Two- and three-dimensional confined granular chute flows: experimental and numericalresults

Abstract

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