Research On A 3D Numerical Flow And Suspended Sediment Model Based On FVM

The motion of tidal current and sediment in estuarine and coastal areas is characterized by 3D variation, which should be simulated by 3D mathematic model. Based on review of the available mathematical models of tidal flow and sediment transport for the estuarine and coastal region, a 3D numerical model for shallow water flow and suspended sediment transport is established based on the finite volume method and unstructured triangular grid, which is characterized by: (1) the mode-splitting solution technique is applied in the model, namely the inner mode accounting for the shear flow and the outer mode accounting for the gravity wave movement; (2) the k -εtwo-equation turbulence model, with more explicit physical meaning, is used to calculate the vertical eddy viscosity; (3) in the numerical method, in order to increase numerical stability, vertical variation of the variables is solved implicitly; (4) in order to fit the irregular boundary better in the natural flow, we adopted the unstructured triangular mesh for the horizontal plane; (5) in the vertical direction,σcoordinate system is adopted for simplification of bottom and surface boundary condition; (6) the governing equations are discretized by finite volume method, in which the Osher's scheme with superior properties is used to compute the horizontal flux through the interface of two adjacent finite volumes, thus the model has a good property of conservation for physical quantity, up-wind property, monotonic-reserving, high resolution in capturing discontinuity, and consistency between boundary procedure and internal scheme without additional numerical boundary conditions; (7) dry-wet grid method is used to simulate the moving boundary in the horizontal direction so as to make the model be adaptive to mild slope topography; (8) the suspended sediment transportation equation is solved by TVD(total variation diminishing) scheme and high order numerical eddy term is added into the scheme to make sure the model has the property of high resolution in capturing discontinuities with good numerical stability.In order to verify the model, a downstream reach of the Guide Hydrology station of the Yellow River was modeled by the numerical model. The calculated results of velocity and water surface elevation agree well with the measured data. The calculated results of discharge at different cross sections show good identity, indicating that the model is well in conservation of physical quantities. The calculated vertical profiles of the velocity and the turbulence energy are all reasonable and can be considered as the basis of the analysis for 3D river flow structure.By using the model, tide process in an ideal rectangle flume is simulated. The computational results indicate that the moving boundary in the horizontal direction is well simulated by the model and the simulated tide level and velocity field are all reasonably good.Finally, 3D suspended sediment diffusion is simulated in an ideal rectangle flume. The simulated results of suspended sediment concentration are compared with the result of theoretical formula based on diffusion theory.