Granular Avalanches in Fluids

TL;DR

This paper investigates how different fluid and grain properties influence granular avalanches, identifying three regimes based on the Stokes number and density ratio, with implications for understanding avalanche dynamics in various fluids.

Contribution

It introduces a classification of granular avalanches into three regimes based on Stokes number and density ratio, analyzing elementary grain motion to explain these behaviors.

Findings

Avalanche amplitude and duration are independent of fluid effects in dry conditions.

In liquids, decreasing St increases avalanche duration and decreases amplitude.

Three distinct avalanche regimes are characterized by Stokes number and density ratio.

Abstract

Three regimes of granular avalanches in fluids are put in light depending on the Stokes number St which prescribes the relative importance of grain inertia and fluid viscous effects, and on the grain/fluid density ratio r. In gas (r >> 1 and St > 1, e.g., the dry case), the amplitude and time duration of avalanches do not depend on any fluid effect. In liquids (r ~ 1), for decreasing St, the amplitude decreases and the time duration increases, exploring an inertial regime and a viscous regime. These regimes are described by the analysis of the elementary motion of one grain.