Shear-induced diffusion of rough and frictional particles in concentrated suspensions*

The shear-induced diffusivity of non-Brownian spheres in viscous, concentrated suspensions was calculated while accounting for particle roughness and friction.  The simulation balances lubrication interactions with contact forces which include a normal and tangential component controlled by the roughness and friction coefficient, respectively. The roughness and friction coefficient were varied independently to explore their effects on shear-induced diffusivities.  Confirming experiments, roughness reduces diffusivities for concentrated suspensions of frictionless and low-friction particles.  However, friction increases the diffusivity and roughened particles have a larger diffusivity at high friction coefficients. The increase of the diffusivity with friction is associated with a significant broadening of the variance of the rotational velocities, while at low friction, the increased roughness promotes organization of the concentrated particles into layered structures aligned in the flow direction. This organization results in a corresponding decrease in the diffusivity for rougher particles. Comparisons of the simulation results with previously published experimental measurements indicate that friction improves the alignment of the results with experiments.