Velocity fluctuation and self diffusion character in a dense granular sheared flow studied by discrete element method

Abstract

The distribution of average velocities, fluctuation of velocities, regional definition, and granular self-diffusion characters in dense granular flows between sheared parallel plates are discussed. In order to study the above problems, we use computer-established discrete element model with an average solid fraction of 0.80. Theoretical results show that the average velocities decrease with increasing height, and are larger for the case of lower plate with greater velocity; the average velocities in y direction are close to 0 because there is no bulk motion in y direction. Flows of the lower plate with a greater velocity induce relatively greater fluctuation of velocities in the x and y directions, the fluctuation of velocities increases with the height and is larger in the area close to the upper plate. The flows consist of a “solid-like” area in the lower test region, but a “fluid-like” region in the upper, and an “oscillating” region in the middle of the channel. By tracking the movements of granules continually, variations of the mean-square self-diffusion relative displacements with square time are plotted, and the mean self-diffusion relative coefficients are determined. As the fluctuation and self-diffusion analysis directly reflect the macroscopic properties of granules and provide bases and references for researching the flow mechanisms of “dense granular sheared flows”.