Direct Simulations of Incipient Erosion of Solid Particle Beds due to Shear Flow

Direct numerical simulations of the shear flow over assemblies of uniformly sized solid spheres have been performed using the lattice-Boltzmann method. First non-moving spheres are considered; the random sphere assemblies comprise monolayers, double layers, and triple layers. Then situations with moving spheres were simulated, directly resolving granular bed erosion. The Reynolds numbers based on the sphere radius and the overall shear rates were smaller than one. For the fixed spheres the results were interpreted in terms of the drag force (the force in streamwise direction) and lift force (the force in wall-normal direction) experienced by the spheres as a function of the denseness of the bed and the depth of the spheres in the bed. For the moving spheres the onset of erosion as a function of the Shields number was studied, with results that were in accordance with experimental data.