摘要:

AbstractIn this paper Roe's flux‐difference splitting is applied for the solution of Reynolds‐averaged Navier‐Stokes equations. Turbulence is modelled using a low‐Reynolds number form of thek‐ϵ tubulence model. The coupling between the turbulence kinetic energy equation and the inviscid part of the flow equations is taken into account. The equations are solved with a diagonally dominant alternating direction implicit (DDADI) factorized implicit time integration method. A multigrid algorithm is used to accelerate the convergence. To improve the stability some modifications are needed in comparison with the application of an algebraic turbulence model. The developed method is applied to three different test cases. These cases show the efficiency of the algorithm, but the results are only marginally better than those obtained with algebr

ISSN:0271-2091    

DOI:10.1002/fld.1650211102

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn order to obtain stable and accurate numerical solutions for the convection‐dominated steady transport equations, we propose a criterion for constructing numerical schemes for the convection term that the roots of the characteristic equation of the resulting difference equation have poles.By imposing this criterion on the difference coefficients of the convection term, we construct two numerical schemes for the convection‐dominated equations. One is based on polynomial differencing and the other on locally exact differencing.The former scheme coincides with the QUICK scheme when the mesh Reynolds number (Rm) is\documentclass{article}\pagestyle{empty}\begin{document}$\mathop \[{\textstyle{{\rm 8} \over {\rm 3}}}\] $\end{document}, which is the critical value for its stability, while it approaches the second‐order upwind scheme asRmgoes to infinity. Hence the former scheme interpolates a stable scheme between the QUICK scheme atRm=\documentclass{article}\pagestyle{empty}\begin{document}$\mathop \[{\textstyle{{\rm 8} \over {\rm 3}}}\] $\end{document}and the second‐order upwind scheme atRm= ∞. Numerical solutions with the present new schemes for the one‐dimensional, linear, steady convection‐diffusion equations showed

ISSN:0271-2091    

DOI:10.1002/fld.1650211103

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe purpose of this paper is to investigate the effect of a non‐uniform mesh in two dimensions (2D). A change in mesh size will, in general, result in spurious refraction (and reflection) which is entirely numerical (rather than physical) in origin. To facilitate the analysis, the mesh geometry has been highly simplified in that only a single change in mesh size is considered. The analysis is based on a finite element wave model.The domain consists of two conterminous regions discernible only by their different nodal spacings in thex‐direction. The interface between the two regions is internal to the mesh and is a straight line. The model is based upon the Crank‐Nicolson linear finite element scheme applied to the second order wave equation. The results of the analysis are confirmed by numerical experiments. It is shown that under particular numerical conditions total internal reflection may occur and when this is the case, the transmitted wave is evanescent. An analysis of the energy flux associated with the incident, reflected and trasmitted waves shows that energy is conserved across the interface between the two re

ISSN:0271-2091    

DOI:10.1002/fld.1650211104

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA segregated algorithm for the solution of laminar incompressible, two‐ and three‐dimensional flow problems is presented. This algorithm employs the successive solution of the momentum and continuity equations by means of a decoupled implicit solution method. The inversion of the coefficient matrix which is common for all momentum equations is carried out through an approximate factorization in upper and lower triangular matrices. The divergence‐free velocity constraint is satisfied by formulating and solving a pressure correction equation. For the latter a combined application of a preconditioning technique and a Krylov subspace method is employed and proved more effecient than the approximate factorization method. The method exhibits a monotonic convergence, it is not costly in CPU time per iteration and provides accurate solutions which are independent of the underrelaxation parameter used in the momentum equations. Results are presented in two‐ and three‐dimensional flow

ISSN:0271-2091    

DOI:10.1002/fld.1650211105

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA new two‐layer, two‐dimensional mathematical model employing a finite difference method based on numerically generated boundary‐fitted orthogonal co‐ordinates and a grid ‘block’ technique for unsteady boundary problems is developed which can be used to simulate flows with density stratification in a natural water‐body with complicated topography. In the model the turbulent exchange across the interface is treated empirically and a time‐splitting finite difference method with two fractional steps is employed to solve the governing equations. The model is calibrated and verified by comparing the computational results with data measured in Tolo Harbour, Hong Kong. The simulation results mimie the field measurements very closely. The computation shows that the model reproduces the two‐layer, two‐dimensional tidal flow with density stratification in Tolo Harbour very well. The computed velocity hodographs show that the tidal circulations at various positions in each layer have different patterns and that the features of the patterns are independent of the tidal type except for their scales. The computed Lagrangian pathlines show that the tidal excursion is dependent on the tidal type, especially in the inner har

ISSN:0271-2091    

DOI:10.1002/fld.1650211106

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn northern countries, subfreezing temperatures during the winter season result in the formation of ice covers on most rivers. Towards the end of the winter season, during the spring break‐up period, stationary ice covers become weak in strength and break up. The resulting broken ice pieces or ice floes are significantly larger in thickness and have a rougher undersurface relative to sheet ice and impose higher hydraulic resistance. The downstream movement of the ice floes may be arrested under conditions such as an intact ice cover, bridge piers or channel constrictions, among others, thereby initiating a break‐up ice jam. These ice jams most often have been observed to cause very high water stages. Detrimental effects caused by these high water levels encompass those of operational and design‐related problems such as the flooding of communities due to ice‐jam‐induced backwater, flood risk assessments, altering of the open water flow regime, bed scour and flooding of bridges.The ability to predict the influence of an ice jam on the main flow is of considerable importance in river engineering and can be viewed upon by its effects on the variation in the water surface levels. All other information is dependent on the foregoing. The ice jam influence on the main flow can be regarded with respect to local and global standpoints.The primary objective of this study is to formulate the influence of the ice jam on the main channel flow. The formulation is then coupled with a two‐dimensional numerical model for the simulation of the water flow regime. The data from different laboratory experiments on ice jams are reproduced numerically. Various simulations are then carried out to compute the water surface levels and velocities in channels under ice jam conditions. The numerical results are then compared with the laboratory data.Results show that the mathematical formulation developed to predict the water surface levels and velocities along the ice jam length as well as upstream and downstream of its leading and trailing edges respectively gives satisfactory

ISSN:0271-2091    

DOI:10.1002/fld.1650211107

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650211108

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650211101

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY