Dynamic transition in conveyor belt driven granular flow

We consider the flow of disks of diameter d driven by a conveyor belt of dynamic friction coefficient mu through an aperture on a flat barrier. The flow rate presents two distinct regimes. At low belt velocities v the flow rate is proportional to v and to the aperture width A. However, beyond a critical velocity, the flow rate becomes independent of v and proportional to (A - kd)(3/2) in correspondence with a two-dimensional Beverloo scaling. In this high-velocity regime we also show that the flow rate is proportional to mu(1/2). We discuss that these contrasting behaviors arise from the competition between two characteristic time scales: the typical time a disk takes to stop on the belt after detaching from the granular pack and the time it takes to reach the aperture. (C) 2014 Elsevier B.V. All rights reserved.