Controlling Rheology via Boundary Conditions in Dense Granular Flows

In the field of granular rheology, an important horizon is the influence of the boundary conditions on granular flows. Understanding how changing the roughness of a boundary changes the resulting flow can lead to developing predictive model for wall slip, roughness may also be changing the propagation of nonlocal effects through the creation of additional fluctuations. We perform experiments in a quasi-2D annular shear cell under 5 different boundaries with controlled roughness. We characterize the properties of granular slip at the boundaries, and investigate which aspects of a dense granular flow can be controlled by the choice of boundary condition. We have observed that boundary roughness strongly controls both the flow profile v(r) and shear rate profile γ(r). We measure the shear and pressure stress fields by coarse-graining photoelastic measurements, and identify how the roughness of the boundary changes these fields. Finally, we investigate how the nonlocal rheology model, proposed by Kamrin and Koval, responds to various boundary conditions and how boundary roughness controls force chain fluctuations.