NUMERICAL SIMULATION OF EROSION AND TRANSPORT OF FINE SEDIMENTS BY LARGE EDDY SIMULATION

In general Reynolds-averaged simulation (RANS) is used in the traditional numerical simulation of water flow and sediment transport.Large eddy simulation (LES) can reflect flow structures more accurately and give more details of water flow compared with RANS.The development of computing technology makes it possible to study the rules of water flow and sediment transport by an LES model.In this paper, we tried to introduce boundary conditions for suspended sediment transport for the LES model under the net-erosion condition.Water flow and sediment transport in a cyclic case and a one-way flow case were calculated via the LES model with a dynamic sub-grid stresses module and a suspended sediment calculation module in the paper.Direct numerical simulation (DNS) results were used to calibrate the LES model and the results from LES showed good agreements with the DNS results.The distribution characteristics of sediment concentration, turbulence intensity and turbulent fluxes of sediment were explored in the paper.Under the neterosion condition, the equilibrium sediment concentration profile was coincident with the line of the Rouse equation.It showed that the turbulence intensity and turbulent fluxes of sediment had peak values near the bottom and then decreased rapidly along the vertical direction.The turbulent viscosity and diffusion coefficients were calculated and their peak values were or near the mid-depth of water.The turbulent Schmidt number was not constant along the vertical direction, and it was larger near the free surface and the bottom while it was smaller near the mid-depth of water flow.