Two- and three-dimensional confined granular chute flows: experimental and numerical results

We present experimental and numerical results on 2D and 3D confined granular chute flows. We address the issue of the role of the lateral boundaries. In particular, we find that the presence of flat frictional lateral walls greatly alters the flow features as soon as the width of the flowing layer is of the order of the spacing between the walls or greater. First, steady and fully developed (SFD) flows are observed up to very large inclination angles where accelerated flows would have been expected. Second, at given inclination angle, there exists an upper bound on the flow rate for SFD flows to occur. When one approaches this critical flow rate, a static heap forms along the chute base, on which is the flowing layer. The heap is stabilized by the flow atop it and was named a sidewall-stabilized heap (SSH) since its angle is much greater than those usually exhibited by granular heaps. Both kinds of flow have been studied in 2D and 3D confined configurations. In particular, it is found that these flows exhibit either a Bagnold velocity profile or an exponential one. Moreover, we identify a dimensionless parameter, depending crucially on the sidewall friction, that is expected to drive the transition between these two regimes. We also point out the differences between purely 2D flows and 3D confined flows.