SHALLOW-WATER TURBULENCE MODELING AND HORIZONTAL LARGE-EDDY COMPUTATION OF RIVER FLOW

By introducing the concept of ''SDS (subdepth scale) turbulence'' to m odel three-dimensional (3D) turbulence with length scales less than th e water depth and treating it explicitly with a proper separate modeli ng, an SDS-2DH model has been developed to simulate the evolution of h orizontal large-scale eddies in shallow water. Applying this model to river flows with transverse shear due to vegetation drag, the horizont al large-scale (HLS) eddies were found to dominate horizontal momentum mixing. The bottom friction and vegetation drag, acting as sinks of v orticity, play the key roles in the development of the horizontal larg e-scale eddies and in Reynolds stress generation. The SDS-2DH model ca n directly describe effects of flow geometry, such as vegetation layer width, on the large-scale eddy development and, hence, predicts turbu lence-mixing better than the k-epsilon model.