Wave Propagation in Rapid Granular Flows

Abstract

One-dimensional wave propagation in granular flow has been investigated using a three-dimensional discrete element model (DEM). Cohesionless, dry, smooth, elastic, hard spheres are randomly distributed in a cylinder-piston system with initial granular temperature and solid fraction. Upon a sudden motion of the piston, subsequent wave propagation in granular materials between two ends of the cylinder is numerically simulated. The simulation results of wave speed normalized by the square root of granular temperature are found to be well correlated as a function of solid fraction. Comparison with several analytical works in the literature shows that the simulated wave speed is in good agreement with the wave speed calculated at the isentropic condition but is higher than that at the constant granular temperature condition. Finally the simulation result is employed to describe shock waves observed in the literature. It has been found that, when particles rapidly flow through an orifice, a shock is formed very near the location of the maximum granular temperature. It has also been observed that a shock can be formed even when the flow does not appear to be choked due to its low density upstream of the orifice.