Development of Accurate Numerical Methods for Turbulent Open Channel Flows with Complex Geometries

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The present study is concerned with the development of numerical methods for flow calculation in River Engineering. Main achievements consist of refining a turbulence model, improving convection schemes, reformulation of basic equations on boundary-fitted coordinate systems and vectorization of computer codes for the reduction of computational time.A new algebraic stress turbulence model was proposed for turbulence-driven secondary flows. The turbulence model keeps the similar structure as the non-linear kappa - epsilon models, but has difference in variable model coefficients which enable the model independent of complex boundary geometries. Comparisons with the experimental data available for compound channel flows showed good agreement as for mean velocities and the Reynolds stresses. Models for the effect of free surface were summarized and the limiting behaviors of turbulence quantities near free surface were also discussed.Usage of boundary fitted coordinates produces new advecti … More on terms in basic equations which have non-conservative forms. This results in the sensitiveness of numerical results to the grid system employed. Combination of two coordinate systems, one for geometry, the other for velocity field was adopted to meet the problem. A regular grid system with a damping technique for pressure oscillation was used. Based on these ideas two computer codes were developed to validate the expected feature.Highly accurate and bounded scheme was proposed for convection process. A limiter was introduced to control the convection flux at the control volume face to suppress the physically meaningless oscillations.The limiter coupled with the QUICKEST scheme showed superior performance to those used so far for both linear and non-linear flow cases.Performance of many iterative solvers for linear systems were compared in terms of computational time to find out that Modified Strongly Implicit Procedure and Conjugate Gradient-like solvers are suitable for flow calculations. Techniques to vectorize many iterative solvers were devised and tested on supercomputers. Less