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Channel Flow (channel + flow)
Kinds of Channel Flow Selected AbstractsParallelization and scalability of a spectral element channel flow solver for incompressible Navier,Stokes equationsCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 10 2007C. W. Hamman Abstract Direct numerical simulation (DNS) of turbulent flows is widely recognized to demand fine spatial meshes, small timesteps, and very long runtimes to properly resolve the flow field. To overcome these limitations, most DNS is performed on supercomputing machines. With the rapid development of terascale (and, eventually, petascale) computing on thousands of processors, it has become imperative to consider the development of DNS algorithms and parallelization methods that are capable of fully exploiting these massively parallel machines. A highly parallelizable algorithm for the simulation of turbulent channel flow that allows for efficient scaling on several thousand processors is presented. A model that accurately predicts the performance of the algorithm is developed and compared with experimental data. The results demonstrate that the proposed numerical algorithm is capable of scaling well on petascale computing machines and thus will allow for the development and analysis of high Reynolds number channel flows. Copyright © 2007 John Wiley & Sons, Ltd. [source] Channel sedimentation and erosion of the Jiangsu reach of the Yangtze River during the last 44 yearsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2009Wang Jian Abstract River channel sedimentation in the lower reaches of the Yangtze River can be affected by both changes in sea level and changes in solid discharge from the upper river. To evaluate dynamic changes of sedimentation and erosion in the Jiangsu reach of the Yangtze River (about 330 km in length) from 1959 to 2003, databases were designed and constructed using a digital elevation model (DEM) of channel topography based on the Jiangsu River Relief Map for 1959, 1970, 1985, 1992, and 2003. The results indicated that the main course of the Yangtze River in Jiangsu Province had experienced an obvious switch from sedimentation to erosion status around 1985 because of the decreasing amount of solid load from the upper parts of the river channel after that year. The sedimentation process in the main course of the Jiangsu reach of the Yangtze River demonstrated the propulsive process of ,downstream-ward aggradations.' Between 1985 and 2003, the erosion rate of the lower segment was greater than those of the middle and upper segments; this is probably because both channel flow and tide current had influenced the lower segment. When channel flow combines with tide current in the same direction, channel erosion can be intensified, especially if there is a solid load shortage in the channel. Copyright © 2009 John Wiley & Sons, Ltd. [source] Experimental study of rill bank collapseEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2007Jovan R. Stefanovic Abstract Rill bank collapse is an important component in the adjustment of channel morphology to changes in discharge and sediment flux. Sediment inputs from bank collapse cause abrupt changes in flow resistance, flow patterns and downstream sediment concentrations. Generally, bank retreat involves gradual lateral erosion, caused by flow shear stress, and sudden bank collapse, triggered by complex interactions between channel flow and bank and soil water conditions. Collapse occurs when bank height exceeds the critical height where gravitational forces overcome soil shear strength. An experimental study examined conditions for collapse in eroding rill channels. Experiments with and without a deep water table were carried out on a meandering rill channel in a loamy sand and sandy loam in a laboratory flume under simulated rainfall and controlled runon. Different discharges were used to initiate knickpoint and rill incision. Soil water dynamics were monitored using microstandpipes, tensiometers and time domain reflectometer probes (TDR probes). Bank collapse occurred with newly developed or rising pre-existing water tables near rill banks, associated with knickpoint migration. Knickpoint scour increased effective bank height, caused positive pore water pressure in the bank toe and reduced negative pore pressures in the unsaturated zone to near zero. Matric tension in unsaturated parts of the bank and a surface seal on the ,interrill' zone behind the bank enhanced stability, while increased effective bank height and positive pore water pressure at the bank toe caused instability. With soil water contents >35 per cent (sandy loam) and >23 per cent (loamy sand), critical bank heights were 0·11,0·12 m and 0·06,0·07 m, respectively. Bank toe undercutting at the outside of the rill bends also triggered instability. Bank displacement was quite different on the two soils. On the loamy sand, the failed block slid to the channel bed, revealing only the upper half of the failure plane, while on the sandy loam the failed block toppled forwards, exposing the failure plane for the complete bank height. This study has shown that it is possible to predict location, frequency and magnitude of the rill bank collapse, providing a basis for incorporation into predictive models for hillslope soil loss or rill network development. Copyright © 2006 John Wiley & Sons, Ltd. [source] Size distributions of suspended particles in open channel flow over bed materialsENVIRONMETRICS, Issue 2 2005B. S. Mazumder Controlled experiments have shown that the grain-size distribution of suspended sediments is related to bed material, flow velocity and height of suspension above the sand bed in an open channel flow. A theoretical model has been developed for computation of suspended grain-size distribution on the basis of continuity equations of sediment and water, using the computed bed-layer concentration as a reference. The proposed model includes the effect of suspension concentration into the mean velocity, turbulent and viscous shear stresses owing to the dynamic coupling between the flow and sediments in suspension. The effect of hindered settling due to the increased concentration in suspension is also taken into account. The model is considered to be a more general one than the existing models, and the results of the present model compare well with the experimental data. Copyright © 2004 John Wiley & Sons, Ltd. [source] DNS of turbulent heat transfer in a channel flow with a varying streamwise thermal boundary conditionHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2006Yohji Seki Abstract Direct numerical simulation (DNS) was performed for the turbulent heat transfer in a channel flow. In the present study, the effect of the thermal boundary condition was examined. DNS was carried out for varying streamwise thermal boundary conditions (Re, = 180) with Pr = 0.71 to obtain statistical mean temperatures, temperature variances, budget terms, and time scale ratios. The results obtained indicate that the time scale ratio varies along the stream direction. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(4): 265,278, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20114 [source] Changing a winning formula: the hydraulics of open channel flow: an introduction By Hubert Chanson, 1999 Arnold, 495 pp.HYDROLOGICAL PROCESSES, Issue 1 2001Central, ISBN 0-340-74067-1 Co-published in North, South America by Wiley ISBN 0-470-36103- No abstract is available for this article. [source] Transient deformation of a poroelastic channel bedINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2002P.C. Hsieh Abstract The coupled transient response of a poroelastic bed form due to stream flow and non-linear water waves is investigated numerically. The theory of potential flow is applied to channel flow while Biot's theory of poroelasticity (J. Appl. Phys. 1962; 33(4):1482) is adopted to deal with the deformable porous bed. A boundary-fitted co-ordinate system is used to calculate the variation in the bed form. The result of a simple periodic wave form over a soft poroelastic bed agrees well with the analytical solution of Hsieh et al. (J. Eng. Mech., ASCE 2000; 126(10):1064). However, due to the rapidly damping second dilatational wave inside the soft poroelastic bed, the solution for transient bed form near the interface is not easy to compute accurately. In order to overcome this difficulty, a simplified numerical model based on the boundary layer correction concept proposed by Hsieh et al. (2000) is established, which neglects Darcy's terms. The transient deformation of an irregular poroelastic bed that includes a trench and a downward step at the channel bed is simulated successfully. Copyright © 2002 John Wiley & Sons, Ltd. [source] The formation of dunes, antidunes, and rapidly damping waves in alluvial channelsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2001L.-H. Huang Abstract Under the effect of a constant current for a long time, a water channel of infinitely long and constant depth interacting with a uniform sandbed of infinite thickness is used to simulate the formation of dunes, antidunes and rapidly damping waves in alluvial channels. The theory of potential flow is applied to the channel flow, while Biot's theory of poroelasticity is adopted to deal with erodible bed material. The governing equations, together with free surface, bed surface, and far field boundary conditions, form a complete boundary-value problem without applying empirical sediment discharge formulas as in conventional researches. The comparison of the present result with Kennedy's (Journal of Fluid Mechanics, 1963; 16: 521,544) instability analysis not only indicates the appropriateness of the present work, but also reveals the advantage of the present study due to its ability to find all kinds of bed forms (including the rapidly damping waves that Kennedy could not find) and of solving for the unclear lagged distance , introduced in Kennedy's work. Copyright © 2001 John Wiley & Sons, Ltd. [source] Particulate flow simulations using lubrication theory solution enrichmentINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2003G. J. Wagner Abstract A technique for the numerical simulation of suspensions of particles in fluid based on the extended finite element method (X-FEM) is developed. In this method, the particle surfaces need not conform to the finite element boundaries, so that moving particles can be simulated without remeshing. The finite element basis is enriched with the Stokes flow solution for flow past a single particle and the lubrication theory solution for flow between particles. The latter enrichment allows the simulation of particles that come arbitrarily close together without refining the mesh in the gap between them. Example problems illustrating both types of enrichment are shown, along with a study of a 50% solution in channel flow. Copyright © 2003 John Wiley & Sons, Ltd. [source] Multiple-relaxation-time lattice Boltzmann computation of channel flow past a square cylinder with an upstream control bi-partitionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2010M. A. Moussaoui Abstract The present paper deals with the application of the multiple-relaxation-time lattice Boltzmann equation (MRT-LBE) for the simulation of a channel flow with a bi-partition located upstream of a square cylinder in order to control the flow. Numerical investigations have been carried out for different heights and positions of the bi-partition at Reynolds number of 250. Key computational issues involved are the computation of fluid forces acting on the square cylinder, the vortex shedding frequency and the impact of such bluff body on the flow pattern. A particular attention is paid to drag and lift coefficients on the square cylinder. The predicted results from MRT-LBE simulations show that in most cases, the interaction was beneficial insofar as the drag of the square block was lower with the bi-partition than without it. Fluctuating side forces due to vortex shedding from the main body were also reduced for most bi-partition positions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance of very-high-order upwind schemes for DNS of compressible wall-turbulenceINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2010G. A. Gerolymos Abstract The purpose of the present paper is to evaluate very-high-order upwind schemes for the direct numerical simulation (DNS) of compressible wall-turbulence. We study upwind-biased (UW) and weighted essentially nonoscillatory (WENO) schemes of increasingly higher order-of-accuracy (J. Comp. Phys. 2000; 160:405,452), extended up to WENO17 (AIAA Paper 2009-1612, 2009). Analysis of the advection,diffusion equation, both as ,x,0 (consistency), and for fixed finite cell-Reynolds-number Re,x (grid-resolution), indicates that the very-high-order upwind schemes have satisfactory resolution in terms of points-per-wavelength (PPW). Computational results for compressible channel flow (Re,[180, 230]; M,CL,[0.35, 1.5]) are examined to assess the influence of the spatial order of accuracy and the computational grid-resolution on predicted turbulence statistics, by comparison with existing compressible and incompressible DNS databases. Despite the use of baseline O(,t2) time-integration and O(,x2) discretization of the viscous terms, comparative studies of various orders-of-accuracy for the convective terms demonstrate that very-high-order upwind schemes can reproduce all the DNS details obtained by pseudospectral schemes, on computational grids of only slightly higher density. Copyright © 2009 John Wiley & Sons, Ltd. [source] Comparing vortex methods and finite difference methods in a homogeneous turbulent shear flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2010R. Yokota Abstract The vortex method is applied to the calculation of a homogeneous shear turbulence, and compared with a finite difference code using identical calculation conditions. The core spreading method with spatial adaptation is selected as the viscous diffusion scheme of the vortex method. The shear rate is chosen so that it matches the maximum value observed in a fully developed channel flow. The isosurface, anisotropy tensors, and joint probability density functions reflect the ability of the present vortex method to quantitatively reproduce the anisotropic nature of strongly sheared turbulence, both instantaneously and statistically. Copyright © 2009 John Wiley & Sons, Ltd. [source] Coupled Navier,Stokes,Molecular dynamics simulations using a multi-physics flow simulation frameworkINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2010R. Steijl Abstract Simulation of nano-scale channel flows using a coupled Navier,Stokes/Molecular Dynamics (MD) method is presented. The flow cases serve as examples of the application of a multi-physics computational framework put forward in this work. The framework employs a set of (partially) overlapping sub-domains in which different levels of physical modelling are used to describe the flow. This way, numerical simulations based on the Navier,Stokes equations can be extended to flows in which the continuum and/or Newtonian flow assumptions break down in regions of the domain, by locally increasing the level of detail in the model. Then, the use of multiple levels of physical modelling can reduce the overall computational cost for a given level of fidelity. The present work describes the structure of a parallel computational framework for such simulations, including details of a Navier,Stokes/MD coupling, the convergence behaviour of coupled simulations as well as the parallel implementation. For the cases considered here, micro-scale MD problems are constructed to provide viscous stresses for the Navier,Stokes equations. The first problem is the planar Poiseuille flow, for which the viscous fluxes on each cell face in the finite-volume discretization are evaluated using MD. The second example deals with fully developed three-dimensional channel flow, with molecular level modelling of the shear stresses in a group of cells in the domain corners. An important aspect in using shear stresses evaluated with MD in Navier,Stokes simulations is the scatter in the data due to the sampling of a finite ensemble over a limited interval. In the coupled simulations, this prevents the convergence of the system in terms of the reduction of the norm of the residual vector of the finite-volume discretization of the macro-domain. Solutions to this problem are discussed in the present work, along with an analysis of the effect of number of realizations and sample duration. The averaging of the apparent viscosity for each cell face, i.e. the ratio of the shear stress predicted from MD and the imposed velocity gradient, over a number of macro-scale time steps is shown to be a simple but effective method to reach a good level of convergence of the coupled system. Finally, the parallel efficiency of the developed method is demonstrated. Copyright © 2009 John Wiley & Sons, Ltd. [source] A Taylor series-based finite volume method for the Navier,Stokes equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2008G. X. Wu Abstract A Taylor series-based finite volume formulation has been developed to solve the Navier,Stokes equations. Within each cell, velocity and pressure are obtained from the Taylor expansion at its centre. The derivatives in the expansion are found by applying the Gauss theorem over the cell. The resultant integration over the faces of the cell is calculated from the value at the middle point of the face and its derivatives, which are further obtained from a higher order interpolation based on the values at the centres of two cells sharing this face. The terms up to second order in the velocity and the terms up to first order in pressure in the Taylor expansion are retained throughout the derivation. The test cases for channel flow, flow past a circular cylinder and flow in a collapsible channel have shown that the method is quite accurate and flexible. Copyright © 2008 John Wiley & Sons, Ltd. [source] Assessment of algorithms for the no-slip boundary condition in the lattice Boltzmann equation of BGK modelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2008Yong Kweon Suh Abstract Three kinds of algorithms for the lattice Boltzmann equation of the BGK model in the implementation of the no-slip boundary condition on the wall are assessed by using the analytical formula for the slip velocity of the fully developed pressure-driven channel flow. It is shown that the bounce-back algorithm results in the spatial accuracy of 1st order, except for the case when the wall is located at half way between the two grid lines. The interpolation scheme proposed by Yu et al. (Prog. Aerospace Sci. 2003; 39:329,367) and the similar one by Bouzidi et al. (Phys. Fluids 2001; 13(11):3452,3459) are of 2nd order, but the error increases quadratically with the relaxation time. The extrapolation scheme of Guo et al. (Phys. Fluids 2002; 14(6):2007,2010) is also shown to be of 2nd order, and the error level increases linearly with the relaxation time, but it turns out that this scheme is unstable for a certain range of parameter values. Numerical experiments with various parameter sets have been performed to obtain the stability diagram. Three algorithms are then applied to a circular-Couette flow and their performance is also studied in terms of the numerical accuracy and stability. Copyright © 2008 John Wiley & Sons, Ltd. [source] Simulations of the turbulent channel flow at Re, = 180 with projection-based finite element variational multiscale methodsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2007Volker John Abstract Projection-based variational multiscale (VMS) methods, within the framework of an inf,sup stable second order finite element method for the Navier,Stokes equations, are studied in simulations of the turbulent channel flow problem at Re, = 180. For comparison, the Smagorinsky large eddy simulation (LES) model with van Driest damping is included into the study. The simulations are performed on very coarse grids. The VMS methods give often considerably better results. For second order statistics, however, the differences to the reference values are sometimes rather large. The dependency of the results on parameters in the eddy viscosity model is much weaker for the VMS methods than for the Smagorinsky LES model with van Driest damping. It is shown that one uniform refinement of the coarse grids allows an underresolved direct numerical simulations (DNS). Copyright © 2007 John Wiley & Sons, Ltd. [source] A modification of the artificial compressibility algorithm with improved convergence characteristicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2007Frank Muldoon Abstract The artificial compressibility algorithm has a significant drawback in the difficulty of choosing the artificial compressibility parameter, improper choice of which leads either to slow convergence or divergence. A simple modification of the equation for pressure in the artificial compressibility algorithm which removes the difficulty of choosing the artificial compressibility parameter is proposed. It is shown that the choice of the relaxation parameters for the new algorithm is relatively straightforward, and that the same values can be used to provide robust convergence for a range of application problems. This new algorithm is easily parallelized making it suitable for computations such as direct numerical simulation (DNS) which require the use of distributed memory machines. Two key benchmark problems are studied in evaluating the new algorithm: DNS of a fully developed turbulent channel flow, and DNS of a driven-cavity flow, using both explicit and implicit time integration schemes. The new algorithm is also validated for a more complex flow configuration of turbulent flow over a backward-facing step, and the computed results are shown to be in good agreement with experimental data and previous DNS work. Copyright © 2007 John Wiley & Sons, Ltd. [source] Acoustic upwinding for sub- and super-sonic turbulent channel flow at low Reynolds numberINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2007H. C. de LangeArticle first published online: 13 FEB 200 Abstract A recently developed asymmetric implicit fifth-order scheme with acoustic upwinding for the spatial discretization for the characteristic waves is applied to the fully compressible, viscous and non-stationary Navier,Stokes equations for sub- and super-sonic, mildly turbulent, channel flow (Re,=360). For a Mach number of 0.1, results are presented for uniform (323, 643 and 1283) and non-uniform (expanding wall-normal, 323 and 643) grids and compared to the (incompressible) reference solution found in (J. Fluid. Mech. 1987; 177:133,166). The results for uniform grids on 1283 and 643 nodes show high resemblance with the reference solution. Expanding grids are applied on 643 - and 323 -node grids. The capability of the proposed technique to solve compressible flow is first demonstrated by increasing the Mach number to 0.3, 0.6 and 0.9 for isentropic flow on the uniform 643 -grid. Next, the flow speed is increased to Ma=2. The results for the isothermal-wall supersonic flows give very good agreement with known literature results. The velocity field, the temperature and their fluctuations are well resolved. This means that in all presented (sub- and super-sonic) cases, the combination of acoustic upwinding and the asymmetric high-order scheme provides sufficient high wave-number damping and low wave-number accuracy to give numerically stable and accurate results. Copyright © 2007 John Wiley & Sons, Ltd. [source] Large eddy simulation of turbulent channel flow using an algebraic modelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2005S. Bhushan Abstract In this paper an algebraic model from the constitutive equations of the subgrid stresses has been developed. This model has an additional term in comparison with the mixed model, which represents the backscatter of energy explicitly. The proposed model thus provides independent modelling of the different energy transfer mechanisms, thereby capturing the effect of subgrid scales more accurately. The model is also found to depict the flow anisotropy better than the linear and mixed models. The energy transfer capability of the model is analysed for the isotropic decay and the forced isotropic turbulence. The turbulent plane channel flow simulation is performed over three Reynolds numbers, Re,=180, 395 and 590, and the results are compared with that of the dynamic model, Smagorinsky model, and the DNS data. Both the algebraic and dynamic models are in good agreement with the DNS data for the mean flow quantities. However, the algebraic model is found to be more accurate for the turbulence intensities and the higher-order statistics. The capability of the algebraic model to represent backscatter is also demonstrated. Copyright © 2005 John Wiley & Sons, Ltd. [source] Assessment of non-Fickian subgrid-scale models for passive scalar in a channel flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2005E. Montreuil Abstract In order to assess new subgrid-scale (SGS) models for a passive scalar, several large eddy simulations of a turbulent channel flow with passive scalar, for various Prandtl numbers ranging from 0.1 to 2.0 are carried out. These models are not based on the classical Fickian approximation and do not necessarily induce an alignment between the SGS heat flux vector and the gradient of the resolved temperature. Five SGS models are investigated on two grids. To validate the simulations, statistical quantities such as mean temperature, temperature variance and turbulent heat flux are compared with available data obtained by direct numerical simulation (DNS). The SGS dissipation is computed for different models in order to analyse its behaviour. The turbulence structures based on instantaneous velocity and temperature are described to study the correlations between these two fields. Among the assessed models, those consisting in Fickian and non-Fickian parts seem to be full of promise. Copyright © 2005 John Wiley & Sons, Ltd. [source] High order interpolation methods for semi-Lagrangian models of mobile-bed hydrodynamics on Cartesian grids with cut cellsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10-11 2005Giorgio Rosatti Abstract High order approximation methods based on radial basis functions are applied to the extension of semi-Lagrangian shallow water models to staggered Cartesian meshes with cut boundary cells. The accuracy and efficiency of the resulting semi-Lagrangian method is demonstrated by test cases simulating open channel flow. The derivative reconstruction provided by radial basis function interpolators is also employed successfully in the discretization of sediment transport models for mobile bed river flow. Copyright © 2005 John Wiley & Sons, Ltd. [source] k,l based hybrid LES/RANS approach and its application to heat transfer simulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2004Bowen Zhong Abstract To improve the compatibility of a k,l based hybrid LES/RANS approach, a controllable transitional zone is introduced to bridge the RANS and LES zones. This allows blending of the very different modelled turbulence length scales in these regions. To obtain a smooth variation of the length scales and transitional zone parameters different weighting functions are proposed. Results show the ,RANS' region has significant coherent unsteadiness. For Unsteady RANS (URANS) theoretical correctness, a favourable spectral gap between the modelled and resolved scales is required. The use of unsteadiness damping and time step filtering to ensure this is explored. Approaches are tested for a plane channel flow and the flow over a matrix of surface mounted cubes. The capability of the new hybrid LES/RANS method in improving heat transfer prediction in a conjugate heat transfer problem is examined. Numerical tests show that, compared to the RANS simulation, the proposed hybrid LES/RANS scheme performs well for the flow with large scale unsteadiness. It is also effective for improving the prediction of heat transfer. Copyright © 2004 John Wiley & Sons, Ltd. [source] Large eddy simulation of turbulent concentric annular channel flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2004Nan-Sheng Liu Abstract Fully developed turbulent concentric annular channel flow has been investigated numerically by use of large eddy simulation (LES) technique coupled with a localized one-equation dynamic subgrid-scale (SGS) model. The objective of this study is to deal with the behaviour of turbulent flow near the inner and outer walls of the concentric annular channel and to examine the effectiveness of LES technique for predicting the turbulent flow influenced by the transverse curvature effect. The computations are performed for the Reynolds number Re,=180, 395 and 640, based on an averaged friction velocity and the annular channel width with the inner and outer cylinder radius being Ri=1 and Ro=2. To validate the present approach, calculated results for turbulent pipe flow and concentric annular channel flow are compared with available experimental data and direct numerical simulation results, which confirms that the present approach can be used to study turbulent concentric annular channel flow satisfactorily. To elucidate turbulence characteristics in the concentric annular channel, some typical quantities, including the resolved velocity, turbulence intensity, turbulent eddy viscosity, SGS kinetic energy, SGS dissipation rate, Reynolds stress budgets, and turbulence structures based on the velocity fluctuations, are analysed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Energy dynamics in a turbulent channel flow using the Karhunen-Loéve approachINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2002G. A. Webber Abstract The dynamical equations for the energy in a turbulent channel flow have been developed by using the Karhunen-Loéve modes to represent the velocity field. The energy balance equations show that all the energy in the flow originates from the applied pressure gradient acting on the mean flow. Energy redistribution occurs through triad interactions, which is basic to understanding the dynamics. Each triad interaction determines the rate of energy transport between source and sink modes via a catalyst mode. The importance of the proposed method stems from the fact that it can be used to determine both the rate of energy transport between modes as well as the direction of energy flow. The effectiveness of the method in determining the mechanisms by which the turbulence sustains itself is demonstrated by performing a detailed analysis of triad interactions occurring during a turbulent burst in a minimal channel flow. The impact on flow modification is discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Analysis of the near-wall behaviour of some self-adaptive subgrid-scale models in finite-differenced simulations of channel flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2002P. Sagaut Abstract Self-adaptive subgrid-scale models are proposed and assessed. They are based on the use of the Germano,Lilly dynamic procedure and the use of a selection function. These models, which do not incorporate any information related to the location of the solid walls, are well suited for the simulation of turbulent flows in complex geometries. Their reliability, when used together with a second-order non-dissipative numerical method, is assessed on the plane channel configuration for two values of the Reynolds number (Re, = 180 and 395) for two grid resolutions. The selection function approach for deriving self-adaptive subgrid models is found to yield results very similar to those obtained using a dynamic model, without requiring any numerical stabilization procedure. The use of the selection function is shown to be the only one which is able to capture the backscatter process in the buffer layer, while producing a strictly positive subgrid viscosity. This is demonstrated to be linked to the capability of the selection function to permit a decorrelation between the mean strain and the fluctuations of the subgrid stresses. That point is illustrated thanks to the introduction of a new decomposition of the fluctuating strain subgrid dissipation. Copyright © 2002 John Wiley & Sons, Ltd. [source] Comparison of c-space and p-space particle tracing schemes on high-performance computers: accuracy and performanceINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2002F. Schäfer Abstract The present paper presents a comparison of four different particle tracing schemes which were integrated into a parallel multiblock flow simulation program within the frame of a co-visualization approach. One p-space and three different c-space particle tracing schemes are described in detail. With respect to application on high-performance computers, parallelization and vectorization of the particle tracing schemes are discussed. The accuracy and the performance of the particle tracing schemes are analyzed extensively on the basis of several test cases. The accuracy with respect to an analytically prescribed and a numerically calculated velocity field is investigated, the latter in order to take the contribution of the flow solver's error to the overall error of the particle traces into account. Performance measurements on both scalar and vector computers are discussed. With respect to practical CFD applications and the required performance especially on vector computers, a newly developed, improved c-space scheme is shown to be comparable to or better than the investigated p-space scheme. According to accuracy the new c-space scheme is considerably more advantageous than traditional c-space methods. Finally, an application to a direct numerical simulation of a turbulent channel flow is presented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Large eddy simulation of turbulent flows by a least-squares finite element methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2001Xu Ding Abstract The least-squares finite element method (LSFEM) based on first-order formulations of governing equations has been used successfully for incompressible and compressible flows and transport processes. It has not been applied to turbulent flows. In this work, large eddy simulation (LES) with dynamic subgrid-scale models is used to simulate turbulent flows. The LSFEM is implemented to solve the filtered LES equations for turbulent flows and transport processes. Numerical experiments have been carried out for three types of turbulent flows, turbulent channel flow, transitional recirculating flow, and thermal convective turbulent flow. Numerical results are compared with experimental data or direct numerical simulation results. Copyright © 2001 John Wiley & Sons, Ltd. [source] Interaction of metamorphism, deformation and exhumation in large convergent orogensJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2002R. A. Jamieson Abstract Coupled thermal-mechanical models are used to investigate interactions between metamorphism, deformation and exhumation in large convergent orogens, and the implications of coupling and feedback between these processes for observed structural and metamorphic styles. The models involve subduction of suborogenic mantle lithosphere, large amounts of convergence (, 450 km) at 1 cm yr,1, and a slope-dependent erosion rate. The model crust is layered with respect to thermal and rheological properties , the upper crust (0,20 km) follows a wet quartzite flow law, with heat production of 2.0 ,W m,3, and the lower crust (20,35 km) follows a modified dry diabase flow law, with heat production of 0.75 ,W m,3. After 45 Myr, the model orogens develop crustal thicknesses of the order of 60 km, with lower crustal temperatures in excess of 700 °C. In some models, an additional increment of weakening is introduced so that the effective viscosity decreases to 1019 Pa.s at 700 °C in the upper crust and 900 °C in the lower crust. In these models, a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where T,600 °C. The channel flow zone is characterised by a reversal in velocity direction on the pro-side of the system, and is driven by a depth-dependent pressure gradient that is facilitated by the development of a temperature-dependent low viscosity horizon in the mid-crust. Different exhumation styles produce contrasting effects on models with channel flow zones. Post-convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust-related exhumation on the flanks. Velocities in the pro-side channel flow zone are enhanced but the channel itself is not exhumed. In contrast, exhumation resulting from erosion that is focused on the pro-side flank of the plateau leads to ,ductile extrusion' of the channel flow zone. The exhumed channel displays apparent normal-sense offset at its upper boundary, reverse-sense offset at its lower boundary, and an ,inverted' metamorphic sequence across the zone. The different styles of exhumation produce contrasting peak grade profiles across the model surfaces. However, P,T,t paths in both cases are loops where Pmax precedes Tmax, typical of regional metamorphism; individual paths are not diagnostic of either the thickening or the exhumation mechanism. Possible natural examples of the channel flow zones produced in these models include the Main Central Thrust zone of the Himalayas and the Muskoka domain of the western Grenville orogen. [source] Rainfall-Runoff Model for Typhoons Making Landfall in Taiwan,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2007Ray-Shyan Wu Abstract:, In this study, we examine a physical raster-based distributed-parameter flood simulation model combining one-dimensional (1D) channel flow and two-dimensional (2D) overland flow. Continuity equations based on the water budget concept and momentum equations based on Manning's formula are included. The Shihmen reservoir watershed, situated in northern Taiwan, is selected as the study site, and data regarding the passage of Typhoons Xangsane [2000] and Nari [2001] are utilized to test the model. Comparative analysis shows that the description of the riverbed obtained by the gradient method is superior to that obtained by the GIS approach. This study suggests the Thiessen polygon method to interpolate spatial precipitation. The best calibrations are obtained at a spatial resolution of 160 m × 160 m, with a simulated time step of less than 5 s. The case study indicates that the proposed model has a good potential for inflow description, but does not accurately simulate the inflow amount. The proposed model is a flash reacting event-based watershed model. To improve simulation accuracy, a good infiltration model and soil moisture model are needed, and their formulation could be our next task. [source] | ||||||||||||||||