Effect of solid fraction on fluctuations and self-diffusion of sheared granular flows

Abstract

The influences of solid fraction on the fluctuations and self-diffusion of sheared granular flows were experimentally studied in a shear cell device. Employing the image processing technology and particle tracking method, the local displacements and velocities of particles were measured. From the measured velocities, the fluctuations, granular temperatures and shear rates could be determined. The self-diffusion coefficients were determined from the history of particles’ diffusive displacements. The periodic cell concept was used for long-time tracking purpose. Because of the gravitation force, the flows consist of both a solid-like region with higher and more uniform velocities in the lower test section and a fluid-like region in the upper part. The velocity fluctuations and self-diffusions were anisotropic with greatest components in the streamwise direction. The flow rheology was very sensitive to the mean solid fraction of the granular flow. The dependence of the diffusion coefficients on the velocity fluctuations and the shear rate were discussed.