A coarse graining CFD–DEM simulation on contact erosion of layered cohesionless soils

A coarse graining computational fluid dynamics–discrete element method (DEM) model is developed to analyze the contact erosion of cohesionless soils at the coarse/fine soil interface. Two benchmark cases are provided to verify the model implementation, including the collision of two groups of particles and collapse of a soil column in water. It is demonstrated the CG approach significantly reduces the computational cost with sufficiently good accuracy. Two typical CG approaches, i.e., the relative overlap scaling (ROS) and absolute overlap scaling approaches, are compared and show similar model performance. While the DEM time step of ROS approach is scaled up by the scaling factor, it is recommended in this study for the better computational performance. The verified model is used to simulate the laboratory contact erosion experiment under various flow conditions. The critical discharge rate calculated from the numerical model is 357 mL/s, which achieves a high consistency with the experimental value of 311 mL/s. Further study shows the scaling factor influences the critical discharge rate, as large parcels introduce boundary effects especially for coarse soils. It is also shown the packing state of coarse soils is a determinant in the erosion initiation, as the void fraction distribution is the key for particle and fluid transports, especially near the contact surface.