A Detached Eddy Simulation Model for Free Surface Flows

Geophysical flows in oceanic shelves, estuaries, and rivers are often studied with the shallow water equations under either hydrostatic or hydrodynamic pressure assumptions. The Reynolds-Averaged Navier Stokes (RANS) equations are widely used for simulating the complex turbulent flows because of their high efficiency. The Directed Numerical Simulation (DNS) and Large Eddy Simulation (LES) are commomly unaffordable under the constraint of the present computer power. In practical applications, one kind of hybrid models, i.e. Detatched-Eddy Simulation (DES), is a good compromise because of the lower computational cost for simulating near-wall flows with RANS. In the paper, a DES model is proposed based on a fully hydrodynamic pressure model instead of hydrostatic model. The numerical scheme is based on the Finite Volume Method (FVM) on unstructured grids in the horizontal plane, and the σ coordinate in the vertical direction to fix the free surface and the uneven bottom. The in-house codes are paralleled using OpenMP. The proposed model is shown to be particularly effective in the prediction of small-scale vortical structures.