Shallow-Water Turbulence Modeling and Horizontal Large-Eddy Computation of River Flow

By introducing the concept of “SDS (subdepth scale) turbulence” to model three-dimensional (3D) turbulence with length scales less than the water depth and treating it explicitly with a proper separate modeling, an SDS-2DH model has been developed to simulate the evolution of horizontal large-scale eddies in shallow water. Applying this model to river flows with transverse shear due to vegetation drag, the horizontal large-scale (HLS) eddies were found to dominate horizontal momentum mixing. The bottom friction and vegetation drag, acting as sinks of vorticity, play the key roles in the development of the horizontal large-scale eddies and in Reynolds stress generation. The SDS-2DH model can directly describe effects of flow geometry, such as vegetation layer width, on the large-scale eddy development and, hence, predicts turbulence-mixing better than the k-e model.