Shock waves in two-dimensional granular flow: effects of rough walls and polydispersity

TL;DR

This study investigates how rough walls and polydispersity influence shock wave formation and behavior in two-dimensional granular flows within funnels, revealing new scaling laws and effects on flow disorder and shock propagation.

Contribution

It demonstrates that rough walls alter shock dynamics and flow disorder, and introduces simple scaling laws for shock velocity and frequency in rough wall flows, extending understanding beyond smooth wall cases.

Findings

Rough walls increase flow disorder and slow shock propagation.

Shock velocity and frequency follow simple scaling laws in rough wall flows.

Strong polydispersity leads to extended blocked regions and breakdown of scaling.

Abstract

We have studied the two-dimensional flow of balls in a small angle funnel, when either the side walls are rough or the balls are polydisperse. As in earlier work on monodisperse flows in smooth funnels, we observe the formation of kinematic shock waves/density waves. We find that for rough walls the flows are more disordered than for smooth walls and that shock waves generally propagate more slowly. For rough wall funnel flow, we show that the shock velocity and frequency obey simple scaling laws. These scaling laws are consistent with those found for smooth wall flow, but here they are cleaner since there are fewer packing-site effects and we study a wider range of parameters. For pipe flow (parallel side walls), rough walls support many shock waves, while smooth walls exhibit fewer or no shock waves. For funnel flows of balls with varying sizes, we find that flows with weak polydispersity behave qualitatively similar to monodisperse flows. For strong polydispersity, scaling breaks down and the shock waves consist of extended areas where the funnel is blocked completely.