Continuum modeling of flow and size-segregation in dense granular materials*

Dense granular systems that consist of particles of disparate size segregate based on size during flow, resulting in complex, coupled segregation and flow fields. In this talk, we study size-segregation phenomenology using discrete-element method (DEM) simulations of dense, bidisperse particles and propose a continuum model for coupled size-segregation and flow in dense, bidisperse granular systems. In our DEM simulations, we consider four flow geometries: (1) gravity-driven flow down a long vertical chute, (2) annular shear flow, (3) gravity-driven flow down a rough, inclined surface, and (4) planar shear flow in the presence of gravity - all while varying system parameters, such as the flow rate, system size, fraction of large/small grains, and grain-size ratio. Selected DEM simulation data inform continuum constitutive equations for the relative flux of large and small particles. The segregation model accounts for two driving forces - shear-strain-rate-gradients and pressure-gradients. When coupled with the nonlocal granular fluidity model - a nonlocal continuum model for dense granular flow - we show that both flow fields and segregation dynamics may be simultaneously captured using the coupled, continuum model.