STUDIES OF GRANULAR SHEAR FLOWS - WALL SLIP VELOCITIES, LAYERING AND SELF-DIFFUSION

The present paper is divided into two main parts. The first part exami nes some features of molecular dynamics type simulations of granular s hear flows of smooth, inelastic, spherical particles between two relat ively closely spaced rough walls. Profiles of granular temperature, so lids fraction and means velocity, and values of the wall slip velociti es are determined for various mean solids concentrations and particle coefficients of restitution. 'Layering' of the particles is observed a t high concentrations. The wall slip velocity is found to decrease as the coefficient of restitution increases. In these computations the wa ll particle spacing corresponded to the overall mean solids fraction. The wall slip velocities determined by the molecular dynamics simulati ons are compared with the kinetic theory predictions of Richman (1988, Acta Mech. 75, 227-240) and those of Hanes et al. (1988, J. Appl. Mec h., 969-974). The second part of the paper considers the problem of se lf-diffusion in 'unbounded' granular flows. Self-diffusion coefficient s are determined by an analysis based upon kinetic theory and by numer ical simulations. The kinetic theory formula reduces to the classical Chapman-Enskog result in the limit of perfectly elastic particles. The self-diffusion coefficients obtained from the simulations are somewha t higher than the kinetic theory at high concentrations, but they are in agreement there with the experimental measurements of Bridgwater et al. (1985, Inst. Chem Eng. Symp. Ser. 69, 171-191).