The effect of sidewall friction on dense granular flows

We present novel results on flow properties using molecular dynamics simulation as well as γγ-densitometry experiments. We show that fundamentally different types of granular flow can be observed in one unique system. Using both frictional and frictionless confining walls, we show that the differences existing between these regimes originate in the frictional properties of the walls. The salient features of each regime are described in detail. In particular, the packing fraction and streamwise velocity profiles are shown to hinge on the frictional properties of the confining walls. Finally, we propose a dimensionless number, independent of the grain size, which helps to delineate the different regimes.