Average outpouring velocity and flow rate of grains discharged from a tilted quasi-2D silo

The flow of granular materials through constricted openings is important in many natural and industrial processes. These complex flows have long been characterized empirically by the Beverloo rule and, recently, modeled successfully using energy balance*. The dependence of flow rate on the silo's angle with respect to gravity, however, is not captured by existing models. We experimentally investigate the role of tilt angle in this work using a quasi-2D monolayer of grains in a silo. We measure mass flow rate, exit velocities of grains, and packing fraction along the orifice with varying tilt angles. We propose a model that describes our results (and findings with 3D systems) by considering the dependence of outpouring speed and angle with respect to the orifice angle and, importantly, the angle of stagnant zones next to the orifice. We conclude by posing questions about possible extensions of our model in order to describe spatial variations of exit velocity and density along the orifice.

*J. R. Darias, et.al., Phys. Rev. E 101, 052905 (2020)