Steady Flow Dynamics during Granular Impact

TL;DR

This study investigates the rapid granular flow during impacts, revealing that near-intruder particle flow scales with intruder speed and remains balanced despite deceleration, with simulations showing insensitivity to grain properties.

Contribution

It demonstrates that granular flow during impact is proportional to intruder speed and independent of grain details, extending static flow models to dynamic impact scenarios.

Findings

Granular flow near impact scales with intruder speed.

Flow remains divergence-free and balanced despite rapid deceleration.

Simulation results are insensitive to grain properties.

Abstract

We study experimentally and computationally the dynamics of granular flow during impacts, where intruders strike a collection of disks from above. In the regime where granular force dynamics are much more rapid than the intruder motion, we find that the particle flow near the intruder is proportional to the instantaneous intruder speed; it is essentially constant when normalized by that speed. The granular flow is nearly divergence-free and remains in balance with the intruder, despite the latter's rapid deceleration. Simulations indicate that this observation is insensitive to grain properties, which can be explained by the separation of time scales between intergrain force dynamics and intruder dynamics. Assuming there is a comparable separation of time scales, we expect our results are applicable to a broad class of dynamic or transient granular flows. Our results suggest that descriptions of static-in-time granular flows might be extended or modified to describe these dynamic flows. Additionally, we find that accurate grain-grain interactions are not necessary to correctly capture the granular flow in this regime.