Drag, lift, and buoyancy forces on a single large particle in dense granular flows

Large particles migrate upward in gravity-driven granular shear flows, which results in size segregation, a phenomenon of considerable practical importance. In this study, we show using extensive discrete element method (DEM) computations that this effect is not caused by a granular lift force or Archimedean buoyancy, rather it stems from a buoyancy force that exceeds the weight of the large particle, which is a result of patches of high-stress concentration on the surface of the large particle caused by strong flow-induced layering.