Physics of Particle Entrainment under the Influence of an Impinging Jet

In the laboratory we used an idealized rotorwash flow—an axisymmetric jet impinges normally on a packed bed of cohesionless particles—and measured the spatially varying flow field and entrainment flux under an axisymmetric jet over a range of jet exit velocities and bed materials. We found that the erosion of the bed is driven by turbulent surface shear stress, quantified by the turbulent kinetic energy of the flow. This observation differs from uniform flow parallel to the bed wherein the flux of particles being removed from the bed depends linearly on the average surface shear stress of the fluid imposed on the bed. We discuss the implications of these findings for applying a general model for capturing particle entrainment under impinging flows.