Influence of lateral confinement on granular flows: comparison between shear-driven and gravity-driven flows

TL;DR

This study compares gravity-driven and shear-driven confined granular flows through simulations, revealing common properties like shear localization, a power law relation between temperature and shear rate, and decreasing sidewall friction with depth.

Contribution

It provides a comparative analysis of two flow types, highlighting shared behaviors and differences due to boundary conditions in confined granular flows.

Findings

Shear localization occurs in both flow types.

A power law relates granular temperature to shear rate.

Friction at sidewalls weakens with depth.

Abstract

The properties of confined granular flows are studied through discrete numerical simulations. Two types of flows with different boundaries are compared: (i) gravity-driven flows topped with a free surface and over a base where erosion balances accretion (ii) shear-driven flows with a constant pressure applied at their top and a bumpy bottom moving at constant velocity. In both cases we observe shear localization over or/and under a creep zone. We show that, although the different boundaries induce different flow properties (e.g. shear localization of transverse velocity profiles), the two types of flow share common properties like (i) a power law relation between the granular temperature and the shear rate (whose exponent varies from 1 for dense flows to 2 for dilute flows) and (ii) a weakening of friction at the sidewalls which gradually decreases with the depth within the flow.