are discussed with the help of Mathematica graphs. The present model is applicable to study the behavior of intestinal flow (chyme movement from small intestine to large intestine. It is also relevant to simulations of biomimetic pumps conveying hazardous materials, polymers, and so forth.
Experimental Investigation of a Synthetic Jet Array in a Laminar Channel Flow
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Trávníček Z.
2013-04-01
Full Text Available The paper deals with an impinging synthetic jet, namely on the case of a synthetic jet array interacting with a laminar channel flow. This arrangement can be useful in many micro-scale applications, such as cooling of micro-electronics. The flow regime in micro-scale is usually laminar with very small Reynolds numbers; therefore synthetic jet array can be used for the profile disturbance and heat transfer enhancement. The paper focuses on the low Reynolds number (in order 102. The working fluid is water and a piezoceramic transducer is used as a moving membrane in the synthetic jet actuator. Experiments are performed with four experimental methods (tin ion visualization, hot wire anemometry in constant temperature mode, laser Doppler vibrometry and particle image velocimetry in three laboratories (at the Eindhoven University of Technology, Netherlands, at the Institute of Thermodynamics CAS, v.v.i. and Technical University of Liberec, both Czech Republic.
Flow structure and heat exchange analysis in internal cooling channel of gas turbine blade
Szwaba, Ryszard; Kaczynski, Piotr; Doerffer, Piotr; Telega, Janusz
2016-08-01
This paper presents the study of the flow structure and heat transfer, and also their correlations on the four walls of a radial cooling passage model of a gas turbine blade. The investigations focus on heat transfer and aerodynamic measurements in the channel, which is an accurate representation of the configuration used in aeroengines. Correlations for the heat transfer coefficient and the pressure drop used in the design of radial cooling passages are often developed from simplified models. It is important to note that real engine passages do not have perfect rectangular cross sections, but include corner fillet, ribs with fillet radii and special orientation. Therefore, this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which possesses very realistic features.
Wall Slip during the Flow of Carbopol Solutions through a Parallel Plate Channel
de Souza Mendes, Paulo R.; Pédron, Jonathan; Pereira, Renata A. B.
2008-07-01
Experiments were performed to investigate the phenomenon of wall slip during the flow of aqueous solutions of carbopol through a parallel plate channel. The Reynolds number is low for all cases investigated, to ensure negligible development length. In the experiments, the pressure drop is measured for different flow rate values, and the results are presented in the form of curves of dimensionless average velocity versus dimensionless wall shear stress. We also performed experiments with glycerol, and the results agreed with the analytical solution available in the literature. Moreover, this agreement ensures the absence of wall slip for this Newtonian case. Comparisons between the experimental and numerical results show that (apparent) wall slip occurs when the wall shear stress is below a threshold stress of a few times the yield stress. Above this threshold, the numerical and experimental curves tend to merge.
Characterization of fluid flow patterns and heat transfer in horizontal channel mixed convection
Energy Technology Data Exchange (ETDEWEB)
Benderradji, A. [University of Batna, Department of Mechanical Engineering, Batna (Algeria); Haddad, A.; Taher, R.; Medale, M.; Abid, C.; Papini, F. [Technopole de Chateau-Gombert, IUSTI-CNRS UMR 6595, Polytech' Marseille, Marseille (France)
2008-10-15
Two mechanisms of roll initiation are highlighted in a horizontal channel flow, uniformly heated from below, at constant heat flux ({gamma}=10, Pr=7, 50{<=}Re{<=}100, 0{<=}Ra{<=}10{sup 6}). The first mechanism is the classical one, it occurs for low Rayleigh numbers and is initiated by the lateral wall effect. The second occurs for higher Rayleigh numbers and combines the previous effect with a supercritical vertical temperature gradient in the lower boundary layer, which simultaneously triggers pairs of rolls in the whole zone in between the two lateral rolls. We have found that in the present configuration, the transition between the two roll initiation mechanisms occurs for Ra/Re{sup 2} {approx}18. Consequently, the heat transfer is significantly enhanced compared to the pure forced convection case owing to the flow pattern responsible of the continuous flooding the heated wall with cold fluid. (orig.)
Verification and validation in CFD for a free-surface gas-liquid flow in channels
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C. Soares
2013-06-01
Full Text Available This work deals with experimental and numerical studies of a 3-D transient free-surface two-phase flow in a bench-scale channel flow. The aim was to determine how well the homogeneous model can predict the fluid dynamics behavior and to validate the model. The model was validated with experimental data acquired for two hydrodynamic situations. The mathematical model was based on the mass conservation equations for liquid and gas phases and on the momentum conservation equation for the mixture, assuming interpenetrating, continuum and homogeneous hypotheses. Turbulence has been considered for the mixture through the standard k-ε model. The numerical methods were the finite volume method with pressure-velocity coupling and a numerical grid on a generalized Cartesian coordinate system. Good qualitative and quantitative agreements were found for both cases, making the prediction of the fluid dynamics behavior quite robust.
Energy Technology Data Exchange (ETDEWEB)
Park, Jong Hark; Chae, Hee Taek; Park, Cheol; Kim, Heon Il
2008-09-15
Since the heat flux of the rod type fuel used in the HANARO, a research reactor being operated in the KAERI, is substantially higher than the heat flux of power reactors, the HANARO fuel has 8 longitudinal fins for enhancing the heat release from the fuel rod surface. This unique shape of a nuclear fuel led us to study the flows and thermal hydraulic characteristics of it. Especially because the flows through the narrow channels built up by these finned rod fuels would be different from the flow characteristics in the coolant channels formed by bare rod fuels, some experimental studies to investigate the flow behaviors and structures in a finned rod bundle were done by other researchers. But because of the very complex geometries of the flow channels in the finned rod bundle only allowed us to obtain limited information about the flow characteristics, a numerical study by a computational fluid dynamics technique has been adopted to elucidate more about such a complicated flow in a finned rod bundle. In this study, for the development of an adequate computational model to simulate such a complex geometry, a mesh sensitivity study and the effects of various turbulence models were examined. The CFD analysis results were compared with the experimental results. Some of them have a good agreement with the experimental results. All linear eddy viscosity turbulence models could hardly predict the secondary flows near the fuel surfaces and in the sub-channel, but the RSM (Reynolds Stress Model) revealed very different results from the eddy viscosity turbulence models. In the transient analysis all turbulence model predicted flow pulsation at the center of a subchannel as well as at the gap between rods in spite of large P/D. The flow pulsation showed different results with turbulence models and the location in the sub-channels.
On the modelling of compressible inviscid flow problems using AUSM schemes
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Hajžman M.
2007-11-01
Full Text Available During last decades, upwind schemes have become a popular method in the field of computational fluid dynamics. Although they are only first order accurate, AUSM (Advection Upstream Splitting Method schemes proved to be well suited for modelling of compressible flows due to their robustness and ability of capturing shock discontinuities. In this paper, we review the composition of the AUSM flux-vector splitting scheme and its improved version noted AUSM+, proposed by Liou, for the solution of the Euler equations. Mach number splitting functions operating with values from adjacent cells are used to determine numerical convective fluxes and pressure splitting is used for the evaluation of numerical pressure fluxes. Both versions of the AUSM scheme are applied for solving some test problems such as one-dimensional shock tube problem and three dimensional GAMM channel. Features of the schemes are discussed in comparison with some explicit central schemes of the first order accuracy (Lax-Friedrichs and of the second order accuracy (MacCormack.
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Yuanyuan Nie
2017-09-01
Full Text Available Vessel traffic flow is a key parameter for channel-through capacity and is of great significance to vessel traffic management, channel and port design and navigational risk evaluation. Based on the study of parameters of characteristics of vessel traffic flow related to channel-through capacity, this paper puts forward a brand-new mathematical model for one-way channel-through capacity in which parameters of channel length, vessel arrival rate and velocity difference in different vessels are involved and a theoretical calculating mechanism for the channel-through capacity is provided. In order to verify availability and reliability of the model, extensive simulation studies have been carried out and based on the historical AIS data, an analytical case study on the Xiazhimen Channel validating the proposed model is presented. Both simulation studies and the case study show that the proposed model is valid and all relative parameters can be readjusted and optimized to further improve the channel-through capacity. Thus, all studies demonstrate that the model is valuable for channel design and vessel management.
McCarroll, R. Jak; Castelle, Bruno; Brander, Robert W.; Scott, Timothy
2015-10-01
Rip currents are a hazard to bathers on surf beaches worldwide, yet due to logistical and ethical concerns there has been minimal examination of how bathers caught in them should attempt to escape. This study presents the first numerical model of simulated bathers escaping from a rip current. An understanding of the underlying coastal geomorphology and hydrodynamics form a critical basis for the model, with the intention that outcomes of the model should be evaluated from a physical science perspective. Field observations of a transverse bar rip channel were used as model inputs. Escape simulations were performed with moderate energy (Hs ≈ 1 m), oblique offshore wave forcing, used to generate two non-stationary, asymmetric flow fields (dominant surfzone exits and dominant recirculation). The model treats bathers as particles that move with the underlying flow, with an additional swimming velocity added, iterating until a safety condition, based on depth and current speed, is satisfied or until a maximum time limit is reached. Simulations compared the strategies of ;stay afloat; and various fixed swim directions, using two bather heights and four swim speeds (up to 0.4 m/s). The overall optimal escape strategy was to swim parallel in the direction of alongshore flow. Time to safety was less for: (i) recirculating flow; (ii) taller bathers; and (iii) greater swim speeds. Across all simulations, 44% of ;floaters; reached safety within 10 min, while 80% of slow swimmers (0.2 m/s) succeeded in the same time interval. This suggests that slow sustainable swimming may be a preferable escape action to floating. Optimal swim direction varied with start location, from onshore (near the shoreline), parallel to shore (mid-rip channel) and diagonally onshore (outer rip channel). At lower swim speeds, the optimal swim direction had greater dependence on the underlying flow field, as opposed to distance to safety, therefore choice of direction is more complex for slower swimmers
Comparison of analytic models of instability of rarefied gas flow in a channel
Energy Technology Data Exchange (ETDEWEB)
Aksenova, Olga A. [St.-Petersburg State University, Department of Mathematics and Mechanics, 198504, Universitetskiy pr., 28, Peterhof, St.-Petersburg (Russian Federation); Khalidov, Iskander A. [St.-Petersburg State Polytechnic University, Department of Mathematics and Mechanics, 195251, Polytechnicheskaya ul., 29, St.-Petersburg (Russian Federation)
2014-12-09
Numerical and analytical results are compared concerning the limit properties of the trajectories, attractors and bifurcations of rarefied gas flows in channels. The cascade of bifurcations obtained in our previous analytical and numerical investigations is simulated numerically for different scattering functions V generalizing the ray-diffuse reflection of gas particles from the surface. The main purpose of numerical simulation by Monte Carlo method is the investigation of the properties of different analytic nonlinear dynamic systems corresponding to rarefied gas flow in a channel. The results are compared as well for the models suggested originally by R. N. Miroshin, as for the approximations considered for the first time or for studied in our subsequent papers. Analytical solutions we obtained earlier for the ray reflection which means only one determined velocity of scattered from the walls gas atoms, generally different from the specular reflection. The nonlinear iterative equation describing a rarefied gas flow in a long channel becomes unstable in some regions of corresponding parameters of V (it means the sensitivity to boundary conditions). The values of the parameters are found from analytical approximations in these regions. Numerical results show that the chaotic behavior of the nonlinear dynamic system corresponds to strange attractors and distinguishes clearly from Maxwellian distribution and from the equilibrium on the whole. In the regions of instability (as the dimension of the attractor increases) the search for a corresponding state requires a lot more computation time and a lot of data (the amount of data required increases exponentially with embedding dimension). Therefore the main complication in the computation is reducing as well the computing time as the amount of data to find a suitably close solution. To reduce the computing time our analytical results are applied. Flow conditions satisfying the requirements to the experiment are
Nag, M.; Rockele, M.; Steudel, S.; Chasin, A.; Myny, K.; Bhoolokam, A.; Willegems, M.; Smout, S.; Vicca, P.; Ameys, M.; Ke, T.H.; Schols, S.; Genoe, J.; Steen, J.L. P.J. van der; Groeseneken, G.; Heremans, P.
2014-01-01
In this study, we report high-quality amorphous indiunrv-galiium-zinc-oxide (a-IGZO) thinfilm transistors (TFTs) fabricated on a polyethylene naphthalate foil using a new back-channel-etch (BCE) process flow. The BCE flow allows a better scalability of TFTs for high-resolution backplanes and related
Directory of Open Access Journals (Sweden)
Sang Soon Hwang
2009-11-01
Full Text Available In fuel cells flow configuration and operating conditions such as cell temperature, humidity at each electrode and stoichiometric number are very crucial for improving performance. Too many flow channels could enhance the performance but result in high parasite loss. Therefore a trade-off between pressure drop and efficiency of a fuel cell should be considered for optimum design. This work focused on numerical simulation of the effects of operating conditions, especially cathode humidity, with simple micro parallel flow channels. It is known that the humidity at the cathode flow channel becomes very important for enhancing the ion conductivity of polymer membrane because fully humidified condition was normally set at anode. To investigate the effect of humidity on the performance of a fuel cell, in this study humidification was set to 100% at the anode flow channel and was changed by 0–100% at the cathode flow channel. Results showed that the maximum power density could be obtained under 60% humidified condition at the cathode where oxygen concentration was moderately high while maintaining high ion conductivity at a membrane.
Lee, Pil Hyong; Hwang, Sang Soon
2009-01-01
In fuel cells flow configuration and operating conditions such as cell temperature, humidity at each electrode and stoichiometric number are very crucial for improving performance. Too many flow channels could enhance the performance but result in high parasite loss. Therefore a trade-off between pressure drop and efficiency of a fuel cell should be considered for optimum design. This work focused on numerical simulation of the effects of operating conditions, especially cathode humidity, with simple micro parallel flow channels. It is known that the humidity at the cathode flow channel becomes very important for enhancing the ion conductivity of polymer membrane because fully humidified condition was normally set at anode. To investigate the effect of humidity on the performance of a fuel cell, in this study humidification was set to 100% at the anode flow channel and was changed by 0-100% at the cathode flow channel. Results showed that the maximum power density could be obtained under 60% humidified condition at the cathode where oxygen concentration was moderately high while maintaining high ion conductivity at a membrane.
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.)
Revisiting the Lie-group symmetry method for turbulent channel flow with wall transpiration
Khujadze, George
2016-01-01
The Lie-group-based symmetry analysis, as first proposed in Avsarkisov et al. (2014) and then later modified in Oberlack et al. (2015), to generate invariant solutions in order to predict the scaling behavior of a channel flow with uniform wall transpiration, is revisited. By focusing first on the results obtained in Avsarkisov et al. (2014), we failed to reproduce two key results: (i) For different transpiration rates at a constant Reynolds number, the mean velocity profiles (in deficit form) do not universally collapse onto a single curve as claimed. (ii) The universally proposed logarithmic scaling law in the center of the channel does not match the direct numerical simulation (DNS) data for the presented parameter values. In fact, no universal scaling behavior in the center of the channel can be detected from their DNS data, as it is misleadingly claimed in Avsarkisov et al. (2014). Moreover, we will demonstrate that the assumption of a Reynolds-number independent symmetry analysis is not justified for th...
Real-Time Flood Forecasting System Using Channel Flow Routing Model with Updating by Particle Filter
Kudo, R.; Chikamori, H.; Nagai, A.
2008-12-01
A real-time flood forecasting system using channel flow routing model was developed for runoff forecasting at water gauged and ungaged points along river channels. The system is based on a flood runoff model composed of upstream part models, tributary part models and downstream part models. The upstream part models and tributary part models are lumped rainfall-runoff models, and the downstream part models consist of a lumped rainfall-runoff model for hillslopes adjacent to a river channel and a kinematic flow routing model for a river channel. The flow forecast of this model is updated by Particle filtering of the downstream part model as well as by the extended Kalman filtering of the upstream part model and the tributary part models. The Particle filtering is a simple and powerful updating algorithm for non-linear and non-gaussian system, so that it can be easily applied to the downstream part model without complicated linearization. The presented flood runoff model has an advantage in simlecity of updating procedure to the grid-based distributed models, which is because of less number of state variables. This system was applied to the Gono-kawa River Basin in Japan, and flood forecasting accuracy of the system with both Particle filtering and extended Kalman filtering and that of the system with only extended Kalman filtering were compared. In this study, water gauging stations in the objective basin were divided into two types of stations, that is, reference stations and verification stations. Reference stations ware regarded as ordinary water gauging stations and observed data at these stations are used for calibration and updating of the model. Verification stations ware considered as ungaged or arbitrary points and observed data at these stations are used not for calibration nor updating but for only evaluation of forecasting accuracy. The result confirms that Particle filtering of the downstream part model improves forecasting accuracy of runoff at
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.
Analytical solutions of heat transfer for laminar flow in rectangular channels
Directory of Open Access Journals (Sweden)
Rybiński Witold
2014-12-01
Full Text Available The paper presents two analytical solutions namely for Fanning friction factor and for Nusselt number of fully developed laminar fluid flow in straight mini channels with rectangular cross-section. This type of channels is common in mini- and microchannel heat exchangers. Analytical formulae, both for velocity and temperature profiles, were obtained in the explicit form of two terms. The first term is an asymptotic solution of laminar flow between parallel plates. The second one is a rapidly convergent series. This series becomes zero as the cross-section aspect ratio goes to infinity. This clear mathematical form is also inherited by the formulae for friction factor and Nusselt number. As the boundary conditions for velocity and temperature profiles no-slip and peripherally constant temperature with axially constant heat flux were assumed (H1 type. The velocity profile is assumed to be independent of the temperature profile. The assumption of constant temperature at the channel’s perimeter is related to the asymptotic case of channel’s wall thermal resistance: infinite in the axial direction and zero in the peripheral one. It represents typical conditions in a minichannel heat exchanger made of metal.
Role of heat advection in a channeled lava flow with power law, temperature-dependent rheology
Filippucci, Marilena; Tallarico, Andrea; Dragoni, Michele
2013-06-01
The cooling of a lava flow, both in the transient and the steady state, is investigated considering that lava rheology is pseudoplastic and dependent on temperature. Lava exits from the vent with constant velocity and flows down a slope under the effect of gravity force inside a channel of rectangular cross section. We consider that cooling of lava is caused by thermal radiation into the atmosphere and thermal conduction at the channel walls and at the ground. The heat equation is solved numerically in a 3-D computational domain, and the solution is tested to evaluate the numerical errors. We study the steady state and the initial transient period of lava cooling. Results indicate that the advective heat transport significantly modifies the cooling rate of lava, slowing down the cooling process. Since the lava velocity depends on temperature, the cooling rate depends on the effusion temperature. Velocity profiles are modified during cooling showing two marginal static zones where the crust can form and remain stable. The fraction of crust coverage is calculated under the assumption that the solid lava is a plastic body with temperature-dependent yield strength. We numerically confirm that heat advection cannot be neglected in the mechanism of formation of lava tubes.
Lagrangian statistics in turbulent channel flow: implications for Lagrangian stochastic models
Stelzenmuller, Nickolas; Polanco, Juan Igancio; Vinkovic, Ivana; Mordant, Nicolas
2016-11-01
Lagrangian acceleration and velocity correlations in statistically one-dimesional turbulence are presented in the context of the development of Lagrangian stochastic models of inhomogeneous turbulent flows. These correlations are measured experimentally by 3D PTV in a high aspect ratio water channel at Reτ = 1450 , and numerically from DNS performed at the same Reynolds number. Lagrangian timescales, key components of Lagrangian stochastic models, are extracted from acceleration and velocity autocorrelations. The evolution of these timescales as a function of distance to the wall is presented, and compared to similar quantities measured in homogeneous isotropic turbulence. A strong dependance of all Lagrangian timescales on wall distance is present across the width of the channel. Significant cross-correlations are observed between the streamwise and wall-normal components of both acceleration and velocity. Lagrangian stochastic models of this flow must therefore retain dependance on the wall-normal coordinate and the components of acceleration and velocity, resulting in significantly more complex models than those used for homogeneous isotropic turbulence. We gratefully acknowledge funding from the Agence Nationale de la Recherche, LabEx Tec 21, and CONICYT Becas Chile.
Laminar thermally developing flow in rectangular channels and parallel plates: uniform heat flux
Smith, Andrew N.; Nochetto, Horacio
2014-05-01
Numerical simulations were conducted for thermally developing laminar flow in rectangular channels with aspect ratios ranging from 1 to 100, and for parallel plates. The simulations were for laminar, thermally developing flow with H1 boundary conditions: uniform heat flux along the length of the channel and constant temperature around the perimeter. In the limit as the non-dimensional length, x* = x/(D h RePr), goes to zero, the Nusselt number is dependent on x* to the negative exponent m. As the non-dimensional length goes to infinity the Nusselt number approaches fully developed values that are independent of x*. General correlations for the local and mean heat transfer coefficients are presented that use an asymptotic blending function to transition between these limiting cases. The discrepancy between the correlation and the numerical results is less than 2.5 % for all aspect ratios. The correlations presented are applicable to all aspect ratios and all non-dimensional lengths, and decrease the discrepancy relative to existing correlations.
Zhang, Jingxian; Yao, Zhaohui; Hao, Pengfei
2016-11-01
Flow in a rectangular channel with superhydrophobic (SH) top and bottom walls was investigated experimentally. Different SH surfaces, including hierarchical structured surfaces and surfaces with different micropost sizes (width and spacing) but the same solid fraction, were fabricated and measured. Pressure loss and flow rate in the channel with SH top and bottom walls were measured, with Reynolds number changing from 700 to 4700, and the corresponding friction factor for the SH surface was calculated. The statuses of the air plastron on different SH surfaces were observed during the experiment. In our experiment, compared with the experiment for the smooth surface, drag reductions were observed for all SH surfaces, with the largest drag reduction of 42.2%. It was found that the hierarchy of the microstructure can increase the drag reduction by decreasing the solid fraction and enhancing the stability of the air-water interface. With a fixed solid fraction, the drag reduction decreases as the post size (width and spacing) increases, due to the increasing curvature and instability effects of the air-water interface. A correlation parameter between the contact angle hysteresis, the air-water interface stability, and the drag reduction of the SH surfaces was found.
Temperature distribution on the MEA surface of a PEMFC with serpentine channel flow bed
Wang, Maohai; Guo, Hang; Ma, Chongfang
Knowledge of the temperature distribution on the membrane electrode assembly (MEA) surface and heat transfer processes inside a proton exchange membrane fuel cell (PEMFC) is helpful to improvement of cell reliability, durability and performance. The temperature fields on the surface of MEA fixed inside a proton exchange membrane fuel cell with a serpentine channel flow bed were measured by infrared imaging technology under non-humidification conditions. The temperature distributions over the MEA surface under whole channel region were achieved. The experimental results show that the downstream temperatures are higher than the upstream. The hot region on the MEA surface is easy to locate from the infrared temperature image. The mean temperature on the MEA surface and the cell temperature both increase with the current density. Higher current density makes the non-uniformity of temperature distribution on the MEA surface worse. The loading time significantly affects the temperature distribution. Compared with the electrical performance of the cell, the MEA's temperatures need much more time to reach stable. The results indicate that isothermal assumption is not appropriate for a modeling of PEMFCs, and monitoring the temperature of external surface of the flow field plate or end plate cannot supply accurate reference to control the temperatures on MEA surface.
Inverse acoustooptic problem: Coherent summing of optical beams into a single optical channel
Antonov, S. N.; Vainer, A. V.; Proklov, V. V.; Rezvov, Yu. G.
2007-05-01
A highly efficient summing of mutually coherent beams (channels) into a single beam with the same divergence and aperture (an inverse acoustooptic problem) is realized via diffraction in a Bragg cell. The multibeam field to be converged is formed as a result of the diffraction (splitting) of a single laser beam. Theoretical and experimental evidence is obtained for the fact that the repeated diffraction can provide a highly efficient (up to 100%) reconstruction of beam with initial parameters. The experiments are performed with a single-mode laser radiation at 0.63 μm and multimode radiation at 0.96 μm. The virtually attained summing efficiency is on the order of 70%. The factors that act to diminish the experimental efficiency below the predicted value, the ways to raise the efficiency, and possible applications of the results of this study are discussed.
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.
Chavan, Rutuja; Kumar, Bimlesh
2017-09-01
Experimental investigations have been carried out to study morpho-hydraulic characteristics such as scour geometry and turbulent flow properties around tandem piers in alluvial channels. Experiments were carried out in a plane sand bed with two circular piers of same diameter arranged in tandem manner under no seepage, 10% seepage and 20% seepage conditions. Downward seepage minimizes the scour depth around piers and restrains the development of scour depth with time. Strong reversal flow is found near the bed at upstream of piers and near free surface at downstream of piers where velocity and Reynolds shear stress are found to be negative which reduce in magnitude with downward seepage. The flow is more critical within the gap between two piers where velocity is lesser near free surface and gradually increasing towards bed. Quadrant analysis shows that contribution of each event to the total Reynolds shear stress increases with downward seepage. Sedimentation effect prevails within the scour hole whereas outside the scour hole erosive forces become more dominant. Reduced reversal flow at upstream of pier because of downward seepage results in decreasing higher order moments and turbulent kinetic energy. At downstream of piers, secondary currents are dominant due to wake vortices. Strouhal number decreases in case of seepage runs than no seepage condition.
Vibration energy harvesting in a small channel fluid flow using piezoelectric transducer
Energy Technology Data Exchange (ETDEWEB)
Hassan, Md. Mehedi, E-mail: buetmehedi10@gmail.com; Hossain, Md. Yeam, E-mail: yeamhossain@gmail.com; Mazumder, Rakib, E-mail: rakibmazumder46075@gmail.com; Rahman, Roussel, E-mail: roussel.rahman@gmail.com; Rahman, Md. Ashiqur, E-mail: ashiqurrahman@me.buet.ac.bd [Department of Mechanical Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka-1000 (Bangladesh)
2016-07-12
This work is aimed at developing a way to harvest energy from a fluid stream with the application of piezoelectric transducers in a small channel. In this COMSOL Multiphysics based simulation study, it is attempted to harvest energy from the abundant renewable source of energy available in the form of kinetic energy of naturally occurring flow of fluids. The strategy involves harnessing energy from a fluid-actuator through generation of couples, eddies and vortices, resulting from the stagnation and separation of flow around a semi-circular bluff-body attached to a cantilever beam containing a piezoceramic layer. Fluctuation of fluidic pressure impulse on the beam due to vortex shedding and varying lift forces causes the flexible cantilever beam to oscillate in the direction normal to the fluid flow in a periodic manner. The periodic application and release of a mechanical strain upon the beam effected a generation of electric potential within the piezoelectric layer, thus enabling extraction of electrical energy from the kinetic energy of the fluid. The piezoelectric material properties and transducer design are kept unchanged throughout the study, whereas the configuration is tested with different fluids and varying flow characteristics. The size and geometry of the obstructing entity are systematically varied to closely inspect the output from different iterations and for finding the optimum design parameters. The intermittent changes in the generated forces and subsequent variation in the strain on the beam are also monitored to find definitive relationship with the electrical energy output.
Reconstruction of the past flow channels in the early Holocene at Lake Tonle Sap, Cambodia
Haraguchi, T.; Yonenobu, H.; Tokunaga, T.; Shimoda, I.
2013-05-01
Lake Tonle Sap is located at the central part of Cambodia, South-East Asia. In rainy season, the water body swells with the water depth accordingly increasing from 1 up to 10 meters due to a pulsive intrusion from the Mekong River. The lake is therefore a vital reservoir that protects the region from flooding. It is paleolimnologically important to better understand how the lake has gained the function controlling water balance of this region. We undertook an extensive echo-sounding exploration at the lake in order to clarify the subsurface structure of Lake Tonle Sap. The survey was conducted in rainy seasons from 2009 to 2012. Sediment cores were collected at three sites at the middle part of the lake. Echo sounding was undertaken over the whole part of the lake using a single-channel sub-bottom profiling system (Stratabox, SyQwest Inc.). A prominent sound frequency of 10 KHz was selected in order to observe structure of reflectance planes up to the 40-m depth. In consequence, we discovered deposited valleys forming a complex network of past flow channels. The subsurface structure of the lake bed was mostly complacent showing a strongly reflecting plane observed at the depth of 1-2 meters; the sediments mainly consisted of mud. A number of valley-shaped reflecting planes were observed at the depth of 10-14 meters. Radiocarbon dates of carbonaceous materials collected at the vally bottom were around 10 ka calBP. A 3-D reconstruction presented a complex network of deposited flow channels.
Termini, Donatella
2013-04-01
Recent catastrophic events due to intense rainfalls have mobilized large amount of sediments causing extensive damages in vast areas. These events have highlighted how debris-flows runout estimations are of crucial importance to delineate the potentially hazardous areas and to make reliable assessment of the level of risk of the territory. Especially in recent years, several researches have been conducted in order to define predicitive models. But, existing runout estimation methods need input parameters that can be difficult to estimate. Recent experimental researches have also allowed the assessment of the physics of the debris flows. But, the major part of the experimental studies analyze the basic kinematic conditions which determine the phenomenon evolution. Experimental program has been recently conducted at the Hydraulic laboratory of the Department of Civil, Environmental, Aerospatial and of Materials (DICAM) - University of Palermo (Italy). The experiments, carried out in a laboratory flume appositely constructed, were planned in order to evaluate the influence of different geometrical parameters (such as the slope and the geometrical characteristics of the confluences to the main channel) on the propagation phenomenon of the debris flow and its deposition. Thus, the aim of the present work is to give a contribution to defining input parameters in runout estimation by numerical modeling. The propagation phenomenon is analyzed for different concentrations of solid materials. Particular attention is devoted to the identification of the stopping distance of the debris flow and of the involved parameters (volume, angle of depositions, type of material) in the empirical predictive equations available in literature (Rickenmanm, 1999; Bethurst et al. 1997). Bethurst J.C., Burton A., Ward T.J. 1997. Debris flow run-out and landslide sediment delivery model tests. Journal of hydraulic Engineering, ASCE, 123(5), 419-429 Rickenmann D. 1999. Empirical relationships
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.
Solving the Liner Shipping Fleet Repositioning Problem with Cargo Flows
DEFF Research Database (Denmark)
Tierney, Kevin; Askelsdottir, Björg; Jensen, Rune Møller
2015-01-01
to reposition vessels as cheaply as possible without disrupting cargo flows. The LSFRP is characterized by chains of interacting activities with a multicommodity flow over paths defined by the activities chosen. Despite its industrial importance, the LSFRP has received little attention in the literature. We...... introduce a novel mathematical model and a simulated annealing algorithm for the LSFRP with cargo flows that makes use of a carefully constructed graph; we evaluate these approaches using real-world data from our industrial collaborator. Additionally, we compare the performance of our approach against...