NUMERICAL STUDY OF FLOW AND TURBULENCE THROUGH SUBMERGED VEGETATION

In this paper, we perform LES (large eddy simulation) for open channel flows through submerged matrix cylinders which are regarded as rigid vegetation. The computational model solves the filtered Navier-stokes equations on a Cartesian grid with local refinement and employs the ghost-cell immersed boundary method to deal with solid boundary. The cylinders are explicitly treated by computational grids. The model is validated through comparison with experimental data of the streamwise velocity profile. The effects of submergence ratio (water depth to vegetation height) on flow and turbulence structure are investigated. The coherent structures are produced above and behind the cylinders and those intensities amplified with decreasing submergence ratio. The large scale vortices, which are a main mechanism of momentum exchange between the vegetation layer and the out of vegetation, are generated above the vegetation and these penetration depths decrease with an increases in the submergence ratio. It is demonstrated that LES can capture large scale vortices originating at the top of vegetation and account for detailed instantaneous flow field through submerged vegetation.