Lift Force on an Intruder in Granular Shear Flows

In order to understand particle-level forces in flowing granular materials, discrete element method (DEM) simulations are conducted to investigate the lift force on a single spherical intruder in uniform shear flows of smaller spheres in the absence of gravity. In the simulations, a constant slip velocity is imposed on the intruder in the streamwise direction, while the intruder’s vertical motion is constrained. The net vertical force on the intruder due to contacts with bed particles is measured as the lift force. Our results show that with increased slip velocity, the vertical lift force rises to a peak before decreasing and eventually changing sign. Analysis of the packing fraction, pressure field, and vertical contact force on the intruder provide insights into the origin of the non-monotonic dependence of the lift force on the slip velocity as well as the influence of confining pressure, and intruder-to-bed-particle-diameter ratio. Funded by NSF grant CBET-1929265.