Granular Flows at High Shear Rates

Abstract

This chapter focuses on granular flows at high shear rates and describes some recent theoretical and experimental work on rapid granular flows. Rapid granular flows belong to one of the limiting types of dispersed two-phase flows of mixtures of particulate solids and fluids. Such flows are characterized by strong and direct interactions between individual particles. In contrast with the flows of dilute suspensions or fluidized beds, the fluid phase generally plays a minor role in the dynamics of granular flows. This is particularly so when the ratio of fluid to solid mass densities is very small, as in the case of a gaseous interstitial fluid. Granular flows occur in a large number of wide-ranging engineering and physical processes. One of the central problems in the theory of granular flows is the determination of the constitutive equations for the fluxes of mass, momentum, and energy. At somewhat higher concentrations, translation between layers is less likely and momentum transport occurs primarily by interparticle collisions as in Bagnold's grain-inertia regime. Because of the collisions, the particles acquire random fluctuating spins and translational fluctuating velocities, in addition to their mean translational velocities.