Granular dynamics of a slurry in a rotating drum.

We study the effects of interstitial fluid viscosity on the rates of dynamical processes in a thin rotating drum half-filled with monodisperse glass beads. The rotating speed is fixed at the rolling regime such that a continuously flowing layer of beads persists at the free surface. While the characteristic speed of a bead in the flowing layer decreases with the fluid viscosity μ, the mixing rate of the beads is found to increase with μ. These findings are consistent to a simple model related to the thickness of the flowing layer. In addition, our results indicate a possible transition from the inertial limit regime to the viscous limit regime (reported previously by S. Courrech du Pont [Phys. Rev. Lett. 90, 044301 (2003)]) when the Stokes number is reduced.