Fluctuations and self-diffusion of sheared granular material flows

Experiments were performed in a shear cell device with adjustable lower wal l velocity. Glass spheres with a mean diameter of 3 mm were used as granula r materials. Image processing technology and a particle tracking method wer e employed to measure the average and fluctuation velocities in the streamw ise and the transverse directions. Because of 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 v elocity fluctuations were anisotropic and were greater in the streamwise di rection. By tracking the movements of particles continually, the variation in the mean-square diffusive displacements with time was plotted and the se lf-diffusion coefficient was determined. The self-diffusion coefficients in the streamwise direction were much higher than those in the transverse dir ection. The dependence of the diffusion coefficients on the velocity fluctu ations and the shear rate were discussed. (C) 1999 The Society of Rheology. [S0148-6055(99)00504-0].