Computation of compound channel flow using an implicit time scheme and a hybrid turbulence model

摘要

We apply a three-dimensional computational fluid dynamics code based on a finite volume discretisation to a compound channel. The numerical method employed makes use of a second order implicit time scheme in order to substantially increase the stability of the simulation compared to explicit time schemes and to reduce the amount of inner iterations as necessary in predictor-corrector methods. Furthermore, we apply a multi-grid technology with a hybrid turbulence model, which allows steady state calculations on the coarser grids employing the standard k-e turbulence closure of the mean quantities and providing the initial conditions for the time dependent large eddy simulations on the finest grid. The LES method provides an efficient numerical tool in order to clarify three-dimensional (3-D) turbulent structures, secondary currents and wall shear stress distributions in open channel flows with complex geometry, like compound channels. The calculations showed that with this method we are able to predict all flow features as present in compound channels, which are: (1) Primary flows and secondary currents in compound open-channel flows (Figure 1, below), (2) Turbulent structures of secondary currents, i.e., inclined upflows from a junction between main channel and floodplains, (3) interaction mechanism and coherent vortices between main channel and floodplains.