Clustering and phase separation in dense shear granular flow

Abstract

We investigate various regimes of steady dense Couette flow of inelastically colliding hard disks in the absence of gravity. The two governing parameters in this two-dimensional system are the inelasticity of particle collisions and the average density of particles. The simplest steady state is the uniform shear flow (USF), where the temperature and the density profiles are homogeneous over the system and the velocity of the flow changes linearly between the two moving walls. The USF becomes unstable when the inelasticity of particle collisions exceeds a certain threshold, which depends on the average density of particles. Then the USF gives a way to a "plug flow" regime, where a solid-like cluster coexists with one or two fluid layers. These regimes are investigated using equations of granular hydrodynamics with constitutive relations that interpolate between low and high densities. The results are tested in event-driven molecular dynamics (MD) simulations, and a good agreement is observed.