Three-dimensional numerical model for simulation of sediment movements in water intakes

摘要

A numerical model for simulating sediment flow in a general three-dimensional geometry is described. The geometry can for example be a part of a river or an intake reservoir. The theoretical basis for the model is a combination of computational fluid dynamics with classic hydraulics and sediment transport theory. The model includes calculations of trap efficiency and deposition/erosion patterns. The model consists of several sub-programs, which include initialization and generation of a non-orthogonal three-dimensional grid which is fitted to the bed of the geometry. The sediment movement is calculated in other routines which solve the convection-diffusion equation for the sediments. Graphics routines are also included. To simulate the sediment concentration in the geometry it was necessary to know the water velocities in all three directions and the turbulent eddy viscosity. This was accomplished by using a numerical model called Spider to solve the Navier-Stokes equations with the k-(epsilon) turbulence model. Spider is a general flow model, and in adapting it to a river environment it was necessary to incorporate specific boundary conditions. This included symmetry conditions for the free surface, procedures for simulating a rough bed and estimation of parameters for inflowing variables. Spider was also modified so that it was possible to block out a region of the geometry. This modification made it possible to simulate flow around a bridge pier or a divide wall. The model was tested on various data sets. One was obtained from a laboratory experiment where sand was inserted into a flume and deposition was recorded. For more complex flows, erosion around a cylinder was simulated. 60 refs., 92 figs., 2 tabs.