摘要:

AbstractThe fully elliptic Reynolds‐averaged Navier–Stokes equations have been used together with Lam and Bremhorst's low‐Reynolds‐number model, Chen and Patel's two‐layer model and a two‐point wall function method incorporated into the standardk‐ϵ model to predict channel flows and a backward‐facig step flow. These flows enable the evaluation of the performance of different near‐wall treatments in flows involving streamwise and normal pressure gradients, flows with separation and flows with non‐equilibrium turbulence characteristics. Direct numerical simulation (DNS) of a channel flow withRe=3200 further provides the detailed budgets of each modelling term of thekand ϵ‐transport equations. Comparison of model results with DNS data to evaluate the performance of each modelling term is also made in the present study. It is concluded that the low‐Reynolds‐number model has wider applicability and performs better than the two‐layer model and wall function approaches. Comparison with DNS data further shows that large discrepancies exist between the DNS budgets and the modelled production and destruction terms of the ϵ equation. However, for simple channel flow the discrepancies are similar in magnitude but opposite in sign, so they are cancelled by each other. This may explain why, even when employing such an inaccurately modelled ϵ‐equation, one can still predict satisfact

ISSN:0271-2091    

DOI:10.1002/fld.1650191002

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe control volume, finite difference method and thek‐ϵ tubulence model are employed in a numerical simulation of the turbulent fluid flow both outside and inside a blunt cylindrical sampler which houses a paper filter in its chamber. The presence of a paper filter, which has a very large resistance, results in a large pressure drop across the filter and this causes difficulties in making the SIMPLE or the SIMPLEC scheme converge. In order to improve the rate of convergence of the SIMPLE‐like algorithm when the resistance of the filter is very large, an average pressure correction formula is proposed. Based on global mass conservation, a line average pressure correction for the paper filter is derived using a modified Darcy law for a porous medium. A combination of this formula and the SIMPLE‐like algorithm can rapidly build up the pressure drop across the filter and hence dramatically improve the rate of convergence of the iterative scheme. Comparisons of the convergence histories and the numerical results for the fluid flow when using SIMPLE and SIMPLEC with the average pressure correction method show that the average pressure correction method for dealing with the paper filter significantly accelerates the rate of convergence of the iterative

ISSN:0271-2091    

DOI:10.1002/fld.1650191003

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe dynamic boundary conditions for vorticity, derived from the incompressible Navier‐Stokes equations, are examined from both theoretical and computational points of view. It is found that these conditions can be either local (Neumann type) or global (Dirichlet type), both containing coupling with the boundary pressure, which is the main difficulty in applying vorticity‐based methods. An integral formulation is presented to analyse the structure of vorticity and pressure solutions, especially the strength of the coupling. We find that for high‐Reynolds‐number flows the coupling is weak and, if necessary, can be effectively bypassed by simple iteration. In fact, even a fully decoupled approximation is well applicable for most Reynolds numbers of practical interest. The fractional step method turns out to be especially appropriate for implementing the decoupled approximation. Both integral and finite difference methods are tested for some simple cases with known exact solutions. In the integral approach smoothed heat kernels are used to increase the accuracy of numerical quadrature. For the more complicated problem of impulsively started flow over a circular cylinder atRe= 9500 the finite difference method is used. The results are compared against numerical solutions and fine experiments with good agreement. These numerical experiments confirm our thoeretical analysis and show the advantages of the dynamic condition in computing high‐Reynolds‐n

ISSN:0271-2091    

DOI:10.1002/fld.1650191004

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA numerical study of confined jets in a cylindrical duct is carried out to examine the performance of two recently proposed turbulence models: an RNG‐basedK‐ϵ model and a realizable Reynolds stress algebraic equation model. The former is of the same form as the standardK‐ϵ model but has different model coefficients. The latter uses an explicit quadratic stress‐strain relationship to model the turbulent stresses and is capable of ensuring the positivity of each turbulent normal stress. The flow considered involves recirculation with unfixed separation and reatachment points and severe adverse pressure gradients, thereby providing a valuable test of the predictive capability of the models for complex flows. Calculations are performed with a finite volume procedure. Numerical credibility of the solutions is ensured by using second‐order‐accurate differencing schemes and sufficiently fine grids. Calculations with the standardK‐ϵ model are also made for comparison. Detailed comparisons with experiments show that the realizable Reynolds stress algebraic equation model consistently works better than does the standardK‐ϵ model in capturing the essential flow features, while the RNG‐basedK‐ϵ model does not seem to give improvements over the standardK‐ϵ model under the

ISSN:0271-2091    

DOI:10.1002/fld.1650191005

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650191006

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650191007

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650191008

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY