Title: Modeling Shear-rate-gradient-driven Size-segregation in Dense, Bidisperse Granular Flows Down a Vertical Chute

Author (Talk): Daren Liu, Brown University

Abstract:

Dense granular systems, consisting of particles of disparate sizes, segregate based on size during flow, resulting in complex, coupled segregation and flow patterns. There are two driving mechanisms of size-segregation during flow: (i) gravity and (ii) shear-strain-rate gradients. The mechanism of shear-rate-gradient-driven segregation has received less attention and, as such, is not as well understood. In this talk, we study this segregation mechanism in a flow configuration that eliminates gravity-driven segregation – gravity-driven flow down a long vertical chute with rough parallel walls. We perform two-dimensional discrete element method (DEM) simulations of vertical chute flow of dense, bidisperse granular systems. Specifically, we systematically study the effect of flow rate, chute width, fraction of large/small grains, and grain-size ratio on the segregation dynamics. This informs the development of continuum constitutive equations for both the shear-rate-gradient-driven size-segregation flux as well as the diffusion flux. When coupled with the nonlocal granular fluidity model – a recently-proposed, nonlocal continuum model for dense granular flow – we show that both the flow field and segregation dynamics may be simultaneously captured using this closed, coupled system.