Numerical Analysis at the Particulate Scale of Sand Erosion Under Impinging Jet

Abstract

The impinging jet test is widely used in laboratory and in situ to determine critical shear stress and erodibility rate of soils. However, quantification of the forces under this test at the soil particulate level is complex and results in varying interpretation of measured data. The computational fluid dynamics (CFD) has shown effectiveness to study the jet flow features and its effects on erosion. But it cannot explicitly account for the interaction forces between the fluid and soil particles during the dynamic erosion process. This study employs a methodology of the coupled CFD and discrete element method (DEM) to account for such interaction forces directly to study the sand erosion mechanisms under an impinging jet. The interaction forces, including the Di Felice drag force, pressure gradient force, viscous force, and buoyant force, between the fluid and sand particles were incorporated and analyzed during the sand erosion process. A total of nine cases with varying jet Reynolds numbers and ratios of jet height to nozzle diameter (H/D) were simulated. The results show that the coupled CFD and DEM analysis can capture the sand erosion features and scour patterns well, which are dependent on the ratios of H/D and jet Reynolds numbers. By examining the evolution of the maximum fluid-particle interaction forces, different erosion stages, including scour onset, scour developing, and scour stabilization, are identified. Finally, the distributions of the fluid-particle interaction forces along the surface of the sand bed provide a better understanding of the formations of different shapes of scour hole and sand erosion mechanisms at the particulate scale.