Friction and the oscillatory motion of granular flows

TL;DR

This study uses numerical simulations to explore oscillatory behaviors in 2D granular flows, revealing that such flows exhibit surface oscillations influenced by grain friction and volume fraction, with implications for understanding sonic sands.

Contribution

It demonstrates that simple granular flows can spontaneously oscillate, and identifies the effects of friction and volume fraction on these oscillations, expanding understanding of granular flow dynamics.

Findings

Flow develops oscillations with frequency inversely proportional to the square root of velocity.

Oscillations are primarily surface phenomena.

Lower volume fractions lead to higher oscillation amplitudes.

Abstract

This contribution reports on numerical simulations of 2D granular flows on erodible beds. The broad aim is to investigate whether simple flows of model granular matter exhibits spontaneous oscillatory motion in generic flow conditions, and in this case, whether the frictional properties of the contacts between grains may affect the existence or the characteristics of this oscillatory motion. The analysis of different series of simulations show that the flow develops an oscillatory motion with a well-defined frequency which increases like the inverse of the velocity's square root. We show that the oscillation is essentially a surface phenomena. The amplitude of the oscillation is higher for lower volume fractions, and can thus be related to the flow velocity and grains friction properties. The study of the influence of the periodic geometry of the simulation cell shows no significant effect. These results are discussed in relation to sonic sands.