Submerged-flow dynamics of granular media in a rotating drum

The dynamics of granular flows are often influenced by viscous interstitial fluids such as water. The majority of granular flow experiments address dry granular flow. However, we now extend such studies to include fluids having viscosities from 1 to 4 mPa s, allowing a direct comparison to the dry case. Using direct grain imaging and particle image velocimetry techniques, we show that varying fluid properties such as density and viscosity changes the dynamics of the flowing layer. At a fixed rotation rate, the dynamic tilt angle and the flow depth increases with fluid viscosity; the most dramatic incremental change occurring between the dry case and the liquid case with 1 mPa s fluid. To better understand the inter-grain interactions governing this behavior, we have performed DEM simulations of the rotatingdrum system, using an inter-grain squeeze force to approximate the fluid effects. While dry flow profiles and trends in the macro-flow behavior as a function of viscosity are reproduced well by these simulations, the magnitude of the incremental fluid effects are somewhat smaller than observed experimentally. The discrepancy may be due to neglected fluid-drag effects and/or improper scaling of grain and drum size between experiments and the model.