Potential flow through channel constriction.
Lee, J.K.
1984-01-01
Potential flow through an eccentric, normal constriction of zero thickness in an infinitely long, straight channel of constant width and unit depth is studied by use of a Schwarz-Christoffel transformation. The transformation is integrated by a direct approach. Parametric equations for streamlines are obtained and used to compute an average streamline length for a potential-flow field. -from ASCE Publications Information
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.
Continental Lower-crustal Flow: Channel Flow and Laminar Flow
LI, Dewei
Numerous geological, geophysical and geochemical investigations and finite element modeling indicate that crustal flow layers exist in the continental crust. Both channel flow model and laminar flow model have been created to explain the flow laws and flow mechanisms. As revealed by the channel flow model, a low-viscosity channel in middle to lower crust in orogen or plateau with thick crust and high elevation would flow outward from mountain root in response to lateral pressure gradient resulted from topographic loading or to denudation. However, according to the laminar flow model proposed based on investigation of the Qinghai-Tibet plateau, circulative movement of crustal lithologies with different rheological properties between basin and orogen would occur, under the driving forces resulted from dehydration and melting of subduction plate on active continental margin and from thermal energy related to upwelling and diapiring of intercontinental mantle plume or its gravitational interactions. Similarly, when driven by gravity, the softened or melted substances of the lower crust in a basin would flow laterally toward adjacent mountain root, which would result in a thinned basin crust and a thickened orogenic crust. Partially melted magma within the thickened orogenic lower crust would cause vertical movement of metamorphic rocks of lower to middle crust due to density inversion, and the vertical main stress induced by thermal underplating of lower crust would in turn lead to formation of metamorphic core complexes and low-angle detachment fault systems. Lateral spreading of uplifting mountain due to gravitation potential would result in thrust fault systems on the border between mountain and basin. Meanwhile, detritus produced synchronously by intense erosion of uplifting mountain would be transported and deposited along the marginal deep depression in the foreland basin dragged by lower crust flow. Channel flow is similar to laminar flow in a variety of aspects
TRANSITIONAL FLOW IN CHANNEL JUNCTIONS
Institute of Scientific and Technical Information of China (English)
NI Han-gen; LIU Ya-kun
2004-01-01
On the basis of energy and continuity equations a simple one-dimensional formulation was proposed to predict the transitional flow at an open-channel junction. An empilical relation between the junction losses, the junction angle, and the discharge ratio was suggested which agrees well with the experimental results. The results calculated by the present formulation for the depth ratio were compared with the results of earlier one-dimensional formulations and experiments. It is found that the present results coincide better with experiments than those of others.
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 in...
An experimental study of rip channel flow
DEFF Research Database (Denmark)
Drønen, Nils Kjetil; Karunarathna, H.; Fredsøe, Jørgen;
2002-01-01
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......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...
Anisotropic flow in striped superhydrophobic channels
Zhou, Jiajia; Schmid, Friederike; Vinogradova, Olga I
2012-01-01
We report results of dissipative particle dynamics simulations and develop a semi-analytical theory and of an anisotropic flow in a parallel-plate channel with two superhydrophobic striped walls. Our approach is valid for any local slip at the gas sectors and an arbitrary distance between the plates, ranging from a thick to a thin channel. It allows us to optimize area fractions, slip lengths, channel thickness and texture orientation to maximize a transverse flow. Our results may be useful for extracting effective slip tensors from global measurements, such as the permeability of a channel, in experiments or simulations, and may also find applications in passive microfluidic mixing.
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.
Parameter estimation in channel network flow simulation
Institute of Scientific and Technical Information of China (English)
Han Longxi
2008-01-01
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.
Axially shaped channel and integral flow trippers
International Nuclear Information System (INIS)
A fuel assembly is described comprising fuel rods positioned in spaced array by upper and lower tie-plates, an open ended flow channel surrounding the array for conducting coolant upward between a lower support plate having coolant communicated thereto to an upper support grid having a steam/water outlet communicated thereto. The flow channel surrounds the array for conducting coolant about the fuel rods. The open ended channel has a polygon shaped cross section with the channel constituting a closed conduit with flat side sections connected at corners to form the enclosed conduit; means separate from the channel for connecting the upper and lower tie-plates together and maintaining the fuel rods in spaced array independent of the flow channel. The improvement in the flow channel comprises tapered side walls. The tapered side walls extend from an average thick cross section adjacent the lower support plate to an average thin cross section adjacent the upper core grid whereby the channel is reduced in thickness adjacent the upper core grid to correspond with the reduced pressure adjacent the upper core grid
Axially shaped channel and integral flow trippers
Energy Technology Data Exchange (ETDEWEB)
Crowther, R.L.; Johansson, E.B.; Matzner, B.
1988-06-07
A fuel assembly is described comprising fuel rods positioned in spaced array by upper and lower tie-plates, an open ended flow channel surrounding the array for conducting coolant upward between a lower support plate having coolant communicated thereto to an upper support grid having a steam/water outlet communicated thereto. The flow channel surrounds the array for conducting coolant about the fuel rods. The open ended channel has a polygon shaped cross section with the channel constituting a closed conduit with flat side sections connected at corners to form the enclosed conduit; means separate from the channel for connecting the upper and lower tie-plates together and maintaining the fuel rods in spaced array independent of the flow channel. The improvement in the flow channel comprises tapered side walls. The tapered side walls extend from an average thick cross section adjacent the lower support plate to an average thin cross section adjacent the upper core grid whereby the channel is reduced in thickness adjacent the upper core grid to correspond with the reduced pressure adjacent the upper core grid.
Axially shaped channel and integral flow trippers
Energy Technology Data Exchange (ETDEWEB)
Crowther, R.L. Jr.; Johansson, E.B.; Matzner, B.
1992-02-11
This patent describes a fuel assembly. It comprises: fuel rods positioned in spaced array by upper and lower tie-plates, and open ended flow channel surrounding the array for conducting coolant upward between a lower support plate having coolant communicated thereto to an upper support grid having a steam/water outlet communicated thereto. The flow channel surrounding the array for conducting coolant about the fuel rods; the open ended channel having a polygon shaped cross section with the channel constituting a closed conduit with flat side sections connected at corners to form the enclosed conduit; means separate from the channel for connecting the upper and lower tie-plates together and maintaining the fuel rods in spaced array independent of the flow channel, the improvement in the flow channel comprising tapered side walls, the tapered side walls extending from an average thick cross section adjacent the lower support plate to an average thin cross section adjacent the upper core grid whereby the channel is reduced in thickness adjacent the upper core grid to correspond with the reduced pressure adjacent the upper core grid.
Bulk flow scaling for turbulent channel and pipe flows
Chen, Xi; She, Zhen-Su
2016-01-01
We report a theory deriving bulk flow scaling for canonical wall-bounded flows. The theory accounts for the symmetries of boundary geometry (flat plate channel versus circular pipe) by a variational calculation for a large-scale energy length, which characterizes its bulk flow scaling by a simple exponent, i.e. $m=4$ for channel and 5 for pipe. The predicted mean velocity shows excellent agreement with several dozen sets of quality empirical data for a wide range of the Reynolds number (Re), with a universal bulk flow constant $\\kappa\\approx0.45$. Predictions for dissipation and turbulent transport in the bulk flow are also given, awaiting data verification.
Elastic turbulence in a curvilinear channel flow
Jun, Yonggun
2011-01-01
We report detailed quantitative studies of elastic turbulence in a curvilinear channel flow in a dilute polymer solution of high molecular weight polyacrylamide in a high viscosity water-sugar solvent. Detailed studies of the average and rms velocity and velocity gradients profiles reveal an emergence of the boundary layer associated with the nonuniform distribution of the elastic stresses across the channel. The characteristic boundary width is independent of the Weissenberg number Wi and proportional to the channel width that follows from our early investigations of the boundary layer in elastic turbulence of different flow geometries. The appearance of the characteristic spatial scales of the order of the boundary layer width of both velocity and velocity gradient in the correlation functions of the velocity and velocity gradient fields in a bulk flow suggests that rare and strong parcels of excessive elastic stresses, concentrated in the boundary layer, are ejected into the bulk flow similar to jets obser...
Secondary Flow Effects in Relatively Narrow Channels
Institute of Scientific and Technical Information of China (English)
Rudolf Dvo(r)ák
2003-01-01
Secondary flow effects were discussed in numerous papers at the past ISAIF Symposia, mainly in connection with turbine or compressor cascades[1]. This paper will complement these papers by looking at the problem from the channel (or blade passages) geometry point of view. If we describe as secondary flows any flows in planes perpendicular to the main flow direction, then there are at least three kinds of secondary flows in a typical turbine rotor cascade: - secondary flows of the 1st kind, generated by centrifugal forces in closed curved channels, - secondary flows of the 2nd kind, generated by interacting boundary layers, mainly in corners (this will include even the horseshoe vortices), - secondary flows due to mass inflow through the tip clearance. Quite often all the secondary flow vortices merge downstream into a passage vortex with a non-negligible contribution to the channel (cascade) losses, and it is worth investigating the individual contributions to these losses to take them into account in the design procedure.
Transverse flow in thin superhydrophobic channels
Feuillebois, Francois; Vinogradova, Olga I
2010-01-01
We provide some general theoretical results to guide the optimization of transverse hydrodynamic phenomena in superhydrophobic channels. Our focus is on the canonical micro- and nanofluidic geometry of a parallel-plate channel with an arbitrary two-component (low-slip and high-slip) coarse texture, varying on scales larger than the channel thickness. By analyzing rigorous bounds on the permeability, over all possible patterns, we optimize the area fractions, slip lengths, geometry and orientation of the surface texture to maximize transverse flow. In the case of two aligned striped surfaces, very strong transverse flows are possible. Optimized superhydrophobic surfaces may find applications in passive microfluidic mixing and amplification of transverse electrokinetic phenomena.
Flag flutter in inviscid channel flow
Alben, Silas
2014-01-01
Using nonlinear vortex-sheet simulations, we determine the region in parameter space in which a straight flag in a channel-bounded inviscid flow is unstable to flapping motions. We find that for heavier flags, greater confinement increases the size of the region of instability. For lighter flags, confinement has little influence. We then compute the stability boundaries analytically for an infinite flag, and find similar results. For the finite flag we also consider the effect of channel walls on the large-amplitude periodic flapping dynamics. We find that multiple flapping states are possible but rare at a given set of parameters, when periodic flapping occurs. As the channel walls approach the flag, its flapping amplitude decreases roughly in proportion to the near-wall distance, for both symmetric and asymmetric channels. Meanwhile, its dominant flapping frequency and mean number of deflection extrema (or "wavenumber") increase in a nearly stepwise fashion. That is, they remain nearly unchanged over a wide...
Topology optimization of Channel flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan; Sigmund, Ole; Haber, R. B.
2005-01-01
]. Further, the inclusion of inertia effects significantly alters the physics, enabling solutions of new classes of optimization problems, such as velocity--driven switches, that are not addressed by the earlier method. Specifically, we determine optimal layouts of channel flows that extremize a cost...... 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....
Scour monitoring via turbulent open channel flow
International Nuclear Information System (INIS)
Scour is the leading cause of bridge failure in the United States. It can result in the loss of lives and costs millions to repair the damage. A novel method is proposed for monitoring scour that exploits the turbulence in natural channels. The method utilizes the dynamic pressure associated with the turbulent velocity fluctuations in the flow to excite a flexible plate. A semi-empirical model is developed to describe the interaction of turbulent open channel flow with the plate. The model describes the variation of turbulent velocity fluctuations across the flow depth in an open channel resulting in a method for determining the average dynamic pressure on the flexible plate. The dynamic response of the plate is then modeled by superimposing the response of multiple modes of the disk to the random, turbulent dynamic pressure spectrum. The model is verified considering the pressure integration across the plate surface to ensure converged solutions. Due to the uncertainties in the material properties of the plate, the experimentally determined natural frequencies and vibration measurements are used to calibrate the model. The calibrated model predictions are then compared against an independent dataset for validation. In addition to describing the physical operation of the device, the semi-empirical model is also employed to optimize the field device. Measurements made using the field device also confirmed the model results, even in a non-design, misaligned flow condition. (paper)
Interannual variability in the Yucatan Channel flow
Athié, Gabriela; Sheinbaum, Julio; Leben, Robert; Ochoa, José; Shannon, Michael R.; Candela, Julio
2015-03-01
Mooring measurements in the Yucatan Channel, from May 2010 to May 2011 and from July 2012 to June 2013 yield a mean transport of 27 and 25 Sv, respectively, with a subinertial standard deviation of 3.5 Sv. These mean transport values are higher than the 23 Sv reported from 21 months of similar measurements (1999-2001). Analysis of low-frequency variations of a transport proxy based on 20 years of altimetry data indicates that during 1999-2001, the flow through Yucatan Channel was anomalously low. This suggests that a sizable compensation through other channels off the Gulf of Mexico is required to match the transport cable measurements of the Florida Current at 27°N.
Flow in channels with superhydrophobic trapezoidal textures
Nizkaya, Tatiana V; Vinogradova, Olga I
2013-01-01
Superhydrophobic one-dimensional surfaces reduce drag and generate transverse hydrodynamic phenomena by combining hydrophobicity and roughness to trap gas bubbles in a microscopic textures. Recent work in this area has focused on specific cases of superhydrophobic stripes. Here we study theoretically and numerically the hydrodynamic flow in a channel with a superhydrophobic trapezoidal texture. These allow us to evaluate the drag reduction and anisotropy of the flow for various trapezoidal reliefs. Our results provide a framework for the rational design of superhydrophobic surfaces for microfluidic applications.
Flow in channels with superhydrophobic trapezoidal textures
Nizkaya, Tatiana V.; Asmolov, Evgeny S.; Vinogradova, Olga I.
2013-01-01
Superhydrophobic one-dimensional surfaces reduce drag and generate transverse hydrodynamic phenomena by combining hydrophobicity and roughness to trap gas bubbles in microscopic textures. Recent works in this area have focused on specific cases of superhydrophobic stripes. Here we provide some theoretical results to guide the optimization of the forward flow and transverse hydrodynamic phenomena in a parallel-plate channel with a superhydrophobic trapezoidal texture, varying on scales larger ...
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
NUMERICAL SIMULATION OF SKIMMING FLOW OVER MILD STEPPED CHANNEL
Institute of Scientific and Technical Information of China (English)
DONG Zhi-yong; LEE Joseph Hun-wei
2006-01-01
Numerical simulation of stepped channel flow was conducted using turbulence models based on the VOF technique. Stepped channel flow is a complicated air-water two-phase flow with free surface, which can be divided into three flow regimes: skimming flow, nappe flow and transition flow. The characteristics of skimming flow over mild stepped channel was investigated, including friction factors, air concentration profiles velocity field, clear-water and bulked depths, static pressure, etc. Smooth channel flow was also simulated to compare the hydraulic characteristics of the stepped channel flow with the smooth one. Comparisons between the computed and the measured were made. Furthermore, comparison of the computed air concentration with Straub and Anderson's data was also performed. The Fluent 6.1 software was employed to conduct this numerical simulation work.
Transient MHD flow through elliptic channel
International Nuclear Information System (INIS)
The alternating direction implicit(ADI) method and five point difference formula is applied to obtain numerical solution of transient MHD flow through non conducting elliptic channel, under the influence of uniform magnetic field. It is also assumed that the flow is symmetrical about major and minor axes. The five point difference formula is applied for discretizing the equations at grid points of unsymmetrical nature. Velocities and induced magnetic field at different grid points of the cross section are determined. The points at which the velocity is maximum is determined for an ellipse whose major and minor axes are in the ratio 6:4, for Hartmann number 1 and 5 and magnetic Prandtl number 10-7. Graphs have been drawn showing velocity distribution along different cross sections parallel to major and minor axes. (author). 5 figs., 6 refs
Static flow instability in subcooled flow boiling in parallel channels
International Nuclear Information System (INIS)
A series of tests for static flow instability or flow excursion (FE) at conditions applicable to the proposed Advanced Neutron Source reactor was completed in parallel rectangular channels configuration with light water flowing vertically upward at very high velocities. True critical heat flux experiments under similar conditions were also conducted. The FE data reported in this study considerably extend the velocity range of data presently available worldwide. Out of the three correlations compared, the Saha and Zuber correlation had the best fit with the data. However, a modification was necessary to take into account the demonstrated dependence of the Stanton (St) and Nusselt (Nu) numbers on subcooling levels, especially in the low subcooling regime
Free-Molecular Gas Flow in Narrow (Nanoscale) Channel
Levdansky, V.V.; Roldugin, V.I.; Žďanov, V.M.; Ždímal, V. (Vladimír)
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.
Borders of disorder: in turbulent channel flow
Malkus, Willem V. R.
2003-08-01
A quantitative theory of the average features of turbulent flow in a channel is described without the introduction of empirical parameters. The qualitative problem consists of maximizing the dissipation rate of the mean flow subject to the Rayleigh condition that the mean flow has no inflections. The quantitative features result from a boundary stability study which determines a smallest scale of motion in the transport of momentum. The velocity fields satisfying these conditions, the averaged equations and the boundary conditions uniquely determine an entire mean velocity profile at all Reynolds numbers within ten per cent of the data. The maximizing condition for the reproducibility of averages emerges from the Navier Stokes equations as a consequence of a novel definition of nonlinear instability. The smallest scale of motion results from a theory for a time-dependent re-stabilization of the boundary layer following a disruptive instability. Computer reassessment of the several asymptotic estimates of the critical boundary eigenstructure can establish the limits of validity of the quantitative results.
Upgrade of Dhruva fuel channel flow instrumentation
International Nuclear Information System (INIS)
Dhruva, a 100 MW Heavy Water moderated and cooled, vertical tank-type Research Reactor, using metallic natural Uranium fuel has flow instrumentation for all the 144 fuel channels, consisting of venturi and triplicate DP gauges for each fuel channel. These gauges provide contacts for generation of reactor trip on low flow through fuel channel. These DP gauges were facing numerous generic and ageing related failures over the years and was also difficult to maintain owing to obsolescence. While considering an upgrade for these DP gauges, it was also planned to replace the existing Coolant Low Flow Trip (CLFT) system with a computer based Reactor Trip Logic System (RTLS). Being a retrofit job, the existing panels for mounting the gauges, cable layout, impulse tubing layout, etc. were retained, thereby simplifying the site execution, reducing reactor down time and also reducing person-milli-Sievert consumption. A customized Electronic DP Indicating Switch (EDPIS) was conceptualized for achieving these objectives. Such a design, utilizing a standard DP transmitter with customized electronic circuitry, was developed, evaluated and finalized after a series of factory trials, field trials and prototyping. The instrument design included contact input for existing CLFT system and also provision for 4-20 mA current output for the proposed computer based RTLS. The display and form factor of the instrument remained identical to older one and ensures familiarity of O and M personnel. Since EDPIS is classified as Safety Class IA, stringent type tests, hardware FMEA and V and V of the micro-controller software were carried out as per the requirements laid down by relevant standards for qualification of these instruments. Being a customized instrument, the manufacturing process was closely monitored and was followed by stringent QA plan and acceptance tests. A total of 396 gauges were replaced in a phased manner during scheduled fuelling outages and thereby did not affect reactor
VELOCITY PROFILES OF TURBULENT OPEN CHANNEL FLOWS
Institute of Scientific and Technical Information of China (English)
WANG Dianchang; WANG Xingkui; YU Mingzhong; LI Danxun
2001-01-01
The log-law and the wake law of velocity profile for open channel flows are discussed and compared in this paper. Experimental data from eight sources are used to verify the velocity distribution models.The effect of bed level on the velocity profile is analyzed. A formula to calculate the maximum velocity is proposed. In the region of y ＜δm , the velocity profile approximately follows the log-law. For the region of y ＞δm , the effect of the aspect ratio is considered. A new velocity profile model on the basis of log-law that can unify all of the hydraulic bed roughness is presented.
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. ...
Magnetohydrodynamic channel flows with weak transverse magnetic fields.
Rothmayer, A P
2014-07-28
Magnetohydrodynamic flow of an incompressible fluid through a plane channel with slowly varying walls and a magnetic field applied transverse to the channel is investigated in the high Reynolds number limit. It is found that the magnetic field can first influence the hydrodynamic flow when the Hartmann number reaches a sufficiently large value. The magnetic field is found to suppress the steady and unsteady viscous flow near the channel walls unless the wall shapes become large. PMID:24936018
Covert Flow Graph Approach to Identifying Covert Channels
Directory of Open Access Journals (Sweden)
XiangMei Song
2011-12-01
Full Text Available In this paper, the approach for identifying covert channels using a graph structure called Covert Flow Graph is introduced. Firstly, the construction of Covert Flow Graph which can offer information flows of the system for covert channel detection is proposed, and the search and judge algorithm used to identify covert channels in Covert Flow Graph is given. Secondly, an example file system analysis using Covert Flow Graph approach is provided, and the analysis result is compared with that of Shared Resource Matrix and Covert Flow Tree method. Finally, the comparison between Covert Flow Graph approach and other two methods is discussed. Different from previous methods, Covert Flow Graph approach provides a deep insight for system’s information flows, and gives an effective algorithm for covert channel identification.
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 sce
Flow and cooling in narrow, vertical rectangular channels
International Nuclear Information System (INIS)
Laminar flows and energy transfers in narrow, vertical rectangular channels has gained considerable attention in recent years. the cooling channels of TR-2 reactor of CNAEM research center are same and the width of channels is 2.1 mm. Natural convention cooling in these channels, in case of a loss of forced circulation cooling, as would happen in a accident, has utmost importance. A simple open loop experiment was set up in Nuclear Engineering Dep. for the simulation of TR-2 channels. The dummy fuel plates defining cooling channels were heated electrically and temperature measurements were made by thin wire thermocouples. The fluid used at the moment is air. Constant heat flux case was studied only. For the comparison purposes, simplified forms of Navie-Stokes equations for free convention cooling and incompressible flows were solved also on a variable mesh grid by relaxation technique. Flow and temperature distributions inside the channel nad some integral parameters, such as Nu number, were obtained
Container terminals in Europe : their position in marketing channel flows
Wiegmans, B.W.; Nijkamp, P.; Rietveld, P.
2001-01-01
This paper aims to address the linkage between logistics (in particular, the management of marketing channel flows) and transport markets, while also the interaction between these two markets and inter-modal container terminals is analysed. The marketing channel theory is used to describe all relevant actors and flows that run through marketing channels, starting with customer needs and ending with customer satisfaction. Porter’s theory of competitive advantages is used to review competitive ...
Inertia-Dominated Capillary Channel Flow in Microgravity
Klatte, Joerg; Grah, Aleksander; Dreyer, Michael
2009-01-01
The fluid dynamics video shows three-dimensional experimental and numerical investigations of open channel flows in microgravity. The dynamic reorientation of the free surface from 1g to 0g environment can be observed in a wedge-shaped channel for subcritical and for supercritical flow rate with a collapse of the interface. In addition three-dimensional computations determine important characteristics of the flow, such as the free surface shape, the velocity field, the dynamics of the reorien...
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 and space were used. Laser-Doppler velocimetry (LDV) was employed to measure velocities and turbulence characteristics. The data obtained from the LDV-measurements was processed on a computer using...
The thermalhydraulic behaviour of a CANDU channel during a channel flow blockage accident
International Nuclear Information System (INIS)
The aim of this paper is to perform an analysis of the thermal-hydraulic behavior of CANDU channel during a channel flow blockage accident and to present the final results. This event assumes a flow blockage in one of the reactor fuel channels, that leads to a reduction of the flow in the affected channel, and consequently to fuel cladding and fuel temperature increase. The main conclusions of this analysis are as follows: - For the complete range of flow blockage the effective shutdown is achieved and a good cooling is maintained in the unblocked channels of both primary circuit loops; - Behaviour of the blocked channel depends on the size of the blockage; - For the blockage which are not large enough to cause coolant superheating, the channel remains intact and there are no release to the containment; - Coolant superheating occurs only if the channel flow is reduced to less than 20 % of the normal flow; - Cooling in the intact loop is maintained by pumped circulation and heat removal by steam generators; - Thermal-hydraulic results are used in containment, fuel and fuel channel analysis. (authors)
Numerical computation of pulsatile flow through a locally constricted channel
Bandyopadhyay, S.; Layek, G. C.
2011-01-01
This paper deals with the numerical solution of a pulsatile laminar flow through a locally constricted channel. A finite difference technique has been employed to solve the governing equations. The effects of the flow parameters such as Reynolds number, flow pulsation in terms of Strouhal number, constriction height and length on the flow behaviour have been studied. It is found that the peak value of the wall shear stress has significantly changed with the variation of Reynolds numbers and constriction heights. It is also noted that the Strouhal number and constriction length have little effect on the peak value of the wall shear stress. The flow computation reveals that the peak value of the wall shear stress at maximum flow rate time in pulsatile flow situation is much larger than that due to steady flow. The constriction and the flow pulsation produce flow disturbances at the vicinity of the constriction of the channel in the downstream direction.
LONGITUDINAL DISPERSION IN SEDIMENT-LADEN OPEN CHANNEL FLOWS
Institute of Scientific and Technical Information of China (English)
Z.AHMAD; U.C.KOTHYARI; K.G.RANGA RAJU
2004-01-01
Laboratory experiments on longitudinal dispersion in clear-water and sediment-laden open channel flows are reported. Data from these experiments and those available from previous studies indicate that the suspended sediment present in the flow affects the longitudinal dispersion process. The observed velocity distributions over the depth of sediment-laden flows indicate that the velocity deviates from the mean velocity more in sediment-laden flows than in clear-water flows. The velocity distributions over the cross section and secondary flow in the channel are also expected to be altered due to the presence of suspended sediments in the flow. For these reasons, more dispersion is found in sediment-laden flows than in corresponding clear-water flows. A predictor for the dispersion coefficient in sediment-laden flows is proposed.
Two-Phase Flow Pressure Drop in Superhydrophobic Channels
Stevens, Kimberly; Crockett, Julie; Maynes, Daniel R.; Iverson, Brian C.
2015-01-01
Superhydrophobic surfaces promote dropwise condensation, which increases the rate of thermal transport, making them desirable for use in condensers. Adiabatic two-phase flow loops have been constructed to gain insight into the hydrodynamics of two-phase systems, laying the groundwork for further study of condensing flow on superhydrophobic surfaces. A two-phase flow loop to measure pressure drop and visualize the flow patterns of two-phase flow in superhydrophobic channels relative to classic...
Stationary magnetohydrodynamic flows in curved coaxial channels
International Nuclear Information System (INIS)
The curvilinear geometry of the channel does not significantly affects the gas parameters. For sufficiently high inflow velocities, the velocity of the plasma and gas over the channel, both in the case of its curvilinear configuration and the configuration with the constant average radius, remains constant, and their other main parameters stop changing
Flow boiling heat transfer in mini-channels
International Nuclear Information System (INIS)
In view of practical significance of a correlation of heat transfer coefficient in the aspect of such applications as engineering design and prediction, some efforts towards correlating flow boiling heat transfer coefficients for mini-channels have been made in this study. Based on analyses of existing experimental investigations of flow boiling, it was found that liquid-laminar and gas-turbulent flow is a common feature in many applications of mini-channels. Traditional heat transfer correlations for saturated flow boiling were developed for liquid-turbulent and gas-turbulent flow conditions and thus may not be suitable in principle to be used to predict heat transfer coefficients in mini-channels when flow conditions are liquid-laminar and gas-turbulent. By considering flow conditions (laminar or turbulent) in the Reynolds number factor F and single-phase heat transfer coefficient hsp, the Chen correlation has been modified to be used for four flow conditions such as liquid-laminar and gas-turbulent one often occurring in mini-channels. A comparison of the newly developed correlation with various existing data for mini-channels shows a satisfactory agreement. In addition, an extensive comparison of existing general correlations with databases for mini-channels has also been made. (author)
Computation of gradually varied flow in compound open channel networks
Indian Academy of Sciences (India)
H Prashanth Reddy; M Hanif Chaudhry; Jasim Imran
2014-12-01
Although, natural channels are rarely rectangular or trapezoidal in cross section, these cross sections are assumed for the computation of steady, gradually varied flow in open channel networks. The accuracy of the computed results, therefore, becomes questionable due to differences in the hydraulic and geometric characteristics of the main channel and floodplains. To overcome these limitations, an algorithm is presented in this paper to compute steady, gradually varied flow in an open-channel network with compound cross sections. As compared to the presently available methods, the methodology is more general and suitable for application to compound and trapezoidal channel cross sections in series channels, tree-type or looped networks. 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 channel geometry are presented to avoid the occurrence of multiple critical depths. The occurrence of only one critical depth in a compound cross section with modified geometry is demonstrated for a tree-type channel network.
Experimental study on flow behavior at open channel confluences
Institute of Scientific and Technical Information of China (English)
WANG Xiekang; WANG Xianye; LU Weizhen; LIU Tonghuan
2007-01-01
Channel confluences are common in natural rivers and hydraulic engineering, and the flow behavior at confluences becomes very complex because of the interactionbetween the tributary and the main river. In this study, the experiments were performed in a combined flume with a 30~ angle between the main and tributary flume located at Sichuan University. The velocity was measured by using a three-component acoustic Doppler velocimeter (ADV) over a grid defined throughout the junction region. Based on the analysis of the velocity at the confluence, the distinctive char- acteristics of a channel confluence flow may be divided into several zones including a zone of separation immediately downstream of the junction branch channel, the maximum and minimum velocity regions at the upstream and down- stream in the confluent channel, and a shear plane developed between the two combining flows downstream of the conflu- ent channel. In addition, secondary circulations in different directions at the higher and lower velocity zones are observed as well.
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 Analysis in Two Pass Smooth Square Channel
Directory of Open Access Journals (Sweden)
R.T.SARATH BABU
2014-08-01
Full Text Available This project aim is to presenting the air flow analysis in two pass smooth square channel experiments. The experiments were carried out on a horizontally oriented two pass smooth square channel with turn in sharp 1800 . The smooth square channel size was 2 cm. Calculations were performed by using CFD software “gambit &fluent”. The predictions results of mass flow rate & heat transfer rate of the air flow inside the sharp 180° turn in square channel with using different Reynolds numbers (10000, 20000, 40000 & 60000 were compared against with experiment results obtained from based on journal. Computational fluid dynamics simulations were performed using Gambit2.3.16&Fluent6.3.26 software with 2D, unsteady and turbulent flow conditions assumed. Three different turbulence models were used namely the k-ε, k and Reynolds stress models in conjunction with non-equilibrium wall functions.
Two-phase flow instabilities in a vertical annular channel
Energy Technology Data Exchange (ETDEWEB)
Babelli, I.; Nair, S.; Ishii, M. [Purdue Univ., West Lafayette, IN (United States)
1995-09-01
An experimental test facility was built to study two-phase flow instabilities in vertical annular channel with emphasis on downward flow under low pressure and low flow conditions. The specific geometry of the test section is similar to the fuel-target sub-channel of the Savannah River Site (SRS) Mark 22 fuel assembly. Critical Heat Flux (CHF) was observed following flow excursion and flow reversal in the test section. Density wave instability was not recorded in this series of experimental runs. The results of this experimental study show that flow excursion is the dominant instability mode under low flow, low pressure, and down flow conditions. The onset of instability data are plotted on the subcooling-Zuber (phase change) numbers stability plane.
Inertia-Dominated Capillary Channel Flow in Microgravity
Klatte, Joerg; Dreyer, Michael
2009-01-01
The fluid dynamics video shows three-dimensional experimental and numerical investigations of open channel flows in microgravity. The dynamic reorientation of the free surface from 1g to 0g environment can be observed in a wedge-shaped channel for subcritical and for supercritical flow rate with a collapse of the interface. In addition three-dimensional computations determine important characteristics of the flow, such as the free surface shape, the velocity field, the dynamics of the reorientation and the flow rate depended collapse of the free surface. The good agreement validates the capabilities of the numerical solver.
NONUNIFORM OPEN CHANNEL FLOW WITH UPWARD SEEPAGE THROUGH LOOSE BEDS
Institute of Scientific and Technical Information of China (English)
Subhasish DEY
2003-01-01
The Reynolds stress and bed shear stress are important parameters in fluvial hydraulics. Steadynonuniform flow in open channels with streamwise sloping beds having upward seepage through loose beds is theoretically analyzed to estimate the Reynolds stress and bed shear stress. Equations of the Reynolds stress and bed shear stress are developed, assuming a modified logarithmic velocity distribution law due to upward seepage, and using the Reynolds and continuity equations of twodimensional flow in open channels.
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
Numerical investigation of developing velocity distributions in open channel flows
International Nuclear Information System (INIS)
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. (author)
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 ...
LARGE EDDY SIMULATION OF PULSATING TURBULENT OPEN CHANNEL FLOW
Institute of Scientific and Technical Information of China (English)
ZOU Li-yong; LIU Nan-sheng; LU Xi-yun
2004-01-01
Pulsating turbulent open channel flow has been investigated by the use of Large Eddy Simulation (LES) technique coupled with dynamic Sub-Grid-Scale (SGS) model for turbulent SGS stress to closure the governing equations. Three-dimensional filtered Navier-Stokes equations are numerically solved by a fractional-step method. The objective of this study is to deal with the behavior of the pulsating turbulent open channel flow and to examine the reliability of the LES approach for predicting the pulsating turbulent flow. In this study, the Reynolds number (Reτ ) is chosen as 180 based on the friction velocity and the channel depth. The frequency of the driving pressure gradient for the pulsating turbulent flow ranges low, medium and high value. Statistical turbulence quantities as well as the flow structures are analyzed.
Report on tests using a flow visualization rig - three channel per pass configuration
International Nuclear Information System (INIS)
The flow visualization rig was upgraded to have 3 heated channels per pass. A series of natural circulation flow tests were done. Under test conditions, long periods of flow stagnation with high heater temperatures were observed in one of the channels. This 3 channel per pass rig shows flow patterns with some reverse channel flows, together with continued heat removal by the boiler
Pulsating laminar fully developed channel and pipe flows.
Haddad, Kais; Ertunç, Ozgür; Mishra, Manoranjan; Delgado, Antonio
2010-01-01
Analytical investigations are carried out on pulsating laminar incompressible fully developed channel and pipe flows. An analytical solution of the velocity profile for arbitrary time-periodic pulsations is derived by approximating the pulsating flow variables by a Fourier series. The explicit interdependence between pulsations of velocity, mass-flow rate, pressure gradient, and wall shear stress are shown by using the proper dimensionless parameters that govern the flow. Utilizing the analytical results, the scaling laws for dimensionless pulsation amplitudes of the velocity, mass-flow rate, pressure gradient, and wall shear stress are analyzed as functions of the dimensionless pulsation frequency. Special attention has been given to the scaling laws describing the flow reversal phenomenon occurring in pulsating flows, such as the condition for flow reversal, the dependency of the reversal duration, and the amplitude. It is shown that two reversal locations away from the wall can occur in pulsating flows in pipes and channels and the reversed amount of mass per period reaches a maximum at a certain dimensionless frequency for a given amplitude of mass-flow rate fluctuations. These analyses are numerically conducted for pipe and channel flows over a large frequency range in a comparative manner. PMID:20365456
Counter-current flow limitation in thin rectangular channels
International Nuclear Information System (INIS)
The phenomenon of counter-current flow limitation (CCFL) in thin rectangular channels is important in determining the heat removal capability of research reactors which use plate-type fuel elements similar to the MTR design. An analytical expression for predicting CCFL in narrow rectangular channels was derived from the momentum equations for the liquid and gas phase. The model assumes that the liquid downflow is in the form of a film along the narrower side walls of the channel, while the gas flow occupies the wide span of the rectangular channel. The average thickness of liquid film is related to the rate of gas flow through a stability criterion for the liquid film. The CCFL correlation agrees with air/water data taken at relatively high gas velocities. Depending on the magnitude of the dimensionless channel width W*, the new CCFL correlation approaches zero liquid penetration either in the form of a Wallis correlation or in terms of a Kutateladze number. The new correlation indicates that for a thin rectangular channel, the constant C in the Wallis flooding correlation depends on the aspect ratio of the channel. The approach to the appropriate asymptotic solutions also justifies the use of twice the wide span as the correct length scale for thin rectangular channels. 14 refs., 6 figs
FLOW FIELD IN SCOURED ZONE OF CHANNEL CONTRACTIONS
Institute of Scientific and Technical Information of China (English)
Rajkumar V. RAIKAR; Subhasish DEY
2004-01-01
Experiments were conducted in a laboratory flume to measure the two-dimensional turbulent flow field in the scoured zone of channel contractions under a clear-water scour condition. The Acoustic Doppler Velocimeter (ADV) was used to detect the flow field at different vertical lines along the centerline of uncontracted (main channel) and contracted zones of the channel. The distributions of time-averaged velocity components, turbulent intensity, turbulent kinetic energy, and Reynolds stresses are presented in nondimensional graphical form. The bed shear stresses are computed from the measured Reynolds stresses being in threshold condition within the zone of contraction where bed was scoured. The data presented in this paper would be useful to the investigators for the development of kinematic flow model and morphological model of scour at a channel or river contraction.
Analysis and comparison between rough channel and pipe flows
Sassun, David; Flores, Oscar; Orlandi, Paolo
2016-04-01
Direct numerical simulations of turbulent channel and pipe flows are presented to highlight the effect of roughness at low Reynolds number (Reτ = 180 ‑ 360). Several surfaces are reproduced with the immersed boundaries method, allowing a one-to-one comparison of the two canonical flows. In general, all rough surfaces produce the same effect on the flow in pipes and channels, with small differences in the roughness function, RMS velocities and spectral energy density of pipes and channels. The only exception is for the rough surfaces made of longitudinal bars. In particular, the triangular bars (riblets) show drag reduction in the channel and drag increase in the pipe. This behaviour is linked to the development of spanwise rollers and wide u-structures near the plane of the crest of the pipe.
Long wavelength flow analysis in a curved channel
Energy Technology Data Exchange (ETDEWEB)
Ali, Nasir [Dept. of Mathematics, International Islamic Univ., Islamabad (Pakistan); Sajid, Muhammad [Theoretical Plasma Physics Div., PINSTECH, P.O. Nilore, Islamabad (Pakistan); Hayat, Tasawar [Dept. of Mathematics, Quaid-i-Azam Univ., Islamabad (Pakistan)
2010-03-15
This study is concerned with the peristaltic flow of a viscous fluid in a curved channel. Mathematically the problem is governed by two partial differential equations. Closed form solutions of the stream function, axial velocity, and pressure gradient are developed under long wavelength and low Reynolds number assumptions. The influence of curvature is analyzed on various flow quantities of interest. (orig.)
Vortex structures in turbulent channel flow behind an orifice
Makino, Soichiro; Iwamoto, Kaoru; Kawamura, Hiroshi
2006-11-01
Direct numerical simulation of a channel flow with an orifice has been performed for Reτ0=10 - 600, where uτ0 is the friction velocity calculated from the mean pressure gradient, δ the channel half width and ν the kinematic viscosity. In the wake region, the mean flow becomes asymmetric by the Coanda effect. The degree of asymmetry increases with increasing the Reynolds number for the laminar flow at Reτ0effect upon the reattachment locations and streamwise vortices near the wall in the wake region.
2-D SIMULATION OF CHANNEL FLOWS WITH MOVEABLE BED
Institute of Scientific and Technical Information of China (English)
Wilhelm BECHTELER; Davood FARSHI
2001-01-01
This paper presents some preliminary results of 2-D numerical simulation of open channel flow with moveable bed. The unsteady two dimensional channel flow and sediment transport are simulated by solving shallow water equations and sediment continuity equation in conservation form based on unstructured finite volume method. Redefining longitudinal and transverse slopes of the bed is implemented in order to consider them in the bedload equation. A simple modeling treatment dealing with secondary flow effect on sediment movement is also discussed. Finally, two examples of numerical simulation are presented.
Flows and mixing in channels with misaligned superhydrophobic walls
Nizkaya, Tatiana V; Zhou, Jiajia; Schmid, Friederike; Vinogradova, Olga I
2014-01-01
Aligned superhydrophobic surfaces with the same texture orientation reduce drag in the channel and generate secondary flows transverse to the direction of the applied pressure gradient. Here we show that a transverse shear, superimposed with the conventional Poiseuille and slip-driven plug flows, can be easily generated by using superhydrophobic channels with misaligned textured surfaces. We propose a general theoretical approach to quantify this transverse flow by introducing the concept of an effective shear tensor. To illustrate its use, we present approximate theoretical solutions and Dissipative Particle Dynamics simulations for striped superhydrophobic channels. Our results demonstrate that the transverse shear leads to complex flow patterns on the length scale of the texture period, which leads to a new mechanism of a passive mixing at low Reynolds number. This vertical mixing occurs at the texture period scale and does not require the contribution of side walls. Our results provide a basis for design ...
Flows and mixing in channels with misaligned superhydrophobic walls
Nizkaya, Tatiana V.; Asmolov, Evgeny S.; Zhou, Jiajia; Schmid, Friederike; Vinogradova, Olga I.
2015-03-01
Aligned superhydrophobic surfaces with the same texture orientation reduce drag in the channel and generate secondary flows transverse to the direction of the applied pressure gradient. Here we show that a transverse shear can be easily generated by using superhydrophobic channels with misaligned textured surfaces. We propose a general theoretical approach to quantify this transverse flow by introducing the concept of an effective shear tensor. To illustrate its use, we present approximate theoretical solutions and Dissipative Particle Dynamics simulations for striped superhydrophobic channels. Our results demonstrate that the transverse shear leads to complex flow patterns, which provide a new mechanism of a passive vertical mixing at the scale of a texture period. Depending on the value of Reynolds number two different scenarios occur. At relatively low Reynolds number the flow represents a transverse shear superimposed with two corotating vortices. For larger Reynolds number these vortices become isolated, by suppressing fluid transport in the transverse direction.
Numerical Method to Predict Slip Length in Turbulent Channel Flow
Directory of Open Access Journals (Sweden)
Nowrouz Mohammad Nouri
2016-01-01
Full Text Available In the present research work, we introduce a new method for estimating the slip length on superhydrophobic surfaces. Hence, a dynamic force is added to momentum equations and velocity boundary condition is rewritten in a new form. Laminar and turbulent channel flows are considered and two force functions are used with different profiles to investigate their effects on results. The turbulent channel flow is considered at Re 180 and the Large Eddy Simulation (LES method has been applied to analyze this flow. All results indicate that this method can predict the streamwise slip length with a good accuracy, which is comparable with the Navier’s method. So, using this numerical solution and also measuring pressure drop and mass flow rate in the channel, slip length can be calculated. Consequently, the errors and difficulties of slip length measurements in typical methods such as AFM and μPIV would be eliminated.
Flow-induced channelization in a porous medium
Mahadevan, Amala
2010-01-01
We propose a theory for erosional channelization induced by fluid flow in a saturated granular porous medium. When the local fluid flow-induced stress is larger than a critical threshold, grains are dislodged and carried away so that the porosity of the medium is altered by erosion. This in turn affects the local hydraulic conductivity and pressure in the medium and results in the growth and development of channels that preferentially conduct the flow. Our multiphase model involves a dynamical porosity field that evolves along with the volume fraction of the mobile and immobile grains in response to fluid flow that couples the spatiotemporal dynamics of the three phases. Numerical solutions of the resulting initial boundary value problem show how channels form in porous media and highlights how heterogeneity in the erosion threshold dictates the form of the patterns and thus the ability to control them.
Ultrasonic flow monitoring of SDS/ECI feeder channels
International Nuclear Information System (INIS)
The indicated flows of some of the instrumented-channels of the CANDU Shutdown System (SDS) and Emergency Cooling Injection (ECI) system can become degraded over time, which will result in reduction of operating margin, nuisance alarms and workarounds. As one mitigation strategy, using Ultrasonic Cross-Correlation Flow Meter (USCCFM) to monitor flow rate of SDS and ECI feeder channels has been implemented in Ontario Power Generation (OPG) Darlington Nuclear Generation Station (DNGS) for years. This paper introduces the methods in data analysis for USCCFM monitoring and the detection of abnormal measurement drift in the feeders' orifice flow meter. Results represented in the paper reveal that the long-term, reliable and stable flow measurement by USCCFM can be used as benchmark when the orifice based Flow Instrument Degradation (FID) occurs. (author)
Thermal-Pressure-Driven Gas Flows through Micro Channels
International Nuclear Information System (INIS)
In this paper we study mass flow rate of rarefied gas flow through micro/nanoscale channels under simultaneous thermal and pressure gradients using an improved direct simulation Monte Carlo (DSMC) method. Before targeting thermal/pressure driven flows, we first analyze pressure-driven flows and verify our DSMC solver. Next, we study micro-/ nanochannels flows under simultaneous pressure-temperature gradients while our main objective is to predict mass flow rate increment due to thermal creep effects. The effects of thermal creep are studied over a wide range of flow rarefaction from the slip to free molecular regime. Our results showed that the non-dimensional thermal creep mass flow rate increments of the Poiseuille flow increases and approaches the value of 0.578 at free molecular limit.
Reynolds number effects on particle agglomeration in turbulent channel flow
M Afkhami; A. Hassanpour; Fairweather, M.; Njobuenwu, DO
2014-01-01
The work described in this paper employs large eddy simulation and a discrete element method to study particle-laden flows, including particle dispersion and agglomeration, in a horizontal channel. The particle-particle interaction model is based on the Hertz- Mindlin approach with Johnson-Kendall-Roberts cohesion to allow the simulation of Van der Waals forces in a dry air flow. The influence of different flow Reynolds numbers, and therefore the impact of turbulence, on particle agglomeratio...
Predictions for particle deposition from LES of ribbed channel flow
International Nuclear Information System (INIS)
Predictions for the deposition of spherical and cylindrical particles from a ribbed channel flow onto adjacent flow boundaries are obtained using large eddy simulation (LES) under the assumption of one-way coupling. Results indicate that spherical particles tend to accumulate on the vertical rib wall facing the mean-flow direction with little particle deposition onto surfaces immediately downstream of the rib. This preferential deposition is not predicted for cylindrical particles
Surface drifter trajectories highlight flow pathways in the Mozambique Channel
Hancke, L.; Roberts, M. J.; Ternon, J. F.
2014-02-01
The pattern of surface circulation in the Mozambique Channel was elucidated from the trajectories of 82 satellite-tracked drifters over the period 2000-2010 and complementary satellite-derived altimetry. Overall, the trajectories indicated that anticyclonic activity was mostly observed on the western side of the Channel, with cyclonic activity being more prevalent in the east. A lack of eddy activity was noted in the southeast corner of the Channel (i.e. SW of Madagascar). Drifter behaviour illustrated that surface water from the Comoros Basin, entrained into anticyclonic eddies during formation, can be retained and isolated for months whilst being transported southwards through the Channel. During a tropical cyclone weather event, a drifter was observed to switch between counter-rotating eddies indicating that horizontal mixing of the Ekman layer does occur. The drifters also illustrated and emphasised the flow field and transport between eddies (i.e. the interstitial flow) in the Mozambique Channel. Despite the dominance of southward propagating anticyclones, drifters were able to move north and south through the Channel in the frontal flow field between eddies within periods of 51-207 days. Cross-channel transport in both directions between the Madagascan and Mozambique shelf regions was similarly observed, with time spans of 19-30 days. Surprisingly, drifters from the southern limb of the East Madagascar Current were transported westward across the channel to the Mozambique shelf. This transport was similarly facilitated by the frontal flow field between eddies. It is hypothesised that the frontal zones between eddies and interstitial waters play an important role in distributing biota in the Mozambique Channel.
Thermal Drawdown-Induced Flow Channeling in Fractured Geothermal Reservoirs
Fu, Pengcheng; Hao, Yue; Walsh, Stuart D. C.; Carrigan, Charles R.
2016-03-01
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.
Statistical simulation of rarefied gas flows in micro-channels
International Nuclear Information System (INIS)
Rarefied gas flows through micro-channels are simulated using particle approaches, named as the information preservation (IP) method and the direct simulation Monte Carlo (DSMC) method. In simulating the low speed flows in long micro-channels the DSMC method encounters the problem of large sample size demand and the difficulty of regulating boundary conditions at the inlet and outlet. Some important computational issues in the calculation of long micro-channel flows by using the IP method, such as the use the conservative form of the mass conservation equation to guarantee the adjustment of the inlet and outlet boundary conditions and the super-relaxation scheme to accelerate the convergence process, are addressed. Stream-wise pressure distributions and mass fluxes through micro-channels given by the IP method agree well with experimental data measured in long micro-channels by Pong et al. (with a height to length ratio of 1.2:3000), Shih et al. (1.2:4800), Arkilic et al. and Arkilic (1.3:7500), respectively. The famous Knudsen minimum of normalized mass flux is observed in IP and DSMC calculations of a short micro-channel over the entire flow regime from continuum to free molecular, whereas the slip Navier-Stokes solution fails to predict it
Logtenberg, Hella; Lopez-Martinez, Maria J.; Feringa, Ben L.; Browne, Wesley R.; Verpoorte, Elisabeth
2011-01-01
An approach to control two-phase flow systems in a poly(dimethylsiloxane) (PDMS) microfluidic device using spatially selective surface modification is demonstrated. Side-by-side flows of ethanol : water solutions containing different polymers are used to selectively modify both sides of a channel by
Channel flow structure measurements using particle image velocimetry
International Nuclear Information System (INIS)
Two different flow structures in a laboratory channel were examined using a flow visualization technique, known as Particle Image Velocimetry (PIV). The first channel flow structure was that of a steady flow over a horizontal channel bottom. Photographs of particle displacements were taken in the boundary layer in a plane parallel to the flow. These photographs were analyzed to give simultaneous measurements of two components of the velocity at hundreds of points in the plane. Averaging these photographs gave the velocity profile a few millimeters from the bottom of the channel to the water surface. The results gave good agreement with the known boundary layer theory. This technique is extended to the study of the structure under a progressive wave in the channel. A wavelength of the propagating wave is divided into sections by photographing it continously for a number of frames. Each frame is analyzed and a velocity field under this wave at various phase points were produced with their respective directions. The results show that velocity vectors in a plane under the wave could be achieved instantaneously and in good agreement with the small amplitude wave theory
Micro-channel convective boiling heat transfer with flow instabilities
International Nuclear Information System (INIS)
Flow boiling heat transfer in micro-channels has attracted much interest in the past decade, and is currently a strong candidate for high performance compact heat sinks, such as those required in electronics systems, automobile air conditioning units, micro-reactors, fuel cells, etc. Currently the literature presents numerous experimental studies on two-phase heat transfer in micro-channels, providing an extensive database that covers many different fluids and operating conditions. Among the noteworthy elements that have been reported in previous studies, is the sensitivity of micro-channel evaporators to oscillatory two-phase instabilities. These periodic fluctuations in flow and pressure drop either result from the presence of upstream compressibility, or are simply due to the interaction among parallel channels in multi-port systems. An oscillating flow presents singular characteristics that are expected to produce an effect on the local heat transfer mechanisms, and thus on the estimation of the two-phase heat transfer coefficients. The present investigation illustrates results for flow boiling of refrigerants R-134a, R-236fa, and R-245fa in a 510 μm circular micro-channel, exposed to various degrees of oscillatory compressible volume instabilities. The data describe the main features of the fluctuations in the temperatures of the heated wall and fluid, and draw attention to the differences in the measured unstable time-averaged heat transfer coefficients with respect to those for stable flow boiling. (author)
A universal transition to turbulence in channel flow
Sano, Masaki; Tamai, Keiichi
2016-03-01
Transition from laminar to turbulent flow drastically changes the mixing, transport, and drag properties of fluids, yet when and how turbulence emerges is elusive even for simple flow within pipes and rectangular channels. Unlike the onset of temporal disorder, which is identified as the universal route to chaos in confined flows, characterization of the onset of spatiotemporal disorder has been an outstanding challenge because turbulent domains irregularly decay or spread as they propagate downstream. Here, through extensive experimental investigation of channel flow, we identify a distinctive transition with critical behaviour. Turbulent domains continuously injected from an inlet ultimately decayed, or in contrast, spread depending on flow rates. Near a transition point, critical behaviour was observed. We investigate both spatial and temporal dynamics of turbulent clusters, measuring four critical exponents, a universal scaling function and a scaling relation, all in agreement with the (2 + 1)-dimensional directed percolation universality class.
The mechanical energy equation for total flow in open channels
Institute of Scientific and Technical Information of China (English)
刘士和; 范敏; 薛娇
2014-01-01
The mechanical energy equation is a fundamental equation of a 1-D mathematical model in Hydraulics and Engineering Fluid Mechanics. This equation for the total flow used to be deduced by extending the Bernoulli’s equation for the ideal fluid in the streamline to a stream tube, and then revised by considering the viscous effect and integrated on the cross section. This derivation is not rigorous and the effect of turbulence is not considered. In this paper, the energy equation for the total flow is derived by using the Navier-Stokes equations in Fluid Mechanics, the results are as follows:(1) A new energy equation for steady channel flows of in-compressible homogeneous liquid is obtained, which includes the variation of the turbulent kinetic energy along the channel, the for-mula for the mechanical energy loss of the total flow can be determined directly in the deduction process. (2) The theoretical solution of the velocity field for laminar flows in a rectangular open channel is obtained and the mechanical energy loss in the energy equa-tion is calculated. The variations of the coefficient of the mechanical energy loss against the Reynolds number and the width-depth ratio are obtained. (3) The turbulent flow in a rectangular open channel is simulated using 3-D Reynolds averaged equations closed by the Reynolds stress model (RSM), and the variations of the coefficient of the mechanical energy loss against the Reynolds number and the width-depth ratio are discussed.
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.
Separation of Particles in Swirling Flow in Coaxial Channel
Vasilevsky, Michail; Zyatikov, Pavel; Deeva, Vera; Kozyrev, Ilya
2016-02-01
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.
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
COMPUTATIONAL ANALYSIS OF PARTICULATE FLOW IN EXPANSION CHANNEL
Directory of Open Access Journals (Sweden)
Nor Azwadi Che Sidik
2013-01-01
Full Text Available Computational prediction of fluid-solid particle interaction in an expansion horizontal channel with wide range of Reynolds numbers. Lagrangian-Lagrangian numerical technique to predict the movement of solid particle. The method is based on mesocale scheme of lattice Boltzmann method for prediction of fluid dynamics and second Newtonâs law for the dynamics of solid particles. The flow behaviour at the downstream of the expansion channel is critically dependence on the Reynolds number of the flow. The removal percentage of the contaminant critically dependence on the flow structure donwstream of the expansion channel. The strength of recirculation region plays significant role due to the step in the cavity.
Observations of the flow in the Mozambique Channel
de Ruijter, Wilhelmus P. M.; Ridderinkhof, Herman; Lutjeharms, Johann R. E.; Schouten, Mathijs W.; Veth, Cornelis
2002-05-01
During a recent research cruise to investigate the nature and continuity of the Mozambique Current, we observed that the flow in the Mozambique Channel is dominated by a train of large anti-cyclonic eddies (diameters >300 km) that reach to the channel bottom and propagate southward. At a frequency of 4 per year they cause a net poleward transport of about 15 Sv (1 Sv = 106 m3/s). In the deep sea, a Mozambique Undercurrent flows equatorward along the continental slope. Using a lowered acoustic Doppler current profiler maximum observed velocities are about 0.2 m/s around 2400 m with another current core around 1000 m. It carries about 5 Sv of intermediate (AAIW) and deep waters (NADW) of Atlantic origin into the Channel. Subsequently, the equatorward flowing AAIW is largely entrained by the eddies and, while mixing with intermediate water from the North Indian Ocean in the eddy core, returned to the Agulhas Retroflection region.
Numerical simulation of separated flows in channels
Czech Academy of Sciences Publication Activity Database
Louda, P.; Příhoda, Jaromír; Sváček, P.; Kozel, K.
2012-01-01
Roč. 21, č. 2 (2012), s. 145-153. ISSN 1003-2169 R&D Projects: GA ČR GA103/09/0977 Institutional research plan: CEZ:AV0Z20760514 Keywords : backward facing step flow * EARSM model * SST model Subject RIV: BK - Fluid Dynamics Impact factor: 0.302, year: 2012 http://www.springerlink.com/content/806t56t72787g643/fulltext.pdf
Ultrasound Doppler Velocimetry Measurements in Turbulent Liquid Metal Channel Flow
Rivero, Michel; Jian, Dandan; Karcher, Christian; Cuevas, Sergio
2010-11-01
Control of molten metal flow using magnetic fields is important in industrial applications. The Electromagnetic Flow Control Channel (EFCO) is an experimental test facility, located at Ilmenau University of Technology, for the development of such kind of control systems. The working fluid is the low-melting liquid metal alloy GaInSn in eutectic composition. In this channel, flow control is realized by combining and coupling the non-contact flow driving technology of electromagnetic pumps based on rotating permanent magnets and the non-contact flow rate measurement technology termed Lorentz Force Velocimetry (LFV). The flow rate is adjusted by controlling the rotation rate of the permanent magnet system. Physically, LFV is based on measuring the force acting on a magnet system. This force is induced by the melt flow passing through the static magnetic field generated by the system and is proportional to the flow. To calibrate such flow meters, we apply UDV technique to measure and analyse both turbulent hydrodynamic and MHD flow profiles in EFCO at various Reynolds numbers.
Behaviour of organised disturbances in fully developed turbulent channel flow
Indian Academy of Sciences (India)
P K Sen; Srinivas V Veeravali
2000-10-01
In our earlier work we have shown the relevance of stability theory in understanding the sustenance of turbulence in turbulent boundary layers. Here we adopt the same model to study the evolution of organised disturbances in turbulent channel flow. Since the dominant modes are wall modes we find that the stability characteristics in the two flows are nearly identical although the boundary conditions (at the edge of the boundary layer and at the centre of the channel) are different. Comparisons with the experiments of Hussain and Reynolds are also presented.
Bijlard, M.J.; Oliemans, R.V.A.; Portela, L.M.; Ooms, G.
2010-01-01
The results of point-particle Eulerian–Lagrangian direct numerical simulation (DNS) calculations of dilute particle-laden turbulent channel flow are used to study the effect of the particles on the local flow topology. It is found that in the viscous sublayer, the flow becomes increasingly more two-dimensional as the two-way coupling effect (due to interaction between particles and fluid flow) increases with increasing particle load. Beyond the viscous sublayer the modifications in flow topol...
LARGE EDDY SIMULATION OF OPEN CHANNEL FLOWS WITH NONSUBMERGED VEGETATION*
Institute of Scientific and Technical Information of China (English)
HUAI Wen-xin; WU Zhen-lei; QIAN Zhong-dong; GENG Chuan
2011-01-01
Results of several Large Eddy Simulations (LES) of open channel flows with non-submerged vegetation are presented in this article. It is shown that the vegetation can make the flow structure in the mainstream direction uniform for both supercritical and subcritical flows. For subcritical flows, the LES results of the ensemble-average of time-averaged velocity distributions at four vertical sections around a single plant are in good agreement with measurements. The velocity sees double peaks at the upper and lower positions of flows. For supercritical flows, the ensemble-average velocities see some discrepancy between LES and measurement results. Some secondary flow eddies appear near the single plant, and they just locate in the positions of the double peaks in stream-wise velocity profiles. It is also found that the vegetation drag coefficient deceases as the Froude number increases.
Flow bifurcations, Eulerian chaos and flow mixing in open block tandem channels
International Nuclear Information System (INIS)
Heat transfer enhancement in open channels with geometrical inhomogeneities may occur when the flow evolves from a laminar to a turbulent regime through a transition scenario by increasing a critical flow parameter as the Reynolds number. In converging-diverging wavy channels for example, flow regimes of Lagrangian chaos -that enhances the flow mixing- and Eulerian chaos are the responsible for the enhancement of heat transfer from a hot surface to a mean flow. Chips attached to a motherboard generate a high amount of heat that needs to be removed. The chip performance depends on the chip temperature, which must remain in a low (reasonable) value. One way of removing heat is through a forced flow that extracts the heat from the chip surface. The heat transport rate depends strongly on the flow characteristics, which vary with the Reynolds number. A set of chips can be seen as a block tandem channel, where each block generates heat that needs to be extracted through the chip surface by a flow that circulates between the block and upper surfaces. This paper reports flow characteristics numerical investigations in a block tandem channel. The flow characteristics are obtained from direct numerical simulations of the Navier-Stokes and continuity equations using spectral element methods for laminar and transitional Reynolds numbers flow regimes. Extended and reduced 2D computational models are used to determine the appropriated computational domain for the simulations, which are meshed to capture and describe flow characteristics, such as velocity gradients, vortex dynamics, and flow mixing that develops for transitional flows. The flow characteristics, obtained in terms of vortex dynamics, Fourier spectra, and pseudo-phase spaces, show a transition scenario characterized by a first Hopf bifurcation as the flow evolves from a laminar to a periodic flow, and a second Hopf bifurcation as the flow evolves to quasi-periodic flow for higher Reynolds numbers. The first flow
Déjardin, P
2013-08-30
The flow conditions in normal mode asymmetric flow field-flow fractionation are determined to approach the high retention limit with the requirement d≪l≪w, where d is the particle diameter, l the characteristic length of the sample exponential distribution and w the channel height. The optimal entrance velocity is determined from the solute characteristics, the channel geometry (exponential to rectangular) and the membrane properties, according to a model providing the velocity fields all over the cell length. In addition, a method is proposed for in situ determination of the channel height. PMID:23885667
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...
Flows of granular material in two-dimensional channels
Bain, Oliver; Billingham, John; Houston, Paul; Lowndes, Ian
2015-01-01
Secondary cone-type crushing machines are an important part of the aggregate production process. These devices process roughly crushed material into aggregate of greater consistency and homogeneity. We apply a continuum model for granular materials (`A Constitutive Law For Dense Granular Flows', Nature 441, p727-730, 2006) to flows of granular material in representative two-dimensional channels, applying a cyclic applied crushing stress in lieu of a moving boundary. Using finite element metho...
Numerical Simulation of slug flow in a micro-channel
Carlson, Andreas
2007-01-01
Multiphase dynamics and characteristics of slug flow in micro channels are investigated computationally by means of advanced numerical simulation methods. Although, due to its importance in many engineering and biomedical applications, the topic has been studied previously, methods for robust and accurate simulation of slug flow remain elusive. Evaluation of current state-of-the-art Computational Multi Fluid Dynamics (CMFD) technology depicts deficiency with advanced computational methods (Vo...
Particle-Interaction Effects in Turbulent Channel Flow
M Afkhami; A. Hassanpour; Fairweather, M.; Njobuenwu, DO
2013-01-01
Large eddy simulation and a discrete element method are applied to study the flow, particle dispersion and agglomeration in a horizontal channel. The particle-particle interaction model is based on the Hertz-Mindlin approach with Johnson-Kendall-Roberts cohesion to allow the simulation of Van der Waals forces in a dry air flow. The influence of different particle surface energies on agglomeration, and the impact of fluid turbulence, are investigated. The agglomeration rate is found to be stro...
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.
Numerical Study of Polymers in Turbulent Channel Flow
Bagheri, Faranggis
2010-01-01
The phenomenon of drag reduction by polymers in turbulent flow has beenstudied over the last 60 years. New insight have been recently gained by meansof numerical simulation of dilute polymer solution at moderate values of theturbulent Reynolds number and elasticity. In this thesis, we track elastic parti-cles in Lagrangian frame in turbulent channel flow at Reτ = 180, by tracking,where the single particle obeys the FENE (finite extendible nonlinear elastic)formulation for dumbbel model. The f...
DNS of turbulent flow in a rod-roughened channel
International Nuclear Information System (INIS)
A numerical investigation has been performed to study pressure-driven turbulent flow in a rod-roughened channel at Reynolds number Reτ=400 based on the mean pressure-gradient. Both channel walls were roughened by square rods with a height k of only 1.7% of the channel height or k+=13.6 in wall units. The pitch-to-height ratio was 8, which corresponds to the so-called 'k-type' roughness and the resulting flow field was classified as 'transitionally rough'. The Reynolds-averaged streamline pattern exhibited two co-rotating vortices which filled the cavity between two consecutive rods. The averaged flow field which separated from one rod did not reattach and a return flow was observed all along the bottom of the cavity. Outside the roughness sublayer, i.e. beyond 5k, no discernible streamwise variation of the mean velocity and second-order statistics could be observed, whereas the correlation between the streamwise and wall-normal mean velocity components persisted somewhat further away from the surface. Inside the roughness sublayer, however, significant differences in the turbulence field between smooth- and rough-wall layers were observed, for instance the high-energy region formed by the shear layer emanating from the crest of the roughness elements. Visualizations of instantaneous flow fields revealed the presence of elongated streaky structures similar to those routinely observed in flows along a smooth surface
Using DNS and Statistical Learning to Model Bubbly Channel Flow
Ma, Ming; Lu, Jiacai; Tryggvason, Gretar
2015-11-01
The transient evolution of laminar bubbly flow in a vertical channel is examined by direct numerical simulation (DNS). Nearly spherical bubbles, initially distributed evenly in a fully developed parabolic flow, are driven relatively quickly to the walls, where they increase the drag and reduce the flow rate on a longer time scale. Once the flow rate has been decreased significantly, some of the bubbles move back into the channel interior and the void fraction there approaches the value needed to balance the weight of the mixture and the imposed pressure gradient. A database generated by averaging the DNS results is used to model the closure terms in a simple model of the average flow. Those terms relate the averaged lateral flux of the bubbles, the velocity fluctuations and the averaged surface tension force to the fluid shear, the void fraction and its gradient, as well as the distance to the nearest wall. An aggregated neural network is used for the statistically leaning of unknown closures, and closure relationships are tested by following the evolution of bubbly channel flow with different initial conditions. It is found that the model predictions are in reasonably good agreement with DNS results. Supported by NSF.
Verification of SOPHT for parallel channel flow stability
International Nuclear Information System (INIS)
As part of a continuing program to verify the thermalhydraulic computer code SOPHT, a number of experimental tests designed to study parallel channel flow instability were simulated. This phenomenon of flow instability could cause dryout of reactor fuel resulting in poor heat transfer to the coolant and increased fuel temperatures. Selected tests from two out reactor experimental programs are predicted with the SOPHT code. Both of these test programs were carried out at Westinghouse Canada Incorporated, Hamilton, Ontario, under contract to Atomic Energy of Canada. The first test facility consisted of a vertical heated channel in parallel with an unheated bypass connected between a common inlet and outlet header. The second test facility was similar to the first, however there were three parallel heated channels as well as an unheated bypass
DNS of turbulent channel flow subject to oscillatory heat flux
Directory of Open Access Journals (Sweden)
Bukhvostova Anastasia
2014-01-01
Full Text Available In this paper we study the heat transfer in a turbulent channel flow, which is periodically heated through its walls. We consider the flow of air and water vapor using direct numerical simulation. We consider the fluid as a compressible Newtonian gas. We focus on the heat transfer properties of the system, e.g., the temperature difference between the walls and the Nusselt number. We consider the dependence of these quantities on the frequency of the applied heat flux. We observe that the mean temperature difference is quite insensitive to the frequency and that the amplitude of its oscillations is such that its value multiplied by the square root of frequency is approximately constant. Next we add droplets to the channel, which can undergo phase transitions. The heat transfer properties of the channel in the case with droplets are found to increase by more than a factor of two, compared to the situation without droplets.
Numerical simulation of particle-laden turbulent channel flow
Li, Y.; McLaughlin, J.B.; Kontomaris, K.; Portela, L.
2001-01-01
This paper presents results for the behavior of particle-laden gases in a small Reynolds number vertical channel down flow. Results will be presented for the effects of particle feedback on the gas-phase turbulence and for the concentration profile of the particles. The effects of density ratio, mas
Free-Molecular Gas Flow in Narrow (Nanoscale) Channel
Czech Academy of Sciences Publication Activity Database
Levdansky, V.V.; Roldugin, V.I.; Žďanov, V.M.; Ždímal, Vladimír
2014-01-01
Roč. 87, č. 4 (2014), s. 802-814. ISSN 1062-0125 Grant ostatní: BRFFI(BY) T12P-018; RFBR(RU) 12-08-90009 Institutional support: RVO:67985858 Keywords : narrow channels * free-molecular gas flow * surface diffusion Subject RIV: CF - Physical ; Theoretical Chemistry
Urban Infrastructure, Channel-Floodplain Morphology and Flood Flow Patterns
Miller, A. J.; Smith, J. A.; Nelson, C. B.
2006-12-01
The relationship between the channel and the floodplain in urban settings is heavily influenced by (1) altered watershed hydrologic response and frequency distribution of flows, (2) channel enlargement resulting from altered hydrology under conditions of limited sediment supply, (3) direct modification of channels and floodplains for purposes of erosion mitigation, flood protection, commercial development and creation of public amenities, (4) valley constrictions and flow obstructions associated with bridges, culverts, road embankments and other types of floodplain encroachment causing fragmentation or longitudinal segmentation of the riparian corridor. Field observation of inundation patterns associated with recurring floods in the Baltimore metropolitan area is used in combination with 2-dimensional hydraulic modeling to simulate patterns of floodplain inundation and to explore the relationships between magnitude and shape of the flood hydrograph, morphology of the urban channel-floodplain system, and the frequency and extent of floodplain inundation. Case studies include a July 2004 flood associated with a 300-year 2-hour rainfall in a small (14.2 km2) urban watershed, as well as several other events caused by summer thunderstorms with shorter recurrence intervals that generated an extraordinary flood response. The influence of urban infrastructure on flood inundation and flow patterns is expressed in terms of altered (and hysteretic) stage-discharge relationships, stepped flood profiles, rapid longitudinal attenuation of flood waves, and transient flow reversals at confluences and constrictions. Given the current level of interest in restoration measures these patterns merit consideration in planning future development and mitigation efforts.
Drop deformation in stokes flow through converging channels
Wrobel, LC; Soares, D.; Das Bhaumik, CL
2009-01-01
This work presents an application of a direct BEM formulation for drop deformation and interaction in Stokes flows through converging channels. Parametric studies are conducted to investigate the effect, on drop deformation, of the channel’s convergence ratio, the drop-fluid viscosity ratio, the interfacial tension and the initial relative position of the drops.
Morphology of Cryogenic Flows and Channels on Dwarf Planet Ceres
Krohn, Katrin; Jaumann, Ralf; Otto, Katharina A.; von der Gathen, Isabel; Matz, Klaus-Dieter; Buczkowski, Debra L.; Williams, David A.; Pieters, Carle M.; Preusker, Frank; Roatsch, Thomas; Stephan, Katrin; Wagner, Roland J.; Russell, Christopher T.; Raymond, Carol A.
2016-04-01
Cereś surface is affected by numerous impact craters and some of them show features such as channels or multiple flow events forming a smooth, less cratered surface, indicating possible post-impact resurfacing [1,2]. Flow features occur on several craters on Ceres such as Haulani, Ikapati, Occator, Jarimba and Kondos in combination with smooth crater floors [3,4], appearing as extended plains, ponded material, lobate flow fronts and in the case of Haulani lobate flows originating from the crest of the central ridge [3] partly overwhelming the mass wasting deposits from the rim. Haulanís crater flanks are also affected by multiple flow events radiating out from the crater and partly forming breakages. Flows occur as fine-grained lobes with well-defined margins and as smooth undifferentiated streaky flows covering the adjacent surface. Thus, adjacent craters are covered by flow material. Occator also exhibits multiple flows but in contrast to Haulani, the flows originating from the center overwhelm the mass wasting deposits from the rim [4]. The flows have a "bluish" signature in the FC color filters ratio. Channels occur at relatively fresh craters. They also show the "bluish" signature like the flows and plains. Only few channels occur at older "reddish" craters. They are relatively fresh incised into flow features or crater ejecta. Most are small, narrow and have lobated lobes with predominant distinctive flow margins. The widths vary between a few tens of meters to about 3 km. The channels are found on crater flanks as well as on the crater floors. The occurrence of flow features indicates viscous material on the surface. Those features could be formed by impact melt. However, impact melt is produced during the impact, assuming similar material properties as the ejecta it is expected to have nearly the same age as the impact itself, but the flows and plains are almost free of craters, thus, they seem to be much younger than the impact itself. In addition, the
A reciprocal theorem for boundary-driven channel flows
Michelin, Sebastien
2015-01-01
In a variety of physical situations, a bulk viscous flow is induced by a distribution of surface velocities, for example in diffusiophoresis (as a result of chemical gradients) and above carpets of cilia (as a result of biological activity). When such boundary-driven flows are used to pump fluids, the primary quantity of interest is the induced flow rate. In this letter we propose a method, based on the reciprocal theorem of Stokes flows, to compute the net flow rate for arbitrary flow distribution and periodic pump geometry using solely stress information from a dual Poiseuille-like problem. After deriving the general result we apply it to straight channels of triangular, elliptic and rectangular geometries and quantify the relationship between bulk motion and surface forcing.
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.
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.
History dependent vortex flow dynamics in mesoscopic channels
International Nuclear Information System (INIS)
Intriguing and novel physical aspects related to the vortex flow dynamics have been recently observed in mesoscopic channel devices of a-NbGe with NbN channel edges. In this work we have studied the flow properties of such confined vortices as a function of the magnetic field history, using dc-transport and mode-locking (ML) measurements. As opposed to the field down situation, in field up case a kink anomaly in the dc I-V curves is detected. The mode-locking measurements unveil the dynamic change in the flow configurations around this anomaly: n moving rows of vortex array at low velocity changes suddenly to n + 2 rows at high velocity around the anomaly
Passive scalars in turbulent channel flow at high Reynolds number
Pirozzoli, Sergio; Bernardini, Matteo; Orlandi, Paolo
2015-11-01
We study passive scalars in turbulent plane channels at computationally high Reynolds number, which allows to observe previously unnoticed effects. The mean scalar profiles are found to obey a generalized logarithmic law which includes a linear correction term in the whole lower half-channel, and they follow a universal parabolic defect profile in the core region. This is consistent with recent findings regarding the mean velocity profiles in channel flow. The scalar variances also exhibit a near universal parabolic distribution in the core flow, and hints of a sizeable log layer, unlike the velocity variances. The energy spectra highlight the formation of large scalar-bearing eddies spanning each half-channel, which are caused by production excess over dissipation, and which are clearly visible in the flow visualizations. Close correspondence of the velocity and scalar eddies is observed, the main difference being that the latter have more convoluted interfaces, which translates into higher scalar dissipation. Another notable Reynolds number effect is the decreased correlation of the scalar field with the vertical velocity field, which is traced to the reduced effectiveness of ejection events. We acknowledge that the results reported in this paper have been achieved using the PRACE Research Infrastructure resource FERMI based at CINECA, Casalecchio di Reno, Italy.
Ferrofluid magnetoviscous control of wall flow channeling in porous media
Institute of Scientific and Technical Information of China (English)
Fa(ic)al Larachi; Damien Desvigne
2007-01-01
We analyzed the phenomenon of ferrofluid magnetoviscosity in high-permeability wall-region non-magnetic porous media of the Müller kind.After upscaling the pore-level ferrohydrodynamic model, we obtained a simplified volume-average zero-order axisymmetric model for non-Darcy non-turbulent flow of steady-state isothermal incompressible Newtonian ferrofluids through a porous medium experiencing external constant bulk-flow oriented gradient magnetic field, ferrofluid self-consistent demagnetizing field and induced magnetic field in the solid. The model was explored in contexts plagued by wall flow maldistribution due to low column-to-particle diameter ratios. It was shown that for proper magnetic field arrangement, wall channeling can be reduced by inflating wall flow resistance through magnetovisco-thickening and Kelvin body force density which reroute a fraction of wall flow towards bed core.
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 with...
Computation of Internal Fluid Flows in Channels Using the CFD Software Tool FlowVision
Kochevsky, A N
2004-01-01
The article describes the CFD software tool FlowVision (OOO "Tesis", Moscow). The model equations used for this research are the set of Reynolds and continuity equations and equations of the standard k - e turbulence model. The aim of the paper was testing of FlowVision by comparing the computational results for a number of simple internal channel fluid flows with known experimental data. The test cases are non-swirling and swirling flows in pipes and diffusers, flows in stationary and rotating bends. Satisfactory correspondence of results was obtained both for flow patterns and respective quantitative values.
The influence on performance of co-flow and counter-flow PEM fuel cell channels
International Nuclear Information System (INIS)
Full text: A three-dimensional computational fluid dynamics model of a PEM fuel cell with serpentine flow field channels that combines co-flow and counter-flow configurations is presented in this paper. The PEM fuel cell performance is significantly influenced by the direction of fuel and oxidant flow. Therefore, the CFD model used in this paper accounts for the major transport phenomena that occur in PEM fuel cells with co-flow and counter-flow configuration. The results will highlight the convective and diffusive heat and mass transfer, the electrode kinetics, and the potential fields. (authors)
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.
Directory of Open Access Journals (Sweden)
I. Khazaee, M. Mohammadiun
2012-01-01
Full Text Available 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.
Modelling of flow and heat transfer in PV cooling channels
Energy Technology Data Exchange (ETDEWEB)
Diarra, D.C.; Harrison, S.J. [Queen' s Univ., Kingston, ON (Canada). Dept. of Mechanical and Materials Engineering Solar Calorimetry Lab; Akuffo, F.O. [Kwame Nkrumah Univ. of Science and Technology, Kumasi (Ghana). Dept. of Mechanical Engineering
2005-07-01
Under sunny conditions, the temperature of photovoltaic (PV) modules can be 20 to 30 degrees C above the ambient air temperature. This affects the performance of PV modules, particularly in regions with hot climates. For silicon solar cells, the maximum power decreases between 0.4 and 0.5 per cent for every degree C of temperature increase above a reference value. In an effort to address this issue, this experimental and numerical study examined an active PV panel evaporative cooling scheme that is typically used in hot arid climates. The cooling system circulated cool air behind the PV modules, extracting heat and lowering solar cell temperature. A fluid dynamic and thermal model of the combined system was developed using the EES program in order to study the configuration of the cooling channel and the characteristics of the cooling flow. Heat transfer and flow characteristics in the cooling channel were then calculated along with pressure drop and fan power associated with the air-circulation. The net power output was also calculated. The objective was to design a cost efficient cooling system and to optimize its flow and pressure drop in order to maximize power output. The study demonstrated how the performance of the PV panel is influenced by the geometry of the cooling channel, the inlet air temperature and the air flow rate. 2 refs.
Flow resistance and its prediction methods in compound channels
Institute of Scientific and Technical Information of China (English)
Kejun Yang; Shuyou Cao; Xingnian Liu
2007-01-01
A series of experiments was carried out in a large symmetric compound channel composed of a rough main channel and rough floodplains to investigate the resistance characteristics of inbank and overbank flows.The effective Manning,Darcy-Weisbach,Chezy coefficients and the relative Nikuradse roughness height were analyzed.Many different representative methods for predicting the composite roughness were systemat-ically summarized.Besides the measured data,a vast number of laboratory data and field data for compoundchannels were collected and used to check the valid-ity of these methods for different subsection divisionsincluding the vertical,horizontal,diagonal and bisec-tional divisions.The computation showed that thesemethods resulted in big errors in assessing the compos-ite roughness in compound channels,and the reasonswere analyzed in detail.The error magnitude is relatedto the subsection divisions.
Flow regimes in inclined open-channel flows of granular materials
Campbell, C. S.; Brennen, C. E.; Sabersky, R. H.
1985-01-01
Open-channel flows of fluids may be classified as supercritical or subcritical, depending on whether their average velocity ῡ is larger, equal to or smaller than the propagation rate of small disturbances √(gh) cos α (where g is the gravitational acceleration, h is the flow depth and [alpha] is the channel inclination). Typically, the flow type is classified by the magnitude of the Froude number, ῡ√(gh), relative to its value under critical conditions Fr_c = √(cosα). Supercritical and subcr...
Thermally stratified sodium channel flow: turbulence and modeling
International Nuclear Information System (INIS)
Numerical simulation of sodium stratification in open channel flow has been studied with Computational Fluid Dynamics (CFD) employing an Algebraic Heat Flux Model (AHFM) closure for the turbulent heat flux. The results are validated against experimental data and the AHFM is compared with the simplified Reynolds analogy employing a constant turbulent Pr number. Influence of buoyancy on turbulence created in the mixing layer has been evaluated and its influence on the momentum and energy transport in the vertical direction assessed. It has been found that the choice of turbulent heat flux model influences the achieved results for temperature and velocity field which might affect the flow developing and persistence of stratification in the channel. Moreover both experiment and validation show the possibility of creation of a strong stratification also for low Pr number fluids, warning the stratification problem as an existing phenomenon likely to occur in liquid metal nuclear power plants. (author)
Nonlinear dispersion of a pollutant ejected into a channel flow
Gorder, Robert; Vajravelu, Kuppalapalle
2011-10-01
In this paper, we study the nonlinear coupled boundary value problem arising from the nonlinear dispersion of a pollutant ejected by an external source into a channel flow. We obtain exact solutions for the steady flow for some special cases and an implicit exact solution for the unsteady flow. Additionally, we obtain analytical solutions for the transient flow. From the obtained solutions, we are able to deduce the qualitative influence of the model parameters on the solutions. Furthermore, we are able to give both exact and analytical expressions for the skin friction and wall mass transfer rate as functions of the model parameters. The model considered can be useful for understanding the polluting situations of an improper discharge incident and evaluating the effects of decontaminating measures for the water bodies.
Coherent vorticity extraction in turbulent channel flow using anisotropic wavelets
Yoshimatsu, Katsunori; Sakurai, Teluo; Schneider, Kai; Farge, Marie; Morishita, Koji; Ishihara, Takashi
2014-11-01
We examine the role of coherent vorticity in a turbulent channel flow. DNS data computed at friction-velocity based Reynolds number 320 is analyzed. The vorticity is decomposed using three-dimensional anisotropic orthogonal wavelets. Thresholding of the wavelet coefficients allows to extract the coherent vorticity, corresponding to few strong wavelet coefficients. It retains the vortex tubes of the turbulent flow. Turbulent statistics, e.g., energy, enstrophy and energy spectra, are close to those of the total flow. The nonlinear energy budgets are also found to be well preserved. The remaining incoherent part, represented by the large majority of the weak coefficients, corresponds to a structureless, i.e., a noise-like background flow.
Distribution of incompressible flow within interdigitated channels and porous electrodes
Kee, Robert J.; Zhu, Huayang
2015-12-01
This paper develops a general model with which to evaluate flow uniformity and pressure drop within interdigitated-channel structures, especially in the context of redox flow batteries. The governing equations are cast in dimensionless variables, leading to a set of characteristic dimensionless parameter groups. The systems of governing equations are solved computationally, with the results presented graphically. Because the results are general, the underlying model itself is not needed to apply the quantitative design guidelines. However, the paper presents and discusses all the information required to recreate the model as needed.
3-D NUMERICAL SIMULATIONS OF FLOW LOSS IN HELICAL CHANNEL
Institute of Scientific and Technical Information of China (English)
ZHAO Ling-zhi; PENG Yan; LU Fang; LI Jian; LI Ran; LIU Bao-lin
2012-01-01
The flow loss of a helical channel Magnetohydrodynamic (MHD) thruster without MHD effect was numerically studied with 3-D simulations,and a flow loss coefficient ξ was defined to quantify the flow loss and its influencing factors were studied.The results show that ξ decreases in a first-order exponential manner with the pitch of a helical wall and the Reynolds number,and it declines slowly when t / T ＞ 0.2 and Re ＞ 105,a flow guide makes the flow more smooth and uniform,especially in the flow guide and helical wall sub-regions and thus reduces the flow loss greatly,by about 30％ with the averaged value of ξ from 0.0385to 0.027,a rectifier weakens the helical flow and strengthens the axial one in the rectifier and outlet sub-regions,thus reduces the rotational kinetic pressure with the averaged value of ξ declining about 4％ from 0.0385 to 0.037,and ξ decreases with a rectifier's axial length when Re ＞ 105.
The effect of wall heating on instability of channel flow
Sameen, A; Govindarajan, Rama
2006-01-01
A comprehensive study of the effect of wall heating or cooling on the linear, transient and secondary growth of instability in channel flow is conducted. The effect of viscosity stratification, heat diffusivity and of buoyancy are estimated separately, with some unexpected results. From linear stability results, it has been accepted that heat diffusivity does not affect stability. However, we show that realistic Prandtl numbers cause a transient growth of disturbances that is an order of magn...
Heat transfer to liquid sodium flowing through annular channel, (4)
International Nuclear Information System (INIS)
An experimental study was carried out to clarify the heat transfer characteristics of liquid sodium flowing turbulently through an annular channel. For a concentric condition, average psi(=average epsilonH/epsilonM) was found to agree with that proposed by Aoki or Ramm for circular tube. For eccentric conditions, circumferential temperature variations around the inner wall were measured and Nusselt numbers were evaluated. Numerical calculations were also made for temperature fields and compared with the measurements. (author)
Communication flow, channels, content and climate in downsizing
Illia, Laura; Lurati, Francesco; La Rocca, Antonella
2006-01-01
Effective internal communication contributes to the overall organizational communication that aims to maintain a sustainable reputation during times of change. Arising from this belief, this paper aims to develop a theoretical framework in which the type of communication content, flows, channels, and climate better fits into the planning, implementation, and revitalization phases within the downsizing process. To this end, a literature review on downsizing studies has been conducted, resultin...
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.
Institute of Scientific and Technical Information of China (English)
Gérard J. Poitras; L.-Emmanuel Brizzi; Yves Gagnon
2001-01-01
The results of different numerical algorithms for the computation of unsteady fluid flows are used to visualize different variables of the flow. In particular, the instantaneous vorticity, velocity and pressure fields, along with streamline plots, are presented as a function of time inside a visualization window of the computational domain.The different forms of visualization are used to analyze the flow inside a two-dimensional channel incorporating an obstacle, which can represent several interesting flows such as the flow over electronic components, heat transfer devices and buildings.
Rain and channel flow supplements to subsurface water beneath hyper-arid ephemeral stream channels
Kampf, Stephanie K.; Faulconer, Joshua; Shaw, Jeremy R.; Sutfin, Nicholas A.; Cooper, David J.
2016-05-01
In hyper-arid regions, ephemeral stream channels are important sources of subsurface recharge and water supply for riparian vegetation, but few studies have documented the subsurface water content dynamics of these systems. This study examines ephemeral channels in the hyper-arid western Sonoran Desert, USA to determine how frequently water recharges the alluvial fill and identify variables that affect the depth and persistence of recharge. Precipitation, stream stage, and subsurface water content measurements were collected over a three-year study at six channels with varying contributing areas and thicknesses of alluvial fill. All channels contain coarse alluvium composed primarily of sands and gravels, and some locations also have localized layers of fine sediment at 2-3 m depth. Rain alone contributed 300-400 mm of water input to these channels over three years, but water content responses were only detected for 36% of the rain events at 10 cm depth, indicating that much of the rain water was either quickly evaporated or taken up by plants. Pulses of water from rain events were detected only in the top meter of alluvium. The sites each experienced ⩽5 brief flow events, which caused transient saturation that usually lasted only a few hours longer than flow. These events were the only apparent source of water to depths >1 m, and water from flow events quickly percolated past the deepest measurement depths (0.5-3 m). Sustained saturation in the shallow subsurface only developed where there was a near-surface layer of finer consolidated sediments that impeded deep percolation.
CHARACTERISTICS OF FLOW RESISTANCE IN OPEN CHANNELS WITH NON-SUBMERGED RIGID VEGETATION
Institute of Scientific and Technical Information of China (English)
WU Fu-sheng
2008-01-01
The flow resistance factors of non-submerged rigid vegetation in open channels were analyzed. The formulas of drag coefficient CD and equivalent Manning's roughness coefficient nd were derived by analyzing the force of the flow of non-submerged rigid vegetation in open channel. The flow characteristics and mechanism of non-submerged rigid vegetation in open channel were studied through flume experiments.
Eruption Constraints for a Young Channelized Lava Flow, Marte Vallis, Mars
Therkelsen, J. P.; Santiago, S. S.; Grosfils, E. B.; Sakimoto, S. E. H.; Mendelson, C. V.; Bleacher, J. E.
2001-01-01
This study constrains flow rates for a specific channelized lava flow in Marte Vallis, Mars. We measured slope-gradient, channel width, and channel depth. Our results are similar to other recent studies which suggests similarities to long, terrestrial basaltic flow. Additional information is contained in the original extended abstract.
International Nuclear Information System (INIS)
For flow boiling systems, it's impossible to make stable operation under certain conditions so that these are of great concerns in the design and operation of such systems. So called two phase flow instability has possibility to cause heat transfer degradation and then it may lead mechanical damages to heat transfer surface, it should be avoided in normal and transient conditions. Among various two phase instabilities, flow excursion, also known as the Lading instability or Onset of Flow Instability (OFI) is major concern of thermal hydraulic design and safety analysis of research reactors which is under low flow and low pressure condition. The preferred configuration for boiling channels is vertical upward flow since buoyancy helps the mixture flow, and the slip velocity between the two phases that is caused by their density difference actually improves the heat transfer. However, boiling with downward flow is also of interest for accident conditions of upward flow system or even normal conditions of research reactors such as Jordan research and training reactor (JRTR) which adopts downward flow for easier fuel loading. JRTR is 5MWth open pool type research reactor which was designed to utilize plate type fuel taking account of efficient heat removal by Korea Atomic Energy Research Institute (KAERI). It is design to be cooled by downward flow through narrow rectangular channels to maximize heat removal efficiency and to minimize fuel vibrations. However, previous OFI data is very limited for narrow rectangular channel and downward flow condition. In this study, data of onset of flow excursion conditions were generated and analyzed
Numerical simulation of secondary flow in bubbly turbulent flow in sub-channel
International Nuclear Information System (INIS)
Secondary flow in bubbly turbulent flow in sub-channel was simulated by using an algebraic turbulence stress model. The mass, momentum, turbulence energy and bubble diffusion equations were used as fundamental equation. The basis for these equations was the two-fluid model: the equation of liquid phase was picked up from the equation system theoretically derived for the gas-liquid two-fluid turbulent flow. The fundamental equation was transformed onto a generalized coordinate system fitted to the computational domain in sub-channel. It was discretized for the SIMPLE algorism using the finite-volume method. The shape of sub-channel causes a distortion of the computational mesh, and orthogonal nature of the mesh is sometimes broken. An iterative method to satisfy a requirement for the contra-variant velocity was introduced to represent accurate symmetric boundary condition. Two-phase flow at a steady state was simulated for different magnitude of secondary flow and void fraction. The secondary flow enhanced the momentum transport in sub-channel and accelerated the liquid phase in the rod gap. This effect was slightly mitigated when the void fraction increased. The acceleration can contribute to effective cooling in the rod gap. The numerical result implied a phenomenon of industrial interest. This suggested that experimental approach is necessary to validate the numerical model and to identify the phenomenon. (author)
Computation of a turbulent channel flow using PDF method
International Nuclear Information System (INIS)
The purpose of the present paper is to present an analysis of a PDF model (Probability Density Function) and an illustration of the possibilities offered by such a method for a high-Reynolds turbulent channel flow. The first part presents the principles of the PDF approach and the introduction of stochastic processes along with a Lagrangian point of view. The model retained is the one put forward by Pope (1991) and includes evolution equations for location, velocity and dissipation of a large number of particles. Wall boundary conditions are then developed for particles. These conditions allow statistical results of the logarithmic region to be correctly reproduced. Simulation of non-homogeneous flows require a pressure-gradient algorithm which is briefly described. Developments are validated by analysing numerical predictions with respect to Comte Bellot experimental data (1965) on a channel flow. This example illustrates the ability of the approach to simulate wall-bounded flows and to provide detailed information such as skewness and flatness factors. (author)
Linear Stability Analysis of Compressible Channel Flow with Porous Walls
Rahbari, Iman
2015-01-01
We have investigated the effects of permeable walls, modeled by linear acoustic impedance with zero reactance, on compressible channel flow via linear stability analysis (LSA). Base flow profiles are taken from impermeable isothermal-wall laminar and turbulent channel flow simulations at bulk Reynolds number, $Re_b$= 6900 and Mach numbers, $M_b$ = 0.2, 0.5, 0.85. For a sufficiently high value of permeability, two dominant modes are excited: a bulk pressure mode, causing symmetric expulsion and suction of mass from the porous walls (Mode 0); a standing-wave-like mode, with a pressure node at the centerline (Mode 1). In the case of turbulent mean flow profiles, both modes generate additional Reynolds shear stresses augmenting the (base) turbulent ones, but concentrated in the viscous sublayer region; the trajectories of the two modes in the complex phase velocity space follow each other very closely for values of wall permeability spanning two orders of magnitude, suggesting their coexistence. The transition fr...
Experimental studies on the flow through soft tubes and channels
Indian Academy of Sciences (India)
V Kumaran
2015-05-01
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 the corresponding value of 1200 for a rigid channel or 2100 for a rigid tube. Experiments conducted with very viscous fluids show that there could be an instability even at zero Reynolds number provided the surface is sufficiently soft. Linear stability studies show that the transition Reynolds number is linearly proportional to the wall shear modulus in the low Reynolds number limit, and it increases as the 1/2 and 3/4 power of the shear modulus for the ‘inviscid’ and ‘wall mode’ instabilities at high Reynolds number. While the inviscid instability is similar to that in the flow in a rigid channel, the mechanisms of the viscous and wall mode instabilities are qualitatively different. These involve the transfer of energy from the mean flow to the fluctuations due to the shear work done at the interface. The experimental results for the viscous instability mechanism are in quantitative agreement with theoretical predictions. At high Reynolds number, the instability mechanism has characteristics similar to the wall mode instability. The experimental transition Reynolds number is smaller, by a factor of about 10, than the theoretical prediction for the parabolic flow through rigid tubes and channels. However, if the modification in the tube shape due to the pressure gradient, and the consequent modification in the velocity profile and pressure gradient, are incorporated, there is quantitative agreement between theoretical predictions and experimental results. The transition has important practical consequences, since there is a significant enhancement of mixing after transition.
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/B_{y}<0 variant. In the 25 July case a several-hour-long interval of steady southwest ICME field (B_{z}<0; B_{y}<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.
Simulation of Flow Pattern in Open Channels with Sudden Expansions
Directory of Open Access Journals (Sweden)
J. Mamizadeh
2012-09-01
Full Text Available Three-dimensional flows in sudden expansions of rectangular channels have been investigated. In this research, CFD simulation model (FLUENT6.2 is used. The k-ε turbulence model is used to simulate turbulence. Desired canal with coarse, medium and fine mesh size is selected for simulation. The results in canal with sudden expansion showed that the vortex formed by coarse mesh size and number of iteration more than 400 is asymmetric and for small and medium mesh size is symmetric. In order to analyze experimentally and numerically more closely, the pattern of flow in a flume with sudden expansion is investigated. Results showed that, asymmetrical flow pattern can be viewed with some minor changes such as roughness coefficient in any part of flume.
On the Analysis of Flows in Vibrating Channels
Zandi, Sahab; Mohammadi, Alireza; Floryan, Jerzy Maciej
2015-11-01
Pressure losses in channels with vibrating walls have been analyzed. Surface vibrations were assumed to have the form of travelling waves. The waves can have arbitrary profiles. The spectrally accurate immersed boundary conditions (IBC) method based on the Fourier expansions in the flow direction and the Chebyshev expansions in the transverse direction has been developed. The results show dependence of the pressure losses on the phase speed of the waves, with the waves propagating in the downstream direction reducing the pressure gradient required to maintain a fixed flow rate. A drag increase is observed when the waves propagate with a phase speed similar to the flow velocity. Analytical solution demonstrates that the drag changes result from the nonlinear interactions and vary proportionally to A2 for small enough A, where A stands for the wave amplitude. This work has been carried out with support from the Natural Sciences and Engineering Research Council (NSERC) of Canada.
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...
Implicit Large Eddy Simulation of Cavitation in Micro Channel Flows
Hickel, S; Schmidt, S J
2014-01-01
We present a numerical method for Large Eddy Simulations (LES) of compressible two-phase flows. The method is validated for the flow in a micro channel with a step-like restriction. This setup is representative for typical cavitating multi-phase flows in fuel injectors and follows an experimental study of Iben et al., 2010. While a diesel-like test fuel was used in the experiment, we solve the compressible Navier-Stokes equations with a barotropic equation of state for water and vapor and a simple phase-change model based on equilibrium assumptions. Our LES resolve all wave dynamics in the compressible fluid and the turbulence production in shear layers.
Directory of Open Access Journals (Sweden)
Szwast Maciej
2015-06-01
Full Text Available The paper presents the mathematical modelling of selected isothermal separation processes of gaseous mixtures, taking place in plants using membranes, in particular nonporous polymer membranes. The modelling concerns membrane modules consisting of two channels - the feeding and the permeate channels. Different shapes of the channels cross-section were taken into account. Consideration was given to co-current and counter-current flows, for feeding and permeate streams, respectively, flowing together with the inert gas receiving permeate. In the proposed mathematical model it was considered that pressure of gas changes along the length of flow channels was the result of both - the drop of pressure connected with flow resistance, and energy transfer by molecules of gas flowing in a given channel to molecules which penetrate this channel from the adjacent channel. The literature on membrane technology takes into account only the drop of pressure connected with flow resistance. Consideration given to energy transfer by molecules of gas flowing in a given channel to molecules which penetrate this channel from the adjacent channel constitute the essential novelty in the current study. The paper also presents results of calculations obtained by means of a computer program which used equations of the derived model. Physicochemical data concerning separation of the CO2/CH4 mixture with He as the sweep gas and data concerning properties of the membrane made of PDMS were assumed for calculations.
Use of Radioisotopes for Open-Channel Flow Measurements
International Nuclear Information System (INIS)
With techniques based upon the salt-dilution method, radioisotopes can be used for discharge measurements in open channels such as canals, streams and rivers. Field measurements with radioisotopes in canals discharging up to 8000 ft3/s have been made by the Bureau of Reclamation. The conditions of the field measurements are described in this paper, and important observations are made relating the results to the use of these methods for discharge measurements in rivers. The field tests were performed to study the general feasibility of the use of isotopes for discharge measurements in open channels and to investigate some of the important field problems which are still under study. These include the field requirements for necessary transverse mixing of the isotopes with die flowing water ; sorption of the isotopes by suspended sediments, channel flow surfaces and aquatic plants; and improvement of field procedures and equipment. Results of present laboratory and field tests lead to a proposed method for employing radioisotopes in river-discharge measurement to provide continuous or periodic discharge determinations. (author)
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
Channel network model for flow and radionuclide migration
International Nuclear Information System (INIS)
The Channel Network model has been developed for simulations of flow and solute transport in fractured rock. The model, and its computer implementation CHAN3D, has been used to simulate and analyse field experiments performed in Sweden. In the performance assessment of repositories for nuclear waste a tool was needed which could handle the release from the near field and simulate the radionuclide migration in the far field. In order to develop the tool the Channel Network model was integrated with a model which calculates the near filed release in detail. The integrated model concept which may be used for performance assessment of a nuclear repository is presented. A compartment model, NUCTRAN, is used to calculate the near field release from a damaged canister. Two main items were studied; the location of a damaged canister in relation to fracture zones, and the barrier function of the host rock. (R.P.)
Lagrangian Structure Function's Scaling Exponents in Turbulent Channel Flow
International Nuclear Information System (INIS)
The Lagrangian structure function's scaling exponents and intermittency of three-dimensional incompressible turbulent channel flow are investigated by using direct numerical simulation. The intermittency in streamwise velocity increments is found to increase in the near-wall region, which can be attributed to the presence of strong mean shear and organized motions in the near-wall region. It is found that the intermittency of transverse velocity increments is weaker than that of longitudinal ones. The present ESS evaluation of ζL(q) for the structure function of the streamwise velocity component in the channel centre is fairly close to experimental estimates of isotropic turbulence. (fundamental areas of phenomenology(including applications))
Energy Technology Data Exchange (ETDEWEB)
Kim, T. H.; Yun, B. J.; Jeong, J. H. [Pusan National University, Geunjeong-gu, Busan (Korea, Republic of)
2015-05-15
Studies were mostly about flow in upward flow in medium size circular tube. Although there are great differences between upward and downward flow, studies on vertical upward flow are much more active than those on vertical downward flow in a channel. In addition, due to the increase of surface forces and friction pressure drop, the pattern of gas-liquid two-phase flow bounded to the gap of inside the rectangular channel is different from that in a tube. The downward flow in a rectangular channel is universally applicable to cool the plate type nuclear fuel in research reactor. The sub-channel of the plate type nuclear fuel is designed with a few millimeters. Downward air-water two-phase flow in vertical rectangular channel was experimentally observed. The depth, width, and length of the rectangular channel is 2.35 mm, 66.7 mm, and 780 mm, respectively. The test section consists of transparent acrylic plates confined within a stainless steel frame. The flow patterns of the downward flow in high liquid velocity appeared to be similar to those observed in previous studies with upward flow. In downward flow, the transition lines for bubbly-slug and slug-churn flow shift to left in the flow regime map constructed with abscissa of the superficial gas velocity and ordinate of the superficial liquid velocity. The flow patterns observed with downward flow at low liquid velocity are different from those with upward flow.
Measurements of local two-phase flow parameters in a boiling flow channel
International Nuclear Information System (INIS)
Local two-phase flow parameters were measured lo investigate the internal flow structures of steam-water boiling flow in an annulus channel. Two kinds of measuring methods for local two-phase flow parameters were investigated. These are a two-conductivity probe for local vapor parameters and a Pitot cube for local liquid parameters. Using these probes, the local distribution of phasic velocities, interfacial area concentration (IAC) and void fraction is measured. In this study, the maximum local void fraction in subcooled boiling condition is observed around the heating rod and the local void fraction is smoothly decreased from the surface of a heating rod to the channel center without any wall void peaking, which was observed in air-water experiments. The distributions of local IAC and bubble frequency coincide with those of local void fraction for a given area-averaged void fraction. (author)
Turbulent flow in a ribbed channel: Flow structures in the vicinity of a rib
DEFF Research Database (Denmark)
Wang, Lei; Salewski, Mirko; Sundén, Bengt
2010-01-01
PIV measurements are performed in a channel with periodic ribs on one wall. The emphasis of this study is to investigate the flow structures in the vicinity of a rib in terms of mean velocities, Reynolds stresses, probability density functions (PDF), and two-point correlations. The PDF distribution......-based visualization is applied to the separation bubble upstream of the rib. Salient critical points and limit cycles are extracted, which gives clues to the physical processes occurring in the flow....
The Effect of Confluence Angle on the Flow Pattern at a Rectangular Open-Channel
Directory of Open Access Journals (Sweden)
F. Rooniyan
2014-02-01
Full Text Available Flow connection in channels is a phenomenon which frequently happens in rivers, water and drainage channels and urban sewage systems. The phenomenon appears to be more complex in rivers than in channels, especially at the y-junction bed joint that causes erosion and sedimentation at some areas resulting to morphological changes. Flow behavior at the channel junction area depends on variables such as channel geometry, discharge ratio, tributary width and y-junction connection angle of the channel, bed level changes at the bed joint, flow characteristic at the bed joint upstream and flow Froude number in different sections. In this research, fluent numerical model and junction angles of 30o, 45o & 60o are used to analyze and evaluate the effect of channel junction geometry on the flow pattern and the flow separation zone dimensions in different ratios of flow discharge (upstream channel discharge to total discharge of the flow. Results for two ratios of flow discharge are represented. Results are in agreement with earlier studies and it is shown that the change of the channel crossing angle affects the flow pattern in the main channel and also that the dimensions of the created separation zone in the main channel become larger when the crossing angle increases. This phenomenon can also be observed when the flow discharge ratio is lower. Analysis showed that the least dimension of the separation zone will be at the crossing angle of 45o .
Stability of stratified two-phase flows in horizontal channels
Barmak, I.; Gelfgat, A.; Vitoshkin, H.; Ullmann, A.; Brauner, N.
2016-04-01
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 a smooth interface is stable only in confined zone of relatively low flow rates, which is in agreement with experiments, but is not predicted by long-wave analysis. Depending on the flow conditions, the critical perturbations can originate mainly at the interface (so-called "interfacial modes of instability") or in the bulk of one of the phases (i.e., "shear modes"). The present analysis revealed that there is no definite correlation between the type of instability and the perturbation wavelength.
International Nuclear Information System (INIS)
Previous flow regime studies have been for horizontal, vertical, and inclined pipe flow. As such, only a few studies have been performed on bundle geometries. The present paper examines the flow regimes for a vertical hexagonal flow channel with and without a finned fuel bundle. This type of a 36 finned rod hexagonal fuel bundle in parallel hexagonal flow channels is used in a MAPLE (Multi- purpose Applied Physics Lattice Experimental) type nuclear reactor. An experiment apparatus was designed consisting of the flow channel, inlet plenum and an air-water separator. The inlet plenum is used to provide a uniform mixture of air and water before entering the hexagonal flow channel. A turbine flow meter is used to determine the water flow rate. The turbine flow meter is calibrated for a low flow range and limits the measurable flow to 50 l/min. Flow pattern observation is determined by a SONY video camera, Real-Time Neutron Radiography, pressure transducer and capacitance transducer. The Sony video camera provides visual observation through a Lucite flow channel. The Real-Time Neutron Radiography system allows for flow visualization through an Aluminum flow channel. The pressure drop is correlated by the Validyne pressure transducer and the capacitance transducer provides the void fraction relationship
Energy dissipation rate limits for flow through rough channels and tidal flow across topography
Kerswell, R R
2016-01-01
An upper bound on the energy dissipation rate per unit mass, $\\epsilon$, for pressure-driven flow through a channel with rough walls is derived for the first time. For large Reynolds numbers, $Re$, the bound - $\\epsilon \\,\\leq \\, c\\, U^3/h$ where $U$ is the mean flow through the channel, $h$ the channel height and $c$ a numerical prefactor - is independent of $Re$ (i.e. the viscosity) as in the smooth channel case but the numerical prefactor $c$, which is only a function of the surface heights and surface gradients (i.e. not higher derivatives), is increased. Crucially, this new bound captures the correct scaling law of what is observed in rough pipes and demonstrates that while a smooth pipe is a singular limit of the Navier-Stokes equations (data suggests $\\epsilon \\, \\sim \\, 1/(\\log Re)^2\\, U^3/h$ as $Re \\rightarrow \\infty$), it is a regular limit for current bounding techniques. As an application, the bound is extended to oscillatory flow to estimate the energy dissipation rate for tidal flow across botto...
Hall Effects on MHD Flow Through a Porous Straight Channel
Directory of Open Access Journals (Sweden)
N. Bhaskara Reddy
1982-10-01
Full Text Available The effect of Hall currents on the flow of a viscous incompressible slightly conducting fluid through a porous straight channel under a uniform transverse magnetic field is considered. The pressure gradient is taken as constant quantity and the case of steady flow is obtained by taking the time since the start of the motion to be infinite. Skin friction, temperature distribution and coefficients of heat transfer at both the plates have been evaluated. The effects of Hall parameter, magnetic parameter and Reynolds number on the above physical quantities have been investigated. Velocity distribution when the pressure gradient (i varies linearly with time, and (ii decreases exponentially with time has also been evaluated.
Fluid flow over arbitrary bottom topography in a channel
Panda, Srikumar
2016-05-01
In this paper, two-dimensional free surface potential flow over an arbitrary bottom in a channel is considered to analyze the behavior of the free surface profile using linear theory. It is assumed that the fluid is inviscid, incompressible and flow is irrotational. Perturbation analysis in conjunction with Fourier transform technique is employed to determine the first order corrections of some important physical quantities such as free surface profile, velocity potential, etc. From the practical point of view, one arbitrary bottom topography is considered to determine the free surface profile since the free surface profile depends on the bottom topography. It is found that the free surface profile is oscillatory in nature, representing a wave propagating downstream and no wave upstream.
Direct numerical simulation of particle entrainment in turbulent channel flow
International Nuclear Information System (INIS)
Particle entrainment process in a turbulent channel flow is studied. The time history of the instantaneous turbulent velocity vector field is generated by the direct numerical simulation of the Navier--Stokes equation with the aid of a pseudospectral code. The equation of motion of submicrometer particles including Stokes drag and Brownian diffusion is used, and typical entrained particle trajectories are evaluated and statistically analyzed. It is shown that the wall coherent structure plays a dominant role on the particle entrainment process. Particles are removed from the wall region by being captured in the high speed streams moving away from the wall, which are formed by the flow structure. Furthermore, single streamwise vortices are shown to be more frequent than pairs of counter-rotating ones at every instance of time. Temporal average of the vorticity field, however, shows roughly periodic sequence of counter-rotating vortices in the wall region. copyright 1995 American Institute of Physics
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.
International Nuclear Information System (INIS)
Experiments of visualized two-phase upward flow were conducted in the packed channel, which filled with 3, 5, 8 mm in diameter of glass sphere respectively. The gas superficial velocity ranges from 0.005 to 1.172 m/s. The liquid superficial velocity ranges from 0.004 to 0.093 m/s. Four representative flow patterns were observed as bubbly flow, cluster flow, liquid-pulse flow and churn-pulse flow, and corresponding flow pattern maps were also presented. It is found that the pulse flow region is dominant. The comparisons of flow pattern map between packed channel and non-packed channel show that the bubbly flow region in packed channel is narrower than that of non-packed channel due to the packing. The comparisons of flow pattern maps for three different packing sizes show that the cluster flow region expands with the increase of the packing diameter. In the low liquid superficial velocity, the cluster flow directly changes to churn-pulse flow in the packed channel with 8 mm packing. (authors)
Ramification of Channel Networks Incised by Groundwater Flow
Yi, R. S.; Seybold, H. F.; Petroff, A. P.; Devauchelle, O.; Rothman, D.
2011-12-01
The geometry of channel networks has been a source of fascination since at least Leonardo da Vinci's time. Yet a comprehensive understanding of ramification---the mechanism of branching by which a stream network acquires its geometric complexity---remains elusive. To investigate the mechanisms of ramification and network growth, we consider channel growth driven by groundwater flow as a model system, analogous to a medical scientist's laboratory rat. We test our theoretical predictions through analysis of a particularly compelling example found on the Florida Panhandle north of Bristol. As our ultimate goal is to understand ramification and growth dynamics of the entire network, we build a computational model based on the following growth hypothesis: Channels grow in the direction that captures the maximum water flux. When there are two such directions, tips bifurcate. The direction of growth can be determined from the expansion of the ground water field around each tip, where each coefficient in this expansion has a physical interpretation. The first coefficient in the expansion determines the ground water discharge, leading to a straight growth of the channel. The second term describes the asymmetry in the water field leading to a bending of the stream in the direction of maximal water flux. The ratio between the first and the third coefficient determines a critical distance rc over which the tip feels inhomogeneities in the ground water table. This initiates then the splitting of the tip. In order to test our growth hypothesis and to determine rc, we grow the Florida network backward. At each time step we calculate the solution of the ground water field and determine the appropriate expansion coefficients around each tip. Comparing this simulation result to the predicted values provides us with a stringent measure for rc and the significance of our growth hypothesis.
An approach to implement virtual channels for flowing magnetic beads
International Nuclear Information System (INIS)
This work demonstrates the feasibility of a novel microfluidic system with virtual channels formed by ‘walls’ of magnetic fields, including collecting channels, transporting channels and function channels. The channels are defined by the nickel patterns. With its own ferromagnetism, nickel can be magnetized using an external magnetic field; the nickel structures then generate magnetic fields that can either guide or trap magnetic beads. A glass substrate is sandwiched between the liquid containing magnetic beads and the chip with nickel structures, preventing the liquid from directly contacting the nickel. In this work, collecting channels, transporting channels and function channels are displayed sequentially. In the collecting channel portion, channels with different shapes are compared. Next, in the transporting channel portion we demonstrate I-, S- and Y-shaped channels can steer magnetic beads smoothly. Finally, in the function channel portion, a switchable trapping channel implemented with a bistable mechanism performs the passing and blocking of a magnetic bead. (paper)
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 ...
Wave-induced topographic formstress in baroclinic channel flow
Olbers, Dirk; Lettmann, Karsten; Wolff, Jörg-Olaf
2007-12-01
Large-scale zonal flow driven across submarine topography establishes standing Rossby waves. In the presence of stratification, the wave pattern can be represented by barotropic and baroclinic Rossby waves of mixed planetary topographic nature, which are locked to the topography. In the balance of momentum, the wave pattern manifests itself as topographic formstress. This wave-induced formstress has the net effect of braking the flow and reducing the zonal transport. Locally, it may lead to acceleration, and the parts induced by the barotropic and baroclinic waves may have opposing effects. This flow regime occurs in the circumpolar flow around Antarctica. The different roles that the wave-induced formstress plays in homogeneous and stratified flows through a zonal channel are analyzed with the BARBI (BARotropic-Baroclinic-Interaction ocean model, Olbers and Eden, J Phys Oceanogr 33:2719-2737, 2003) model. It is used in complete form and in a low-order version to clarify the different regimes. It is shown that the barotropic formstress arises by topographic locking due to viscous friction and the baroclinic one due to eddy-induced density advection. For the sinusoidal topography used in this study, the transport obeys a law in which friction and wave-induced formstress act as additive resistances, and windstress, the effect of Ekman pumping on the density stratification, and the buoyancy forcing (diapycnal mixing of the stratified water column) of the potential energy stored in the stratification act as additive forcing functions. The dependence of the resistance on the system parameters (lateral viscosity ɛ, lateral diffusivity κ of eddy density advection, Rossby radius λ, and topography height δ) as well as the dependence of transport on the forcing functions are determined. While the current intensity in a channel with homogeneous density decreases from the viscous flat bottom case in an inverse quadratic law ~ δ -2 with increasing topography height and
Three dimensional computation of turbulent flow in meandering channels
Energy Technology Data Exchange (ETDEWEB)
Van Thinh Nguyen
2000-07-01
In this study a finite element calculation procedure together with two-equation turbulent model k-{epsilon} and mixing length are applied to the problem of simulating 3D turbulent flow in closed and open meandering channels. Near the wall a special approach is applied in order to overcome the weakness of the standard k-{epsilon} in the viscous sub-layer. A specialized shape function is used in the special near wall elements to capture accurately the strong variations of the mean flow variables in the viscosity-affected near wall region. Based on the analogy of water and air flows, a few characteristics of hydraulic problems can be examined in aerodynamic models, respectively. To study the relationships between an aerodynamic and a hydraulic model many experiments have been carried out by Federal Waterway Engineering and Research Institute of Karlsruhe, Germany. In order to test and examine the results of these physical models, an appropriated numerical model is necessary. The numerical mean will capture the limitations of the experimental setup. The similarity and the difference between an aerodynamic and a hydraulic model will be found out by the results of numerical computations and will be depicted in this study. Despite the presence of similarities between the flow in closed channels and the flow in open channels, it should be stated that the presence of a free surface in the open channel introduces serious complications to three dimensional computation. A new unknown, which represents the position of nodes on this free surface, is introduced. A special approach is required for solving this unknown. A procedure surface tracking is applied to the free surface boundary like a moving boundary. Grid nodes on the free surface are free to move in such a way that they belong to the spines, which are the generator lines to define the allowed motion of the nodes on the free surface. (orig.) [German] Die numerische Simulation ist heute ein wichtiges Hilfsmittel fuer die
Unstable fluid flow in a water-cooled heating channel
International Nuclear Information System (INIS)
Experimental investigations of the instable behavior of a pressurized water flow in forced convection in a heating channel, with subcooled or bulk boiling have been carried. Tests were conducted at 1140, 850 and 570 psi. The test section was 35 in. high, surmounted by a 25.4 in. riser, these sections were by-passed by a pipe where the flow was between 1 and 4 times the flow in the test section. The water velocity (in the test section) was between 1.6 and 6.6 ft/s. Under certain conditions oscillations with a period of several seconds and perfectly stable have been observed. A mathematical model has been defined and a good agreement obtained for the main characteristics of the oscillations. It seems that the dimensions of the riser have a determining effect: the inception of bulk boiling gives an important variation of the driving head which can generate oscillations due to the non-zero delay for the system to reach its equilibrium. (author)
Hydraulics of combining flow in a right-angled compound open channel junction
Indian Academy of Sciences (India)
Sushant K Biswal; Pranab Mohapatra; K Muralidhar
2016-01-01
Although combining flows are common in natural streams, no comprehensive experimental data has been compiled to characterize the three-dimensional flow field within the compound channel confluence. The present study examines the time-averaged flow structure at confluence over a rigid bed. Current knowledge of channel confluence, based on laboratory observation indicates that cross flow interactions exert a significant influence on confluence events. Secondary current and turbulent stresses are reproduced well by the hydraulic model and found greater in the interface region as relative flow ratio decreases. Velocity fields in combining flow region arising from varying discharge ratios are presented. A zone of depression in surface elevation in compound channel junction is observed as well. The flow field in compound channel is seen to be moderately different from that of simple channel junction. This study contributes to a better knowledge of hydraulic key processes into fundamental aspect of combining flow dynamics.
Numerical simulation of the channel flow affected by synthetic jet
Czech Academy of Sciences Publication Activity Database
Dančová, Petra; Vít, T.
Kyjev: Міністерство Освіти і Науки України, 2009, s. 14-15. [Міжнародної науково-методичної конференції ВИВЧЕННЯ САПР УКРАЇНСЬКИМИ ІНЖЕНЕРАМИ. Kyjev (UA), 25.06.2009-27.06.2009] R&D Projects: GA AV ČR(CZ) IAA200760801 Institutional research plan: CEZ:AV0Z20760514 Keywords : numerical simulation * synthetic jet * channel flow Subject RIV: BK - Fluid Dynamics
DRAG REDUCTION IN A TURBULENT CHANNEL FLOW WITH HYDROPHOBIC WALL
Institute of Scientific and Technical Information of China (English)
NOURI Nowrouz Mohammad; SEKHAVAT Setareh; MOFIDI Alireza
2012-01-01
This paper investigates a theoretical prediction of friction drag reduction in turbulent channel flow which is achieved by using superhydrophobic surfaces.The effect of the hydrophobic surface is considered to be a slip boundary condition on the wall,and this new boundary condition is added to Large Eddy Simulation (LES) equations.The predicted drag reduction at Rer =180 is approximately 30％,which concurs with results obtained from Direct Numerical Simulation (DNS).An important implication of the present finding is that the near-wall turbulence structures are modified with streamwise slip velocity.In addition,a noticeable effect on the turbulence structure occurs when the slip length is greater than a certain value.
Experimental analysis of the flow structure in the laboratory model of SOFC fuel cell channels
International Nuclear Information System (INIS)
In the presented paper a flow structure in the gas channel of planar SOFC fuel cell is presented. The model taken for analysis was constructed based on the channel geometry manufactured by SOFC Power company. The shape of a channel was rectangular filled with large number of obstacles which role is to divide the flow into segments with possibly homogenous velocity distribution. The model itself was constructed from Plexiglas and the reactant gases flow was modelled by water motion. To investigate and visualize the flow structures a PIV technique was applied. Three different flow rates were taken for investigations and the flow uniformity and time dependence was studied.
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.
Analytical study on mechanism of countercurrent flow limitation in vertical rectangular channels
International Nuclear Information System (INIS)
A quantitative analysis of countercurrent flow limitation (CCFL) or flooding was successfully carried out using the existing experimental data for the vertical rectangular channels, adopting the criterion that the CCFL condition is determined by maximizing the falling water mass velocity with respect to the thickness of falling water film for the whole flow channel, without any additional conditions. It was found that significant factors were the flow pattern, that is, which walls were wet, interfacial friction factor between liquid and gas based on the relative velocity, wall friction factors for laminar, transition, and turbulent flow of liquid and gas, and aspect ratio of rectangular channels. Thus it was clarified that the analytical results give good predictions of the existing experimental data of air-water system for vertical rectangular channels of 33 and 66 mm in channel width, 2.3 to 12.3 mm in channel gap, and 362 and 782 mm in channel length under atmospheric pressure
Coalescence and breakup of large droplets in turbulent channel flow
Scarbolo, Luca; Bianco, Federico; Soldati, Alfredo
2015-07-01
Coalescence and breakup of large deformable droplets dispersed in a wall-bounded turbulent flow are investigated. Droplets much larger than the Kolmogorov length scale and characterized by a broad range of surface tension values are considered. The turbulent field is a channel flow computed with pseudo-spectral direct numerical simulations, while phase interactions are described with a phase field model. Within this physically consistent framework, the motion of the interfaces, the capillary effects, and the complex topological changes experienced by the droplets are simulated in detail. An oil-water emulsion is mimicked: the fluids are considered of same density and viscosity for a range of plausible values of surface tension, resulting in a simplified system that sets a benchmark for further analysis. In the present conditions, the Weber number (We), that is, the ratio between inertia and surface tension, is a primary factor for determining the droplets coalescence rate and the occurrence of breakups. Depending on the value of We, two different regimes are observed: when We is smaller than a threshold value (We 1), a permanent dynamic equilibrium between coalescence and breakup events is established.
Natural transition to turbulence in polymeric channel flow
Lee, Sang Jin; Zaki, Tamer
2015-11-01
Natural transition in viscoelastic channel flow is investigated using direct numerical simulations (DNS), where the polymer is modeled using the FENE-P constitutive equations. The computations capture the amplification of the primary two-dimensional Tollmien-Schlichting (TS) waves, their secondary instability and ultimately the onset of turbulence. Various Weissenberg numbers (Wi) are simulated in order to assess the influence of elasticity. As Wi is increased, the primary TS waves initially become more linearly unstable, but are subsequently stabilized at higher Wi. This trend suggests that elasticity can either promote or delay transition to turbulence, and the DNS substantiate this prediction. In order to isolate the effect of the polymer on the secondary instability process, simulations are performed for a set of elastic parameters where the primary TS wave has the same linear growth rate as the Newtonian configuration. As a result, while the linear disturbance amplification is similar in the viscoelastic and Newtonian flows, the nonlinear saturated state of the TS waves differs in the two cases, as well as their secondary instability and breakdown to turbulence. The changes in the transition process are examined by analyzing the disturbance energy budget and spectra.
Evaluation of Correlations of Flow Boiling Heat Transfer of R22 in Horizontal Channels
Zhanru Zhou; Xiande Fang; Dingkun Li
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 corr...
Effect of the Flow Channel Structure on the Nanofiltration Separation Performance
Directory of Open Access Journals (Sweden)
Zhi Chen
2013-01-01
Full Text Available Two kinds of newly designed feed channels, for example, a spiral and a serpentine feed channels, for a bench-scale nanofiltration module were developed to improve the filtration performance. The experiments were carried out with the modules using a commercial flat NF membrane to investigate the effects of Reynolds number (Re and flow channel structures on the flux of permeate and Mg2+ rejection. It was shown from the experimental results that although the effects of Reynolds number on fluxes were not obvious for the two new feed channels compared with a normal flow channel structure, the Mg2+ rejections varied apparently with Re. The Mg2+ rejections were almost the same for the modules with two new feed channels and larger than that for the module with normal feed channel. The numerical simulations of fluid flow in the three kinds of feed channels were completed at Re of 4800 to explain the phenomena. The results demonstrated that there was a secondary flow in both new feed channels, which strongly influences the Mg2+ rejection. The rejection increased with increasing average shear stress at the membrane wall. The spiral feed channel was the best one among the flow channel structures investigated.
Radionuclide Release after Channel Flow Blockage Accident in CANDU-6 Plant
Energy Technology Data Exchange (ETDEWEB)
Choi, Hoon; Jun, Hwang Yong [Korea Electric Power Corporation Research Institute, Daejeon (Korea, Republic of)
2011-05-15
The channel flow blockage accident is one of the in core loss of coolant accidents, the release path of radionuclide is very different from conventional loss of coolant accidents. The large amount of radionuclide released from broken channel is being washed during it passes through the moderator in Calandria. The objective of containment behavior analysis for channel flow blockage event is to assess the amount of radionuclide release to the ambient atmosphere. Radionuclide release rates in case of channel flow blockage with all safety system available, that is containment building is intact, as well as with containment system impairment are analyzed with GOTHIC and SMART code
Transport of self-propelling bacteria in micro-channel flow
Costanzo, A.; Di Leonardo, R.; Ruocco, G.; Angelani, L.
2012-02-01
Understanding the collective motion of self-propelling organisms in confined geometries, such as that of narrow channels, is of great theoretical and practical importance. By means of numerical simulations we study the motion of model bacteria in 2D channels under different flow conditions: fluid at rest, steady and unsteady flow. We find aggregation of bacteria near channel walls and, in the presence of external flow, also upstream swimming, which turns out to be a very robust result. Detailed analysis of bacterial velocity and orientation fields allows us to quantify the phenomenon by varying cell density, channel width and fluid velocity. The tumbling mechanism turns out to have strong influence on velocity profiles and particle flow, resulting in a net upstream flow in the case of non-tumbling organisms. Finally we demonstrate that upstream flow can be enhanced by a suitable choice of an unsteady flow pattern.
Institute of Scientific and Technical Information of China (English)
Wang Yongan; Tian Shujun; Jia Chunqiang; Cao Yuning
2008-01-01
Computational fluid dynamics (CFD) was used in conjunction with BP neural network to study the flow resistance characteristic of the combination-channel inside hydraulic manifold block (HMB).The in put parameters of the combination-channel model were confirmed to have effect on the pressure-drop by the numerical method, and a BP neural network model was accordingly constructed to predict the channel pressure-drops.The flow resistance characteristic curves of various channels were achieved, and a performance parameter was given to evaluate the through-flow characteristic of the channel according to the curves.The predictions are in agreement with the numerical computation, indicating that the method can be utilized to accurately determine the flow characteristic of the combination channel with high efficiency.
Analysing Gas-Liquid Flow in PEM Electrolyser Micro-Channels
DEFF Research Database (Denmark)
Lafmejani, Saeed Sadeghi; Olesen, Anders Christian; Kær, Søren Knudsen
2016-01-01
further understanding of the gas-liquid flow in both the porous media and the channel is necessary for insuring proper oxygen, water and heat management of the electrolysis cell. In this work, the patterns of vertical upward gas-liquid flow in a 5×1×94 mm micro-channel are experimentally analysed. A sheet...
Flow Patterns and Thermal Drag in a One-Dimensional Inviscid Channel with Heating or Cooling
Institute of Scientific and Technical Information of China (English)
无
1993-01-01
In this paper investigations on the flow patterns and the thermal drag phenomenon in one -dimensional inviscid channel flow with heating or cooling are described and discussed:expressions of flow rate ratio and thermal drag coefficient for different flow patterns and its physical mechanism are presented.
Directory of Open Access Journals (Sweden)
Rajesh Khatri
2012-03-01
Full Text Available In this paper heat transfer and fluid flow characteristics in a channel has been theoretically investigated. In this study, FEM is employed to analyze a fluid flow inside a channel and then solve for the heat flow transfer through the same channel. The fluid flow is expressed by partial differential equation (Poisson’s equation.While, heat transfer is analyzed using the energy equation. The Navier Stokes equations along with the energy equation have been solved by using simple technique. The domain is discretized using 2626 elements and that corresponds to a total number of nodes 2842. The channel has a constant heat flux at the two walls and the threedimensional numerical simulations. Numerical solutions were obtained using commercial software Ansys Fluent. The working fluid was air (Pr=0.7. The local Nusselt numbers are obtained, which can be used inestimation of flow and heat transfer performance in a channel In addition, local Nusselt numbers, velocity magnitude and temperature profiles, and pressure profiles are analyzed. Results showed that both fluid flow and temperature flow are influenced significantly with changing entrance velocity. The overall objective of thispaper is to study the flow characteristics and heat transfer analysis inside a channel while increasing entrance velocity.
Bittagopal Mondal; Dipankar Chatterjee
2016-01-01
The serpentine flow channel can be considered as one of the most common and practical channel layouts for a polymer electrolyte membrane fuel cell (PEMFC) since it ensures an effective and efficient removal of water produced in a cell with acceptable parasitic load. Water management is one of the key issues to improve the cell performance since at low operating temperatures in PEMFC, water vapor condensation starts easily and accumulates the liquid water droplet within the flow channels, thus...
Contribution of KV7 Channels to Basal Coronary Flow and Active Response to Ischemia
DEFF Research Database (Denmark)
Khanamiri, Saereh; Soltysinska, Ewa; Jepps, Thomas A;
2013-01-01
The goal of the present study was to determine the role of KCNQ-encoded KV channels (KV7 channels) in the passive and active regulation of coronary flow in normotensive and hypertensive rats. In left anterior descending coronary arteries from normotensive rats, structurally different KV7.2 to 7....... Overall, these data establish KV7 channels as crucial regulators of coronary flow at resting and after hypoxic insult....
Heat Transfer Enhancement by Flow Control in a Rectangular Horizontal Channel
Ghazali Mebarki; Samir Rahal; Abdelhek Hamza
2013-01-01
Laminar fluid flows and heat transfers, by forced convection, in a rectangular horizontal channel, have been numerically investigated. Three blocks, simulating electronic components, have been attached to the channel bottom wall. In order to control the flow and enhance the heat transfer rate, a rectangular cross section bar, acting as a vortex generator, has been attached to the channel top wall. The Navier-Stokes and energy equations are solved using FLUENT. Velocity and temperature fields ...
GATE REGULATION SPEED AND TRANSITION PROCESS OF UNSTEADY FLOW IN CHANNEL
Institute of Scientific and Technical Information of China (English)
TAN Guang-ming; DING Zhi-liang; WANG Chang-de; YAO Xiong
2008-01-01
The operation methods of channel and the speed of gate regulation have great influence on the transformation of flow in water conveyance channels. Based on characteristics method, a 1-D unsteady flow numerical model for gate regulation was established in this study. The process of water flow was simulated under different boundary conditions. The influence of gate regulation speed and channel operation methods on flow transition process was analyzed. The numerical results show that under the same conditions, with increasing regulation speed of the gate, the change rates of discharge and water level increase, while the response time of channel becomes shorter, and ultimately the discharge and water level will transit to the same equilibrium states. Moreover, the flow is easier to reach stable state, if the water level in front of the sluice is kept constant, instead of behind the sluice. This study will be important to the scheme design of automatic operation control in water conveyance channels.
Morphological impacts of flow events of varying magnitude on ephemeral channels in a semiarid region
Hooke, J. M.
2016-01-01
Flows in ephemeral channels in semiarid areas are only occasional, and channel changes are episodic; but the flash floods can be devastating and have major geomorphological impacts. Data on morphological impacts of flows in semiarid areas are needed to increase understanding of the dynamics and variability of geomorphic responses in such channels. For this purpose nine reaches of river channel in three catchments in SE Spain - the Nogalte, Torrealvilla, and Salada - have been sites for measurement of flows and their effects over the period 1997-2012. The sites encompass a range of channel size, channel morphology, substrate, vegetation, and position within the catchments. A major difference is between schist and marl bedrock areas. Peak flow stage has been recorded and topography surveyed at frequent intervals and after major flow events. Over the 16-year period, an average of 0.5 flow events per year has been recorded at the schist sites, and an average of one per year at the marl sites; but occurrence has been highly variable from year to year. Threshold daily rainfall for channel flow is mostly 15-20 mm, but higher rainfalls do not always produce flow. One to two major floods have occurred in each of the catchments in the period, including the extreme flood event of September 2012 in the Nogalte catchment. Measured morphological changes have occurred between 2 and 10 times at the monitored sites. The same size flow can have differing effects depending on the state of the system. Low flow can mobilise sediment without producing much morphological change. The long-term trajectory of the reaches and the sediment substrate has a major influence on response to events. Channel change is governed by threshold values of hydraulic conditions. The measurements provide an indication of the scale of maximum erosion and deposition that occurs within the channels and on the floodplains over a range of flow magnitudes and the flow impacts that need to be considered in
Analysis Of The Effect Of Flow Channel Width On The Performance Of PEMFC
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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.
Evolution of the Detached Westward Flow Channel as Observed by the Unwin HF Radar
Makarevich, R. A.; Dyson, P. L.
2005-12-01
We examine the spatial and temporal evolution of latitudinally narrow regions with enhanced Doppler velocity observed by the Unwin TIGER HF radar equatorward of Auroral Westward Flow Channels. AWFCs were detected by both the Bruny Island and New Zealand (Unwin) TIGER radars as regions with enhanced westward convection, at about -62 deg MLAT. A second, more equatorward (~ -60 deg MLAT) channel with enhanced westward convection was detected only by the Unwin radar. The spatio-temporal behaviour of the second channel and its characteristics were found to be significantly different from those of AWFCs, e.g. both the channel and flow directions were significantly non-L-shell-aligned. We also investigate the relationship between the flow speeds within the two types of flow channels. In all cases, the second channel appeared to originate within or close to the AWFC, with the flow deviation from the magnetic L-shell direction and latitudinal separation between channels increasing with time. In sharp contrast to the AWFC that persisted for 2-3 hours, the second channel was recognizable only for 30-50 min. A relation between multiple flow channels and other subauroral phenomena such as subauroral ion drifts (SAID) and subauroral polarization streams (SAPS), and the implications of observations for models of SAID and SAPS formation are discussed.
Institute of Scientific and Technical Information of China (English)
Liu Haiyong; Liu Cunliang; Wu Wenming
2015-01-01
A series of numerical analyses have been performed to investigate the flow structures in a narrow confined channel with 12 staggered circular impingement holes and one bigger exit hole. The flow enters the channel through the impingement holes and exits through the far end outlet. The flow fields corresponding to two jet Reynolds numbers (25000 and 65000) and three channel con-figurations with different ratios of the channel height to the impingement hole diameter (Zr=1, 3, 5) are analyzed by solving the Reynolds averaged Navier–Stokes equations with the realizable k–e turbulence model. Detailed flow field information including the secondary flow, the interaction between the jets and the cross flow, and flow distribution along the channel has been obtained. Comparisons between the numerical and experimental results of the flow fields at the four planes along the channel are performed to validate the numerical method. The calculated impingement pattern, high velocity flow distribution, low velocity separation region and vortices are in good agreement with the experimental data, implying the validity and effectiveness of the employed numerical approach for analyzing relevant flow field.
Factors affecting measurement of channel thickness in asymmetrical flow field-flow fractionation.
Dou, Haiyang; Jung, Euo Chang; Lee, Seungho
2015-05-01
Asymmetrical flow field-flow fractionation (AF4) has been considered to be a useful tool for simultaneous separation and characterization of polydisperse macromolecules or colloidal nanoparticles. AF4 analysis requires the knowledge of the channel thickness (w), which is usually measured by injecting a standard with known diffusion coefficient (D) or hydrodynamic diameter (dh). An accurate w determination is a challenge due to its uncertainties arising from the membrane's compressibility, which may vary with experimental condition. In the present study, influence of factors including the size and type of the standard on the measurement of w was systematically investigated. The results revealed that steric effect and the particles-membrane interaction by van der Waals or electrostatic force may result in an error in w measurement. PMID:25817708
Navier-Stokes solver using Green's functions I: channel flow and plane Couette flow
Viswanath, Divakar
2012-01-01
Numerical solvers of the incompressible Navier-Stokes equations have reproduced turbulence phenomena such as the law of the wall, the dependence of turbulence intensities on the Reynolds number, and experimentally observed properties of turbulence energy production. In this article, we begin a sequence of investigations whose eventual aim is to derive and implement numerical solvers that can reach higher Reynolds numbers than is currently possible. Every time step of a Navier-Stokes solver in effect solves a linear boundary value problem. The use of Green's functions leads to numerical solvers which are highly accurate in resolving the boundary layer, which is a source of delicate but exceedingly important physical effects at high Reynolds numbers. The use of Green's functions brings with it a need for careful quadrature rules and a reconsideration of time steppers. We derive and implement Green's function based solvers for the channel flow and plane Couette flow geometries. The solvers are validated by repro...
Critical heat flux for low flow boiling in vertical uniformly heated thin rectangular channels
International Nuclear Information System (INIS)
Steady-state, subcooled, low flow, critical heat flux (CHF) experiments simulating natural convection boiling are performed in a thin rectangular vertical channel. The aluminum channel is heated on one side: the other side of the channel is a Pyrex window allowing visual observation of the CHF event. Both upward and downward flow conditions are tested with exit pressure varying from 20 to 85 kPa, inlet water temperature varying from 295 to 343 K (inlet subcooling 5-72 K), and mass flux varying from 30 to 80 kg s-1 m-2. Measured test results indicate downward flow dryout CHF occurring at 85% of upward flow dryout CHF values. This percentage is believed to result from the flow instability and reduced inlet subcooling induced by the counter-current flow. New dryout CHF correlations for low flow rates, representative of natural convection boiling, are recommended for both upward and downward flow. (Author)
Experimental and numerical study of proton exchange membrane fuel cell with spiral flow channels
International Nuclear Information System (INIS)
Highlights: ► Numerical and experimental study of the fuel cell with spiral channels is performed. ► Secondary vortices in cross section of the spiral channels are found. ► Enhancement in the performance of the fuel cell by the secondary vortices is discussed. ► The spiral channels also lead to a reduction in the pressure drop of the gas flow. -- Abstract: Numerical simulation of the performance of a proton exchange membrane fuel cell (PEMFC) with spiral channels is performed in this study. Experiments are also conducted to verify the numerical predictions. The spiral channel pattern produces secondary vortices which lead to enhancement in heat and mass transfer in the curved channels and appreciably improves the performance of the fuel cell. In addition, the spiral channels may also lead to a reduction in the pressure drop of the gas flow through the fuel cell. When the sizes of the outlet channels are designed to be smaller than those of the inlet channels, water flooding in the catalyst layers can be further improved. In the present study, the spiral channel pattern consists of five inlet channels and five outlet channels. Radius and area of the active zone are 28.2 mm and 2500 mm2, respectively. A comparison between the spiral and the serpentine channels shows that the average current density with the former is higher than that with the latter by 11.9%. It is found that numerical predictions are in close agreement with the experimental results.
Transport coefficients for laminar and turbulent flow through a four-cusp channel
International Nuclear Information System (INIS)
The heat transfer coefficients for laminar and turbulent flow in a four-cusp channel were determined. A numerical solution was developed for laminar flow an and experimental study for turbulent flow was carried out. Systematic variations of the Reynolds number were done in the range 900-30000. The results show that the heat transfer coefficients for the four-cusp channel are much lower than the coefficients for the circular tube. (author)
Surface drifter trajectories highlight flow pathways in the Mozambique Channel
Hancke, L.; Roberts, M J; Ternon, Jean-François
2014-01-01
The pattern of surface circulation in the Mozambique Channel was elucidated from the trajectories of 82 satellite-tracked drifters over the period 2000-2010 and complementary satellite-derived altimetry. Overall, the trajectories indicated that anticyclonic activity was mostly observed on the western side of the Channel, with cyclonic activity being more prevalent in the east. A lack of eddy activity was noted in the southeast corner of the Channel (i.e. SW of Madagascar). Drifter behaviour i...
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...
Does the choice of the forcing term affect flow statistics in DNS of turbulent channel flow?
Quadrio, Maurizio; Frohnapfel, Bettina; Hasegawa, Yosuke
2016-01-01
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 of such events explains their negligible contribution to the commonly computed statistics; however, the very existence of a difference in the PDF demonstrates that the forcing term is not entirely uninfluential. Other statistics for wall-based quantities (the two components of friction and pressure) are examined; in particular spatio-temporal autocorrelations show small differences at large temporal separations, where unfortunately the residual statistical uncertainty is still of the same order of the observed difference. Hence we suggest that the specific choice of the forcing term does not produce important statistical consequences, unless one is interested in the strongest events of high wall friction, that are underestimated by a simulation run at constant flow rate.
Width adjustment in experimental gravel-bed channels in response to overbank flows
Pitlick, John; Marr, Jeff; Pizzuto, Jim
2013-06-01
We conducted a series of flume experiments to investigate the response of self-formed gravel-bed channels to floods of varying magnitude and duration. Floods were generated by increasing the discharge into a channel created in sand- and gravel-sized sediment with a median grain size of 2 mm. Flooding increased the Shields stress along the channel perimeter, causing bank erosion and rapid channel widening. The sediment introduced to the channel by bank erosion was not necessarily deposited on the channel bed, but was rather transported downstream, a process likely facilitated by transient fining of the bed surface. At the end of each experiment, bank sediments were no longer in motion, "partial bed load transport" characterized the flat-bed portion of the channel, and the Shields stress approached a constant value of 0.056, about 1.2 times the critical Shields stress for incipient motion. Furthermore, the discharge was entirely accommodated by flow within the channel: the creation of a stable channel entirely eliminated overbank flows. We speculate that similar processes may occur in nature, but only where bank sediments are non-cohesive and where channel-narrowing processes cannot counteract bank erosion during overbank flows. We also demonstrate that a simple model of lateral bed load transport can reproduce observed channel widening rates, suggesting that simple methods may be appropriate for predicting width increases in channels with non-cohesive, unvegetated banks, even during overbank flows. Last, we present a model for predicting the equilibrium width and depth of a stable gravel-bed channel with a known channel-forming Shields stress.
Flow pattern map and multi-scale entropy analysis in 3 × 3 rod bundle channel
International Nuclear Information System (INIS)
Highlights: • Flow patterns of steam–water two-phase flow in a 3 × 3 rod bundle were visualized. • The flow pattern map obtained for the rod bundle was compared with some existing flow pattern maps. • Multi-scale entropy was used to characterize the dynamic characteristics of the different flow patterns. • Rate of multi-scale entropy can effectively identify flow patterns in a rod bundle channel. - Abstract: The characteristics of the heat transfer and two-phase flow resistance in a rod bundle channel are closely related to flow patterns. In the present study, two-phase flow patterns for vapor–water flows in a 3 by 3 rod bundle channel were obtained at atmospheric pressure and relatively low mass flow condition. Under the current experimental conditions, slug flow found in circular tubes was not observed. Comparisons with some existing flow pattern maps and transition criteria were likewise conducted. Results show that the transition boundary of circular tube deviated from the transition boundary of the boiling two-phase flow of the rod bundle channel. Using the differential pressure signal of the vapor–liquid two-phase flow, multi-scale entropy algorithm is employed to reveal the dynamic characteristics of the different flow patterns in the rod bundle. The multi-scale entropy rate could effectively classify the flow patterns in the rod bundle channel. Results suggest that multi-scale entropy can be an effective method to reveal the dynamic details of macro and local vantages
Investigation of reversed flow channel events by the ICI-3 sounding rocket
Moen, J. I.; Dabakk, Y.; Oksavik, K.; Bekkeng, T.; Bekkeng, J. K.; Lorentzen, D. A.; Baddeley, L. J.; Abe, T.; Saito, Y.; Ogawa, Y.; Robert, P.; Yoeman, T.
2012-12-01
Transient flow channel events are a key characteristic of solar wind - magnetosphere coupling to the cusp ionosphere. One class of flow channels, Reversed Flow Events (RFE),was first discovered by the EISCAT Svalbard Radar and later also documented by the SuperDARN radar system. An RFE is typically a 100-200 km wide longitudinally elongated flow channel near the cusp inflow region, inside which the flow direction is opposite to the large scale ionospheric background convection. These events are hence associated with strong flow shears, and this category of flow events has been attributed to Birkeland current arcs. There are two possible explanations for their existence: (1) the RFE channel may be a region where two MI current loops, forced by independent voltage generators, couple through a poorly conducting ionosphere and (2) the reversed flow channel may be the ionospheric footprint of an inverted V-type coupling region. Electron beams of DC electric field and magnetic field experiments, and a low energy electron spectrometer (10 eV-10 keV). The auroral activity and flow context during the flight was provided by ground based optics, the EISCAT Svalbard Radar and the SuperDARN HF radars. In this talk we will present the ICI-3 test of the two physical explanations given above for the RFE phenomenon, and we will provide a quantitative measure of the Kelvin-Helmholtz instability growth rate associated with the flow shears.
Renshaw, C.; Curtis, K.; Magilligan, F.; Dade, W.
2008-12-01
By resupplying the mainstem with water and sediment, tributaries are a primary mechanism for mitigating the impacts of flow regulation. As a result, morphological and ecological adjustments associated with flow regulation may be particularly pronounced at tributary junctions. Despite the extensive literature on how dams alter channel morphology, few studies have focused specifically on the relationship between flow regulation and consequent changes in bedload sediment transport at tributary junctions. Using historical aerial photographs, modern channel surveys, and flow modeling, we compare temporal changes between regulated and unregulated tributary junction morphology and sediment transport dynamics. In contrast to what has been observed along the Colorado River, where flow regulation has led to a reduction in the number and size of channel bars, we observe significant bar growth post-regulation along the West River in southern Vermont. In some cases exposed bar area increased more than 50 percent in the first three decades after regulation and coincides with a corresponding reduction in channel width. Revegetation of former floodplain surfaces has begun to reduce the exposed bar area. However, flow modeling indicates that the channel remains underfit with respect to the new flow regime, with the current 2- and 50-yr floods lacking sufficient competence to transport the bedload sediment discharged by tributaries. Thus even 50 years post regulation, additional morphological changes are still required for the mainstem channel to fully adjust to the new flow regime.
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. Cle
Experimental and numerical modelling of flow around the obstacles placed on a channel bottom
Hoření, Bohumír
2004-01-01
The paper deals with an application of integral equations on a wake flow. Two square cylinders oriented perpendicularly to flow direction are placed on the bottom of an open channel. The results of integral method are compared with LDA measurements and with Fluent k-? simulation. Besides the averaged results that offers Fluent simulation, the integral method can also simultae dynamical properties of the flow
Numerical Modeling of Surface and Volumetric Cooling using Optimal T- and Y-shaped Flow Channels
Kosaraju, Srinivas
2015-11-01
The T- and Y-shaped flow channels can be optimized for reduced pressure drop and pumping power. The results of the optimization are in the form of geometric parameters such as length and diameter ratios of the stem and branch sections. While these flow channels are optimized for minimum pressure drop, they can also be used for surface and volumetric cooling applications such as heat exchangers, air conditioning and electronics cooling. In this paper, we studied the heat transfer characteristics of multiple T- and Y-shaped flow channel configurations using numerical simulations. All configurations are subjected to same pumping power and heat generation constraints and their heat transfer performance is studied.
Heat transfer and pressure drop in serpentine {mu}DMFC flow channels
Energy Technology Data Exchange (ETDEWEB)
Hsieh, Shou-Shing; Her, Bing-Shyan [Department of Mechanical and Electro Mechanical Engineering, National Sun Yat-Sen University, Kaohsiung 80424 (China)
2007-12-15
In this paper, a 3-D mathematical model incorporated with Fluent computer code is described to investigate the flow and heat transfer for developing laminar flow in the micro direct methanol fuel cell ({mu}DMFC) with serpentine flow fields. The continuity, momentum, and energy equations are simultaneously solved by a general computational fluid dynamics code. Local, channel-mean, bended region-mean, and overall channel mean friction factors and Nusselt numbers were thus calculated and discussed. Finally, overall channel mean friction factor and Nusselt number were correlated in terms of the relevant parameters. (author)
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.
Interaction of droplet and sidewalls with modified surfaces in a PEMFC gas flow channel
Shah, Mihir M.
A Proton Exchange Membrane Fuel Cell (PEMFC) is a clean and highly efficient way of power generation used primarily for transportation applications. Hydrogen and air are supplied to the fuel cell through gas channels, which also remove liquid water generated in the fuel cell. The clogged channels prevent reactant transport to the electrochemically active sites which comprise one of the channel walls and thus, degrading the performance of the cell. Proper management of the product water is a current topic of research interest in commercialization of fuel cell vehicles. Liquid water, produced as by-product of the fuel cell reaction, can clog the gas channels easily since surface tension of water is significant at this length scale. In a PEMFC channel cross-section, water is assumed to be produced in the channel at the center along the flow axis. This assumption is primarily valid and extensively used for experimental purposes. However in a real PEMFC, the water entry is not constrained at the channel center. Hence, more investigations are made using water entry at channel corner (land region) which resulted in contradicting prior results for the water feature behavior for all relevant PEMFC operating conditions, leading to adverse two-phase flow behavior- including slug blockage and fluctuations at channel end. Very limited research is available to study the effect of gas channel surface modifications on the two-phase flow behavior and local PEMFC performance. In this study, the droplet--sidewall dynamic interactions and two--phase local pressure drop across the water droplet present in a PEMFC channel with trapezoidal geometries with surface modifications are studied. These surface modifications include micro-grooves that possess a hybrid wetting regime that will initiate and guide the water feature at channel ends to eject with general ease. Slugs are reduced to films after ejection and thus channel blockage is avoided overcoming the problems caused by water influx
Wasklewicz, T. A.; Staley, D. M.
2010-12-01
Debris flows are important geomorphic agents in alpine drainages. They have been linked with channel initiation in headwater streams, connectivity of organic material and sediment through drainage basins, and as hazards to human development in and adjacent to steep watersheds. Debris flows also significantly alter channel morphometry at a variety of spatial scales. Of particular interest are topographic changes associated with multiple surge fronts within a debris flow as well as between several debris flows. An unnamed tributary stream to Chalk Creek, CO has over the last decade experienced one to four debris flow events annually. Four field sampling campaigns were conducted in the summer and fall of 2009. A Leica ScanStation 2, in conjunction with a robust local control network, were used to capture channel morphodynamics along five stream reaches prior to the debris flow season and after three debris flows. Point cloud data from the scanner permit the generation of two centimeter planimetric resolution digital terrain models (DTM). DTM-of-difference analyses and measures of slope, roughness, sediment transport volumes and channel dimensions were employed to detect spatial and temporal morphometric changes. The first debris flow occurred on unsaturated bed material and resulted in aggradation along 3 of the 5 reaches. One reach, a bedrock step, remained relatively unchanged, while the final reach saw significant erosion along boulder steps in the channel and an associated mass failure adjacent to the stream bank through this section. The second debris flow resulted in net aggradation along all of the reaches. The third and largest debris flow took place on saturated bed materials. The flow produced net erosion along all reaches. Significant channel changes were associated with the headward erosion of debris flow snouts and bank failures associated with undercutting of angle-of-repose slopes during debris flow erosion. Analysis of the potential relationships
FINITE-VOLUME TVD ALGORITHM FOR DAM-BREAK FLOWS IN OPEN CHANNELS
Institute of Scientific and Technical Information of China (English)
Wang Jia-song; He You-sheng
2003-01-01
A finite-volume Total Variation Diminishing (TVD) scheme is presented for modeling dam-break flows in open channels.This method is used for solving the 2D shallow water equations on arbitrary quadrilateral meshes, based upon a second-order hybrid TVD scheme with an optimum-selected limiter in the space discretization and a two-step Runge-Kutta approach in the time discretization.Verification for a circular dam-break problem is carried out by comparing the present results with others and very good agreement is shown.The present algorithm is then used to predict dam-break flow characteristics in open channels such as in furcated channels.More complicated unsteady flow characteristics in these furcated channels than in the regular channels studied previously can observed in this work.
International Nuclear Information System (INIS)
In this study, we consider the heat transfer characteristics of channel flow in the presence of an infinite streamwise array of equispaced identical rotating circular cylinders. This flow configuration can be regarded as a model representing a micro channel or an internal heat exchanger with cylindrical vortex generators. A numerical parametric study has been carried out by varying Reynolds number based on the bulk mean velocity and the cylinder diameter, and the gap between the cylinders and the channel wall for some selected angular speeds. The presence of the rotating circular cylinders arranged periodically in the streamwise direction causes a significant topological change of the flow, leading to heat transfer enhancement on the channel walls. More quantitative results as well as qualitative physical explanations are presented to justify the effectiveness of varying the gap to enhance heat transfer from the channel walls
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...
3D Simulation of Velocity Profile of Turbulent Flow in Open Channel with Complex Geometry
Kamel, Benoumessad; Ilhem, Kriba; Ali, Fourar; Abdelbaki, Djebaili
Simulation of open channel flow or river flow presents unique challenge to numerical simulators, which is widely used in the applications of computational fluid dynamics. The prediction is extremely difficult because the flow in open channel is usually transient and turbulent, the geometry is irregular and curved, and the free-surface elevation is varying with time. The results from a 3D non-linear k- ɛ turbulence model are presented to investigate the flow structure, the velocity distribution and mass transport process in a meandering compound open channel and a straight open channel. The 3D numerical model for calculating flow is set up in cylinder coordinates in order to calculate the complex boundary channel. The finite volume method is used to disperse the governing equations and the SIMPLE algorithm is applied to acquire the coupling of velocity and pressure. The non-linear k- ɛ turbulent model has good useful value because of taking into account the anisotropy and not increasing the computational time. The main contributions of this study are developing a numerical method that can be applied to predict the flow in river bends with various bend curvatures and different width-depth ratios. This study demonstrates that the 3D non-linear k- ɛ turbulence model can be used for analyzing flow structures, the velocity distribution and pollutant transport in the complex boundary open channel, this model is applicable for real river and wetland problem.
Vertical flow of a multiphase mixture in a channel
Massoudi Mehrdad; Rao C. Lakshmana
2000-01-01
The flow of a multiphase mixture consisting of a viscous fluid and solid particles between two vertical plates is studied. The theory of interacting continua or mixture theory is used. Constitutive relations for the stress tensor of the granular materials and the interaction force are presented and discussed. The flow of interest is an ideal one where we assume the flow to be steady and fully developed; the mixture is flowing between two long vertical plates. The non-linear boundary value pro...
Peng, Zhangli; Pak, On Shun; Young, Yuan-Nan; Liu, Allen; Stone, Howard
2015-11-01
We investigate the gating of mechanosensing channels (Mscls) on vesicles and cell membranes under different flow conditions using a multiscale approach. At the cell level (microns), the membrane tension is calculated using a 3D two-component whole-cell membrane model based on dissipative particle dynamics (DPD), including the cortex cytoskeleton and its interactions with the lipid bilayer. At the Mscl level (nanometers), we predict the relation between channel gating and the membrane tension obtained from a cell-level model using a semi-analytical model based on the bilayer hydrophobic mismatch energy. We systematically study the gating of Mscls of vesicles and cell membranes in constricted channel flows and shear flows, and explore the dependence of the gating on flow rate, cell shape and size. The results provide guidance for future experiments in inducing Mscl opening for various purposes such as drug delivery.
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
EXPERIMENTAL STUDY ON THE RELATION OF BED MORPHOLOGY WITH SURFACE FLOW IN MEANDER CHANNELS
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Alternate bars have the property that they migrate downstream whenever floods occur. However,in meander channels whose bend angles are larger than a critical value, the migration of bars can be suppressed, and the positions of bank erosion and flood attack also will be steady. In this study, the bed morphology in flume channels with bends of various lengths and angles is investigated at various flow discharges, and the relation of bed morphology to surface flow is investigated in detail using fluid measuring software. An effort is made to obtain guidelines for the plane shape design of meander channels. Based on the experimental results of bed topography and measurement of surface flow direction and velocity distribution, from the viewpoint of bank erosion and the concentration and dispersion of flood flow the most suitable plane shape for meandering channels is suggested through which the migration of alternate bars is suppressed.
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.
Burnout and distribution of liquid between the flow core and wall films in narrow slot channels
Boltenko, E. A.; Shpakovskii, A. A.
2010-03-01
Previous works on studying distribution of liquid between the flow core and wall films in narrow slot channels are briefly reviewed. Interrelation between mass transfer processes and burnout is shown. A procedure for calculating burnout on convex and concave heat-transfer surfaces in narrow slot channels is presented.
Effect of macromolecular polymer structures on drag reduction in a turbulent channel flow
International Nuclear Information System (INIS)
This paper presents the influence of injected polymer solutions on turbulence in fully developed channel flows. In particular, it investigates the impact of concentration and mixing of the polymer solution on drag reduction. It is observed, via flow visualization and birefringence measurements, that for large injection concentrations macromolecular polymer structures exist in the flow. They are found to be mostly located in the neighborhood of the channel centerline. Laser Doppler velocimetry was used to characterize the mean and turbulent flow with and without the presence of macromolecular polymer structures
Flow with boiling in four-cusp channels simulating damaged core in PWR type reactors
International Nuclear Information System (INIS)
The study of subcooled nucleate flow boiling in non-circular channels is of great importance to engineering applications in particular to Nuclear Engineering. In the present work, an experimental apparatus, consisting basically of a refrigeration system, running on refrigerant-12, has been developed. Preliminary tests were made with a circular tube. The main objective has been to analyse subcooled flow boiling in four-cusp channels simulating the flow conditions in a PWR core degraded by accident. Correlations were developed for the forced convection film coefficient for both single-phase and subcooled flow boiling. The incipience of boiling in such geometry has also been studied. (author)
Effect of Slip on Peristaltic Flow of Powell-Eyring Fluid in a Symmetric Channel
Directory of Open Access Journals (Sweden)
T. Hayat
2014-01-01
Full Text Available Peristaltic flow of non-Newtonian fluid in a symmetric channel with partial slip effect is examined. The non-Newtonian behavior of fluid is characterized by the constitutive equations of Powell-Eyring fluid. The motion is induced by a sinusoidal wave traveling along the flexible walls of channel. The flow is analyzed in a wave frame of reference moving with the velocity of wave. The equations governing the flow are solved by adopting lubrication approach. Series solutions for the stream function and axial pressure gradient are obtained. Impact of slip and other emerging flow parameters is plotted and analyzed graphically.
Experimental study of fluid flow in the entrance of a sinusoidal channel
International Nuclear Information System (INIS)
An experimental flow visualization study of the entrance section of channels formed with sinusoidal plates was made. The experiments were conducted in a water tunnel and a laser illuminated particle tracking was used as the technique of flow visualization. The geometric parameters of the plates were maintained constant while the distance between plates, phase angle, and the Reynolds number were varied during the experiments. The flow regimes that were found in the experiments are steady, unsteady and significantly-mixed flows. Instabilities of the flow first appear near the exit of the channel, and move closer to the inlet waves as the Reynolds number grows, but in the first wave from inlet the flow is always steady. The results show that, for all other parameters fixed, the Reynolds number at which unsteady flow first appears grows with the distance between plates. The phase angle that best promotes unsteady flow depends on the average distance between plates: for certain average distance between plates, there is a phase angle that best disturbs the flow. For the set of parameters used in this experiment, a channel with eight waves is sufficiently long and the flow features presented in the first eight waves of a longer channel will be similar to what was observed here
A MODIFIED SIMPLE ALGORITHM FOR 2-D FLOW IN OPEN CHANNEL
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
For two-dimensional water flow in open channel, by discritizing hydrodynamic differential equation of conservative form, the corresponding algebraic equations were derived which involve the relationship between velocity and depth. Based on the relationship, this paper deduced a modified formula of velocity correction for SIMPLE algorithm. As a test case, the flow in a prismatic channel with two different slopes was computed and a good result was obtained.
Evaluation of RANS turbulence models for the simulation of channel flow
Hedlund, André
2014-01-01
The objective of this report is to investigate how RANS models perform on fully developed channel flow, for Re = 13 350, and the simulations are made with the open source software OpenFOAM. The velocity and turbulent kinetic energy profiles are compared with previously published DNS results. A short introduction to turbulence modelling is presented with focus on channel flow and the boundary layer. In total eleven models are evaluated, and the results are of varying quality. A convergence stu...
Canfield, P. J.; Bronowicki, P. M.; Chen, Y.; Kiewidt, L.; Grah, A.; Klatte, J.; Jenson, R.; Blackmore, W.; Weislogel, M. M.; Dreyer, M. E.
2013-05-01
This paper describes the experiments on flow rate limitation in open capillary channel flow that were performed on board the International Space Station in 2011. Free surfaces (gas-liquid interfaces) of open capillary channels balance the pressure difference between the flow of the liquid in the channel and the ambient gas by changing their curvature in accordance with the Young-Laplace equation. A critical flow rate of the liquid in the channel is exceeded when the curvature of the free surface is no longer able to balance the pressure difference and, consequently, the free surface collapses and gas is ingested into the liquid. This phenomenon was observed using the set-up described herein and critical flow rates are presented for steady flow over a range of channel lengths in three different cross-sectional geometries (parallel plates, groove, and wedge). All channel shapes displayed decreasing critical flow rates for increasing channel lengths. Bubble ingestion frequencies and bubble volumes are presented for gas ingestion at supercritical flow rates in the groove channel and in the wedge channel. At flow rates above the critical flow rate, bubble ingestion frequency appears to depend on the flow rate in a linear fashion, while bubble volume remains more or less constant. The performed experiments yield vast data sets on flow rate limitation in capillary channel flow in microgravity and can be utilised to validate numerical and analytical methods.
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 by......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...... 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 to...
''HFLOWR'' - a computer code for predicting flow regimes in a horizontal channel with rod cluster
International Nuclear Information System (INIS)
Indian Pressurised Heavy Water Reactors have horizontal channels containing rod clusters. Occurrence of flow stratification under postulated accident conditions , significantly affects the temperatures of the exposed fuel rods. The various thermodynamic models that are to be used for the analysis depend on the flow regimes, which are expected to occur in the channel. A computer program HFLOWR has been developed to obtain the dimensionless flow regime maps and flow patterns in reactor channels of Indian PHWR under various coolant conditions. This code can be integrated with the safety analysis code, for flow regime prediction under transient/accident conditions. This report describes the various mathematical formulations used in the code and the various analyses done using this code. (author). 6 refs., 1 appendix, 34 figs
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 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.
Review of Critical Heat Flux Correlations for Upward Flow in a Vertical Thin Rectangular Channel
International Nuclear Information System (INIS)
From the view point of safety, this type of fuel has higher resistance to earthquake and external impact. The cross section of coolant flow channel in the reactor core composed with the plate fuel is a thin rectangular shape. Thermal-hydraulic characteristics of this thin rectangular channel are different with those of general circular rod fuel bundle flow channel. Accordingly it could be thought that the CHF correlation in a thin rectangular channel is different with that in a circular channel, for which a large number of researches on CHF prediction have been carried out. The objective of this paper is to review previous researches on CHF in a thin rectangular channel, summarize the important conclusion and propose the new simple CHF correlation, which is based on the data set under high pressure and high flow rate condition. The researches on CHF in rectangular channel have been partially carried out according to the pressure, heated surface number, heated surface wettability effect, flow driving force and flow direction conditions. From the literature researches on CHF for upward flow in a vertical thin rectangular channel, some CHF prediction methods were reviewed and compared. There is no universal correlation which can predict CHF at all conditions, but generally, Katto empirical correlation is known to be useful at high pressure and high flow rate. The new simple correlation was developed from the restricted data set, the CHF prediction capacity of which is better than that of Katto. Even though the prediction consistency of the new simple correlation is lower, MAE and RMS error decreased quite. For the more development of the new simple CHF correlation, the more advanced regression analysis method and theoretical analysis should be studied in future
Arsenic removal from flowing irrigation water in bangladesh: impacts of channel properties.
Lineberger, Ethan M; Badruzzaman, A Borhan M; Ali, M Ashraf; Polizzotto, Matthew L
2013-11-01
Across Bangladesh, dry-season irrigation with arsenic-contaminated well water is loading arsenic onto rice paddies, leading to increased arsenic concentrations in plants, diminished crop yields, and increased human health risks. As irrigation water flows through conveyance channels between wells and rice fields, arsenic concentrations change over space and time, indicating that channels may provide a location for removing arsenic from solution. However, few studies have systematically evaluated the processes controlling arsenic concentrations in irrigation channels, limiting the ability to manipulate these systems and enhance arsenic removal from solution. The central goal of this study was to quantify how channel design affected removal of dissolved arsenic from flowing irrigation water. Field experiments were conducted in Bangladesh using a chemically constant source of arsenic-contaminated irrigation water and an array of constructed channels with varying geometries. The resulting hydraulic conditions affected the quantity of arsenic removed from solution within the channels by promoting known hydrogeochemical processes. Channels three times the width of control channels removed ∼3 times the mass of arsenic over 32 min of flowing conditions, whereas negligible arsenic removal was observed in tarp-lined channels, which prevented soil-water contact. Arsenic removal from solution was ∼7 times higher in a winding, 200-m-long channel than in the straight, 45-m-long control channels. Arsenic concentrations were governed by oxidative iron-arsenic coprecipitation within the water column, sorption to soils, and phosphate competition. Collectively, these results suggest that better design and management of irrigation channels may play a part in arsenic mitigation strategies for rice fields in Southern Asia. PMID:25602413
Nanson, Rachel A.; Nanson, Gerald C.; Huang, He Qing
2010-04-01
At-a-station and bankfull hydraulic geometry analyses of peatland channels at Barrington Tops, New South Wales, Australia, reveal adjustments in self-forming channels in the absence of sediment load. Using Rhodes ternary diagram, comparisons are made with hydraulic geometry data from self-forming channels carrying bedload in alluvial settings elsewhere. Despite constraints on channel depths caused at some locations by the restricted thickness of peat, most stations have cohesive, near-vertical, well-vegetated banks, and width/depth (w/d) ratios of ∼ 2 that are optimal for sediment-free flow. Because banks are strong, resist erosion and can stand nearly vertical, and depth is sometimes constrained, adjustments to discharge are accommodated largely by changes in velocity. These findings are consistent with the model of maximum flow efficiency and the overarching least action principle in open channels. The bankfull depth of freely adjusting laterally active channels in clastic alluvium is well known to be related to the thickness of floodplain alluvium and a similar condition appears to apply to these swamps that grow in situ and are formed almost entirely of organic matter. The thickness of peat in these swamps rarely exceeds that required to form a bankfull channel of optimum w/d ratio for the transport of sediment-free water. Swamp vegetation is highly dependent on proximity to the water table. To maintain a swamp-channel and associated floodplain system, the channels must flow with sufficient water much of the time; they not only offer an efficient morphology for flow but do so in a way that enables bankfull conditions to occur many times a year. They also prevent the swamp from growing above a level linked to the depth of the channel. Once the channel attains the most efficient cross section, further growth of the swamp vertically is restricted by enhanced flow velocities and limited flow depths. This means that the volume of peat in such swamps is determined
Effects of gas properties and inclination angle on exchange flow through a rectangular channel
International Nuclear Information System (INIS)
This study deals with the exchange flow of two different gases (He-air, Ar-air, and SF6-air) through a rectangular channel that has a 5-mm width, a 50-mm height, and a 200-mm length. The net exchange flow rate is measured by an electronic mass balance, and velocity distribution is measured by a laser-Doppler anemometer. Flow patterns of the exchange flow are made visual with a tracer method using smoke. The effects of gas densities, molecular diffusion coefficients, inclination angles (θ) of the channel, on the flow patterns and the net exchange flow rates, are discussed. Based on the experimental results, the net exchange flow data are correlated by the equation derived by dimensional analysis: Q*=2.87 x 10-7 Gr2.17Sc0.41θ-1.09. (author)
Sediment and polyacrylamide effects on seepage losses from channeled flows
Seepage from water streams into unlined channels determines the proportion of water distributed to adjacent soil for plant use or soil or groundwater recharge, or conveyed to downstream reaches. We conducted a laboratory study to determine how inflow amendment and related factors, sediment type (no...
Model evaluation of flow boiling heat characteristics calculation in narrow rectangular channels
International Nuclear Information System (INIS)
Both the flow boiling heat transfer characteristics and its influence factors in narrow rectangular channel were studied experimentally. The applicability of the empirical correlations for calculating boiling heat transfer was evaluated against the experimental data. The results show that the effect of the mass flux appears to be primary, the heat transfer coefficients increase with the mass flux under the same void fraction. The correlations based on conventional channels are not suitable for mini-channels very much. The LEELEE correlation based on narrow channels give better agreement than the other evaluated. (authors)
Deformation of an Elastic beam due to Viscous Flow in an Embedded Channel Network
Matia, Yoav; Gat, Amir
2015-11-01
Elastic deformation due to embedded fluidic networks is currently studied in the context of soft-actuators and soft-robotic applications. In this work, we analyze the time dependent interaction between elastic deformation of a slender beam and viscous flow within a long serpentine channel, embedded in the elastic structure. The channel is positioned asymmetrically with regard to the midplane of the elastic beam, and thus pressure within the channel creates a local moment deforming the beam. We focus on creeping flows and small deformations of the elastic beam and obtain, in leading order, a convection-diffusion equation governing the pressure-field within the serpentine channel. The beam time-dependent deformation is then obtained as a function of the pressure-field and the geometry of the embedded network. This relation enables the design of complex time-dependent deformation patterns of beams with embedded channel networks. Our theoretical results were illustrated and verified by numerical computations.
Bruce NGS: A discharge channel flow simulation using MODTURC-CLAS
International Nuclear Information System (INIS)
Better understanding of the total residual chlorine (TRC) distribution and characteristics of water flow in the open discharge channel is desired to identify a representative sampling location for TRC in the cooling water discharge channel of a nuclear generating station. A three-dimensional flow simulation for Bruce NGS A was carried out using a state-of-the-art computer code MODTURC-CLAS. The results of this model are compared with data collected from a field measurement at Bruce A discharge channel in the summer of 1993. This model can be used to predict the characteristics of the discharge flows for various operating conditions of the station, and to help optimize the selection of a representative sampling point for TRC in the discharge channel. (author) 4 refs., 1 tab., 17 refs
Institute of Scientific and Technical Information of China (English)
SHAO Xuejun; WANG Hong; CHEN Zhi
2004-01-01
Turbulence structure in a helically coiled open channel flow is numerically simulated using three different turbulence models--the Launder and Ying model, the Naot and Rodi model, and the nonlinear k-ε Model (SY model). Simulation results were compared with observation of (i) turbulent flows in alternating point-bar type channel bends with rectangular sections, and (ii) straight open channel flows with compound cross-sections. Based on calculations of the impact of various channel curvatures on turbulence characteristics, accuracy of the three turbulence models was analyzed with observed data as a qualitative reference. It has been found out that the Launder and Ying model and the nonlinear k-ε Model are able to predict the same general trend as measured data, and the simulation of the effect of the centrifugal force on the formation of secondary currents produces a correct pattern.
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.
Rahmani, Amir M; Jupiterwala, Mehlam; Colosqui, Carlos E
2015-01-01
Plane Poiseuille flow past a nanoscale cylinder that is arbitrarily confined (i.e., symmetrically or asymmetrically confined) in a slit channel is studied via hydrodynamic lubrication theory and molecular dynamics simulations, considering cases where the cylinder remains static or undergoes thermal motion. Lubrication theory predictions for the drag force and volumetric flow rate are in close agreement with molecular dynamics simulations of flows having molecularly thin lubrication gaps, despite the presence of significant structural forces induced by the crystalline structure of the modeled solid. While the maximum drag force is observed in symmetric confinement, i.e., when the cylinder is equidistant from both channel walls, the drag decays significantly as the cylinder moves away from the channel centerline and approaches a wall. Hence, significant reductions in the mean drag force on the cylinder and hydraulic resistance of the channel can be observed when thermal motion induces random off-center displace...
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.
FIBER ORIENTATION DISTRIBUTIONS IN SLIT CHANNEL FLOWS WITH ABRUPT EXPANSION FOR FIBER SUSPENSIONS
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
The lattice Boltzmann method was used to investigate numerically the fiber orientation distributions in slit channel flows with abrupt expansion for fiber suspensions even in the concentrated regime. The channels have a thin slit geometry with 1:4 and 1:3 expansions. Both the interactions between fibers and that between fibers and channel walls were taken into consideration. Some of numerical results are qualitatively in agreement with the experiment data. It is found that most of fibers are aligned in the flow direction in all the suspensions in the entrance region of the expansion. Fiber orientation distributions, having different patterns in different regions of the flow, depend on the expansion ratio of the channel. The mechanical fiber-fiber interaction largely affects the fiber orientation in the downstream of the expansion and in the salient corner for the cases of concentrated suspensions. The hydrodynamic interaction plays an important role on the fiber orientation in the dilute suspension.
Modeling water droplet condensation and evaporation in DNS of turbulent channel flow
Russo, E.; Kuerten, J.G.M.; Geld, van der C.W.M.; Geurts, B.J.
2011-01-01
In this paper a point particle model for two-way coupling in water droplet-laden incompressible turbulent flow of air is proposed. The model is based on conservation laws and semi-empirical correlations. It has been implemented and tested in a DNS code based for turbulent channel flow with an Euleri
Interchannel stability analysis of oscillatory instable parallel channel two phase flow regimes
International Nuclear Information System (INIS)
Conditions for interchannel hydrodynamic stability of oscillatory unstable parallel channel two-phase flow regimes are being analysed. For experimental determined transfer functions Nyquist diagrams for one-phase and two-phase flow regimes are being considered. The results are presented show interchannel stability oscillatory unstable linear experimental regimes and interchannel instability nonlinear experimental regimes
Modelling of supercritical turbulent flow over transversal ribs in an open channel
Czech Academy of Sciences Publication Activity Database
Příhoda, Jaromír; Šulc, J.; Sedlář, M.; Zubík, P.
2009-01-01
Roč. 16, č. 1 (2009), s. 65-74. ISSN 1802-1484 R&D Projects: GA ČR GA103/06/0461 Institutional research plan: CEZ:AV0Z20760514 Keywords : turbulent flow in open channels * flow over obstacles Subject RIV: BK - Fluid Dynamics
Direct numerical simulation of sharkskin denticles in turbulent channel flow
Boomsma, A.; Sotiropoulos, F.
2016-03-01
The hydrodynamic function of sharkskin has been under investigation for the past 30 years. Current literature conflicts on whether sharkskin is able to reduce skin friction similar to riblets. To contribute insights toward reconciling these conflicting views, direct numerical simulations are carried out to obtain detailed flow fields around realistic denticles. A sharp interface immersed boundary method is employed to simulate two arrangements of actual sharkskin denticles (from Isurus oxyrinchus) in a turbulent boundary layer at Reτ ≈ 180. For comparison, turbulent flow over drag-reducing scalloped riblets is also simulated with similar flow conditions and with the same numerical method. Although the denticles resemble riblets, both sharkskin arrangements increase total drag by 44%-50%, while the riblets reduce drag by 5%. Analysis of the simulated flow fields shows that the turbulent flow around denticles is highly three-dimensional and separated, with 25% of the total drag being form drag. The complex three-dimensional shape of the denticles gives rise to a mean flow dominated by strong secondary flows in sharp contrast with the mean flow generated by riblets, which is largely two-dimensional. The so resulting three-dimensionality of sharkskin flows leads to an increase in the magnitude of the turbulent statistics near the denticles, which further contributes to increasing the total drag. The simulations also show that, at least for the simulated arrangements, sharkskin, in sharp contrast with drag-reducing riblets, is unable to isolate high shear stress near denticle ridges causing a significant portion of the denticle surface to be exposed to high mean shear.
International Nuclear Information System (INIS)
The boiling-induced natural circulation flow in the engineered cooling channel is modelled and solved by considering the conservation of mass, momentum and energy in the two-phase mixture, along with the two-phase friction drop and void fraction. The model has been applied to estimate the induced mass flow rates through a uniform and non-uniform annular gap between the reactor vessel and insulation under the IVR-ERVC conditions, and also the engineered corium cooling system of an ex-vessel core catcher during a severe accident for various system parameters including the channel gap size, inlet diameter, inlet subcooling, and wall heat flux. (author)
Structure of two-phase slug flow in vertical channels
International Nuclear Information System (INIS)
Based on a suggested model of two-phase slug flow in a wide range of varying regime parameters the available literary data and experimental data obtained by the authors on the intensity of void fraction fluctuations, lengths of slugs and liquid plugs are generalized. It is shown that the magnitude of the void fraction is the determining parameter in the formation of the flow regime and structure. The technique for calculating the characteristic frequency of fluctuations of a two-phase flow is suggested
Two-phase flow boiling in small channels: A brief review
Indian Academy of Sciences (India)
Madhavi V Sardeshpande; Vivek V Ranade
2013-12-01
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). The key design issues in two phase flow boiling are variation in flow regimes, occurrence of dry out condition, flow instabilities, and understanding of heat transfer coefficient and vapor quality. This paper briefly reviews published experimental and modeling work in these areas. An attempt is made to provide a perspective and to present available information on boiling in small channels in terms of channel size, flow regimes, heat transfer correlations, pressure drop, critical heat flux and film thickness. An attempt is also made to identify strengths and weaknesses of published approaches and computational models of boiling in small channels. The presented discussion and results will provide an update on the state-of-the-art and will be useful to identify and plan further research in this important area.
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.
Flow characteristics on the blade channel vortex in the Francis turbine
Guo, P. C.; Wang, Z. N.; Luo, X. Q.; Wang, Y. L.; Zuo, J. L.
2016-05-01
Depending on the long-term hydraulic development of Francis turbine, the blade channel vortex phenomenon was investigated systematically from hydraulic design, experimental and numerical computation in this paper. The blade channel vortex difference between the high water head and low water head turbine was also analyzed. Meanwhile, the relationship between the blade channel vortex and the operating stability of hydraulic turbine was also investigated. The results show that the phenomenon of blade channel vortex is an intrinsic property for Francis turbine under small flow rate condition, the turning-point of the blade channel vortex inception curve appears at low unit speed region, and the variation trend of the blade channel vortex inception curve is closely related to the blade inlet edge profile. In addition to, the vortex of the high water head turbine can generally be excluded from the stable operation region, while which is more different for the one of the low water head turbine.
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
Unsteady Porous Channel Flow of a Conducting Fluid with Suspended Particles
Directory of Open Access Journals (Sweden)
Jagjit Pal Kaur
1988-01-01
Full Text Available The flow of a viscous incompressible fluid embedded with a small spherical particle in the presence of a transverse magnetic field in a channel has been discussed. The cross-section of the channel is a porous regular hexagonal of side 4a and the walls are non-conducting. The analysis applied to the flows with pressure gradient which are arbitrary function of time. A few particular cases, flow for impulsive pressure gradient and for constant pressure gradient have been studied. The velocity of the fluid and particle decrease with increase in the intensity of the magnetic field.
Patterning electrohydrodynamic flows with conductive obstacles in microfluidic channels.
Energy Technology Data Exchange (ETDEWEB)
Hill, Tyrone F.; Simmons, Blake Alexander; Barrett, Louis C.; Cummings, Eric B.; Fiechtner, Gregory J.; Harnett, Cindy K.; Skulan, Andrew J.
2005-03-01
Flow patterns with both recirculating and unidirectional characteristics are useful for controlled mixing and pumping within microfluidic devices. We have developed a fabrication process that converts injection-molded polymer chips into devices that demonstrate induced-charge electroosmosis (ICEO) effects (1,2) in AC fields. Polymeric insulating posts are coated with metal to produce a nonuniform zeta potential under an applied electric field. Induced flows are analyzed by particle image velocimetry. Stable, recirculating flow patterns are discussed, along with their potential to produce well-characterized and reversible streamlines for on-chip mixing in chemical separation and synthesis devices. Asymmetric conductive features can bias the flow direction, generating unidirectional pumping in an AC field. This pumping approach will be discussed in comparison with DC electrokinetic pumps we have studied.
Flow Patterns and Void Fraction in Thin-Gap Channel
Czech Academy of Sciences Publication Activity Database
Křišťál, Jiří; Havlica, Jaromír; Jiřičný, Vladimír
- : -, 2007, s. 578. [International Conference on Multiphase Flow /6./. Congress Center Leipzig (DE), 09.07.2007-13.07.2007] R&D Projects: GA ČR(CZ) GP104/05/P554 Grant ostatní: IMPULSE(XE) 0111816-2 Institutional research plan: CEZ:AV0Z40720504 Source of funding: R - rámcový projekt EK Keywords : flow pattern * void fraction * microchannel Subject RIV: CI - Industrial Chemistry, Chemical Engineering
Analysing Gas-Liquid Flow in PEM Electrolyser Micro-Channels
DEFF Research Database (Denmark)
Lafmejani, Saeed Sadeghi; Olesen, Anders Christian; Kær, Søren Knudsen
2016-01-01
annular flow, are observed in the present micro-channel. The phenomenon is also analysed numerically in 3D, unsteady, euler/euler multiphase method using the commercial software ANSYS FLUENT 17 and the results show good agreement with the experimental data. Influence of each multiphase flow regime is...... described in the study as well as the recommendation for improving the performance. A well management of the multiphase flow regime along the whole micro-channel length can assure a proper distribution of water inside the titanium felt....... are fairly expensive. One means of increasing the hydrogen yield to cost ratio of such systems, is to increase the operating current density. However, at high current densities, management of heat transfer and fluid flow in the anode GDL and channel becomes crucial. This entails that further...
LARGE EDDY SIMULATION OF FREE SURFACE TURBULENT CHANNEL FLOW WITH HEAT TRANSFER
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
In this paper, the Large Eddy Simulation (LES) was used to study the free-surface turbulent channel flow with passive heat transfer. The three-dimensional filtered incompressible Navier-Stokes equations and energy equation were numerically solved with dynamic Subgrid Scale (SGS) models for modeling turbulent stresses and heat flux. To compare the turbulent behavior of the free-surface and two-walled channel flows, the LES of two-walled turbulent channel flow was performed. The statistical quantities and flow structures of the free-surface turbulence with heat transfer in the vicinity of the free-surface were investigated. The results are also in good agreement with theoretical analysis and available results by Direct Numerical Simulation (DNS).
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.
Fast Vortex Method for the Simulation of Flows Inside Channels With and Without Injection
Institute of Scientific and Technical Information of China (English)
YvesGAGNON; HUANGWeiguang
1993-01-01
A fast vortex method is presented for the simulation of fluid flows inside two-dimensional channels,The first channel studied is formed by two parallel walls simulating the entrance length of a developing flow.The second channel is similar to the first one but with an injection of a secondary fluid through a slot on one of its walls,In both cases,results are presented for flows at low Reynolds numbers and for flows at a high Reynolds number The numerical method used is based on the Random Vortex Method and on the Vortex-In-Cell Algorithm.Physical analyses of the numerical results are also presented.mostly in application to film cooling.
Numerical investigation of the mechanism of two-phase flow instability in parallel narrow channels
Energy Technology Data Exchange (ETDEWEB)
Hu, Lian [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China); Chen, Deqi, E-mail: chendeqi@cqu.edu.cn [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China); CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Huang, Yanping, E-mail: hyanping007@163.com [CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Yuan, Dewen; Wang, Yanling [CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Pan, Liangming [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China)
2015-06-15
Highlights: • A mathematical model is proposed to predict the two-phase flow instability. • The mathematical model predicted result agrees well with the experimental result. • Oscillation characteristics of the two-phase flow instability is discussed in detail. - Abstract: In this paper, the mechanism of two-phase flow instability in parallel narrow channels is studied theoretically, and the characteristic of the flow instability is discussed in detail. Due to the significant confining effect of the narrow channel on the vapor–liquid interface, the two-phase flow resistance in the narrow channel is probably different from that in conventional channel. Therefore, the vapor confined number (N{sub conf}), defined by the size of narrow channel and bubble detachment diameter, is considered in the “Chisholm B model” to investigate the two-phase flow pressure drop. The flow instability boundaries are plotted in parameter plane with phase-change-number (N{sub pch}) and subcooling-number (N{sub sub}) under different working conditions. It is found that the predicted result agrees well with the experimental result. According to the predicted result, the oscillation behaviors near the flow instability boundary indicate that the Supercritical Hopf bifurcation appears in high sub-cooled region and the Subcritical Hopf bifurcation appears in low sub-cooled region. Also, a detailed analysis about the effects of key parameters on the characteristic of two-phase flow instability and the flow instability boundary is proposed, including the effects of inlet subcooling, heating power, void distribution parameter and drift velocity.
Institute of Scientific and Technical Information of China (English)
Yoichi KINOUE; Toshiaki SETOGUCHI; Mohammad MAMUN; Norimasa SHIOMI; Kenji KANEKO
2005-01-01
An experimental investigation was made into three-dimensional separated flow and the vortices within the flow separation in a decelerating channel flow generated by the suction from a porous side wall. The flows along the side and bottom walls were visualized by the surface tuft method. The turbulent internal flow was measured by the split-film probe to investigate the turbulent flow including the reverse flow. In the flow visualization for the strong decelerating flow (the suction flow ratio:0.8), two typical flow patterns appear alternatively. One is that the flow near the bottom wall separates more upstream than the flow near the top wall and a clockwise vortex can be seen in the separation region. Another is the reversal flow pattern with a counterclockwise vortex. By the turbulent flow measurement using the split-film probe, two peaks of turbulence level are observed for the strong decelerating flow case. These peaks can be related with two flow patterns mentioned above.
DEFF Research Database (Denmark)
Hilgers, Rob H P; Janssen, Ger M J; Fazzi, Gregorio E;
2010-01-01
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...
International Nuclear Information System (INIS)
Subcooled flow boiling in a vertical rectangular channel was experimentally investigated to enhance the understanding of the CHF and the effect of the two-phase flow instability on it under low pressure conditions, especially for downward flow which was adopted for Jordan Research and Training Reactor (JRTR) and Kijang research reactor (KJRR) to achieve easier fuel and irradiation rig loading. In addition, visual observations of subcoold flow boiling was conducted by using high-speed video (HSV) for a clear understanding of both phenomena. We concluded that flow excursion (which is static instability) could be induced due to the OPDF (which is dynamic instability) when a system has no resistibility to the pressure drop perturbation, which is caused by the coalescence of facing bubbles on opposing heated surfaces. In more stable system with throttling applied, flow rate could be maintained and stable CHF could be reached. The static flow instability (FI) and critical heat flux (CHF) for subcooled flow boiling in a vertical narrow channels under low pressure condition are fairly crucial phenomena relative to thermal-hydraulic design and safety analysis for pool-type research reactors. It has been recommended that RRs and MTRs be designed to have sufficient margins for CHF and the onset of FI as well, since unstable flow could leads to premature CHF under very low wall heat flux in comparison to stable CHF. Even the fact and previous studies, however, the understanding of relationship among FI, premature CHF and stable CHF is not sufficient to date
Two-phase fluid flow measurements in small diameter channels using real-time neutron radiography
International Nuclear Information System (INIS)
A series of real-time, neutron radiography, experiments are ongoing at the Texas A and M Nuclear Science Center Reactor (NSCR). These tests determine the resolving capabilities for radiographic imaging of two phase water and air flow regimes through small diameter flow channels. Though both film and video radiographic imaging is available, the real-time video imaging was selected to capture the dynamic flow patterns with results that continue to improve. (author)
Trade flows as a channel for the transmission of business cycles
Berk, J.M.
1997-01-01
The interdependence between business cycles of different countries has grown in recent decades. Many factors act as conductors of cyclical fluctuations between countries. In this context, the influence of trade flows in the global transmission of business cycles is examined. The author aims to identify empirically the line of causality of international cyclical movements as suggested by trade flows, presenting an estimate of the quantitive importance of trade flows as transmission channel.
International Nuclear Information System (INIS)
The generalized hydrodynamic equations, wherein the Kolmogorov fluctuations of hydrodynamic values are obviously accounted for, are used for mathematical modeling of the gas vortex flows. The calculations are carried out within the Reynolds numbers 64-10000 for two-dimensional nonisothermal flows of a compressed gas in a channel with a step. The mathematical modeling makes it possible to obtain sufficiently extensive information on the flow hydrodynamic parameters, which is difficultly to represent graphically. Only spatial and time pressure evolution is indicated
3D numerical investigation of turbulent flow through lateral intake in open channel
International Nuclear Information System (INIS)
The flow at a channel bifurcation is turbulent, highly three-dimensional (3D) and has many complex features. There is transverse motion accompanying the main flow and an extensive separation zone that develops in the branch channel. This zone causes hydraulic and sedimentation problems that must be known before designing the system. This necessitates a deeper insight into the flow patterns and shear stress distributions near the solid boundaries. This paper reports a 3D numerical investigation of flow pattern and shear stress distribution at a lateral intake in an open channel. Simulations are done on rectangular channel geometry, with smooth bed and sidewalls. The CFD model uses the standard k-ε and k-ω model of Wilcox turbulence closure schemes as implemented in the FLUENT code. The simulation results were compared with available experimental data. It was found that both turbulence models used accurately predicted velocity profiles in the main channel but in the branch channel, the k-ω model is performed better than the k-ε turbulence model. (author)
Impact of vegetation density on flow characteristics in a straight compound channel
International Nuclear Information System (INIS)
Vegetation exists on the floodplains of almost all natural channels. This vegetation results in a number of changes in flow features of open channel flows. Sometimes vegetation also exists within the main channel. This paper presents a numerical study in which the impact of vegetation density on different flow features has been considered. The variables investigated included velocity profiles, bed shear stresses, Reynolds stresses and side wall shear stresses. A compound channel with floodplain on both sides of the main channel has been considered. Four different vegetation densities were considered in this work. It was revealed that increase in vegetation density results in a decrease in the velocity values close to the bed and in the upper regions of the flood plains. The Reynolds stresses were also influenced considerably in the lower regions of the channel. Similar patterns were observed in case of bed shear stresses. The vertical profiles of side wall shear stresses were also investigated in this work. Such an investigation will help in enhancing the understanding and improving different conveyance and flow resistance calculation formulae. (author)
Effects of roughness on density-weighted particle statistics in turbulent channel flows
Energy Technology Data Exchange (ETDEWEB)
Milici, Barbara [Faculty of Engineering and Architecture, Cittadella Universitaria - 94100 - Enna (Italy)
2015-12-31
The distribution of inertial particles in turbulent flows is strongly influenced by the characteristics of the coherent turbulent structures which develop in the carrier flow field. In wall-bounded flows, these turbulent structures, which control the turbulent regeneration cycles, are strongly affected by the roughness of the wall, nevertheless its effects on the particle transport in two-phase turbulent flows has been still poorly investigated. The issue is discussed here by addressing DNS combined with LPT to obtain statistics of velocity and preferential accumulation of a dilute dispersion of heavy particles in a turbulent channel flow, bounded by irregular two-dimensional rough surfaces, in the one-way coupling regime.
Effects of roughness on density-weighted particle statistics in turbulent channel flows
Milici, Barbara
2015-12-01
The distribution of inertial particles in turbulent flows is strongly influenced by the characteristics of the coherent turbulent structures which develop in the carrier flow field. In wall-bounded flows, these turbulent structures, which control the turbulent regeneration cycles, are strongly affected by the roughness of the wall, nevertheless its effects on the particle transport in two-phase turbulent flows has been still poorly investigated. The issue is discussed here by addressing DNS combined with LPT to obtain statistics of velocity and preferential accumulation of a dilute dispersion of heavy particles in a turbulent channel flow, bounded by irregular two-dimensional rough surfaces, in the one-way coupling regime.
Empirical Formulation of Flow Characteristics in Trapezoidal Channels
Gandhi, S.; Singh, R. P.
2016-05-01
Empirical relations for hydraulic jump characteristics, viz. sequent depth ratio (Y2/Y1), efficiency of jump (E2/E1) and relative length of jump (Lj/Y1) in trapezoidal channel with/without appurtenances are developed by introducing dimensionless Reynolds number, and neglecting the frictional effect for approach Froude number (varied between 2 and 10 under different conditions). Developed empirical models were also validated and compared with acquired experimental data as well as with literature data. Close fitness of the empirical models with appurtenances under varying dimensions, positions of baffle blocks provides accurate prediction of same for higher value of Froude number.
Effects of wall roughness on flow stability analysis of supercritical heated channel
International Nuclear Information System (INIS)
This thesis has sought to study the effect of surface wall roughness on flow stability analysis of a supercritical heated circular channel. Although the supercritical water does not experience a phase change, there are large property variations near the pseudo-critical point which can bring together instabilities at either low mass flows or high power levels. Both static and dynamic instabilities were discussed in the literature review. STAR-CCM+ was used as a Computational Fluid Dynamics tool to conduct this study using a circular channel of length 4.267 m and internal diameter of 8.36 mm. Six different roughness heights which include smooth pipe of zero roughness, 1e-5 m, 1e-4 m, 5e-4 m, 1e-3 m and 5e-3 m were used in the study. Four out of the six roughness heights were super-imposed on a stability map generated by previous research. The flow through the smooth pipe was found to be in the unstable region of the stability map among the other roughness heights used because it recorded the highest instability value on the stability map. The flow through the channel of roughness height of 1e-5 m and 5e-4 m were found to be on the stable region on the stability map showing that roughness height of a channel cannot be ignored since it deteriorates the flow within the channel. (au)
MHD mixed convection flow through a diverging channel with heated circular obstacle
Alam, Md. S.; Shaha, J.; Khan, M. A. H.; Nasrin, R.
2016-07-01
A numerical study of steady MHD mixed convection heat transfer and fluid flow through a diverging channel with heated circular obstacle is carried out in this paper. The circular obstacle placed at the centre of the channel is hot with temperature Th. The top and bottom walls are non-adiabatic. The basic nonlinear governing partial differential equations are transformed into dimensionless ordinary differential equations using similarity transformations. These equations have been solved numerically for different values of the governing parameters, namely Reynolds number (Re), Hartmann number (Ha), Richardson number (Ri) and Prandtl number (Pr) using finite element method. The streamlines, isotherms, average Nusselt number and average temperature of the fluid for various relevant dimensionless parameters are displayed graphically. The study revealed that the flow and thermal fields in the diverging channel depend significantly on the heated body. In addition, it is observed that the magnetic field acts to increase the rate of heat transfer within the channel.
Deformation of an Elastic Beam due to Viscous Flow in an Embedded Parallel Channel Network
Matia, Yoav
2015-01-01
Elastic deformation due to embedded fluidic networks is currently studied in the context of soft-actuators and soft-robotic applications. In this work, we analyze interaction between the elastic deflection of a slender beam and viscous flow within a long serpentine channel, embedded in the elastic beam. The channel is positioned asymmetrically with regard to the midplane of the beam, and thus pressure within the channel creates a local moment deforming the beam. We focus on creeping flows and small deflections of the elastic beam and obtain, in leading order, a fourth-order partial integro-differential equation governing the time-dependent deflection field. This relation enables the design of complex time-dependent deformation patterns of beams with embedded channel networks, including inertia-like standing and moving wave solutions in configurations with negligible inertia.
Three dimensional analysis of boundary layers in magnetohydrodynamic open channel flow
International Nuclear Information System (INIS)
The pumping of liquid metals through open channels by MHD effects can be applied to slag separation or continuous casting processes by the metallurgy industry. This study involves the analysis of the boundary layer structure of non-uniform open channel flow in a rectangular channel, with perfectly conducting sidewalls, an insulating bottom and a uniform magnetic field applied perpendicular to the bottom, the plane of which is sloped with respect to the horizontal. To supply the non-trivial three-dimensional sidewall boundary layer structure a boundary value problem is posed and reduced to two integral equations coupled in two unknowns. The twenty-four point Gauss-Legendre quadrature scheme used to represent the integrals, leads to a set of forty-eight simultaneous equations which is solved numerically for the unknowns. Once obtained, these unknowns are used in the numerical calculation of sample velocity profiles which illustrate and contrast MHD effects in open channel and closed duct flows
Characteristics of oscillating flow through a channel filled with open-cell metal foam
International Nuclear Information System (INIS)
An experimental study was performed to investigate the characteristics of oscillating flow through a channel filled with open-cell metal foam with a fully inter-connected pore structure. Detailed experimental data of oscillating flow pressure drops and velocities for a wide range of oscillatory frequency and the maximum flow displacement were presented. A correlation equation for the maximum friction factor of metal foams subject to oscillating flow was obtained and compared with the results for channels inserted with wire-screens obtained by other investigators. The results showed that oscillating flow characteristics in an open-cell metal foam are governed by a hydraulic ligament diameter based kinetic Reynolds number Re ω(Dh) and the dimensionless flow displacement amplitude A Dh. The effects of kinetic Reynolds number on the variations of pressure drop and flow velocity in metal foam are more significant than that of the dimensionless flow displacement amplitude. The maximum friction factor of oscillating flow in open-cell metal foams is much smaller than that of oscillating flow in wire-screens for large flow displacement amplitudes
DEPTH-AVERAGED 2-D CALCULATION OF FLOW AND SEDIMENT TRANSPORT IN CURVED CHANNELS
Institute of Scientific and Technical Information of China (English)
Weiming WU; Sam S. Y. WANG
2004-01-01
The helical flow significantly affects the flow, sediment transport and morphological evolution in curved channels. A semi-empirical formula is proposed to determine the cross-stream distribution of the helical flow intensity in the developed regions of a channel bend. It is then used to evaluate the dispersion terms in the depth-averaged 2-D momentum equations and suspended-load transport equation as well as the bed-load transport angle, thus enhancing the depth-averaged 2-D model to account for the effect of helical flow. The tests in several experimental and field cases show that the enhanced depth-averaged 2-D model can much more reasonably predict the shifting of main flow from inner bank to outer bank, the erosion along outer bank and deposition along inner bank than the depth-averaged 2-D model without considering this effect.
DNS of heat transfer in turbulent and transitional channel flow obstructed by rectangular prisms
International Nuclear Information System (INIS)
Direct numerical simulation (DNS) of heat transfer in a channel flow obstructed by rectangular prisms has been performed for Reτ = 80-20, where Reτ is based on the friction velocity, the channel half width and the kinematic viscosity. The molecular Prandtl number is set to be 0.71. The flow remains unsteady down to Reτ = 40 owing to the disturbance induced by the prism. For Reτ = 30 and 20, the flow results in a steady laminar flow. In the vicinity of the prism, the three-dimensional complex vortices are generated and heat transfer is enhanced. The Reynolds number effect on the time-averaged vortex structure and the local Nusselt number are investigated. The mechanism of the heat transfer enhancement is discussed. In addition, the mean flow parameters such as the friction factor and the Nusselt number are examined in comparison with existing DNS and experimental data
Flow reversal and heat transfer of fully developed mixed convection in vertical channels
Cheng, Chin-Hsiang; Kou, Hong-Sen; Huang, Wen-Hsiung
1990-07-01
The present analysis is concerned with flow reversal phenomena and heat transfer characteristics of the fully developed laminar combined free and forced convection in the heated vertical channels. Three fundamental combinations of thermal boundary conditions on the respective wall surface (namely isoflux-isoflux, isoflux-isothermal, and isothermal-isothermal) are considered separately so as to investigate extensively their distinct influence on the flow pattern. Results of the velocity distribution and temperature distribution as well as the Nusselt number in terms of bulk mean temperature are carried out. Based on the analytical solutions obtained, flow reversal adjacent to the relatively colder wall is found to exist within the channel as Re/Gr is below a threshold value related to the thermal boundary conditions. Parameter zones for the occurrence of reversed flow are presented. Comparisons and verification are made using the existing numerical solutions at locations far downstream of developing flow.
Channelization of viscoplastic flow in a rough Hele-Shaw cell
Hewitt, Duncan; Balmforth, Neil
2015-11-01
The flow of viscoplastic fluid down slender conduits or through porous media has application in a range of industrial and geophysical settings, from the plumbing of mud volcanoes to the transport of proppant slurries in hydraulic fracturing. The yield stress can cause the fluid locally to clog up, which can significantly affect the flow patterns. Flow of a viscoplastic fluid in a Hele-Shaw cell that has randomly ``roughened'' walls is investigated, both numerically and using analogue laboratory experiments. Fluid injected into the centre of the rough cell, which is initially full of the same fluid, show pronounced channelization: above a critical pressure drop (below which there is no flow and all the fluid is unyielded and stagnant), one or more thin conduits of yielded, flowing fluid develop. At larger pressure drops, more channels of yielded fluid develop. The quantity and width of the channels, and the value of the critical pressure drop, depend on the amplitude of the roughness of the walls of the cell. If this roughness is known, the locations of the first channels to flow and the corresponding pressure drop can be predicted by an optimization algorithm.
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.
Flatness-based control of open-channel flow in an irrigation canal using SCADA
Rabbani, T.; Munier, S.; Dorchies, D.; Malaterre, P.O.; Bayen, A.; Litrico, X.
2009-01-01
Open channels are used to distribute water to large irrigated areas. In these systems, ensuring timely water delivery is essential to reduce operational water losses. This article derives a method for open-loop control of open channel flow, based on the Hayami model, a parabolic partial differential equation resulting from a simplification of the Saint-Venant equations. The open-loop control is represented as infinite series using differential flatness. Experimental results show the effective...
Peristaltic Flow of Phan-Thien-Tanner Fluid in an Asymmetric Channel with Porous Medium
Kuppalapalle Vajravelu; S.Sreenadh; Lakshminarayana, P; G. Sucharitha; Rashidi, M. M.
2016-01-01
This paper deals with peristaltic transport of Phan-Thien-Tanner fluid in an asymmetric channel induced by sinusoidal peristaltic waves traveling down the flexible walls of the channel. The flow is investigated in a wave frame of reference moving with the velocity of the waveby using the long wavelength and low Reynolds number approximations.The nonlinear governing equations are solved employing a perturbation method by choosing as the perturbation parameter. The expressions for velocity, s...
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.
A Computer Method of Steady Non-Uniform Gradually Varied Flow in Open Channel & in River
Institute of Scientific and Technical Information of China (English)
无
1999-01-01
Most of water flow in open channel or in river belongs to steady non-uniform flow. The surface profiles are caused by changes of channel section. It is very important to analyze its computation. According to the regularity of its surface change, the suitable sectional dimensions of open channel or flood control work can be designed. Commonly, computation of non-uniform flow adopts the traditional methods by hand or by graphic method. The speed and precision of computation are restricted. In this paper, a software to calculate water surface profile is introduced. The software is put forward by using C++ .By means of interpolate method and dialogue between user and computer, we can calculate the water surface profile much more quickly and exactly.
Convective Heat Transfer Augmentation by Flexible fins in Laminar Channel Pulsating flow
Joshi, Rakshitha U; Bhardwaj, Rajneesh
2015-01-01
Fluid-structure interaction (FSI) of thin flexible fins coupled with convective heat transfer has applications in energy harvesting and in understanding functioning of several biological systems. We numerically investigate FSI of the thin flexible fins involving large-scale flow-induced deformation as a potential heat transfer enhancement technique. An in-house, strongly-coupled fluid-structure interaction (FSI) solver is employed in which flow and structure solvers are based on sharp-interface immersed boundary and finite element method, respectively. We consider twin flexible fins in a heated channel with laminar pulsating cross flow. The vortex ring past the fin sweep higher sources of vorticity generated on the channel walls out into the downstream - promoting the mixing of the fluid. The moving fin assists in convective mixing, augmenting convection in bulk and at the walls; and thereby reducing thermal boundary layer thickness and improving heat transfer at the channel walls. The thermal augmentation is...
Modeling water droplet condensation and evaporation in DNS of turbulent channel flow
International Nuclear Information System (INIS)
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.
Suppression of nano-channel ion conductance by electro-osmotic flow
Liu, Yang; Zhu, Xin; Ran, Qiushi; Dutton, Robert
2016-01-01
This theoretical study concerns a basic understanding of ion transport in nano-channels that have weakly overlapping electric double layers. Numerical simulations reveal that the electro-osmotic flow (EOF) interplays with the concentration-polarization process and drives the ion depletion zone into 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. Further analysis are conducted based on a 1-D, long channel model, and analytic expressions derived to quantitatively account for the EOF-driven ion depletion process. A limiting-conductance behavior is revealed as intrinsically different from the classical limiting-current behavior.
Onsager's Cross Coupling Effects in Gas Flows Confined to Micro-channels
Wang, Ruijie; Xu, Kun; Qian, Tiezheng
2016-01-01
In rarefied gases, mass and heat transport processes interfere with each other, leading to the mechano-caloric effect and thermo-osmotic effect, which are of interest to both theoretical study and practical applications. We employ the unified gas-kinetic scheme to investigate these cross coupling effects in gas flows in micro-channels. Our numerical simulations cover channels of planar surfaces and also channels of ratchet surfaces, with Onsager's reciprocal relation verified for both cases. For channels of planar surfaces, simulations are performed in a wide range of Knudsen number and our numerical results show good agreement with the literature results. For channels of ratchet surfaces, simulations are performed for both the slip and transition regimes and our numerical results not only confirm the theoretical prediction [Phys. Rev. Lett. 107, 164502 (2011)] for Knudsen number in the slip regime but also show that the off-diagonal kinetic coefficients for cross coupling effects are maximized at a Knudsen n...
Ferrofluid magnetoviscous control of wall flow channeling in porous media
Institute of Scientific and Technical Information of China (English)
Faal; Larachi
2007-01-01
[1]Bacri,J.C.,Perzynski,R.,Shliomis,M.I.,& Burde,G.I.(1995).Negative viscosity effect in a magnetic fluid.Physical Review Letters,75(11),2128-2131.[2]Felderhof,B.U.(2001).Flow of a ferrofluid down a tube in an oscillating magnetic field.Physical Review E,64(021508),1-7.[3]Khuzir,P.,Bossis,G.,Bashtovoi,V.,& Volkova,O.(2003).Flow of magnetorheological fluid through porous media.European Journal of Mechanics B/Fluids,22,331-343.[4]McTague,J.P.(1969).Magnetoviscosity of magnetic colloids.Journal of Chemical Physics,51,133-136.[5]Odenbach,S.(2003).Magnetic fluids-Suspensions of magnetic dipoles and their magnetic control.Journal of Physics:Condensed Matter,15,S 1497-S1508.[6]Rinaldi,C.,& Zahn,M.(2002).Effects of spin viscosity on ferrofluid flow profiles in alternating and rotating magnetic fields.Physics of Fluids,14,2847-2870.[7]Rosensweig,R.E.(1997).Ferrohydrodynamics.New York:Dover Publications.[8]Schumacher,K.R.,Sellien,I.,Knoke,G.S.,Cadet,T.,& Finlayson,B.A.(2003).Experiment and simulation of laminar and turbulent ferrofluid pipe flow in an oscillating magnetic field.Physical Review E,67(026308),1-11.[9]Shliomis,M.I.(1972).Effective viscosity of magnetic suspensions.Soviet Physics JETP,34,1291-1294.[10]Whitaker,S.(1999).Theory and applications of transport in porous media.Dordrecht:Kluwer Academic Press.[11]Zeuner,A.,Richter,R.,& Rehberg,I.(1998).Experiments on negative and positive magnetoviscosity in an alternating magnetic field.Physical Review E,58,62876293.
Numerical comparison of unsteady compressible viscous flow in convergent channel
Czech Academy of Sciences Publication Activity Database
Pořízková, P.; Kozel, Karel; Horáček, Jaromír
Prague : Institute of Mathematics AS CR, 2012 - (Brandts, J.; Chleboun, J.; Korotov, S.), s. 203-213 ISBN 978-80-85823-60-8. [Application of Mathematics 2012. Prague (CZ), 02.05.2012-05.05.2012] R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional research plan: CEZ:AV0Z20760514 Keywords : finite volume method * simulation of flow in vibrating glottis * biomechanics of voice Subject RIV: BI - Acoustics
Dynamics of nuclear fuel assemblies in vertical flow channels
International Nuclear Information System (INIS)
DYNMOD is a computer program designed to predict the dynamic behaviour of nuclear fuel assemblies in axial flow. The calculations performed by DYNMOD and the input data required by the program are described in this report. Examples of DYNMOD usage and a brief assessment of the accuracy of the dynamic model are also presented. It is intended that the report will be used as a reference manual by users of DYNMOD
Fluctuation model of a nonequilibrium two-phase channel flow
International Nuclear Information System (INIS)
An ill-posed Cauchy problem for a model of a nonequilibrium two-phase flow in the barotropic approximation is transformed into a well-posed problem by changing the type of the initial hyperbolic equations. Approximation of fluctuations of the phase velocities by a random delta-correlated process and averaging of the equations over its realizations generate a system of parabolic equations. Results of numerical integration of this system are compared with experiment and calculations by well-known models
Fluctuation model of a nonequilibrium two-phase channel flow
Energy Technology Data Exchange (ETDEWEB)
Krivoshei, F.A. [Inst. of Engineering Thermophysics, Kiev (Ukraine)
1994-12-01
An ill-posed Cauchy problem for a model of a nonequilibrium two-phase flow in the barotropic approximation is transformed into a well-posed problem by changing the type of the initial hyperbolic equations. Approximation of fluctuations of the phase velocities by a random delta-correlated process and averaging of the equations over its realizations generate a system of parabolic equations. Results of numerical integration of this system are compared with experiment and calculations by well-known models.
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
Analysis of the Onset of Flow Instability in rectangular heated channel using drift flux model
International Nuclear Information System (INIS)
Two-phase flow excursion (Ledinegg) instability in boiling channels is of great concern in the design and operation of numerous practical systems especially in Research Reactors. Such instability can lead to significant reduction in channel flow, thereby causing premature burnout of the heated channel before the CHF point. The present work focuses on a simulation of pressure drop in forced convection boiling in vertical narrow and parallel uniformly heated channels. The objective is to determine the point of Onset of Flow Instability (OFI) by varying input flow rate. The axial void distribution is also provided. The numerical model is based on the finite difference method which transforms the partial differential conservation equation of mass, momentum and energy, in algebraic equations. Closure relationships based upon the drift flux model and other constitutive equations are considered to determine the channel pressure drop under steady state boiling conditions. The model validation is performed by confronting the calculations with the Oak Ridge National Laboratory thermal Hydraulic Test Loop (THTL) experimental data set. Further verification of this model is performed by code- to code verification using the results of RELAP5/Mod 3.2 code. (author)
Directory of Open Access Journals (Sweden)
Bittagopal Mondal
2016-01-01
Full Text Available The serpentine flow channel can be considered as one of the most common and practical channel layouts for a polymer electrolyte membrane fuel cell (PEMFC since it ensures an effective and efficient removal of water produced in a cell with acceptable parasitic load. Water management is one of the key issues to improve the cell performance since at low operating temperatures in PEMFC, water vapor condensation starts easily and accumulates the liquid water droplet within the flow channels, thus affecting the chemical reactions and reducing the fuel cell performance. In this article, a comprehensive three dimensional numerical simulation is carried out to understand the water droplet mobility in a serpentine gas flow channel for a wide range of surface properties, inlet air velocities, droplet positions (center or off-center, bottom or top and droplet sizes by deploying a finite volume based methodology. The liquid-gas interface is tracked following the volume-of-fluid (VOF method. The droplet transport is found to be greatly influenced by the surface wettability properties, inlet velocities, number of droplets emerged and initial droplet positions. Super hydrophobic surface property is not always preferable for designing the gas flow channels. It depends upon the inlet velocity conditions, droplet positions, number of droplets and surface properties.
Development of Pressure-Sensitive Channel Chip for Micro Gas Flows
Matsuda, Yu; Yamaguchi, Hiroki; Niimi, Tomohide
2012-05-01
Optical measurement techniques are useful for experimental studies on micro gas flows, which enable us to non-intrusively measure the flows with a high spatial resolution. The pressure-sensitive paint (PSP) technique, which is based on the emission of photons from luminophore, is a potential diagnostic tool for pressure measurement of micro gas flows. However, measurements by conventional PSPs are limited to the sub-millimeter order spatial resolution of ca. 200 μm, indicating the difficulty of the micro scale measurements. The present study proposes pressure-sensitive channel chip (PSCC) which is a micro channel with the capability of measuring pressure. We focused on the poly (dimethylsiloxane) (PDMS) micro-molding technique, which is one of the most popular techniques to fabricate a micro channel easily. Moreover, PDMS is a polymer used as a binder in PSP because of high optical transparency, gas permeability, and gas diffusivity. Thus, we developed a micro channel by the PDMS micro-molding technique with mixing a pressure-sensitive luminophore into PDMS: i.e. a micro channel fabricated by PSP, which is named PSCC. A flow through a micro converging-diverging nozzle with the throat width of 120 μm was demonstrated. The pressure distribution on the nozzle surface was successfully obtained by PSCC.
Development of Pressure-Sensitive Channel Chip for Micro Gas Flows
International Nuclear Information System (INIS)
Optical measurement techniques are useful for experimental studies on micro gas flows, which enable us to non-intrusively measure the flows with a high spatial resolution. The pressure-sensitive paint (PSP) technique, which is based on the emission of photons from luminophore, is a potential diagnostic tool for pressure measurement of micro gas flows. However, measurements by conventional PSPs are limited to the sub-millimeter order spatial resolution of ca. 200 μm, indicating the difficulty of the micro scale measurements. The present study proposes pressure-sensitive channel chip (PSCC) which is a micro channel with the capability of measuring pressure. We focused on the poly (dimethylsiloxane) (PDMS) micro-molding technique, which is one of the most popular techniques to fabricate a micro channel easily. Moreover, PDMS is a polymer used as a binder in PSP because of high optical transparency, gas permeability, and gas diffusivity. Thus, we developed a micro channel by the PDMS micro-molding technique with mixing a pressure-sensitive luminophore into PDMS: i.e. a micro channel fabricated by PSP, which is named PSCC. A flow through a micro converging-diverging nozzle with the throat width of 120 μm was demonstrated. The pressure distribution on the nozzle surface was successfully obtained by PSCC.
Large Eddy Simulation of turbulent flows in compound channels with a finite element code
International Nuclear Information System (INIS)
This paper presents the numerical investigation of the developing flow in a compound channel formed by a rectangular main channel and a gap in one of the sidewalls. A three dimensional Large Eddy Simulation computational code with the classic Smagorinsky model is introduced, where the transient flow is modeled through the conservation equations of mass and momentum of a quasi-incompressible, isothermal continuous medium. Finite Element Method, Taylor-Galerkin scheme and linear hexahedrical elements are applied. Numerical results of velocity profile show the development of a shear layer in agreement with experimental results obtained with Pitot tube and hot wires. (author)
Report on tests using a flow visualization rig - two channel per pass configuration
International Nuclear Information System (INIS)
The flow visualization rig at Monserco Limited has been modified and commissioned, and then used to conduct several tests with two channels in each pass. Single phase thermosyphoning in the rig was demonstrated, and two phase experiments with different starting conditions were done. Results of the tests are presented here. The two phase tests resulted in flow patterns with the same characteristics, independent of the starting condition. Based on results presented here, a recommendation for adding another heated channel in each pass is made
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...
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
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.
Heterogeneous physical and chemical processes in a rarefied-gas flow in channels
Rebrov, A. K.; Yudin, I. B.
2016-05-01
A flow with physical and chemical reactions on hot surfaces is investigated. On the basis of physical experiments, determining the hydrogen-dissociation degree in rarefied gas and calculation of the flow by the method of direct simulation Monte Carlo (DSMC), it is possible to specify certain unknown constants of interaction of molecules and atoms with a tungsten surface. By the example of the hydrogen flow in a hightemperature tungsten cylindrical channel, the role of dissociation, sorption, and recombination processes is shown in a wide range of flow regimes from free-molecular to continuum.
Energy Technology Data Exchange (ETDEWEB)
Korichi, Abdelkader [Centre Universitaire de Medea, Quartier Ain D' heb, Medea 26000 (Algeria)], E-mail: a_korichi@hotmail.com; Oufer, Lounes [Universite des Sciences et de la Technologie Houari Boumediene, Faculte de Genie Mecanique et de Genie des Procedes, Departement de Genie Chimique et de Cryogenie, Laboratoire des Phenomenes de Transfert, BP 32, El-Alia, Bab-Ezzouar, Alger (Algeria)], E-mail: lounesoufer@yahoo.com
2007-10-15
A numerical investigation is conducted in a rectangular channel with heated obstacles mounted alternatively on the upper and lower walls. Time-dependent two dimensional laminar flow with constant thermophysical properties is assumed for air at three values of the Reynolds number (50, 500 and 1000). A detailed analysis is carried out to investigate flow pattern and Nusselt number. Streamwise periodic contraction-expansion of the cross-section induces bifurcation from steady to unsteady flow. In the unsteady state, a self-sustained periodic oscillatory flow occurs. It is also found that a travelling wave generated by the vortex shedding contributes mainly to heat transfer enhancement.
Rotating annulus laboratory experiments with application to baroclinic channel flows with narrows
Harlander, Uwe; Wenzel, Julia; Egbers, Christoph
2010-05-01
The differentially heated rotating annulus is a classical experiment of geophysical fluid dynamics that shows many similarities with large-scale atmospheric flows. Still, many features of the annulus flow are not well understood and modern non-intrusive measurement techniques can help to clarify them. Moreover, blocked or partly blocked annulus flows are less well studied although such flows show resemblance with oceanic channel flows. We present experimental results from a heated rotating annulus with a barrier that constricts the flow along the inner wall and at the bottom [1]. For the experiments a flow regime has been chosen that is characterized by an Eady wave with azimuthal wave number three. Without the barrier, the wave propagates prograde with no significant structural change. In contrast, when the barrier is mounted, wave crests break approaching it but redevelop downstream of the barrier. We are interested in the transient wave behavior and in particular in the dominant frequencies that occur in the narrow and downstrean or upstream of it. Moreover, we study the impact of a slowly varying radial temperature gradient on the wave's phase speed and the period it takes for the reestablishment of the baroclinic wave downstream of the barrier. It is suggested that the experiments are useful in understanding some features of the flow through the Mozambique Channel. It has been shown that the flow characteristic within the Channel is quite different from the one downstream of it [2]. [1] J. Wenzel (2009): Barokline Wellen in einem rotierenden asymmetrischen Tank, Studienarbeit BTU Cottbus, Univ. Leipzig, 55pp. [2] U. Harlander, H. Ridderinkhof, M.W. Schouten, and W.P.M. De Ruijter (2009): Long term observations of transport, eddies, and Rossby waves in the Mozambique Channel, J. Geophys. Res., 114, C02003, doi:10.1029/2008JC004846.
Laws of turbulent flow in pipes and channels
International Nuclear Information System (INIS)
With a list of 322 publications, some of which have only recently been published, with 92 sketches and diagrams and 12 tables, the paper gives a survey on the prsent state of research on turbulent flow in pipes and ducts. Also included is a chapter on the analogy between impulse, heat and material transfer, which provides the basic knowledge for a quick understanding of the most recent research findings in the field of heat and material transfer which are constantly being published. (orig./AK)
Premature and stable critical heat flux for downward flow in a narrow rectangular channel
International Nuclear Information System (INIS)
It has been recommended that RRs and MTRs be designed to have sufficient margins for CHF and the onset of FI as well, since unstable flow could leads to premature CHF under very low wall heat flux in comparison to stable CHF. Even the fact and previous studies, however, the understanding of relationship among FI, premature CHF and stable CHF is not sufficient to date. In this regards, subcooled flow boiling in a vertical rectangular channel was experimentally investigated to enhance the understanding of the CHF and the effect of the two-phase flow instability on it under low pressure conditions, especially for downward flow which was adopted for Jordan Research and Training Reactor (JRTR) and Kijang research reactor (KJRR) to achieve easier fuel and irradiation rig loading. In this study, CHF for downward flow of water under low pressure in narrow rectangular channel was experimentally investigated. For conditions such as downward flow, narrow rectangular channel and low pressure, it has been deduced from literature that flow instability could largely influence on triggering CHF at lower heat flux, i. e. premature CHF. Total 54 CHF data, which includes premature and stable data was obtained for various fluid conditions and system configurations including inlet stiffness. The upper and lower boundaries of CHF were newly proposed based on the experiment
Energy Technology Data Exchange (ETDEWEB)
Xi, Xi; Xiao, Zejun, E-mail: fabulous_2012@sina.com; Yan, Xiao; Li, Yongliang; Huang, Yanping
2014-10-15
Highlights: • Flow instability experiment between two heated channels with supercritical water is carried out. • Two kinds of out of phase flow instability are found and instability boundaries under different working conditions are obtained. • Dynamics characteristics of flow instability are analyzed. - Abstract: Super critical water reactor (SCWR) is the generation IV nuclear reactor in the world. Under normal operation, water enters SCWR from cold leg with a temperature of 280 °C and then leaves the core with a temperature of 500 °C. Due to the sharp change of temperature, there is a huge density change in the core, which could result in potential flow instability and the safety of reactor would be threatened consequently. So it is necessary to carry out relevant investigation in this field. An experimental investigation which concerns with out of phase flow instability between two heated parallel channels with supercritical water has been carried out in this paper. Due to two INCONEL 625 pipes with a thickness of 6.5 mm are adopted, more experimental results are attained. To find out the influence of axial power shape on the onset of flow instability, each heated channel is divided into two sections and the heating power of each section can be controlled separately. Finally the instability boundaries are obtained under different inlet temperatures, axial power shapes, total inlet mass flow rates and system pressures. The dynamics characteristics of out of phase oscillation are also analyzed.
Effects of viscosity in a partially ionized channel flow with thermionic emission
International Nuclear Information System (INIS)
The flow of the partially ionized gas inside thermionic hollow cathodes spans a diverse range of theoretical disciplines in plasma physics and fluid mechanics. Understanding and predicting the evolution of such flows has many practical implications because hollow cathodes are critical components of electric propulsion systems used onboard scientific and commercial spacecraft presently in space or in the mission planning stages. As space missions become more demanding of the propulsion system in terms of throughput, understanding and predicting failure mechanisms of the system becomes imperative. Two-dimensional numerical simulations of the partially ionized gas generated by a thermionic hollow cathode have been performed to quantify the effects of viscosity inside the cylindrical channel of the device. A comparison of the inviscid and fully viscous flow fields shows that viscosity has a significant impact on the atomic species and a lesser effect on the ions. The internal pressure is determined to be more than 40% higher compared to the inviscid solution and the Reynolds number for the flow of atoms is found to be less than 20 inside the channel. Although the Mach number is computed to be <0.1 for approximately 95% of the channel, the solution for the velocity flow field begins to deviate from the Poiseuille (parabolic) solution at about 50% of the channel due mainly to collisional drag with ions.
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.
The influence of flow obstructions on flooding phenomena in vertical channels
International Nuclear Information System (INIS)
Flooding phenomenon limits the stability of a liquid film falling downwards along the walls of a channel inside which an upwards gas flow takes place. As known, this entrainment effect can completely prevent the liquid fall from its natural flow. A local reduction of the flow channel cross section, due for instance to an obstruction, will affect the flooding parameters, depending on the position at which the obstruction is located and on the obstruction flow cross section. The present work deals with an air-water experiment carried out with a transparent circular duct test section, inside which it is possible to insert orifices having several diameters, to test the influence of the obstruction on flooding parameters. Predictions by the correlations available in literature are compared and a method to evaluate the influence of the obstruction is proposed
An experimental study of flow boiling in a rectangular channel with offset strip fins
International Nuclear Information System (INIS)
An experimental study on saturated flow boiling heat transfer of R113 was performed in a vertical rectangular channel with offset strip fins. Two-phase pressure gradients and boiling heat transfer coefficients in an electrically heated test section were measured for the quality range of 0-0.6, mass flux range of 17-43 kg/m2 s and heat flux of 500-3000 W/m2. Two-phase frictional multiplier was determined as a function of Martinelli parameter. The two-phase forced convective component of the local boiling heat transfer coefficient was found to be well correlated with the Reynolds number factor. A superposition method for the flow boiling heat transfer coefficient that included the contribution of saturated nucleate boiling was verified also for flow boiling in a channel with offset strip fins. The predictions of local flow boiling heat transfer coefficients were found to be in good agreement with experimental data
Channel, Lava Tube, and Edifice Flow Models: Developments and Recent Applications for Mars
Sakimoto, S. E.; Gregg, T. K.; Riedel, S. J.
2001-12-01
Recent advances in modeling of lava channels, lava tubes, and small edifice construction allow us to put more physically realistic constraints on effusion rates and rheologies. For this study, we combine these models with the new precise altimetry for Mars from the Mars Global Surveyor mission. The model suite includes solutions for Newtonian and Bingham rectangular channel flow, Newtonian and Bingham sheet flow, Newtonian and Bingham tube flow, and a percolation model for shield emplacement. We find that the new data and model accuracy allows us to apply these models for different flow regimes and regions to reveal probable differences in eruption rates or rheologies across Mars. Our estimations of effusions rates (for example) improve from a range of five to six orders of magnitude to a few, which allow possible discrimination of flow rate differences between regions of several orders of magnitude. Some, but not all, of the largest flow rates are found on the steepest slopes, but much of the variation is directly attributable to either effusion rate variations or rheology differences. We suggest that some of the differences are revealing characteristic eruption styles for specific martian regions, such as lower flow rates (after correction for different slopes) in Tyrrhena's flow field than are seen on the major shield volcanoes. However, some differences simply seem to reveal natural scatter within any given eruption style and model application. We will discuss results of models for several martian regions, and implications for regional and temporal changes in flow and effusion rate properties.
Wakes from submerged obstacles in an open channel flow
Smith, Geoffrey B.; Marmorino, George; Dong, Charles; Miller, W. D.; Mied, Richard
2015-11-01
Wakes from several submerged obstacles are examined via airborne remote sensing. The primary focus will be bathymetric features in the tidal Potomac river south of Washington, DC, but others may be included as well. In the Potomac the water depth is nominally 10 m with an obstacle height of 8 m, or 80% of the depth. Infrared imagery of the water surface reveals thermal structure suitable both for interpretation of the coherent structures and for estimating surface currents. A novel image processing technique is used to generate two independent scenes with a known time offset from a single overpass from the infrared imagery, suitable for velocity estimation. Color imagery of the suspended sediment also shows suitable texture. Both the `mountain wave' regime and a traditional turbulent wake are observed, depending on flow conditions. Results are validated with in-situ ADCP transects. A computational model is used to further interpret the results.
Duan, Y.; S. He
2016-01-01
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 Stro...
Numerical Simulation of Confluence Flow in Open Channel with Dynamic Meshes Techniques
Yang, Q. Y.; T H Liu; Lu, W. Z.; Wang, X. K.
2013-01-01
Due to the interaction between branch flow and main stream at confluence zone in open channel, the water level of free surface often varies dramatically. In three dimensional simulations of confluence flow, multi-phase models are usually adopted in treating the free-surface boundary, for example, the Volume of Fluid model. The major dilemma for adopting multi-phase modes is that the method consumes more time and computation resources. In this study, the new mesh technique, the dynamic meshes,...
Modelling of supercritical turbulent flow over an inclined backward-facing step in a open channel
Czech Academy of Sciences Publication Activity Database
Příhoda, Jaromír; Zubík, P.; Šulc, J.; Sedlář, M.
Prague : Institute of Thermomechanics AS CR, v. v. i., 2011 - (Fuis, V.), s. 495-498 ISBN 978-80-87012-33-8. [Engineering Mechanics 2011 /17./. Svratka (CZ), 09.05.2011-12.05.2011] R&D Projects: GA ČR GA103/09/0977 Institutional research plan: CEZ:AV0Z20760514 Keywords : open channel flow * inclined backward-facing step * supercritical flow Subject RIV: BK - Fluid Dynamics
On the Flow of a Paramagnetic Fluid in a Differentially Heated Channel
Directory of Open Access Journals (Sweden)
H. Sadat
2011-01-01
Full Text Available In the present study, we investigate the flow of a paramagnetic fluid in a two dimensional heated channel when an external magnetic gradient is imposed. In the fully developed regime, an analytical solution shows that a flow reversal may occur; the condition of this is given n terms of the Reynolds number. Numerical simulations are then carried out for more general situations. It is shown that the analytical model gives good qualitative predictions.
Collecting nuclear reaction products by adsorption from a gas flow in a slit channel
International Nuclear Information System (INIS)
Experimental results of collecting recoil atoms produced in reactions with heavy ions are presented. The recoil atoms thermalized in gas are transported by the gas flow into a 1 mm wide slit channel formed by the sensitive surfaces of radioactive decay detectors. Due to the adsorption from the gas flow it is possible to collect ≥ 50% of the initial recoil atoms on the detector surfaces within a time interval of ≤ 0.1 s. 20 refs., 7 figs
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.
Method for Flow Measurement in Microfluidic Channels Based on Electrical Impedance Spectroscopy
Arjmandi, Nima; Van Roy, Willem; Lagae, Liesbet; Borghs, Gustaaf; 10.1007/s10404-011-0843-0
2012-01-01
We have developed and characterized two novel micro flow sensors based on measuring the electrical impedance of the interface between the flowing liquid and metallic electrodes embedded on the channel walls. These flow sensors are very simple to fabricate and use, are extremely compact and can easily be integrated into most microfluidic systems. One of these devices is a micropore with two tantalum/platinum electrodes on its edges; the other is a micro channel with two tantalum /platinum electrodes placed perpendicular to the channel on its walls. In both sensors the flow rate is measured via the electrical impedance between the two metallic electrodes, which is the impedance of two metal-liquid junctions in series. The dependency of the metal-liquid junction impedance on the flow rate of the liquid has been studied. The effects of different parameters on the sensor's outputs and its noise behavior are investigated. Design guidelines are extracted and applied to achieve highly sensitive micro flow sensors wit...
Wan, Gang; Jin, Yong; Li, Haiyuan; Li, Baoming
2016-03-01
Active boundary layer flow control and boundary layer manipulation in the channel flow that was based on low temperature plasma were studied by means of a lattice Boltzmann method. Two plasma actuators were placed in a row to obtain the influence rule of their separation distance on the velocity profile at three locations and maximum velocity in the flow field. Two plasma actuators were placed symmetrically inside a channel to examine the effect of channel height and voltage on the velocity profile and flow rate. It was found that the channel height controls the distribution of flow velocity, which affected the flow rate and its direction. Increasing plasma voltage had a negative effect on the flow rate due to the generation of a larger and stronger flow vortex.
Heat removal increase in steam generating channels containing local flow swirl generators
International Nuclear Information System (INIS)
An approach is suggested to investigate heat removal increase in steam generating channels containing a lot of local flow swirl generators. An exponential dependence of the heat flux density changes over the channel length is obtained on the basis of experimental data. Experiments were carried out in freon-12 flow at a pressure of 1.06-2.25 MPa (equivalent water pressures are 6.87-13.74 MPa), moss velocity of 1000-4000 kg/(m2xs). Dependences for calculating the heat flux changes in the RBMK channel with operating parameters being equal to 6.87-12.75 MPa and 1000-2500 kg/(m2xs), are obtained by recalculating the data from freon to water. Good agreement with expermetal data is obtained
Pressure drop characteristic of flow boiling in narrow rectangular channel under rolling motion
International Nuclear Information System (INIS)
Experimental investigation and analysis of the pressure drop characteristic of flow boiling in narrow rectangular channel were conducted under rolling motion. Several correlations for the two-phase frictional pressure drop were evaluated against the experimental data. The results show that the correlations for conventional channel poorly predict the results. While the Zhang-Mishima and Sun-Mishima correlations developed for narrow channel are better than other correlations. On the other hand, the pressure drop characteristic of flow boiling was analyzed under rolling motion. The two-phase pressure drop changes cyclically due to the rolling motion, rolling angle and period almost have no effect on the fluctuation of pressure drop and the average two-phase frictional pressure drop. (authors)
The Discuss of the Formula of Flow Loss and Water Using Coefficient on Seepage Proofed Channel
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
On the basis of the analysis about present water resource situation in China ,the disadvantage of the for mula of flow loss and water using coefficient on anti－seep channel which have been applying in channel de sign and water saving irrigation administration will be indicated in the paper. The characteristics of that the loss of conveying water is changeable with the flow changing have been take into account in the new formula. The formula is validated by the example of middle permeable channel (A ＝ 1.90,m ＝ 0.40). The calculate re sult is more precision. Also some formula has been given,they can be referred to the worker of the irrigation administration.
NAIAD, LOCA Transient and Steady-State 2 Phase Flow in Channel Network
International Nuclear Information System (INIS)
1 - Nature of physical problem solved: The transient (including LOCA) and steady state flow of two-phase compressible light water in a network of heated channels. The momentum flux term is included and unequal phase velocities allowed. A lumped fuel model and detailed surface heat transfer are included. Thermodynamic equilibrium of the two phases is assumed. Discharge flow is calculated intrinsically from the hydraulic equations. The ANC pump model is included. 2 - Method of solution: The one-dimensional conservation equations of mass, momentum and energy are solved in each channel by a numerically stable implicit finite difference scheme. The network is then solved by an accelerated Gauss-Seidel iteration scheme. 3 - Restrictions on the complexity of the problem: Versions of the code can be easily generated to handle any size problem. Standard code is limited to 50 axial nodes and 10 channels
Numerical investigation of flow through vegetated multi-stage compound cha-nnel
Institute of Scientific and Technical Information of China (English)
王雯; 槐文信; 高猛
2014-01-01
This paper addresses the problem of the renormalization group k-e turbulence modeling of a vegetated multi-stage compound channel. Results from Micro acoustic Doppler velocimeter (ADV) tests are used with time and spatial averaging (double-averaging method) in the analysis of the flow field and the characterization. Comparisons of the mean velocity, the Reynolds stress, and the turbulent energy distribution show the validity of the computational method. The mean velocity profile sees an obvious de-celeration in the terraces because of vegetation. Secondary flow exists mainly at the junction of the main channel and the vegetation region on the first terrace. The bed shear stress in the main channel is much greater than that in the terraces. The difference of the bed shear stress between two terraces is insignificant, and the presence of vegetation can effectively reduce the bed shear stress.
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...
Numerical Simulation of Open-Channel Flow in 90-Degree Combining Junction
Institute of Scientific and Technical Information of China (English)
武蓉; 茅泽育
2003-01-01
Combining flows often occur in open channel networks of drainage systems and river engineering. Open-channel junction flows were analyzed by solving the depth-averaged two-dimensional, elliptic Reynolds-averaged Navier-Stokes equations with the Hanjalic-Launder (H-L) modification to the k-ε turbulence model without the free surface "rigid lid" approximation with an efficient finite-volume procedure. The model can also analyze flows with separation. The model was used to analyze the relative importance of various factors and was compared with laboratory measurements. The H-L modification produced much better simulations of the separation zone size with 20% better accuracy than the standard k-ε model. The H-L modification was then used to study the characteristic of junction flows and the separation zones with different discharge ratios. The simulational results show that separation zone size decreases as the discharge ratio of the upstream main channel to the downstream channel increases.
DISCONTINUOUS FLOW OF TURBID DENSITY CURRENTS I. CHANNEL EXPANSION AND CONTRACTION
Institute of Scientific and Technical Information of China (English)
Jiahua FAN
2005-01-01
Laboratory experiments on turbid density currents were conducted to observe the flow features of these currents with abrupt contracted and expanded reaches. Experimental data were used to determine water entrainment coefficients for both channel expansion and contraction. Expressions for turbid density currents with water entrainment coefficients in abrupt contracted and expanded reaches were derived,and compared with experimental data.
Laboratorial studies on the seepage impact in open-channel flow turbulence
International Nuclear Information System (INIS)
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.
HOW WELL CAN YOU ESTIMATE LOW FLOW AND BANKFULL DISCHARGE FROM STREAM CHANNEL HABITAT DATA?
Modeled estimates of stream discharge are becoming more important because of reductions in the number of gauging stations and increases in flow alteration from land development and climate change. Field measurements of channel morphology are available at thousands of streams and...
Pressure losses at forced flow of boiling nitrogen in horizontal channels
International Nuclear Information System (INIS)
Experimental results on pressure losses at forced flow of two-phase nitrogen in horizontal channels with circular and rectangular cross sections are considered. The effect of pressure, mass velocity and vapor quality at pressure losses are derived. Formulas for predicting friction losses under regime parameters are developed. Dependence of two-phase friction coefficient on mixture velocity are given. 17 refs.; 14 figs
Modeling of steady-state flow in heated (BWR) parallel channels
International Nuclear Information System (INIS)
The FIBWR computer code has been developed to predict the distributions of quality and void fraction in Boiling Water Reactors. This study describes the analytical methodology used to solve the conservation equations of continuity, momentum and energy in steady-state, heated, parallel channel, two-phase flow. 11 refs
Flageul Cédric, Benhamadouche Sofiane, Lamballais Éric, Laurence Dominique.
2014-01-01
The present work provides budgets of turbulent heat fluxes and temperature variance for a channel flow with different thermal boundary conditions: an imposed temperature, an imposed heat flux and with conjugate heat transfer combined with an imposed heat flux at the outer wall.
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...
NUMERICAL SIMULATION OF TWO-DIMENSIONAL DAM-BREAK FLOWS IN CURVED CHANNELS
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Two-dimensional transient dam-break flows in a river with bends were theoretically studied. The river was modeled as a curved channel with a constant width and a flat bottom. The water was assumed to be an incompressible and homogeneous fluid. A channel-fitted orthogonal curvilinear coordinate system was established and the corresponding two-dimensional shallow-water equations were derived for this system. The governing equations with well-posed initial and boundary conditions were numerically solved in a rectangular domain by use of the Godunov-type finite-difference scheme, which can capture the hydraulic jump of dam-break flows. The comparison between the obtained numerical results and the experimental data of Miller and Chaudry in a semicircle channel shows the validity of the present numerical scheme. The mathematical model and the numerical method were applied to the dam-break flows in channels with various curvatures. Based on the numerical results, the influence of river curvatures on the dam-break flows was analyzed in details.
Directory of Open Access Journals (Sweden)
S. Kouchakzadeh
2006-10-01
Full Text Available The sensitivity analysis approach should be regarded as a new means which has recently been proposed for assessing flow of the irrigation networks. This approach uses the flow steady state equations and the physical conditions of irrigation channels to evaluate the response of the system to input perturbations. In this paper, some structural hydraulic sensitivity indicators were developed and utilized in studying the flow of an irrigation channel. For evaluating the efficiency of indicators and proposed analysis method, a real case was simulated by SOBEK model. Using the simulation results and introduced indicators, the flow regulation and distribution process within channel was studied. The results indicated a successful application of sensitivity indicators in evaluating system's potential in relation to alternative operational scenarios. With the calculation of these indicators, a comprehensive information system could be provided and applied in the analysis of the response potential of channel to structural perturbations, estimation of structure setting accuracy, and in the choice of suitable operation frequency there of.
Wall Shear Stress Induced by Taylor Bubbles in Inclined Flow Channels
Directory of Open Access Journals (Sweden)
Vejražka J.
2013-04-01
Full Text Available The motion of single air bubbles in flat channels is experimentally investigated. The electrodiffusion technique of near-wall flow diagnostics is applied to measure the wall shear stress distribution under large rising bubbles. The measurements are synchronized with the visual observation of bubble movement by a high-speed camera. The analysis of video records provides information on the bubble shape and terminal velocity. The experiments are carried out for three different channel configuration (with heights of 1.5, 4, and 8 mm, cover a wide range of channel inclination angles (from horizontal to vertical position, and dealing with both the bubbles in stagnant and in co-flowing water. The directionally sensitive, two-strip electrodiffusion probe is proved to be an effective tool to investigate the near-wall flow response to translating bubbles. It provides information not only on the wall shear rate distribution, but also detects the location of near-wall flow reversal, gives an estimate of the thickness of liquid film separating the large bubble from the wall, and provides also the characteristics of capillary waves appearing in the bubble tail region. The effect of channel inclination angle on the modification of wall shear stress distribution along the upper and bottom wall is also discussed.
Laboratorial studies on the seepage impact in open-channel flow turbulence
Energy Technology Data Exchange (ETDEWEB)
Herrera Granados, Oscar; Kostecki, Stanislaw, E-mail: Oscar.Herrera-Granados@pwr.wroc.pi [Institute of Geotechnics and Hydro-engineering (I-10), Wroclaw University of Technology. Plac Grunwaldzki 9 D-2 p.112. 50-377 Wroclaw (Poland)
2011-12-22
In natural streams, the interaction between water in motion and movable beds derives in transport of material. This is a fact that causes several problems for river regulation, above all in streams which were heavily modified by human interferences. Therefore, to find solutions or at least to alleviate the negative effects that sediment transport can bring with is a topic to be researched. The impact of seepage on river sedimentation processes and open-channel flow is important for environmental issues but it is commonly neglected by water specialists. The present contribution presents the output of a series of experimental works where the influence of seepage on the open channel turbulence is analyzed at the laboratory scale. Even though that the magnitude of the groundwater flow is significantly smaller than the magnitude of the open channel flow; the output of the experiments demonstrates that seepage not only modifies the water-sediment interaction as demonstrated Herrera Granados (2008; 2010); but also is affecting the velocity field and turbulence dynamics of the open-channel flow.
Critical contribution of KV1 channels to the regulation of coronary blood flow.
Goodwill, Adam G; Noblet, Jillian N; Sassoon, Daniel; Fu, Lijuan; Kassab, Ghassan S; Schepers, Luke; Herring, B Paul; Rottgen, Trey S; Tune, Johnathan D; Dick, Gregory M
2016-09-01
Ion channels in smooth muscle control coronary vascular tone, but the identity of the potassium channels involved requires further investigation. The purpose of this study was to evaluate the functional role of KV1 channels on porcine coronary blood flow using the selective antagonist correolide. KV1 channel gene transcripts were found in porcine coronary arteries, with KCNA5 (encoding KV1.5) being most abundant (P muscle layer of both porcine and human coronary arteries, including microvessels. Whole-cell patch-clamp experiments demonstrated significant correolide-sensitive (1-10 µM) current in coronary smooth muscle. In vivo studies included direct intracoronary infusion of vehicle or correolide into a pressure-clamped left anterior descending artery of healthy swine (n = 5 in each group) with simultaneous measurement of coronary blood flow. Intracoronary correolide (~0.3-3 µM targeted plasma concentration) had no effect on heart rate or systemic pressure, but reduced coronary blood flow in a dose-dependent manner (P metabolic vasodilation and intracoronary correolide (3 µM) significantly reduced coronary blood flow at any given level of myocardial oxygen consumption (P metabolism and transient ischemia. PMID:27496159
Uniform flow in open channel design techniques%明渠均匀流水力设计技术
Institute of Scientific and Technical Information of China (English)
黄民标
2013-01-01
明渠是指人工渠道、天然河道以及非满管水流的管道，明渠水流具有共同的水力特征，即具有自由表面，且自由表面上的气体大气压，依靠重力能流动。明渠水流分为恒定流与非恒定流，明渠恒定流又分为明渠均匀流与明渠非均匀流。%Open channel is the artificial channel, natural and non-full pipe flow channel pipe, open channel flow have a common hydraulic characteristics, have a free surface, and the free surface of the gas pressure, to flow by gravity. Constant flow and open channel flow into unsteady flow;open channel flow is divided into a constant uniform open channel flow and non-uniform open channel flow.
A critical heat flux experiment with water flow at low pressures in thin rectangular channels
International Nuclear Information System (INIS)
Highlights: • The CHF experiments were performed in thin rectangular channels at low pressure. • Different test sections were tested with different heating length and width. • A new CHF correlation was derived by considering the heating length effect. • Large pressure drop was found in test section at high flow rate condition. - Abstract: Experimental investigation was performed on the critical heat flux (CHF) in thin rectangular channels with very wide mass velocity range at low pressures. Different test sections were adopted with the different heated length and heated width. Both the vertical upward flow and downward flow were tested during the experiment. The results prove that the effect of the heated length on the CHF exists in the high mass velocity test but it is not very strong. The CHF rises with shorter heated length. At low mass velocities, the CHF at downward flow is much lower than that at upward flow. Empirical correlations were compared with the experimental data both from present and others’ studies. Empirical correlations provided by Katto and Gambill gave out good prediction for the low upflow and the high downflow respectively. The Sudo correlation had wide flow range but it overestimated at low mass velocity and underestimated at high mass velocity. A new CHF correlation for the large flow rate shows good agreement with the present and others’ studies. High pressure drop was found in the experiment at high flow rate conditions. It was analyzed and discussed in the paper
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.
A study on the stability of laminar open-channel flow over a sandy rippled bed
Institute of Scientific and Technical Information of China (English)
BAI; Yuchuan; XU; Haijue
2005-01-01
The bed of a river often features some kinds of bedform, such as sand ripples, dunes, and so on. Even if the bed is smooth initially, disturbances arising from the bed or other external sources will cause the laminar flow in an open channel to become unstable as soon as the flow develops, thereby leading to the formation of sand ripples on the bed. In return, the formation of the sand ripples will modify the instability path of the laminar flow passing over them. The wavy character of the bed will induce further instability of the flow, which is essentially different from that on a smooth bed: the neutral curve will move forward and the critical Reynolds number will decrease. The flow is unstable in response to a wider range of the disturbance wave number, or the laminar flow instability can happen more easily. The propagation speed of the sand ripples also affects the flow instability, since the stability of open channel flow over a movable bed is fundamentally different from that on a rigid bed. These instability effects are discussed in detail in this paper.
Yamamoto, Takehiro; Yamasaki, Yasuo; Tanaka, Yusuke; Mori, Noriyasu
2006-07-01
Three-dimensional flows of liquid crystalline polymers (LCPs) in a rectangular 3 to 1 abrupt contraction channel and a rectangular 1 to 3 abrupt expansion channel are numerically analyzed to investigate the molecular orientation behavior of LCPs in complex flows. A modified Doi model is used as a constitutive equation and MAC (marker and cell)-based finite difference method is employed for the numerical technique for solving the basic equations. In the contraction flow, most molecules are aligned in the flow direction near the contraction owing to elongational flow except for a vortex region. Just downstream of the contraction, the velocity overshoot occurs owing to the molecular orientation near the contraction. In the expansion flow, on the other hand, molecules near the mid-plane are aligned perpendicular to the flow direction just downstream of the expansion. This alignment is related to a concave velocity profile appeared in this region. Moreover, the decelerating flow downstream of the expansion causes a three-dimensional structure of directors called a twist structure.
Bucs, Szilard S.
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.
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. PMID:23863280
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.
Simulations of peristaltic slip-flow of hydromagnetic bio-fluid in a curved channel
Ali, N.; Javid, K.; Sajid, M.
2016-02-01
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).
Hydrodynamic chromatography and field flow fractionation in finite aspect ratio channels.
Shendruk, T N; Slater, G W
2014-04-25
Hydrodynamic chromatography (HC) and field-flow fractionation (FFF) separation methods are often performed in 3D rectangular channels, though ideal retention theory assumes 2D systems. Devices are commonly designed with large aspect ratios; however, it can be unavoidable or desirable to design rectangular channels with small or even near-unity aspect ratios. To assess the significance of finite-aspect ratio effects and interpret experimental retention results, an ideal, analytical retention theory is needed. We derive a series solution for the ideal retention ratio of HC and FFF rectangular channels. Rather than limiting devices' ability to resolve samples, our theory predicts that retention curves for normal-mode FFF are well approximated by the infinite plate solution and that the performance of HC is actually improved. These findings suggest that FFF devices need not be designed with large aspect ratios and that rectangular HC channels are optimal when the aspect ratio is unity. PMID:24674643
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.
Stability analysis of parallel-channel systems with forced flows under supercritical pressure
International Nuclear Information System (INIS)
Highlights: → A frequency-domain model for supercritical flow stability analysis was developed. → The marginal stability boundaries for parallel-channel system were constructed. → The sensitivities of several parameters were studied for system stability boundary. → A time-domain model was developed and applied to nonlinear stability analysis. - Abstract: The flow in the core of supercritical water reactors (SCWRs) experiences drastic change in its thermodynamic properties and transport properties near the pseudo-critical temperature, thus the core flow may be susceptible to density wave oscillation instability, which is a challenge to the system safety and must be studied carefully. This paper studies the dynamic stability characteristics of the fast-spectrum zone of a newly designed mixed-spectrum SCWR (SCWR-M), which is characterized as a parallel-channel system. A frequency-domain model has been developed for linear stability analysis, and marginal stability boundaries under several conditions for the parallel-channel system are generated, which indicate that the system normal operational condition is in the stable region. The stability of parallel-channel systems is dominated by the hottest channel. The higher the power density of the hottest channel is, the less stable the system will be. Increasing mass flow is beneficial for the system stability. Systems with uniformly axial power distribution are less stable than those with cosine-shaped or stair-shaped axial power distributions. In the time-domain, a single-phase one-dimensional model has been developed for non-linear analysis, and several perturbation transients are calculated. The results of analysis show a good agreement with that of the frequency-domain analyses, and the existence of transitional stable region has been verified.
Numerical simulation of turbulent buoyant flows in horizontal channels
International Nuclear Information System (INIS)
A numerical method is presented, to calculate the three-dimensional, time-dependent large scale structure of turbulent buoyant flows. The subject of the study is the Rayleigh-Benard-convection with air (Pr=0.71, Ra=2.5 106, 107) and sodium (Pr=0.006, Ra=8.4 104, 2.5 105, 106, 107) and a fluid layer with water and an internal heat source (Pr=7.0, RaI=1.5 1010) at moderate and high Rayleigh-numbers. The goal of the work is both, the analysis of structures of instantaneous as well as the statistical analysis of spatially and/or time averaged data, to give a contribution to the investigation of the characteristics of turbulent natural convection mainly in fluids with small Prandtl-numbers. The large eddy simulation of natural convection requires the development of appropriate momentum and heat subgrid scale models and the formulation of new boundary conditions. The used energy-length-models in the computer code TURBIT are extended methodically by modification of the characteristic length scales of the sub scale turbulence. The reduction or the increase of the sub scale turbulence correlations, caused by the influence of solid boundaries or the stratification, is considered. In the same way the new boundary conditions for the diffusive terms of the conservation equations are seen to be necessary, when the thermal or in the case of liquid metals the more critical hydrodynamic boundary layer is resolved insufficiently or not at all. The extended and new methods, models and boundary conditions, which enabled the realization of the planned simulations, are presented. (orig.)
ADCP measured flow current of the middle-lower Changjiang River channel
Institute of Scientific and Technical Information of China (English)
Qiang ZHANG; Yafeng SHI; Zhongyuan CHEN; Tong JIANG
2008-01-01
The water column flow velocity of 36 river sections in the river reach between Hankou (Wuhan) and Wuxue of the middle-lower Changjiang River.Their cross sectional distribution patterns in relation to the river channel morphologies were examined by using shipmounted ADCP (Acoustic Doppler Current Profiler) instrument.The results indicate four (Ⅰ-Ⅳ) types of river channel morphology associated flow patterns:Ⅰ-laterally deepening riverbed topographic pattern; Ⅱ-symmetrical to asymmetrical riverbed topographic pattern; Ⅲ-relative fiat riverbed topographic pattern,and Ⅳ-sandbar supported riverbed topographic pattern.All these correspond to the different patterns of flow velocity distribution.The maximum flow velocity is usually related to the deeper water depth,but irregular water column distribution of flow current velocity results often from the vortices' current associated with river knots.Deeper river water depth is usually identified in the river reach located slightly downstream to the river knot,where faster flow velocity occurs.Downward change in flow velocity fits semi-log law,showing an exponential decreasing flow current with the maximum flow velocity near the water surface.However,in the river reach near the river knots,the water column distribution of flow current velocity does not fit the semi-log law,showing the irregular flow current pattern.This study,in context of river catchment management,highlights the controls of riverbed morphology to the flow current structure,which will shed light on the post study of Three Gorges damming in 2009.
Taymaz Imdat; Aslan Erman; Benim Ali Cemal
2015-01-01
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 us...
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 couple stresses on hydromagnetic Eyring-Powell fluid flow through a porous channel
Directory of Open Access Journals (Sweden)
Adesanya Samuel O.
2015-01-01
Full Text Available In this paper, the flow of hydromagnetic non-Newtonian fluid under couple stresses through a porous channel is investigated using the Eyring-Powell model. The fluid is driven by an axial constant pressure gradient. Approximate solutions of the nonlinear dimensionless equations governing the fluid flow are obtained using a new modification of Adomian decomposition method (ADM. The effects of the variation of various flow parameters on both the velocity and temperature fields are deduced and discussed including surface-fluid interface friction and rate of heat transfer.
Hermite-Pade approximation approach to hydromagnetic flows in convergent-divergent channels
International Nuclear Information System (INIS)
The problem of two-dimensional, steady, nonlinear flow of an incompressible conducting viscous fluid in convergent-divergent channels under the influence of an externally applied homogeneous magnetic field is studied using a special type of Hermite-Pade approximation approach. This semi-numerical scheme offers some advantages over solutions obtained by using traditional methods such as finite differences, spectral method, shooting method, etc. It reveals the analytical structure of the solution function and the important properties of overall flow structure including velocity field, flow reversal control and bifurcations are discussed. (author)
Transient Taylor-Aris dispersion for time-dependent flows in straight channels
DEFF Research Database (Denmark)
Vedel, Søren; Bruus, Henrik
2012-01-01
–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...... we both recover the known results for steady and single-frequency pulsating flows, and find new, richer structure of the dispersion as function of system parameters in multi-frequency systems. We show that the effective diffusivity is enhanced significantly by those parts of the time...
Direct Numerical Simulation of turbulent magnetohydrodynamic flows in an open-channel
Energy Technology Data Exchange (ETDEWEB)
Yamamoto, Y.; Kunugi, T.; Serizawa, A. [Kyoto Univ. (Japan). Dept. of Nuclear Engineering
2000-10-01
In this study, Direct Numerical Simulation (DNS) of magnetohydrodynamic (MHD) flows simulated the liquid wall concept in nuclear fusion applications, i.e., turbulent open-channel flows heating under the isoflux condition at the free-surface and insulting condition at the bottom wall, was employed. The magnetic field was imposed in the spanwise direction and the erect of Lorenz force was expressed in terms of the electrostatic potential with an assumption of a low magnetic Reynolds number. As the result, new method for the thermal boundary condition at the free-surface is advanced and numerical investigation of MHD flow was conducted. (author)
Numerical analysis of steady state fluid flow in a two-dimensional wavy channel
International Nuclear Information System (INIS)
A simple geometry of the flow passage that may be used to enhance the heat transfer rate is called wavy and periodic channel. Wavy channel can provide significant heat transfer augmentation and was always important for heat transfer engineering and so far many researches have been done in this field. In this paper, the effects of channel geometry and Reynolds number on the heat transfer coefficient, heat flux and pressure drop for the laminar fully developed flow in a two dimensional channel whereas the walls are considered fix temperature is numerically investigated. The problem is solved for channel with one and two wavy walls and comparisons with the straight channel, in the same flow rate, have been performed. Results indicate that, by decreasing the channel wave length and the distance between the channel walls the pressure drop, heat flux and heat transfer coefficient increase. Results and Conclusions: The following conclusion may be drawn: 1. In a specified channel, for the fluid flow with the constant Reynolds number, by decreasing the wave length from 0.2 m to 0.1 m, the pressure drop, heat flux and heat transfer coefficient increase by 37% , 54% and 29% respectively, whereas by decreasing the wave length from the same value the above mentioned parameters decrease to 108% , 143% and 47% respectively. 2. In a specified wave length, where the amplitude and the Reynolds number is constant, by increasing the distance between the walls from 0.15 m to 0.25 m, the pressure drop, heat flux and heat transfer coefficient decrease by 41% ,8% and 7.8% respectively. References [1] J.C. Burns, T. Parks, J. Fluid Mesh, 29(1967), 405-416. [2] J.L. Goldestein, E.M. Sparrow, ASME J. Heat Transfer, 99 (1977), 187. [3] J.E.O. Brain, E.M. Sparrow, ASME J. Heat Transfer, 104 (1982), 410 [4] N. Sanie, S. Dini, ASME J. Heat Transfer, 115 (1993), 788. [5] G. Wang, P. Vanka, Int. J. Heat Mass Transfer, 38 (17) (1995), 3219. [6] T.A. Rush, T.A. Newell, A.M. Jacobi, Int, J. Heat Mass
International Nuclear Information System (INIS)
In this study, numerical analysis of curved channel steam-methanol reformer was conducted using the computational fluid dynamics (CFD) commercial code STAR-CCM. A pre-numerical analysis of reference model with a cylindrical channel reactor was performed to validate the combustion model of the CFD commercial code. The result of advance validation was in agreement with reference model over 95%. After completing the validation, a curved channel reactor was designed to determine the effects of shape and length of flow path on methanol conversion efficiency and generation of hydrogen. Numerical analysis of the curved-channel reformer was conducted under various flow rate (10/15/20 μl/min). As a result, the characteristics of flow and mass transfer were confirmed in the cylindrical channel and curved channel reactor, and useful information about methanol conversion efficiency and hydrogen generation was obtained for various flow rate.
Evaluation of the Natural Circulation Flow Loop with Inclined Downward Heating Channel
Energy Technology Data Exchange (ETDEWEB)
Wi, Kyung Jin; Ha, Kwang Soon; Park, Rae Joon [KAERI, Daejeon (Korea, Republic of); Yoo, Seong Yeon [Chungnam National University, Daejeon (Korea, Republic of)
2015-05-15
Versatile measures have been suggested and applied to mitigate severe accidents in nuclear power plants as recently presented by Rempe et al. In general, an increase in the natural circulation mass flow rate of the coolant leads to an increase in the critical heat flux (CHF) on the hot wall, thus enhancing the thermal margin. An ex-vessel core catcher under consideration, which is one of the engineered corium cooling systems, is a passive system consisting of an inclined engineered cooling channel made of a single channel between the body of the core catcher and the inside wall of the reactor cavity. Under severe accident conditions, water is supplied from the IRWST to the engineered cooling channel. The water in the inclined channel absorbs the decay heat transferred from the corium through the carbon steel structure of the core catcher body and boils off as steam. The latter is subsequently released into the free volume of the containment above the corium spreading compartment. Water continues to flow from the IRWST to the cooling channel as a result of buoyancy-driven natural circulation. The engineered cooling channel is designed to provide effective long-term cooling and stabilization of the corium mixture in the core catcher body while facilitating steam venting. To maintain the integrity of the ex-vessel core catcher, however, it is necessary that the water coolant be circulated at a sufficiently high rate through the inclined cooling channel for decay heat removal by downward facing boiling of the water circulated from the IRWST. KAERI performed the experimental study to evaluate the cooling performance of ex-vessel core catcher system with inclined downward facing heating surface. A scaling analysis is applied to design the test facility compared with the prototypic core catcher cooling system. The natural circulation flow experiments were performed along with the inlet subcooling, wall heat flux, and water level. The void fraction model with inclined
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.
International Nuclear Information System (INIS)
The present note describes a method for use in conjunction with a scanning electron microscope (SEM) that has been developed to visualize a liquid flow under a high-level vacuum and to measure a velocity field in a small-scale flow through an open channel. In general, liquid cannot be observed via a SEM, because liquid evaporates under the high-vacuum environment of the SEM. As such, ionic liquid and room temperature molten salt having a vapor pressure of nearly zero is used in the present study. We use ionic liquid containing Au-coated tracer particles to visualize a small-scale flow under a SEM. Furthermore, the velocity distribution in the open channel is obtained by particle tracking velocimetry measurement and a parabolic profile is confirmed. (technical design note)
Application of the lattice Boltzmann method to transition in oscillatory channel flow
Cosgrove, J A; Tonge, S J; Munro, C G; Greated, C A; Campbell, D M
2003-01-01
In this study the applicability of the lattice Boltzmann method to oscillatory channel flow with a zero mean velocity has been evaluated. The model has been compared to exact analytical solutions in the laminar case (Re subdelta < 100, where Re subdelta is the Reynolds number based on the Stokes layer) for the Womersley parameter 1 < alpha < 31. In this regime, there was good agreement between numerical and exact analytical solutions. The model was then applied to study the primary instability of oscillatory channel flow with a zero mean velocity. For these transitionary flows the parameters were varied in the range 400 < Re subdelta < 1000 and 4 < alpha < 16. Disturbances superimposed on the numerical solution triggered the two-dimensional primary instability. This phenomenon has not been numerically evaluated over the range of alpha or Re subdelta currently investigated. The results are consistent with quasi-steady linear stability theories and previous numerical investigations.
A rapid response 64-channel photomultiplier tube camera for high-speed flow velocimetry
International Nuclear Information System (INIS)
In this technical design note, the development of a rapid response photomultiplier tube camera, leveraging field-programmable gate arrays (FPGA) for high-speed flow velocimetry at up to 10 MHz is described. Technically relevant flows, for example, supersonic inlets and exhaust jets, have time scales on the order of microseconds, and their experimental study requires resolution of these timescales for fundamental insight. The inherent rapid response time attributes of a 64-channel photomultiplier array were coupled with two-stage amplifiers on each anode, and were acquired using a FPGA-based system. Application of FPGA allows high data acquisition rates with many channels as well as on-the-fly preprocessing techniques. Results are presented for optical velocimetry in supersonic free jet flows, demonstrating the value of the technique in the chosen application example for determining supersonic shear layer velocity correlation maps. (technical design note)
A rapid response 64-channel photomultiplier tube camera for high-speed flow velocimetry
Ecker, Tobias; Lowe, K. Todd; Ng, Wing F.
2015-02-01
In this technical design note, the development of a rapid response photomultiplier tube camera, leveraging field-programmable gate arrays (FPGA) for high-speed flow velocimetry at up to 10 MHz is described. Technically relevant flows, for example, supersonic inlets and exhaust jets, have time scales on the order of microseconds, and their experimental study requires resolution of these timescales for fundamental insight. The inherent rapid response time attributes of a 64-channel photomultiplier array were coupled with two-stage amplifiers on each anode, and were acquired using a FPGA-based system. Application of FPGA allows high data acquisition rates with many channels as well as on-the-fly preprocessing techniques. Results are presented for optical velocimetry in supersonic free jet flows, demonstrating the value of the technique in the chosen application example for determining supersonic shear layer velocity correlation maps.
Large-eddy simulation of suspended sediment transport in turbulent channel flow
Institute of Scientific and Technical Information of China (English)
ZHU Hai; WANG Ling-ling; TANG Hong-wu
2013-01-01
The numerical simulation of the non-cohesive sediment transport in a turbulent channel flow with a high concentration is a challenging but practical task.A modified coherent dynamic eddy model of the Large Eddy Simulation (LES) with a pick-up function is used in the present study to simulate the sediment erosion and the deposition in a turbulent channel flow.The rough wall model is used instead of the LES with the near-wall resolution to obtain the reasonable turbulent flow characteristics while avoiding the high costs in the computation.Good results are obtained,and are used to analyze the sediment transport properties.The results show that the streamwise vortices play an important role in the riverbed erosion and the sediment pick-up,which may serve as guidelines for the sediment management and the water environment protection engineering.
Prediction of post-dryout heat transfer in channels with flow obstacles
International Nuclear Information System (INIS)
Post-dryout heat transfer can occur in heated channels with an annular two-phase flow regime, when the liquid film is partly or wholly removed from the heated wall and the critical heat flux is reached and exceeded. Under such conditions the heat transfer coefficient dramatically drops as compared with the pre-dryout heat transfer regime. Due to that an accurate prediction of the post-dryout heat transfer is of interest in the heat-flux-controlled equipment, where the sudden heat transfer deterioration can lead to the heater damage. In the present paper a new method to predict post-dryout heat transfer in channels with flow obstacles is shown and validated against experimental data. The new approach takes into account the influence of flow obstacles on the dryout location and on the post-dryout heat transfer intensity, and demonstrates a significant improvement of accuracy of predictions compared with other presently available prediction methods. (author)
An experimental study on turbulent-stripe structure in transitional channel flow
Tsukahara, Takahiro
2014-01-01
Turbulent stripe, which would occur in turbulent channel flows at transitional Reynolds numbers, was studied experimentally by flow visualization using reflective flake particles. In a range of bulk mean Reynolds number Re = 1700-2000, the turbulent stripe was observed to be inclined at angles of 20-30 degree against the streamwise direction, and its streamwise wave length was about 60 times of the channel half width (delta). The longitudinal streaks with the spanwise spacing of 1.6delta were found in the quasi-laminar regions. The critical Reynolds number was Re = 1300. Time traces of the streamwise velocity were measured by laser Doppler velocimetry, revealing similarity to the equilibrium turbulent puff in the transitional pipe flow.
On the structural features of fiber suspensions in converging channel flow
Institute of Scientific and Technical Information of China (English)
林建忠; 张凌新
2003-01-01
The structural features of fiber suspensions are dependent on the fiber alignment in the flows. In this work the orientation distribution function and orientation tensors for semi-concentrated fiber suspensions in converging channel flow were calculated, and the evolutions of the fiber alignment and the bulk effective viscosity were analyzed. The results showed that the bulk stress and the effective viscosity were functions of the rate-of-strain tensor and the fiber orientation state; and that the fiber suspensions evolved to steady alignment and tended to concentrate to some preferred directions close to but not same as the directions of local streamlines. The bulk effective viscosity depended on the product of Reynolds number and time. The decrease of effective viscosity near the boundary benefited the increase of the rate of flow. Finally when the fiber alignment went into steady state, the structural features of fiber suspensions were not dependent on the Reynolds number but on the converging channel angle.
Peitersen, M. N.; Zimbelman, J. R.; Christensen, P. R.; Bare, C.
2003-01-01
Long lava flows (discrete flow units with lengths exceeding 50 km) are easily identified features found on many planetary surfaces. An ongoing investigation is being conducted into the origin of these flows. Here, we limit our attention to long lava flows which show evidence of channel-like structures.
Large eddy simulation study of spanwise spacing effects on secondary flows in turbulent channel flow
Aliakbarimiyanmahaleh, Mohammad; Anderson, William
2015-11-01
The structure of turbulent flow over a complex topography composed of streamwise-aligned rows of cones with varying spanwise spacing, s is studied with large-eddy simulation (LES). Similar to the experimental study of Vanderwel and Ganapathisubramani, 2015: J. Fluid Mech., we investigate the relationship between secondary flow and s, for 0 . 25 2 , domain-scale rollers freely exist. These had previously been called ``turbulent secondary flows'' (Willingham et al., 2014: Phys. Fluids; Barros and Christensen, 2014: J. Fluid Mech.; Anderson et al., 2015: J. Fluid Mech.), but closer inspection of the statistics indicates these are a turbulent tertiary flow: they only remain ``anchored'' to the conical roughness elements for s / δ > 2 . For s / δ tertiary flows are prevented from occupying the domain by virtue of proximity to adjacent, counter-rotating tertiary flows. Turbulent secondary flows are associated with the conical roughness elements. These turbulent secondary flows emanate from individual conical topographic elements and set the roughness sublayer depth. The turbulent secondary flows remain intact for large and small spacing. For s / δ tertiary flow is not present. This work was supported by the Air Force Office of Sci. Research, Young Inv. Program (PM: Dr. R. Ponnoppan and Ms. E. Montomery) under Grant # FA9550-14-1-0394. Computational resources were provided by the Texas Adv. Comp. Center at the Univ. of Texas.
Analysis of two-phase flow and boiling heat transfer in inclined channel of core-catcher
International Nuclear Information System (INIS)
Passive Corium Cooling System (CCS) provides a function of ex-vessel debris cooling and molten core stabilization during a severe accident. CCS features inclined cooling channels arranged axi-symmetrically below the core-catcher basin. In order to estimate the coolability of the inclined cooling channel, it is indispensable to identify the flow pattern of the two-phase flow in the cooling channel. Several former studies for the two-phase flow pattern in the inclined channel are referred. Taitel and Dukler (1976) developed a prediction method of the flow pattern transition in horizontal and near horizontal tubes. Barnea et al. (1980) showed the flow pattern map of upward flow with 10 degrees inclination. Sakaguti et al. (1996) observed the two-phase flow patterns in the horizontal pipe connected with slightly upward pipe, in which the flow pattern in the pipe with a bending part was expressed by the combination of a basic flow pattern and some auxiliary flow patterns. Then we investigated these studies In order to identify the flow patterns observed in the inclined cooling channel of CCS. Furthermore we experimentally observed the flow patterns in the inclined cooling channel with various inlet conditions. As a result of the investigation and observation, typical flow patterns in the inclined cooling channel were identified. Two typical flow patterns were observed depending on the steam flow rate, one of which is 'elongated bubble 'flow, and the other is 'churn with collapsing backward and upward slug 'flow The flow and heat transfer in the inclined channel of CCS is analyzed by using a two-phase analysis code employing two-fluid model in which the constitutive equations for the two-phase flow in inclined channels are incorporated. That is, drift flux parameter for each of the elongated bubble flow, and the churn with collapsing backward and upward slug flow are incorporated to the two-phase analysis code, which are based on the rising velocity of the long bubble in
Dynamics of the outflow and its effect on the hydraulics of two-layer exchange flows in a channel
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
This paper reports that an experimental study is conducted to examine the dynamics of the outflow in two-layer exchange flows in a channel connecting between two water bodies with a small density difference. The experiments reveal the generation of Kelvin-Helmholtz (KH) instabilities within the hydraulically sub-critical flow region of the channel. During maximal exchange, those KH instabilities develops into large-amplitude KH waves as they escape the channel exit into the reservoir. The propagation speed ...
Analytical study of narrow channel flow for a spallation target system design
International Nuclear Information System (INIS)
Heat transfer and pressure drop characteristics under fully developed turbulent water flow condition were analyzed over a two-dimensional narrow rectangular channel whose height is H=1.2 mm. The channel configuration and water flow condition simulate forced convection cooling of a spallation target system components design such as a solid target and a proton beam window. The high-Reynolds number form of the standard k - ε and RNG k - ε models employing wall functions for the Reynolds number (Re) range of 7,000 to 22,000 were used in the analyses. As for heat transfer characteristics of a smooth channel, the Nusselt number obtained by the standard k - ε model agreed very well with the Dittus-Boelter correlation. No significant differences in friction factors for the smooth channel were observed for these two models, which agreed well with the Blasius correlation. However, the standard k - ε model could not predict friction factors well for the rib-roughened channel. (author)
MHD Boundary Layer Flow of Dilatant Fluid in a Divergent Channel with Suction or Blowing
Institute of Scientific and Technical Information of China (English)
Krishnendu Bhattacharyya; G.C.Layek
2011-01-01
@@ An analysis is carried out to study a steady magnetohydrodynamic(MHD) boundary layer How of an electrically conducting incompressible power-law non-Newtonian fluid through a divergent channel.The channel walls are porous and subjected to either suction or blowing of equal magnitude of the same kind of fluid on both walls.The fluid is permeated by a magnetic field produced by electric current along the line of intersection of the channel walls.The governing partial differential equation is transformed into a self-similar nonlinear ordinary differential equation using similarity transformations.The possibility of boundary layer flow in a divergent channel is analyzed with the power-law fluid model.The analysis reveals that the boundary layer flow (without separation) is possible for the case of the dilatant fluid model subjected to suitable suction velocity applied through its porous walls,even in the absence of a magnetic field.Further, it is found that the boundary layer flow is possible even in the presence of blowing for a suitable value of the magnetic parameter.It is found that the velocity increases with increasing values of the power-law index for the case of dilatant fluid.The effects of suction/blowing and magnetic field on the velocity are shown graphically and discussed physical尔
DNS of turbulent channel flow at high Reynolds number under a uniform magnetic field
International Nuclear Information System (INIS)
A direct numerical simulation (DNS) of turbulent channel flow with high Reynolds number has been carried out to show the effects of magnetic field. In this study, the Reynolds number for channel flow based on bulk velocity ub, kinematic viscosity ν, and channel width 2δ was set to be constant; Reb=2δub/ν=45818. A uniform magnetic field was applied in the direction of the wall normal. The Hartmann number was Ha=2δB0√σ/ρν=32.5 and 65. Turbulent quantities such as the mean flow, turbulent stress, and the turbulent statistics were obtained by DNS. Although the influence of the magnetohydrodynamic dissipation terms in the turbulent kinetic energy budget was small, large-scale turbulent structures, such as vertical structures, low-speed streaks, ejection, and sweep, disappear at the central region of the channel. Consequently, the difference between production and dissipation in the turbulent kinetic energy decreases with increasing Hartmann number at the central region and large-scale structures at this region disappear. (author)
Reynolds number effects in DNS of pipe flow and comparison with channels and boundary layers
International Nuclear Information System (INIS)
Highlights: • New direct numerical simulations of turbulent pipe flow up to Reτ=2003. • Streamwise and spanwise variances do not exhibit inner scaling due to large-scale. • Transverse velocity statistics show differences between pipes and boundary layers. • Difference in variance of transverse velocities due to higher turbulence production. -- Abstract: Direct numerical simulations of turbulent pipe flow were performed at four Reynolds numbers: Reτ=180,500,1002and2003. Beyond Reτ=1000 viscous scaling holds near the wall for the mean velocity, Reynolds shear stress and wall-normal velocity variance. Streamwise and spanwise velocity variances do not exhibit inner (viscous) scaling due to increasing large-scale energy contributions. A comparison with channel and boundary layer DNS data shows negligible statistical differences between pipes and channels, whereas the transverse velocities for pipes/channels are significantly different when compared with boundary layers. A further comparison displays that the boundary layer pressure fluctuations is greater than pipes/channels. In addition, is it shown that the higher pressure fluctuations in the boundary layer is not the sole mechanism responsible for a stronger wake region in the flow
International Nuclear Information System (INIS)
Printed circuit heat exchanger (PCHE) is recently considered as a recuperator for the high-temperature gas cooled reactor. In this study, shape optimization of zigzag flow channels in a PCHE has been performed to enhance heat transfer performance and reduce the friction loss based on three-dimensional Reynolds-averaged Navier-Stokes analysis with the Shear Stress Transport Turbulence model. A multi-objective genetic algorithm is used for the multi-objective optimization. Two non-dimensional objective functions related to heat transfer performance and friction loss are employed. The shape of a flow channel is defined by two geometric design variables, viz. the cold channel angle and the ellipse aspect ratio of the cold channel. The experimental points within the design space are selected using Latin hypercube sampling as the design of the experiment. The response surface approximation model is used to approximate the Pareto-optimal front. Five optimal designs on the Pareto-optimal front have been selected using k-means clustering. The flow and heat transfer characteristics, as well as the objective function values, of these designs have been compared with those of the reference design. (author)
Use of finite volume radiation for predicting the Knudsen minimum in 2D channel flow
International Nuclear Information System (INIS)
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
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.
EXPERIMENTS ON FLOW AROUND A CYLINDER IN A SCOURED CHANNEL BED
Institute of Scientific and Technical Information of China (English)
I.ISTIARTO; W.H. GRAF
2001-01-01
The flow pattern around a cylinder, installed in a scoured channel bed, was experimentally investigated. Detailed measurements of the instantaneous 3D velocities were performed by using an Acoustic Doppler Velocity Profiler (ADVP), from which the profiles of the time-averaged velocities and turbulence stresses were obtained. It is shown that the influence of the cylinder and of the scour hole alters the approach flow; this is essentially confined to the vicinity of the cylinder and to the inside of the scour hole. The horseshoe vortex is measured as a flow reversal inside the scour hole, formed by the downward flow along the cylinder face and the reversed flow at the scour bed.
Lattice Boltzmann simulation of fluid flows in two-dimensional channel with complex geometries
International Nuclear Information System (INIS)
Boundary conditions (BCs) play an essential role in lattice Boltzmann (LB) simulations. This paper investigates several most commonly applied BCs by evaluating the relative L2-norm errors of the LB simulations for two-dimensional (2-D) Poiseuille flow. It is found that the relative L2-norm error resulting from FHML's BC is smaller than that from other BCs as a whole. Then, based on the FHML's BC, it formulates an LB model for simulating fluid flows in 2-D channel with complex geometries. Afterwards, the flows between two inclined plates, in a pulmonary blood vessel and in a blood vessel with local expansion region, are simulated. The numerical results are in good agreement with the analytical predictions and clearly show that the model is effective. It is expected that the model can be extended to simulate some real biologic flows, such as blood flows in arteries, vessels with stenosises, aneurysms and bifurcations, etc. (classical areas of phenomenology)
Numerical Study of Non-Newtonian Flow Characteristics in Sudden Contraction-Expansion Channel
International Nuclear Information System (INIS)
Because most existing non-Newtonian models are not suitable for application to the lattice Boltzmann method, theoretical and numerical studies in this regard remain challenging. In this study, the hydro kinetic (HK) model was modified and applied to a 3a sudden contraction-expansion channel flow, and the characteristics of the H K model flow were evaluated to generate non-trivial predictions in three-dimensional strong shear flows. The HK model is very efficient for application to the lattice Boltzmann method because it utilizes the shear rate and relaxation time. However, the simulation would be unstable in a high shear flow field because the local relaxation time sharply decreases with an increase in the shear rate in a strong shear flow field. In the HK model, it may become necessary to truncate the relaxation time and non-dimensional parameter to obtain stable numerical results
Stability characteristics of the open channel flow above the asymmetrical irregular sand ripples
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
Sandy bed cannot keep its original smoothness as the flows pass. With the increase of the flow intensity, the bed forms will appear as sand ripples and dune in turn. Among these morphologies, the sand ripple scale is the smallest, which is generally symmetrical when it just appears, but as time goes on, the asymmetrical form gradually develops. Just because of this sand ripples asymmetry, it manifests the influence of the flow on the bed morphology and also the impact on the laminar flow dynamical process, especially the stability characteristics. The stability features of laminar flow on open channels with the asymmetrical sand ripples are discussed, and also the results on the symmetrical sand ripples are compared in detail.
Numerical Study of Non-Newtonian Flow Characteristics in Sudden Contraction-Expansion Channel
Energy Technology Data Exchange (ETDEWEB)
Kim, Hyung Min [Kyonggi Univ., Suwon (Korea, Republic of)
2013-06-15
Because most existing non-Newtonian models are not suitable for application to the lattice Boltzmann method, theoretical and numerical studies in this regard remain challenging. In this study, the hydro kinetic (HK) model was modified and applied to a 3a sudden contraction-expansion channel flow, and the characteristics of the H K model flow were evaluated to generate non-trivial predictions in three-dimensional strong shear flows. The HK model is very efficient for application to the lattice Boltzmann method because it utilizes the shear rate and relaxation time. However, the simulation would be unstable in a high shear flow field because the local relaxation time sharply decreases with an increase in the shear rate in a strong shear flow field. In the HK model, it may become necessary to truncate the relaxation time and non-dimensional parameter to obtain stable numerical results.
Institute of Scientific and Technical Information of China (English)
Ling Li; Ming-Shun Yuan
2011-01-01
In this paper the effects of hydrophobic wall on skin-friction drag in the channel flow are investigated through large eddy simulation on the basis of weaklycompressible flow equations with the MacCormack's scheme on collocated mesh in the FVM framework. The slip length model is adopted to describe the behavior of the slip velocities in the streamwise and spanwise directions at the interface between the hydrophobic wall and turbulent channel flow. Simulation results are presented by analyzing flow behaviors over hydrophobic wall with the Smagorinky subgrid-scale model and a dynamic model on computational meshes of different resolutions. Comparison and analysis are made on the distributions of timeaveraged velocity, velocity fluctuations, Reynolds stress as well as the skin-friction drag. Excellent agreement between the present study and previous results demonstrates the accuracy of the simple classical second-order scheme in representing turbulent vertox near hydrophobic wall. In addition, the relation of drag reduction efficiency versus time-averaged slip velocity is established. It is also found that the decrease of velocity gradient in the close wall region is responsible for the drag reduction. Considering its advantages of high calculation precision and efficiency, the present method has good prospect in its application to practical projects.
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.
Peristaltic flow in an asymmetric channel with convective boundary conditions and Joule heating
Institute of Scientific and Technical Information of China (English)
Abbasi Fahad Munir; Hayat Tasawar; Ahmad Bashir
2014-01-01
The peristaltic transport of viscous fluid in an asymmetric channel is concentrated. The channel walls exhibit convective boundary conditions. Both cases of hydrodynamic and magnetohydrodynamic (MHD) fluids are considered. Mathematical analysis has been presented in a wave frame of reference. The resulting problems are non-dimensionalized. Long wavelength and low Reynolds number approximations are employed. Joule heating effect on the thermal equation is retained. Analytic solutions for stream function and temperature are constructed. Numerical integration is carried out for pressure rise per wavelength. Effects of influential flow parameters have been pointed out through graphs.
Biastoch, A.; Reason, C. J. C.; Lutjeharms, J. R. E.; Boebel, O.
The temporal variability of the greater Agulhas Current system has important climatological consequences. Some recent results have suggested that this variability contains a large seasonal component, due to changes in the circulation at latitudes poleward of Madagascar only. A model simulation shows that the contribution of Tropical Surface Water to Agulhas Current waters, via the Mozambique Channel, also has a distinct seasonal characteristic that is brought about by the seasonal wind stress over the tropical Indian Ocean. This simulated flow through the Channel contributes substantially to the seasonality of the Agulhas Current. This model result is shown to be not inconsistent with available hydrographic observations.
International Nuclear Information System (INIS)
A physical model has been developed for the flow mechanism in channels with turbulizers, utilizing the concepts of the quasiboundary layer, quasiwall, turbulization factor, and form factor. The pattern of flow velocity variation from a quasiwall to the turbulent stream core is established. A generalized equation is derived for calculating the drag coefficient, one that characterizes a single fluid dynamic flow rule extending from the laminar case to mature turbulent flow in channels with complex geometry. A special form factor is employed to take into account both the influence of viscosity and the specific features of channel design. 14 refs., 10 figs., 1 tab
International Nuclear Information System (INIS)
The main goal in this study is to provide deep physical descriptions on the behaviour of supersonic micro-/nano-channel flow using the direct simulation Monte Carlo method. We found some unique physical aspects of micro-/nano-flows including mixed supersonic–subsonic regimes in constant-area ducts. This mixed regime is due to the formation of entrance shocks and their reflection from the thick boundary layer developed in a rarefied medium. We studied the effects of Mach number, channel aspect ratio and flow rarefaction on the channel inflow condition. The effects of wall thermal state on flow behaviour and shock wave structures were also investigated. (paper)
The characteristics of secondary flows in compound channels with vegetated floodplains
Institute of Scientific and Technical Information of China (English)
LIU Chao; SHAN Yu-qi; YANG Ke-jun; LIU Xing-nian
2013-01-01
The experiments were conducted in compound channels with vegetated floodplains for investigating the influence of vegetation types on the characteristics of secondary flows.In terms of the streamwise and transverse velocities and the depth-averaged velocity,the secondary flow coefficient,M,is proposed,with good physical meanings,and it may characterize the rotational direction and the intensity of the secondary currents.The experimental results show that,for the cases without vegetation and with grass,the rotational directions of the secondary flows are all anticlockwise while for the cases with shrubs,they are all changed to the clockwise direction in the whole cross-section.However,when trees are planted,the secondary flows rotate in the anticlockwise direction in the main channel and in the clockwise direction on the floodplain.In addition,for all cases,the intensities of the secondary currents on the floodplain are stronger than those in the main channel.
Combined effects of rotation and rib-roughness - a dns study of turbulent channel flow
Andersson, Helge I.; Narasimhamurthy, Vagesh D.
2014-11-01
The combined effects of system rotation and rib-roughness on turbulent channel flow have been investigated by means of direct numerical simulations. Square ribs were placed on both walls in a non-staggered arrangement and the channel was subjected to steady rotation about a spanwise axis for a series of rotation numbers up to Ro = 24. A pressure-loss reduction of about 20 per cent resulted from the imposed rotation at Ro = 6. In spite of the 10 per cent blockage due to the wall-mounted ribs, the flow field exhibited statistical streamwise homogeneity in the core region. The mean velocity varied linearly with a slope such that the mean fluid rotation exactly outweighed the imposed system rotation. The flow field in the vicinity of the ribs was affected differently at the two sides of the rotating channel. The separated flow region behind the ribs on the anti-cyclonic pressure side shrinked with increasing Ro due to the enhanced turbulent mixing caused by the Coriolis force. The original d-type roughness was thus turned into a k-type roughness.
Directory of Open Access Journals (Sweden)
E. Rajabi
2014-01-01
Full Text Available In this research a direct numerical simulation (DNS of turbulent flow is performed in a geometrically standard case like plane channel flow. Pseudo spectral (PS method is used due to geometry specifications and very high accuracy achieved despite relatively few grid points. A variable time-stepping algorithm is proposed which may reduce requirement of computational cost in simulation of such wall-bounded flow. Channel flow analysis is performed with both constant and varied time-step for 128 × 65×128 grid points. The time advancement is carried out by implicit third-order backward differentiation scheme for linear terms and explicit forward Euler for nonlinear convection term. PS method is used in Cartesian coordinates with Chebychev polynomial expansion in normal direction for one non-periodic boundary condition. Also Fourier series is employed in stream-wise and span-wise directions for two periodic boundary conditions. The friction Reynolds number is about Reτ=175 based on a friction velocity and channel half width. Standard common rotational form was chosen for discritization of nonlinear convective term of Navier-Stocks equation. The comparison is made between turbulent quantities such as the turbulent statistics, Reynolds stress, wall shear velocity, standard deviation of (u and total normalized energy of instantaneous velocities in both time-discretization methods. The results show that if final decision rests on economics, the proposed variable time-stepping algorithm will be proper choice which satisfies the accuracy and reduces the computational cost.
NUMERICAL SIMULATION OF DROP MIGRATION IN CHANNEL FLOW UNDER ZERO-GRAVITY
Institute of Scientific and Technical Information of China (English)
LIU Tao; LU Xiyun
2004-01-01
The migration of deformable drops in the channel flow neglecting the gravity influence is investigated numerically by solving the incompressible Navier-Stokes equations using the finitedifference method coupled with the front-tracking technique. The objectives of this study are to examine the effectiveness of the present approach for predicting the migration of drops in a shear flow and to investigate the behavior of the drop migration in the channel flow under zero-gravity. To validate the present calculation, some typical results are compared with available computational and theoretical data, which confirms that the present approach is reliable in predicting the drop migration.With respect to the drop migration in the channel flow at finite Reynolds numbers, the drops either move to an equilibrium lateral position or undergo an oscillatory motion under different conditions.The effects of some typical parameters, e.g., the Reynolds number, the Weber number, the viscosity ratio and the density ratio of the drop fluid to the suspending medium, and the drop size, on the migration of drops are discussed and analyzed.
Generation of hairpin vortex packet in channel flow at Reτ <= 590
Kim, Kyoungyoun
2012-11-01
The generation of hairpin vortex packet from an initial single vortex is examined by direct numerical simulation for channel flows at Reτ = 180, 395, and 590. The initial vortex structure is given by conditionally averaged flow field with the Q2 event specified at y+ = 50 in fully developed turbulent channel flow. The vortex packet formation in higher Reynolds number flows is very similar to that in Reτ =180 reported by Zhou et al. (1999, J. Fluid Mech.); the initial vortex is developed to a primary hairpin vortex (PHV) and the secondary hairpin vortex is generated upstream of PHV. As time proceeds, the vortices move downstream with almost the same convection velocity and little dispersion, forming a vortex packet. Comparison of the packet formation for different Reτ reveals that the secondary hairpin vortex is generated with time scales based on the wall units. At the time when the head of PHV has grown to the channel center, the inclination angle of the vortex packet is approximately 12 ~14° which is insensitive to Reτ , consistently with linear stochastic estimation results with PIV measurement by Christensen & Adrian (2001, J. Fluid Mech.). Supported by NRF Grant 2010-0007901.
A study on heat transfer enhancement using flow channel inserts for thermoelectric power generation
International Nuclear Information System (INIS)
Highlights: • Thermal enhancement in a thermoelectric liquid generator is tested. • Thermal enhancement is brought upon by flow impeding inserts. • CFD simulations attribute thermal enhancement to velocity field alterations. • Thermoelectric power enhancement is measured and discussed. • Power enhancement relative to adverse pressure drop is investigated. - Abstract: Thermoelectric power production has many potential applications that range from microelectronics heat management to large scale industrial waste-heat recovery. A low thermoelectric conversion efficiency of the current state of the art prevents wide spread use of thermoelectric modules. The difficulties lie in material conversion efficiency, module design, and thermal system management. The present study investigates thermoelectric power improvement due to heat transfer enhancement at the channel walls of a liquid-to-liquid thermoelectric generator brought upon by flow turbulating inserts. Care is taken to measure the adverse pressure drop due to the presence of flow impeding obstacles in order to measure the net thermoelectric power enhancement relative to an absence of inserts. The results illustrate the power enhancement performance of three different geometric forms fitted into the channels of a thermoelectric generator. Spiral inserts are shown to offer a minimal improvement in thermoelectric power production whereas inserts with protruding panels are shown to be the most effective. Measurements of the thermal enhancement factor which represents the ratio of heat flux into heat flux out of a channel and numerical simulations of the internal flow velocity field attribute the thermal enhancement resulting in the thermoelectric power improvement to thermal and velocity field synergy
MHD two-layered unsteady fluid flow and heat transfer through a horizontal channel between
Directory of Open Access Journals (Sweden)
Raju T. Linga
2014-02-01
Full Text Available An unsteady magnetohydrodynamic (MHD two-layered fluids flow and heat transfer in a horizontal channel between two parallel plates in the presence of an applied magnetic and electric field is investigated, when the whole system is rotated about an axis perpendicular to the flow. The flow is driven by a constant uniform pressure gradient in the channel bounded by two parallel insulating plates, when both fluids are considered as electrically conducting, incompressible with variable properties, viz. different viscosities, thermal and electrical conductivities. The transport properties of the two fluids are taken to be constant and the bounding plates are maintained at constant and equal temperatures. The governing partial differential equations are then reduced to the ordinary linear differential equations using two-term series. Closed form solutions for primary and secondary velocity, also temperature distributions are obtained in both the fluid regions of the channel. Profiles of these solutions are plotted to discuss the effects of the flow and heat transfer characteristics, and their dependence on the governing parameters involved, such as the Hartmann number, rotation parameter, ratios of the viscosities, heights, electrical and thermal conductivities
Stability analysis of two phase stratified flow in a rectangular channel
Bhagavatula, Dinesh; S, Pushpavanam
2015-11-01
Two phase stratified flows arise in extraction operations in microfluidic systems. It is well established that stratified flows in between two infinite plates is always unstable. However such flows are experimentally observed in micro channels. To understand this paradox we perform a linear stability analysis of stratified two phase Poiseuille flow in a rectangular duct. A two-dimensional fully developed flow through the rectangular channel is considered. The linearized equations along with the boundary conditions in primitive variable formulation are numerically solved using Chebyshev collocation method. All the primitive variables, which are the velocity and pressure fields, are retained in the linearised governing equations. Since boundary conditions for disturbance pressure do not exist, the corresponding compatibility conditions derived from the Navier-Stokes equations are collocated both at the walls and the interface. The resulting eigen-value problem is solved using a shift and invert Arnoldi algorithm. The role of different parameters such as Aspect ratio, density ratio, viscosity ratio on the stability characteristics is analyzed. The stability results are validated in the limit of large Aspect Ratios. The flow fields are sought as a combination of Chebyshev polynomials in both y and z directions. Ministry of Human Resource and Development (MHDR).
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Highlights: • Pressure drop fluctuation is enhanced with increasing rolling amplitude and period. • The phase difference between flow rate and pressure drop fluctuation is 1/4 period. • Amplitude of boiling heat transfer coefficient increases with increasing heat flux. • The curve of boiling heat transfer coefficient fluctuations is close to sine curve. - Abstract: Experimental investigations on thermal–hydraulic characteristics of boiling flow in a rectangular narrow channel under rolling motion conditions are carried out. This experiment is designed to elucidate the phenomena of boiling flow under rolling motion and to give the corresponding rational explanations. The results show that the amplitudes of fluctuations of pressure drop, flow rate, fluid and wall temperatures, and boiling heat transfer coefficient increase with the increasing of rolling amplitude and rolling period. The phase difference of flow rate fluctuation and pressure drop fluctuation is 1/4 period, and the saturated water temperature fluctuations of the test section delay 2–3 s behind the pressure drop fluctuations. The time average boiling heat transfer coefficients of the rectangular narrow channel under rolling motion are equal to those under static conditions. The amplitude of boiling heat transfer coefficient of test section increases with increasing heat flux and flow rate, while decreases with increasing system pressure
Investigation of a corrugated channel flow with an open source PIV software
Sivas, Deniz; Bahadır Olcay, A.; Ahn, Hojin
2016-03-01
In this study, the corrugated channel flow was investigated by using an open-source particle image velocimetry (PIV) software. The open-source software called OpenPIV was first verified by using images of an earlier experimental work of a vortex ring formation. The corrugated channel flow images were taken with 200 W power LED light source and a high speed camera and those images were analysed with these spatial and temporal tools of OpenPIV. Laminar, transient and turbulent flow regimes were identified when Reynolds number was below 1100, in between 1100 and 2000 and higher than 2000, respectively. The velocity vectors were found to be about 20% lower than the previous study results. The flow inside the grooves was also investigated with OpenPIV and flow characteristics at the grooves were captured when interrogation window size was lowered. The visualization of the flow was presented for different Reynolds numbers with the relative scale values. As a result of this study, OpenPIV software was determined as promising open source PIV analysis software.
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.
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The additional force arising from rolling motion causes the change of two phase flow resistance. The characteristics of air-water mixture flow resistance in narrow rectangular channel (40 mm × 1.6 mm) in rolling motions were experimentally studied with the rolling periods of 8 s, 12 s, 16 s and the angles of 10°, 15°, 30°, respectively. The experimental results show that the transient frictional factor changes periodically. The larger the mass quality and the maximum rolling angle and the smaller the rolling period, the larger the fluctuation amplitude of frictional pressure drop. A new correction for predicting the transient frictional factor of two-phase flow in rolling motion is proposed with a good accuracy. (authors)
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 predict that channels exhibit a low sinuosity and have
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Air-water counter-current flow limit experiments were conducted in thin rectangular channels at atmospheric pressure. The parameters were: narrow channel width, either 1.1 mm or 2.2 mm; inlet water temperature, ranging from 294 K to 330 K; channel surface condition, either clean aluminum, aluminum oxide, or acrylic; location and geometry of the air inlet; method of forcing air through the channel; and liquid head above the channel. Experimental results for each set of parameters can be linearly correlated using the square root of the non-dimensional superficial velocities. Channel surface wetting and location and geometry of the air injection had the greatest effect. Narrow channel width, water temperature, method used to force air through the channel, and liquid head above the channel had little effect on the flooding characteristics. ((orig.))
Oscillatory electro-osmotic flow through a slit channel with slipping stripes on walls
International Nuclear Information System (INIS)
A theoretical model is presented in this paper for time-oscillating electro-osmotic flow through a plane channel bounded by two parallel plates, which are patterned with periodic stripes of distinct hydrodynamic slippage and wall potential. The flow is driven by oscillatory pressure gradient and electric field of the same frequency in the axial direction. Flows that are longitudinal or transverse to the stripes are investigated. Based on the Debye–Hückel approximation, and assuming Stokes flow, the electric potential and the velocity fields are found by the methods of eigenfunction expansion and point collocation. The phenomenological coefficients of the Onsager relations for the fluid and current fluxes are deduced as functions of the channel height, the area fraction of wall with slippage, the intrinsic slip length, the Debye parameter, the zeta potentials and the oscillation parameter. Considering several kinds of wall patterns, we extend the theoretical limits in the steady-flow regime to the oscillatory-flow regime. For a uniformly charged wall, the effective slip length obtained from the hydrodynamic problem can still be used directly in the electro-osmotic flow as if the wall were uniformly slipping. When the slipping stripes are perfectly slipping but uncharged, the presence of such stripes will always have a decreasing effect on the streaming conductance, unlike the steady case in which it gives no net effect on the flow in the limit of a very thin double layer. Furthermore, we confirm the presence of a threshold frequency, beyond which the flow will diminish significantly. The slipping fraction of the wall will always introduce a phase lag to the response and lower the threshold frequency. Increasing the wall potential in the presence of slippage can appreciably increase the streaming conductance and the phase lag. (paper)
Matia, Yoav; Gat, Amir
2014-11-01
We analyze the time dependent interaction between the flow-field and the elastic deformation-field of a viscous liquid within a long serpentine channel, embedded in an elastic beam. The channel is positioned asymmetrically with regard to the midplane of the elastic beam. We focus on creeping flows and small deformations of the elastic beam and obtain, in leading order, a diffusion equation governing the pressure-field within the serpentine channel. The deformation of the beam is then related to the propagation of pressure within the channel. We thus obtain a viscous-elastic equation governing the deformation of the beam due to the viscous flow within the serpentine channel. This equation enables to design complex time-dependent deformation patterns of beams with embedded channel networks, relevant to soft-robotic applications. Our theoretical results were illustrated and verified using numerical computations. Israel Science Foundation 818/13.
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Experimental study has been performed to study periodical-boiling instability in parallel channels, which occurs at low heat fluxes and is of concern in the start-up process of an SBWR. Three channels, made of glass tubes to facilitate visual observation, are placed in bulk water and are heated with electric heaters inserted in the channels. Two types of channels of different length are used to investigate the effect of unheated risers or chimney on periodical boiling. Relationship of bubble development and flow instability is also studied. It is found that slug bubbles are usually followed by rapid boiling, which results in high fluctuation of the flow. Refilling of the subcooled water from the top causes bubble condensation. Sometimes rapid condensation occurs and results in crack sounds. The longer channel does not necessarily have better coolability and stability characteristics; the average flow rate is actually lower and fluctuation amplitude is higher compared to those for the shorter channel
The coefficientof hydraulic friction of laminar open flows in smooth channels
Directory of Open Access Journals (Sweden)
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.
Heat transfer and pressure drop measurement in wavy channels with flow disturbers
Energy Technology Data Exchange (ETDEWEB)
Dini, S.; Veronesi, R.; Hryniewicz, E.V.
1999-07-01
In the current work, the transient method was employed to obtain the local heat transfer coefficient for a 6 in. x 3/8 in. x 12 in. (15.24cm x .9525cm x 30.48cm) Plexiglas {reg_sign} wavy channel with and without flow disturbers. A short duration transient test was performed to measure the heat transfer coefficient by introducing heated air over test specimen that had been sprayed with calibrated thermochromic liquid crystals. This technique allowed the experimenter to observe the temperature changes using a video camera. because a Plexiglas surface has a low thermal diffusivity, a one-dimensional assumption is a reasonable approximation because the surface temperature response is limited to a thin layer near the surface and lateral conduction is small. The heat transfer coefficient using the transient technique is then determined from the response of the surface temperature to a step change in the local temperature. Using this method, the axial variation in the heat transfer coefficient for Reynolds numbers in the laminar (1100) and turbulent region (2900) were obtained. These Reynolds numbers were based on the hydraulic diameter at the inlet of the wavy channel. Also, in this investigation, the region of greatest heat transfer and the pressure drop were both experimentally and analytically determined and the friction factor across an in-phase corrugated wall channel (wavy channel) at Reynolds numbers of 1100 and 2900 were obtained. A manometer and a pressure transducer were employed to measure pressure drop across the channel. The effect of flow disturbers mounted on each peak, alternate peaks and the first six peaks of a twelve-peak channel were also investigated. For all cases, the pressure drop and friction factor were shown to moderately increase with rib placement in the test section when compared to the results obtained from a similar smooth wavy channel without ribs. Additionally, for all cases, the friction factor also decreased with an increase in the
The effect of flow data resolution on sediment yield estimation and channel design
Rosburg, Tyler T.; Nelson, Peter A.; Sholtes, Joel S.; Bledsoe, Brian P.
2016-07-01
The decision to use either daily-averaged or sub-daily streamflow records has the potential to impact the calculation of sediment transport metrics and stream channel design. Using bedload and suspended load sediment transport measurements collected at 138 sites across the United States, we calculated the effective discharge, sediment yield, and half-load discharge using sediment rating curves over long time periods (median record length = 24 years) with both daily-averaged and sub-daily streamflow records. A comparison of sediment transport metrics calculated with both daily-average and sub-daily stream flow data at each site showed that daily-averaged flow data do not adequately represent the magnitude of high stream flows at hydrologically flashy sites. Daily-average stream flow data cause an underestimation of sediment transport and sediment yield (including the half-load discharge) at flashy sites. The degree of underestimation was correlated with the level of flashiness and the exponent of the sediment rating curve. No consistent relationship between the use of either daily-average or sub-daily streamflow data and the resultant effective discharge was found. When used in channel design, computed sediment transport metrics may have errors due to flow data resolution, which can propagate into design slope calculations which, if implemented, could lead to unwanted aggradation or degradation in the design channel. This analysis illustrates the importance of using sub-daily flow data in the calculation of sediment yield in urbanizing or otherwise flashy watersheds. Furthermore, this analysis provides practical charts for estimating and correcting these types of underestimation errors commonly incurred in sediment yield calculations.
Stability of fluid flow through deformable tubes and channels: An overview
Indian Academy of Sciences (India)
V Shankar
2015-05-01
The aim of this paper is to provide a systematic overview of the study of instabilities in flow past deformable solid surfaces, with particular emphasis on internal flows through tubes and channels. The subject is certainly more than five decades old, and arguably began with Kramer’s pioneering experiments on drag reduction by compliant surfaces. This was immediately followed by the theoretical studies of Benjamin and Landhal in the early 1960s. Most earlier theoretical studies were focused on stability of external flows such as boundary layers, and used relatively simple wall models composed of spring-backed plates. There has been a resurgence in the field since the mid-1980s, and more attention was focused on internal flows through deformable tubes and channels. The wall deformation was described by both phenomenological spring-backed plate models and continuum linear viscoelastic solid models. All these studies predict several types of instabilities in flow past deformable surfaces. This paper will attempt to place the various theoretical results in perspective, and to classify the instabilities predicted by various studies. Recent studies have also emphasized the importance of using a frame-invariant constitutive model, such as the neo-Hookean model, for the solid deformation. Until recently, however, the field has been dominated by theoretical and numerical studies, with very little experimental observations to corroborate the theoretical predictions. Recent experiments in flow through deformable tubes and channels indeed show instability at Reynolds number much lower than their rigid counterparts, and the experimental observations are in qualitative agreement with some of the theoretical predictions. There have also been a few studies on the non-linear aspects of the instability using the weakly non-linear formulation to determine the nature of the bifurcation at the linear instability. A brief discussion on weakly nonlinear analyses is also provided in
Nanoscale grain boundary channels in fracture cement enhance flow in mudrocks
Landry, Christopher J.; Eichhubl, Peter; Prodanović, Maša.; Wilkins, Scott
2016-05-01
Hydrocarbon production from mudrock or shale reservoirs typically exceeds estimates based on mudrock laboratory permeability measurements, with the difference attributed to natural fractures. However, natural fractures in these reservoirs are frequently completely cemented and thus assumed not to contribute to flow. We quantify the permeability of nanoscale grain boundary channels with mean apertures of 50-130 nm in otherwise completely cemented natural fractures of the Eagle Ford Formation and estimate their contribution to production. Using scanning electron imaging of grain boundary channel network geometry and a digital rock physics workflow of image reconstruction and direct flow modeling, we estimate cement permeability to be 38-750 nd, higher than reported permeability of Eagle Ford host rock (~2 nd) based on laboratory measurements. Our results suggest that effective fracture-parallel mudrock permeability can exceed laboratory values by upward of 1 order of magnitude in shale reservoirs of high macroscopic cemented fracture volume fraction.
Analysis of Pulsatile Flow of Blood in a Porous Channel under Effect of Magnetic Field
Directory of Open Access Journals (Sweden)
Mitali Sarma
2011-11-01
Full Text Available To study the effect of magnetic field on pulsatile flow of blood in a porous channel a numerical model has been developed. An approximate solution is presented to the problem of pulsatile flow of blood in a porous channel in presence of transverse magnetic field. The blood is assumed to be an incompressible non Newtonian fluid. To reduce the equation of motion to an ordinary differential equation, a dimensionless variable is used. Numerical results were obtained for different values of the magnetic parameter, frequency parameter and Reynolds number. It is observed that when the Hartmann number increases, the fluid velocity as well as magnitude as well as magnitude of mass flux decrease.
Effects of subfilter velocity modelling on dispersed phase in LES of heated channel flow
International Nuclear Information System (INIS)
A non-isothermal turbulent flow with the dispersed phase is modelled using the Large Eddy Simulation (LES) approach for fluid, one-way coupled with the equations of point-particle evolution. The channel is heated at both walls and isoflux boundary conditions are applied for fluid. Particle velocity and thermal statistics are computed. Of particular interest are the r.m.s. profiles and the probability density function of particle temperature in the near-wall region. We compare our findings with available reference data for particle-laden, heated channel flow. Moreover, an open issue in LES is the influence of non-resolved (residual) scales of fluid velocity and temperature fields on particles. In the present contribution, we apply a stochastic model for subfilter fluid velocity at the particle positions that aims at reconstructing the effects of the smallest scales of turbulence on particle dynamics. We analyse the impact of this model on particle thermal statistics.
Analytical Investigation of the Flow Hydrodynamics in Micro-Channels at High Zeta Potentials
Directory of Open Access Journals (Sweden)
A. Elazhary
2009-05-01
Full Text Available This paper investigates the effect of the EDL at the solid-liquid interface on the liquid flow through a micro-channel formed by two parallel plates. The complete Poisson-Boltzmann equation (without the frequently used linear approximation was solved analytically in order to determine the EDL field near the solid-liquid interface. The momentum equation was solved analytically taking into consideration the electrical body force resulting from the EDL field. Effects of the channel size and the strength of the zeta-potential on the electrostatic potential, the streaming potential, the velocity profile, the volume flow rate, and the apparent viscosity are presented and discussed. Results of the present analysis, which are based on the complete Poisson-Boltzmann equation, are compared with a simplified analysis that used a linear approximation of the Poisson-Boltzmann equation.
Capillary Flows along Open Channel Conduits: the Open-Star Section
Weislogel, Mark; Chen, Yongkang; Nguyen, Thanh; Geile, John; Callahan, Michael
2014-11-01
Capillary rise in tubes, channels, and grooves has received significant attention in the literature for over 100 years. In yet another incremental extension of related work, a transient capillary rise problem is solved for spontaneous flow along an interconnected array of open channels forming what is referred to as an ``open-star'' section. This geometry possesses several attractive characteristics including passive phase separations and high diffusive gas transport rates. Despite the complex geometry, novel and convenient approximations for capillary pressure and viscous resistance enable closed form predictions of the flow. As part of the solution, a combined scaling approach is applied that identifies unsteady-inertial-capillary, convective-inertial-capillary, and visco-capillary transient regimes in a single parameter. Drop tower experiments are performed employing 3-D printed conduits to corroborate all findings. NASA NNX09AP66A, Glenn Research Center.
Analysis of fluid flow and heat transfer in a channel with intermittent heated porous blocks
Chikh, S.; Boumedien, A.; Bouhadef, K.; Lauriat, G.
A numerical study of forced convection enhancement in a channel intermittently heated is presented in this work. The use of porous blocks mounted on the heated parts of the channel to improve thermal performance is investigated. In order to account for the inertia, drag and boundary effects, the Brinkman-Forchheimer-extended Darcy model is adopted for the flow inside the porous regions. The effects of several parameters such as Darcy number, the block dimensions, the number of blocks and the thermal conductivity ratio are documented. The results show that the blocks may alter substantially the flow pattern depending on the permeability of the porous medium, and may improve the heat transfer and reduce the wall temperature under certain circumstances.
Self-organized phenomena of pedestrian counter flow in a channel under periodic boundary conditions
Institute of Scientific and Technical Information of China (English)
Li Xiang; Duan Xiao-Yin; Dong Li-Yun
2012-01-01
In this paper we investigate self-organized phenomena such as lane formation generated by pedestrian counter flow in a channel.The lattice gas model is extended to take the effect of walkers in the opposite direction into account simultaneously when they are in the view field of a walker,i.e.,walkers tend to follow the leaders in the same direction and avoid conflicts with those walking towards them.The improved model is then used to mimic pedestrian counter flow in a channel under periodic boundary conditions.Numerical simulations show that lane formation is well reproduced,and this process is rather rapid which coincides with real pedestrian traffic.The average velocity and critical density are found to increase to some degree with the consideration of view field.
Self-organized phenomena of pedestrian counter flow in a channel under periodic boundary conditions
Li, Xiang; Duan, Xiao-Yin; Dong, Li-Yun
2012-10-01
In this paper we investigate self-organized phenomena such as lane formation generated by pedestrian counter flow in a channel. The lattice gas model is extended to take the effect of walkers in the opposite direction into account simultaneously when they are in the view field of a walker, i.e., walkers tend to follow the leaders in the same direction and avoid conflicts with those walking towards them. The improved model is then used to mimic pedestrian counter flow in a channel under periodic boundary conditions. Numerical simulations show that lane formation is well reproduced, and this process is rather rapid which coincides with real pedestrian traffic. The average velocity and critical density are found to increase to some degree with the consideration of view field.
Analysis of fluid flow and heat transfer in a channel with intermittent heated porous blocks
Energy Technology Data Exchange (ETDEWEB)
Chikh, S.; Boumedien, A.; Bouhadef, K. [Institut de Genie Mecanique USTHB, El Alia, Bab Ezzouar (Algeria); Lauriat, G. [Universite de Marne-la-Vallee (France)
1998-04-01
A numerical study of forced convection enhancement in a channel intermittently heated is presented in this work. The use of porous blocks mounted on the heated parts of the channel to improve thermal performance is investigated. In order to account for the inertia, drag and boundary effects, the Brinkman-Forchheimer-extended Darcy model is adopted for the flow inside the porous regions. The effects of several parameters such as Darcy number, the block dimensions, the number of blocks and the thermal conductivity ratio are documented. The results show that the blocks may alter substantially the flow pattern depending on the permeability of the porous medium, and may improve the heat transfer and reduce the wall temperature under certain circumstances. (orig.) With 11 figs., 2 tabs., 13 refs.
Effect of induced magnetic field on peristaltic flow of a micropolar fluid in an asymmetric channel
Shit, G C; Ng, E Y K; 10.1002/cnm.1397
2010-01-01
Of concern in this paper is an investigation of peristaltic transport of a physiological fluid in an asymmetric channel under long wave length and low-Reynolds number assumptions. The flow is assumed to be incompressible, viscous, electrically conducting micropolar fluid and the effect of induced magnetic field is taken into account. Exact analytical solutions obtained for the axial velocity, microrotation component, stream line pattern, magnetic force function, axial-induced magnetic field as well as the current density distribution across the channel. The flow phenomena for the pumping characteristics, trapping and reflux are also investigated. The results presented reveal that the velocity decreases with the increase of magnetic field as well as the coupling parameter. Moreover, the trapping fluid can be eliminated by the application of an external magnetic field. Thus, the study bears the promise of important applications in physiological systems.
Institute of Scientific and Technical Information of China (English)
CHANG Wei-Tze; HSIEH Shang-Hsien; YANG Fu-Ling; CHEN Chuin-Shan
2008-01-01
This paper proposes a numerical scheme that employs the discrete element method (DEM) to simulate the motion of a wet granular flow down an inclined channel.To account for the liquid influences on the dynamics between paired particles,this paper presents a wet soft-sphere contact model with liquid-modified parameters.The developed scheme takes full advantage of DEM and avoids the expensive simula-tion of the solid-liquid interactions with conventional Navier-Stokes equation solver.This wet contact model has been implemented in an in-housed parallel discrete objects simulation system-KNIGHT and ANNE/IRIS口to compute the dynamic behaviors of both dry and wet granular particles flowing down an in-dined channel.
Turbulent channel flow simulations using a coarse-grained extension of the Lattice Boltzmann method
Amati, G; Benzi, R; Amati, Giorgio; Succi, Sauro; Benzi, Roberto
1996-01-01
A coarse-grained version of the Lattice Boltzmann (LB) method is developed with the intent of enhancing its geometrical flexibility so as to be able to tackle a wider class of flows of engineering interest. To this purpose, the original uniform LB technique is combined with standard finite-volume techniques based upon a blend of piecewise constant and piecewise linear interpolation schemes. A series of validation tests for the three dimensional channel flow with one-dimensional (cross-channel) statistical behaviour are presented. The main conclusion is that, although the method does indeed mark a significant stride forward with respect to the original uniform LB scheme, better interpolation schemes should be developed before the coarse-grain LB can become fully competitive with modern CFD schemes.
Scrutiny of underdeveloped nanofluid MHD flow and heat conduction in a channel with porous walls
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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.
Fabrication of micro-flow channels on graphite composite bipolar plates using microplaning
Institute of Scientific and Technical Information of China (English)
万珍平; 梁德杰; 陆龙生; 汤勇
2015-01-01
A new method of manufacturing micro-flow channels on graphite composite bipolar plate (GCBPP) microplaning using specially designed multi-tooth tool is proposed. In this method, several or even dozens of parallel micro-flow channels ranging from 100μm to 500μm in width can be produced simultaneously. But, edge chippings easily occur on the rib surface of GCBPP during microplaning due to brittleness of graphite composites. Experimental results show that edge chippings result in the increase of contact resistance between bipolar plate and carbon paper at low compaction force. While the edge chippings scarcely exert influence on the contact resistance at high compaction force. Contrary to conventional view, the edge chippings can significantly improve performance of microfuel cell and big edge chippings outperform small edge chippings. In addition, the influence of technical parameters on edge chippings was investigated in order to obtain big, but not oversized edge chippings.
Large Eddy Simulations of particle-fluid interaction in a turbulent channel flow
International Nuclear Information System (INIS)
This paper presents a comparison between results obtained using Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) in particle-laden turbulent channel flow. In the case of LES method computations were performed using the dynamic model, Smagorinski model, with and without Van Driest damping at the wall, and without sub-grid scale turbulence modelling. The focus is on the difference in the computed forces acting on a particle in the particle equation of motion. Results for turbulent flow in a channel at Reτ = 150 are presented, focusing on point-particle statistics. DNS provides a point of reference for assessing LES with different sub-filter eddy-viscosity models.
Channel orientation and geometry influence on heat transfer with two-phase forced flow of nitrogen
Klimenko, V. V.; Fyodorov, M. V.; Fomichyov, Yu. A.
The results of an investigation of tube diameter and orientation influence on two-phase forced flow heat transfer of nitrogen are presented. In vertical channels a diameter effect is revealed in a transition from convective to less intensive nucleate boiling when the Froude number of a mixture, Fr m = w m(gd) - 1/2 decreases from 40 to 10. On the contrary, in horizontal non-stratified flow, the reduction of the Frm number is accompanied by heat transfer enhancement in the upper part of the channel because of the formation of a thin liquid film there. This leads to a notable increase (20-30%), averaged over the cross-section, of heat transfer coefficient in the nucleate boiling region. If Frm ≳ 40 then geometry and orientation do not affect the heat transfer coefficient which can be calculated using the Klimenko correlation.
Droplet in micro-channels: A numerical approach using an adaptive two phase flow solver
Fullana, Jose-Maria; Popinet, Stéphane; Josserand, Christophe
2015-01-01
We propose a numerical approach to study the mechanics of a flowing bubble in a constraint micro channel. Using an open source two phase flow solver (Gerris, gfs.sourceforge.net) we compute solutions of the bubble dynamics (i.e. shape and terminal velocity) induced by the interaction between the bubble movement, the Laplace pressure variation, and the lubrication film near the channel wall. Quantitative and qualitative results are presented and compared against both theory and experimental data for small Capillary numbers. We discuss the technical issues of explicit integration methods on small Capillary numbers computations, and the possibility of adding Van der Walls forces to give a more precise picture of the Droplet-based microfluidic problem.
Effect of Local Junction Losses in the Optimization of T-shaped Flow Channels
Kosaraju, Srinivas
2015-11-01
T-shaped channels are extensively used in flow distribution applications such as irrigation, chemical dispersion, gas pipelines and space heating and cooling. The geometry of T-shaped channels can be optimized to reduce the overall pressure drop in stem and branch sections. Results of such optimizations are in the form of geometric parameters such as the length and diameter ratios of the stem and branch sections. The traditional approach of this optimization accounts for the pressure drop across the stem and branch sections, however, ignores the pressure drop in the T-junction. In this paper, we conduct geometry optimization while including the effect of local junction losses in laminar flows. From the results, we are able to identify a non-dimensional parameter that can be used to predict the optimal geometric configurations. This parameter can also be used to identify the conditions in which the local junction losses can be ignored during the optimization.
Effects of subfilter velocity modelling on dispersed phase in LES of heated channel flow
Pozorski, Jacek; Knorps, Maria; Łuniewski, Mirosław
2011-12-01
A non-isothermal turbulent flow with the dispersed phase is modelled using the Large Eddy Simulation (LES) approach for fluid, one-way coupled with the equations of point-particle evolution. The channel is heated at both walls and isoflux boundary conditions are applied for fluid. Particle velocity and thermal statistics are computed. Of particular interest are the r.m.s. profiles and the probability density function of particle temperature in the near-wall region. We compare our findings with available reference data for particle-laden, heated channel flow. Moreover, an open issue in LES is the influence of non-resolved (residual) scales of fluid velocity and temperature fields on particles. In the present contribution, we apply a stochastic model for subfilter fluid velocity at the particle positions that aims at reconstructing the effects of the smallest scales of turbulence on particle dynamics. We analyse the impact of this model on particle thermal statistics.
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.
Coherent structure extraction in turbulent channel flow using boundary adapted wavelets
Sakurai, Teluo; Schneider, Kai; Farge, Marie; Morishita, Koji; Ishihara, Takashi
2016-01-01
We present a construction of isotropic boundary adapted wavelets, which are orthogonal and yield a multi-resolution analysis. We analyze direct numerical simulation data of turbulent channel flow computed at a friction Reynolds number of 395, and investigate the role of coherent vorticity. Thresholding of the vorticity wavelet coefficients allows to split the flow into two parts, coherent and incoherent vorticity. The coherent vorticity is reconstructed from their few intense wavelet coefficients. The statistics of the coherent part, i.e., energy and enstrophy spectra, are close to the statistics of the total flow, and moreover, the nonlinear energy budgets are very well preserved. The remaining incoherent part, represented by the large majority of the weak wavelet coefficients, corresponds to a structureless, i.e., noise-like, background flow whose energy is equidistributed.
An experimental study on the local two phase distributions in the ERVC flow channel
International Nuclear Information System (INIS)
During ex-vessel cooling two-phase flow around the outside of the inverted hemisphere geometry of the lower reactor head results in a variety void fraction distributions. To study the local features of the void fraction distribution we performed an experimental study with a quarter-circle geometry test section to simulate the RPV lower head. Air is injected in the test section to simulate the two phase flow phenomena and a conductivity probe is used to measure the local void fraction distribution. The test results show that the local void fraction near the bottom of the lower head is a wall peak distribution which then transitions to a near-wall peak distribution near the top of the lower head, and eventually develops into a center-peak distribution outside of the cylindrical shell. A sensitivity study has shown that the air flow rate has a significant effect on the local void fraction distribution in the flow channel. (author)
Isotropic boundary adapted wavelets for coherent vorticity extraction in turbulent channel flows
Farge, Marie; Sakurai, Teluo; Yoshimatsu, Katsunori; Schneider, Kai; Morishita, Koji; Ishihara, Takashi
2015-11-01
We present a construction of isotropic boundary adapted wavelets, which are orthogonal and yield a multi-resolution analysis. We analyze DNS data of turbulent channel flow computed at a friction-velocity based Reynolds number of 395 and investigate the role of coherent vorticity. Thresholding of the wavelet coefficients allows to split the flow into two parts, coherent and incoherent vorticity. The statistics of the former, i.e., energy and enstrophy spectra, are close to the ones of the total flow, and moreover the nonlinear energy budgets are well preserved. The remaining incoherent part, represented by the large majority of the weak wavelet coefficients, corresponds to a structureless, i.e., noise-like, background flow and exhibits an almost equi-distribution of energy.
International Nuclear Information System (INIS)
Based on the Fluent, numerical simulation of single-phase flow and heat transfer in vertical and rectangular channel under the rolling effect of motion had been studied firstly with the modification of momentum equation, which is induced by the additional inertia forces. The additional inertia forces were added to the source term of momentum equation through User Defined Function (UDF). The results show that, the flow rate and temperature fluctuate around the stationary value with sinusoid, and the fluctuation period coincides with the rolling period. The extremum of flow rate and temperature appears between the maximum rolling angle and equilibrium position. Phase difference exists among the rolling, flow rate and temperature. The decrease of rolling period and increase of maximum rolling angle enlarge the amplitude of fluctuation, and the fluctuation can be reduced when the system distribution is symmetric around the rolling axis. The simulation conclusions agree well with the experimental results in the released literatures. (authors)
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 ...
The impact of plasma induced flow on the boundary layer in a narrow channel
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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.
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.
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.
International Nuclear Information System (INIS)
Numerical solutions on the influence of surface radiation on the laminar air flow induced by natural convection in vertical, asymmetrically-heated channels are discussed. Variable property effects are accounted for in a full-elliptic mathematical formulation. The density variation is determined from the state equation for ideal gas. The experimental design and data reported in Webb and Hill [1] are taken as the base cases for carrying out the computations. The occurrence of flow reversals is first considered and revisited for pure natural convection, and the Nusselt number correlations derived from the numerical results are favorably compared with those reported in [1]. It is shown that the general effect of surface radiation is to delete the onset of pocket-like re-circulations at the top part of the channel, to reduce the heated wall temperatures, and to increase the facing wall temperatures. Comparisons with usual methods used for decoupling the surface radiation effects are discussed. In the range of parameters investigated, increases in differences between inlet and maximum wall temperatures up to 200 K are shown to have small influences on the flow field and negligible effects on heat transfer performances. (authors)
Control by blowing of the separated flow in a channel with a stepwise expansion
Czech Academy of Sciences Publication Activity Database
Jonáš, Pavel; Mazur, Oton; Uruba, Václav
Praha : UTAM AV ČR, 2006 - (Náprstek, J.; Fischer, C.), s. 148-149 ISBN 80-86246-27-2. [Engineering mechanics 2006 : national conference with international participation. Svratka (CZ), 15.05.2006-18.05.2006] R&D Projects: GA AV ČR(CZ) IAA200760614; GA ČR(CZ) GA101/03/0018 Institutional research plan: CEZ:AV0Z20760514 Keywords : backward facing step * flow control by blowing/suction * narrow channel flow Subject RIV: BK - Fluid Dynamics
The $Re$-number dependence of the longitudinal dispersion in a turbulent channel flow
Hawkins, Christopher; Krotkiewski, Marcin; Jamtveit, Bjørn
2016-01-01
In Taylor's theory, the longitudinal dispersion in turbulent pipe flows approaches, on long timescales, a diffusive behavior with a constant diffusivity $K_L$, that depends \\emph{empirically} on the Reynolds number $Re$. We show that the dependence on $Re$ can be determined from the turbulent energy spectrum. By using the intimate connection between the friction factor and longitudinal dispersion in wall-bounded turbulence, we predict different asymptotic scaling laws of $K_L(Re)$ depending on the different turbulent cascades in two-dimensional turbulence. We also explore numerically the $K_L(Re)$ dependence in turbulent channel flows with smooth and rough walls using a lattice Boltzmann method.
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.
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.
Large Eddy Simulation of high Reynolds number channel flow on coarse grids
International Nuclear Information System (INIS)
Large Eddy Simulation (LES) is a promising method for the prediction and study of turbulence, but it requires a grid resolution that scales as the square of the Reynolds number in attached boundary layers. In the present paper the inner region of the boundary layer is modeled in a statistical sense using a Reynolds Averaged Navier-Stokes (RANS) model. The purpose of the present study is to investigate and improve the combination of LES/RANS in boundary layers. The test case chosen is fully developed channel flow, which, despite its geometrical simplicity, is a very challenging flow for LES
Institute of Scientific and Technical Information of China (English)
Sohail Nadeem; Safia Akram
2011-01-01
In the present paper we discuss the magnetohydrodynamic (MHD) peristaltic flow of a hyperbolic tangent fluid model in a vertical asymmetric channel under a zero Reynolds number and long wavelength approximation. Exact solution of the temperature equation in the absence of dissipation term has been computed and the analytical expression for stream function and axial pressure gradient are established. The flow is analyzed in a wave frame of reference moving with the velocity of wave. The expression for pressure rise has been computed numerically. The physical features of pertinent parameters are analyzed by plotting graphs and discussed in detail.
The experimental study of the features of water flowing through a sharpcrested weir in channel
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Turalina Dinara
2015-01-01
Full Text Available This article contains the experimental research of water flowing through a weir in a rectangular open channel. Nine regimes of water flowrate investigated in this study. Upstream water levels partially determined for each regime. The coefficient of discharge to the weir determined from the flowrate equation. The determined coefficient of discharge value compared to the value from the Rehbock formula. The diagram of values shows the dependence of the coefficient of discharge Cd on the upstream water level yc/h. Experimental study conducted on the Armfield S16 hydraulic flow demonstrator and hydraulic bench F1-10.
Hall Effect in the Viscous Incompressible Flow Through a Rotating Channel Between Two Porous Walls
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V.V. Ramana Rao
1990-07-01
Full Text Available Exact solutions for the velocity and induced magnetic field distributions, accounting for Hall currents have been obtained for the flow of a conducting porous walls under the action of a constant pressure gradient and in the presence of a uniform magnetic field transversely applied to the flow. Further, the channel is rotated with constant angular velocity about an axis perpendicular to the walls. For the purpose of mathematical simplicity, the magnetic prandtl number is assumed to be negligible. An expression for the boundary layer thickness dependent on Taylor, Hartmann, suction Reynolds numbers and Hall parameter has been obtained.
Numerical investigation of turbulent flow and heat transfer in channel with ribs
DEFF Research Database (Denmark)
Myllerup, Lisbeth; Larsen, Poul Scheel
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 = 37,200 ......,200 and Re = 12,600, for which experimental data are available for the flow field and heat transfer, respectively. Comparison with experimental data includes the Nusselt number distribution along ribbed surface and profiles of mean velocity....
Stability and Drag Reduction in Transient Channel Flow of Fibre Suspension
Institute of Scientific and Technical Information of China (English)
游振江; 林建忠; 邵雪明; 张卫峰
2004-01-01
Drag reduction features in the transition regime of channel flow with fibre suspension were analyzed in terms of the linear stability theory. The modified stability equation was obtained based on the slender-body theory and natural closure approximation. Results of the stability analysis show attenuating effects of fibre additives to the flow instability. For the cases leading to transition, drag reduction rate increases with the characteristic parameter H of fibres. The mechanism of drag reduction by fibres is revealed through the variation of velocity profile and the decrease of wall shear stress. The theoretical results are qualitatively consistent with some typical experiments.
DNS of viscoelastic turbulent channel flow with rectangular orifice at low Reynolds number
International Nuclear Information System (INIS)
Direct numerical simulations of turbulent viscoelastic-fluid flow in a channel with a rectangular orifice were performed to investigate the influence of viscoelasticity on turbulence statistics and turbulent structures downstream of the orifice. The geometry considered is periodic rectangular orifices with 1:2 expansion. The constitutive equation follows the Giesekus model, valid for polymer (or surfactant) solutions, which are generally capable of reducing the turbulent frictional drag in a smooth channel. The friction Reynolds number and the Weissenberg number were set to 100 and 20-30, respectively. A drag reduction of about 20% was achieved in the viscoelastic flows. The onset Reynolds number for the transition from a symmetric to an asymmetric state was found to be shifted to higher values than that for the Newtonian flow. In the viscoelastic flow, the turbulent kinetic energy was decreased and fewer turbulent eddies were observed, as the Kelvin-Helmholtz vortices were quickly damped. Away from the orifice, quasi-streamwise vortices in the viscoelastic flow were sustained for a longer period, accompanied by energy exchange from elastic energy of the viscoelastic fluid to kinetic energy.
Directory of Open Access Journals (Sweden)
Mandana Samari Kermani
2016-01-01
Full Text Available The interaction of spherical solid particles with turbulent eddies in a 3-D turbulent channel flow with friction Reynolds number was studied. A generalized lattice Boltzmann equation (GLBE was used for computation of instantaneous turbulent flow field for which large eddy simulation (LES was employed. The sub-grid-scale (SGS turbulence effects were simulated through a shear-improved Smagorinsky model (SISM, which can predict turbulent near wall region without any wall function. Statistical properties of particles behavior such as root mean square (RMS velocities were studied as a function of dimensionless particle relaxation time ( by using a Lagrangian approach. Combination of SISM in GLBE with particle tracking analysis in turbulent channel flow is novelty of the present work. Both GLBE and SISM solve the flow field equations locally. This is an advantage of this method and makes it easy implementing. Comparison of the present results with previous available data indicated that SISM in GLBE is a reliable method for simulation of turbulent flows which is a key point to predict particles behavior correctly.
Particle-laden viscous channel flows - model regularization and parameter study
O'Naraigh, Lennon
2016-01-01
We characterize the flow of a viscous suspension in an inclined channel where the flow is maintained in a steady state under the competing influences of gravity and an applied pressure drop. The basic model relies on a diffusive-flux formalism. Such models are common in the literature, yet many of them possess an unphysical singularity at the channel centreline where the shear rate vanishes. We therefore present a regularization of the basic diffusive-flux model that removes this singularity. This introduces an explicit (physical) dependence on the particle size into the model equations. This approach enables us to carry out a detailed parameter study showing in particular the opposing effects of the pressure drop and gravity. Conditions for counter-current flow and complete flow reversal are obtained from numerical solutions of the model equations. These are supplemented by an analytic lower bound on the ratio of the gravitational force to the applied pressure drop necessary to bring about complete flow reve...
Contrasting turbulence–radiation interaction in supersonic channel and pipe flow
International Nuclear Information System (INIS)
Highlights: • LES-code directly coupled with RTE solver based on discrete ordinates method. • New findings due to competition between TRI and transverse curvature effects. • Changes in mean density control changes in pressure–strain correlations. • Radiative heat flux into wall reaches values of 40% of total wall heat flux. - Abstract: The Large Eddy Simulation (LES) technique is used to explore similarities and differences between turbulence–radiation interaction (TRI) in fully developed supersonic plane channel flow and axisymmetric non-swirling pipe flow, bounded by isothermal black and diffusive walls which are kept at a temperature of 800 K. The comparison between both flows is based on equal friction Mach number, friction Reynolds number, Prandtl number and ratio of specific heats. The Reynolds number is defined with the channel half-width and pipe radius. An explicit filtering scheme based on approximate deconvolution is applied to treat the closure problem of the low-pass filtered compressible Navier–Stokes equations. The working fluid is water vapour and its radiative properties are accounted for using a grey gas model with a Planck mean absorption coefficient varying with temperature. Simulations have been performed for two different optical thicknesses. Results for mean flow quantities, Reynolds stresses and pressure–strain correlations are presented, contrasting radiative effects in both flows and indicating their interaction with curvature effects in the pipe. An analysis of the total enthalpy balance reveals the role of radiative heat transfer, compared to turbulent and mean molecular heat transport
International Nuclear Information System (INIS)
The possibility to generate a gas flow inside a channel just by imposing a tangential temperature gradient along the walls without the existence of an initial pressure difference is well known. The gas must be under rarefied conditions, meaning that the system must operate between the slip and the free molecular flow regimes, either at low pressure or/and at micro/nano-scale dimensions. This phenomenon is at the basis of the operation principle of Knudsen pumps, which are actually compressors without any moving parts. Nowadays, gas flows in the slip flow regime through microchannels can be modeled using commercial Computational Fluid Dynamics softwares, because in this regime the compressible Navier-Stokes equations with appropriate boundary conditions are still valid. A simulation procedure has been developed for the modeling of thermal creep flow using ANSYS Fluent®. The implementation of the boundary conditions is achieved by developing User Defined Functions (UDFs) by means of C++ routines. The complete first order velocity slip boundary condition, including the thermal creep effects due to the axial temperature gradient and the effect of the wall curvature, and the temperature jump boundary condition are applied. The developed simulation tool is used for the preliminary design of Knudsen micropumps consisting of a sequence of curved and straight channels.
Numerical Analysis of Cavitating Flow of Liquid Helium inHorizontal Converging-Diverging Channel
Ishimoto, Jun; Kamijo, Kenjiro
The basic characteristics of the two-dimensional cavitating flow of liquid helium through a horizontal converging-diverging channel near the lambda point are numerically investigated to realize the further development and high performance of new multiphase superfluid cooling systems. First, the governing equations of the cavitating flow of liquid helium based on the unsteady thermal nonequilibrium multifluid model with generalized curvilinear coordinates system are presented, and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the cavitating flow of liquid helium though horizontal converging-diverging channel is shown in detail, and it is also found that the generation of superfluid counterflow against normal fluid flow based on the thermo mechanical effect is conspicuous in the large gas phase volume fraction region where the liquid- to gas-phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase.
Numerical simulation of cavitating flow of liquid helium in venturi channel
Ishimoto, Jun; Kamijo, Kenjiro
2003-01-01
The fundamental characteristics of the two-dimensional cavitating flow of liquid helium through a venturi channel near the lambda point are numerically investigated to realize the further development and high performance of new multi-phase superfluid cooling systems. First, the governing equations of the cavitating flow of liquid helium based on the unsteady thermal nonequilibrium multi-fluid model with generalized curvilinear coordinates system are presented, and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the cavitating flow of liquid helium though venturi channel is shown in detail, and it is also found that the generation of superfluid counterflow against normal fluid flow based on the thermomechanical effect is conspicuous in the large gas phase volume fraction region where the liquid-to-gas phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase.
Application of the homotopy method for analytical solution of non-Newtonian channel flows
International Nuclear Information System (INIS)
This paper presents the homotopy series solution of the Navier-Stokes and energy equations for non-Newtonian flows. Three different problems, Couette flow, Poiseuille flow and Couette-Poiseuille flow have been investigated. For all three cases, the nonlinear momentum and energy equations have been solved using the homotopy method and analytical approximations for the velocity and the temperature distribution have been obtained. The current results agree well with those obtained by the homotopy perturbation method derived by Siddiqui et al (2008 Chaos Solitons Fractals 36 182-92). In addition to providing analytical solutions, this paper draws attention to interesting physical phenomena observed in non-Newtonian channel flows. For example, it is observed that the velocity profile of non-Newtonian Couette flow is indistinctive from the velocity profile of the Newtonian one. Additionally, we observe flow separation in non-Newtonian Couette-Poiseuille flow even though the pressure gradient is negative (favorable). We provide physical reasoning for these unique phenomena.
Application of the homotopy method for analytical solution of non-Newtonian channel flows
Energy Technology Data Exchange (ETDEWEB)
Roohi, Ehsan [Department of Aerospace Engineering, Sharif University of Technology, PO Box 11365-8639, Azadi Avenue, Tehran (Iran, Islamic Republic of); Kharazmi, Shahab [Department of Mechanical Engineering, Sharif University of Technology, PO Box 11365-8639, Azadi Avenue, Tehran (Iran, Islamic Republic of); Farjami, Yaghoub [Department of Computer Engineering, University of Qom, Qom (Iran, Islamic Republic of)], E-mail: roohi@sharif.edu
2009-06-15
This paper presents the homotopy series solution of the Navier-Stokes and energy equations for non-Newtonian flows. Three different problems, Couette flow, Poiseuille flow and Couette-Poiseuille flow have been investigated. For all three cases, the nonlinear momentum and energy equations have been solved using the homotopy method and analytical approximations for the velocity and the temperature distribution have been obtained. The current results agree well with those obtained by the homotopy perturbation method derived by Siddiqui et al (2008 Chaos Solitons Fractals 36 182-92). In addition to providing analytical solutions, this paper draws attention to interesting physical phenomena observed in non-Newtonian channel flows. For example, it is observed that the velocity profile of non-Newtonian Couette flow is indistinctive from the velocity profile of the Newtonian one. Additionally, we observe flow separation in non-Newtonian Couette-Poiseuille flow even though the pressure gradient is negative (favorable). We provide physical reasoning for these unique phenomena.
DNS of turbulent channel flow at ReΤ=395, 590 AND Pr=0.01
International Nuclear Information System (INIS)
The paper presents results of the Direct Numerical Simulation of turbulent channel flow at friction Reynolds numbers 395 and 590 with passive scalar at Prandtl number 0.01, which corresponds to the Prandtl number of liquid sodium. Fluctuating and non-fluctuating temperature boundary conditions are analyzed and compared. Results clearly describe the minor role of the turbulent Prandtl number in the integral wall-to-fluid heat transfer. (author)
Flow and Heat Transfer Characteristics in Rotating Two-pass Channels Cooled by Superheated Steam
Institute of Scientific and Technical Information of China (English)
WANG Wei; GAO Jianmin; XU Liang; SHI Xiaojun
2012-01-01
In a modern gas turbine,using superheated steam to cool the vane and blade for internal convection cooling is a promising alternative to traditional compressor air.However,further investigations of steam cooling need to be performed.In this paper,the three-dimensional flow and heat transfer characteristics of steam are numerically investigated in two-pass square channels with 45° ribbed walls under stationary and rotating conditions.The investigated rotation numbers are 0 and 0.24.The simulation is carried out by solving the Reynolds averaged Navier-Stokes equations employing the Reynolds stress turbulence model,cspccially considering two additional terms for Coriolis and rotational buoyancy forces caused by the rotating effect.For comparison,calculations for the air-cooled channels are done first at a Reynolds number of 25 000 and inlet coolant-to-wall density ratio of 0.13.The results are compared with the experiment data.Then the flow and heat transfer in steam-cooled channels are analyzed under the same operating conditions.The results indicate that the superheated steam has better heat transfer performance than air.Due to the combined effect of rotation,skewed ribs and 180° sharp turn,the secondary flow pattern in steam-cooled rotating two-pass channels is quite complex.This complex secondary flow pattern leads to strong anisotropic turbulence and high level of anisotropy of Reynolds stresses,which have a significant impact on the local heat transfer coefficient distributions.
Mixed Convection Flow of Couple Stress Fluid in a Vertical Channel with Radiation and Soret Effects
Directory of Open Access Journals (Sweden)
Kaladhar Kolla
2016-01-01
Full Text Available The radiation and thermal diffusion effects on mixed convection flow of couple stress fluid through a channel are investigated. The governing non-linear partial differential equations are transformed into a system of ordinary differential equations using similarity transformations. The resulting equations are then solved using the Spectral Quasi-linearization Method (QLM. The results, which are discussed with the aid of the dimensionless parameters entering the problem, are seen to depend sensitively on the parameters.
The impact of plasma induced flow on the boundary layer in a narrow channel
Czech Academy of Sciences Publication Activity Database
Procházka, Pavel P.; Uruba, Václav
Les Ulis Cedex : E D P SCIENCES, 2015 - (Dančová, P.; Vít, T.), s. 509-514 ISSN 2100-014X. - (EPJ Web of Conferences). [Experimental Fluid Mechanics 2014. Český Krumlov (CZ), 18.11.2014-21.11.2014] R&D Projects: GA ČR(CZ) GP14-25354P Institutional support: RVO:61388998 Keywords : plasma actuator * flow control * channel Subject RIV: BK - Fluid Dynamics
A free surface model for incompressible pipe and open channel flow.
Ersoy, Mehmet
2013-01-01
We present the full derivation of a free surface pipe or open channel model including friction, changes of section and changes of slope/topography. This 1D free surface model (also named \\textbf{FS}-model) is obtained from the incompressible 3D Navier-Stokes equation under shallow water assumptions with well-suited boundary conditions. It was introduced in the general framework of unsteady mixed flows in closed water pipes and is largely used by the engineers community.
Steady flow for incompressible fluids in domains with unbounded curved channels
Santos, Marcelo M.
2015-01-01
We give an overview on the solution of the stationary Navier-Stokes equations for non newtonian incompressible fluids established by G. Dias and M.M. Santos (Steady flow for shear thickening fluids with arbitrary fluxes, J. Differential Equations 252 (2012), no. 6, 3873-3898)*, propose a de?nition for domains with unbounded curved channels which encompasses domains with an unbounded boundary, domains with nozzles, and domains with a boundary being a punctured surface, and argue on the existen...
M. K. Chaube; Tripathi, D.; O. Anwar Bég; Shashi Sharma; PANDEY, V.S.
2015-01-01
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 profi...
International Nuclear Information System (INIS)
Direct numerical simulation (DNS) have been performed for the turbulent heat transfer in a channel flow. In the present study, effect of thermal boundary condition is examined. DNS has been carried out for streamwisely thermal boundary conditions (Reτ=180) with Pγ=0.71 to obtain statistical mean temperatures, temperature variances, budget terms and time scale ratios etc. The obtained results have indicated that the time scale ratio varies along a streamwise. (author)
Effect of induced magnetic field on peristaltic flow of a micropolar fluid in an asymmetric channel
Shit, G. C.; Roy, M.; E. Y. K. Ng
2010-01-01
Of concern in this paper is an investigation of peristaltic transport of a physiological fluid in an asymmetric channel under long wave length and low-Reynolds number assumptions. The flow is assumed to be incompressible, viscous, electrically conducting micropolar fluid and the effect of induced magnetic field is taken into account. Exact analytical solutions obtained for the axial velocity, microrotation component, stream line pattern, magnetic force function, axial-induced magnetic field a...
Reasoning About Information Flow Security of Separation Kernels with Channel-based Communication
Zhao, Yongwang; Sann, David; Zhang, Fuyuan; Liu, Yang
2015-01-01
Assurance of information flow security by formal methods is mandated in security certification of separation kernels. As an industrial standard for separation kernels, ARINC 653 has been complied with by mainstream separation kernels. Security of functionalities defined in ARINC 653 is thus very important for the development and certification of separation kernels. This paper presents the first effort to formally specify and verify separation kernels with ARINC 653 channel-based communication...
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...
Heat Transfer on Steady MHD rotating flow through porous medium in a parallel plate channel
Dr. G. Prabhakara Rao,; M. Naga Sasikala
2015-01-01
We discussed the combined effects of radiative heat transfer and a transverse magnetic field on steady rotating flow of an electrically conducting optically thin fluid through a porous medium in a parallel plate channel and non-uniform temperatures at the walls. The analytical solutions are obtained from coupled nonlinear partial differential equations for the problem. The computational results are discussed quantitatively with the aid of the dimensionless parameters entering in t...
Heat Transfer on Steady MHD rotating flow through porous medium in a parallel plate channel
Directory of Open Access Journals (Sweden)
Dr. G. Prabhakara Rao,
2015-04-01
Full Text Available We discussed the combined effects of radiative heat transfer and a transverse magnetic field on steady rotating flow of an electrically conducting optically thin fluid through a porous medium in a parallel plate channel and non-uniform temperatures at the walls. The analytical solutions are obtained from coupled nonlinear partial differential equations for the problem. The computational results are discussed quantitatively with the aid of the dimensionless parameters entering in the solution.
Development of a Methodology to Measure Aerodynamic Forces on Pin Fins in Channel Flow
Brumbaugh, Scott J
2006-01-01
The desire for smaller, faster, and more efficient products places a strain on thermal management in components ranging from gas turbine blades to computers. Heat exchangers that utilize internal cooling flows have shown promise in both of these industries. Although pin fins are often placed in the cooling channels to augment heat transfer, their addition comes at the expense of increased pressure drop. Consequently, the pin fin geometry must be judiciously chosen to achieve the desired he...
PLUGM: a coupled thermal-hydraulic computer model for freezing melt flow in a channel
International Nuclear Information System (INIS)
PLUGM is a coupled thermal-hydraulic computer model for freezing liquid flow and plugging in a cold channel. PLUGM is being developed at Sandia National Laboratories for applications in Sandia's ex-vessel Core Retention Concept Assessment Program and in Sandia's LMFBR Transition Phase Program. The purpose of this paper is to introduce PLUGM and demonstrate how it can be used in the analysis of two of the core retention concepts under investigation at Sandia: refractory brick crucibles and particle beds
Soliton solutions and their stability for the flow of relativistic fluids through channels
Lerche, I.; Wiita, P. J.
1980-01-01
The flow of a perfect relativistic fluid through channels of various cross-sections is considered with reference to models of radio galaxies. Soliton-like solutions are found and their topologies are discussed. The calculations show that these solutions are unstable. It is suggested that under realistic astrophysical conditions the growth rate of the instabilities is so slow that soliton-type blobs may persist for a significant time.
Wall Shear Stress Induced by Taylor Bubbles in Inclined Flow Channels
Czech Academy of Sciences Publication Activity Database
Tihon, Jaroslav; Pěnkavová, Věra; Vejražka, Jiří
Bratislava: Slovak Society of Chemical Engineering, 2013 - (Markoš, J.), s. 153 ISBN 978-80-89475-09-4. [International Conference of Slovak Society of Chemical Engineering /40./. Tatranské Matliare (SK), 27.05.2013-31.05.2013] R&D Projects: GA ČR(CZ) GAP101/12/0585 Institutional support: RVO:67985858 Keywords : iInclined flow channel * taylor bubbles * bubble rise velocity Subject RIV: CI - Industrial Chemistry, Chemical Engineering
Near-Wall Flow Induced by Large Bubbles Rising in Flat Channels
Czech Academy of Sciences Publication Activity Database
Tihon, Jaroslav; Pěnkavová, Věra; Vejražka, Jiří
Bratislava: Slovak University of Technology, 2010 - (Markoš, J.), s. 133 ISBN 978-80-227-3290-1. [International Conference of Slovak Society of Chemical Engineering /37./. Tatranské Matliare (SK), 24.05.2010-28.05.2010] R&D Projects: GA ČR GA104/08/0428 Institutional research plan: CEZ:AV0Z40720504 Keywords : two-phase flow * inclined channel * single large bubbles Subject RIV: CI - Industrial Chemistry, Chemical Engineering
Analytical Method in Solving Flow of Viscoelastic Fluid in a Porous Converging Channel
M. Esmaeilpour; Naeem Roshan; Negar Roshan; D.D. Ganji
2011-01-01
An analytical method, called homotopy perturbation method (HPM), is used to compute an approximation to the solution of the nonlinear differential equation governing the problem of two-dimensional and steady flow of a second-grade fluid in a converging channel. The table and figures are presented for influencing various parameters on the velocity field. The results compare well with those obtained by the numerical method. The method is straightforward and concise, and it can also be applied t...
Hydrodynamic modeling of mineral wool fiber suspensions in a two-dimensional channel flow
International Nuclear Information System (INIS)
A consequence of a loss of coolant accident is the damage of adjacent insulation materials (IM). IM may then be transported to the containment sump strainers where water is drawn into the ECCS (emergency core cooling system). Blockage of the strainers by IM lead to an increased pressure drop acting on the operating ECCS pumps. IM can also penetrate the strainers, enter the reactor coolant system and then accumulate in the reactor pressure vessel. An experimental and theoretical study that concentrates on mineral wool fiber transport in the containment sump and the ECCS is being performed. The study entails fiber generation and the assessment of fiber transport in single and multi-effect experiments. The experiments include measurement of the terminal settling velocity, the strainer pressure drop, fiber sedimentation and resuspension in a channel flow and jet flow in a rectangular tank. An integrated test facility is also operated to assess the compounded effects. Each experimental facility is used to provide data for the validation of equivalent computational fluid dynamic models. The channel flow facility allows the determination of the steady state distribution of the fibers at different flow velocities. The fibers are modeled in the Eulerian-Eulerian reference frame as spherical wetted agglomerates. The fiber agglomerate size, density, the relative viscosity of the fluid-fiber mixture and the turbulent dispersion of the fibers all affect the steady state accumulation of fibers at the channel base. In the current simulations, three fiber phases are separately considered. For two phases, the particle size is kept constant while the density is modified and the third phase has a reduced diameter, both of which affect the terminal velocity and the volume fraction. The relative viscosity is only significant at higher concentrations. The numerical model finds that the fibers accumulate at the channel base even at high velocities; therefore, modifications to the drag
Xuan Wu; Bo Yu(Brookhaven National Lab); Yi Wang
2013-01-01
Direct numerical simulation has been performed to study a polymer drag-reducing channel flow by using a discrete-element model. And then, wavelet analyses are employed to investigate the multiresolution characteristics of velocity components based on DNS data. Wavelet decomposition is applied to decompose velocity fluctuation time series into ten different frequency components including approximate component and detailed components, which show more regular intermittency and burst events in dr...
Turbulent heat transfer in a channel flow at transitional Reynolds numbers
Tsukahara, Takahiro; Kawamura, Hiroshi
2014-01-01
Direct numerical simulation of a turbulent channel flow with heat transfer was performed at very low Reynolds numbers. Two different thermal boundary conditions were studied, and temperature was considered as a passive scalar. The computations were carried out with huge computational boxes (up to 327.7 x 2 x 128 in the streamwise, wall-normal, and spanwise directions, respectively). The emphases of this paper are to investigate the large-scale structure (puff) in the intermittent-turbulent fl...
On the influence of plasma DBD actuator on the flow in a rectangular channel
Czech Academy of Sciences Publication Activity Database
Procházka, Pavel P.; Uruba, Václav
2014-01-01
Roč. 14, č. 1 (2014), s. 727-728. ISSN 1617-7061. [Annual Meeting of the International Association of Applied Mathematics and Mechanics /85./. Erlangen, 10.03.2014-14.03.2014] R&D Projects: GA ČR(CZ) GP14-25354P Institutional support: RVO:61388998 Keywords : plasma DBD * boundary layer * channel flow Subject RIV: BK - Fluid Dynamics http://onlinelibrary.wiley.com/doi/10.1002/pamm.201410346/abstract
A Comparison of Recursive Least Squares Estimation and Kalman Filtering for Flow in Open Channels
DURDU, Ömer Faruk
2005-01-01
An integrated approach to the design of an automatic control system for canals using a Linear Quadratic Gaussian regulator based on recursive least squares estimation was developed. The one-dimensional partial differential equations describing open channel flow (Saint-Venant) equations are linearized about an average operating condition of the canal. The concept of optimal control theory is applied to drive a feedback control algorithm for constant-level control of an irrigation cana...
Influence of macro-roughness of walls on steady and unsteady flow in a channel
Meile, Tobias
2007-01-01
High-head storage hydropower plants mainly operate their turbines during periods of high energy demand. The sudden starting and stopping of turbines (hydropeaking) lead to highly unsteady flow in channels and rivers. Besides hydropeaking, other anthropogenic actions and natural events such as sluice gate operations, flushing of reservoirs, debris jam and break up, ice jam and break up, sudden stopping and starting of turbines of runoff river hydropower plants, flashfloods or dambreaks can als...
Influence of macro-roughness of walls on steady and unsteady flow in a channel
Meile, T.; Schleiss, Anton
2008-01-01
High-head storage hydropower plants mainly operate their turbines during periods of high energy demand. The sudden starting and stopping of turbines (hydropeaking) lead to highly unsteady flow in channels and rivers. Besides hydropeaking, other anthropogenic actions and natural events such as sluice gate operations, flushing of reservoirs, debris jam and break up, ice jam and break up, sudden stopping and starting of turbines of runoff river hydropower plants, flashfloods or dambreaks can als...
Accident analysis of flow blockage to coolant channels of upgraded JRR-3, using EUREKA-2 code, (1)
International Nuclear Information System (INIS)
This report describes the results about thermo-hydraulic behavior in the accident of flow blockage to coolant channels of upgraded JRR-3. Analysis was carried out using EUREKA-2 code. Flow blockage to coolant channels accident occur by some extraneous things which come from outside of the reactor pool, may block the coolant flow channels of the core. If flow blockage to coolant channels would occur, fuel temperature will increase due to flow rate decrease of coolant channels. And at last, fission products will be released from inside of fuel plates to the primary cooling system due to failure of fuel plates. In the analysis, one standard type fuel element was supposed as flow blockage channels, in the same way sa one of credible accidents, which postulated in the JRR-3 safety assessment. From the results, it was shown that about 16.7 % of the fuel element which was supposed as flow blockage channels, would fail, assuming that fuel plates might fail when the fuel meat temperatures riseover 400 deg C. (author)
Suspended sediment dynamics in a tidal channel network under peak river flow
Achete, Fernanda Minikowski; van der Wegen, Mick; Roelvink, Dano; Jaffe, Bruce
2016-05-01
Peak river flows transport fine sediment, nutrients, and contaminants that may deposit in the estuary. This study explores the importance of peak river flows on sediment dynamics with special emphasis on channel network configurations. The Sacramento-San Joaquin Delta, which is connected to San Francisco Bay (California, USA), motivates this study and is used as a validation case. Besides data analysis of observations, we applied a calibrated process-based model (D-Flow FM) to explore and analyze high-resolution (˜100 m, ˜1 h) dynamics. Peak river flows supply the vast majority of sediment into the system. Data analysis of six peak flows (between 2012 and 2014) shows that on average, 40 % of the input sediment in the system is trapped and that trapping efficiency depends on timing and magnitude of river flows. The model has 90 % accuracy reproducing these trapping efficiencies. Modeled deposition patterns develop as the result of peak river flows after which, during low river flow conditions, tidal currents are not able to significantly redistribute deposited sediment. Deposition is quite local and mainly takes place at a deep junction. Tidal movement is important for sediment resuspension, but river induced, tide residual currents are responsible for redistributing the sediment towards the river banks and to the bay. We applied the same forcing for four different channel configurations ranging from a full delta network to a schematization of the main river. A higher degree of network schematization leads to higher peak-sediment export downstream to the bay. However, the area of sedimentation is similar for all the configurations because it is mostly driven by geometry and bathymetry.
Swain, Ratnakar; Sahoo, Bhabagrahi
2015-11-01
In this study, the fully volume conservative simplified hydrodynamic-based variable parameter McCarthy-Muskingum (VPMM) flow transport model advocated by Perumal and Price in 2013 is extended to exclusively incorporate the distributed non-uniform lateral flow in the routing scheme accounting for compound river channel flows. The revised VPMM formulation is exclusively derived from the combined form of the de Saint-Venant's continuity and momentum equations with the spatiotemporally distributed lateral flow which is solved using the finite difference box scheme. This revised model could address the earlier model limitations of: (i) non-accounting non-uniformly distributed lateral flow, (ii) ignoring floodplain flow, and (iii) non-consideration of catchment dynamics of lateral flow generation restricting its real-time application. The efficacy of the revised formulation is tested to simulate 16 years (1980-1995) river runoff from real-time storm events under scarce morpho-hydrological data conditions in a tropical monsoon-type 48 km Bolani-Gomlai reach of the Brahmani River in eastern India. The spatiotemporally distributed lateral flows generated in real-time is computed by water balance approach accounting for catchment characteristics of normalized network area function, land use land cover classes, and soil textural classes; and hydro-meteorological variables of precipitation, soil moisture, minimum and maximum temperatures, wind speed, relative humidity, and solar radiation. The multiple error measures used in this study and the simulation results reveal that the revised VPMM model has a greater practical utility in estimating the event-based and long-term meso-scale river runoff (both discharge and its stage) at any ungauged site, enhancing its application for real-time flood estimation.