Crucial role of side walls for granular surface flows: consequences for the rheology

TL;DR

This study demonstrates that side walls critically influence steady granular surface flows, with experimental and theoretical analyses showing wall effects dominate flow behavior and support a specific rheological model.

Contribution

It reveals the dominant role of side walls in granular surface flows and validates a local constitutive law through experimental and theoretical agreement.

Findings

Flow is entirely controlled by side wall effects.

Theoretical model accurately predicts flow behavior.

Supports the relevance of the proposed rheological law.

Abstract

In this paper we study the steady uniform flows that develop when granular material is released from a hopper on top of a static pile in a channel. We more specifically focus on the role of side walls by carrying out experiments in setup of different widths, from narrow channels 20 particle diameters wide to channels 600 particle diameters wide. Results show that steady flows on pile are entirely controlled by side wall effects. A theoretical model, taking into account the wall friction and based on a simple local constitutive law recently proposed for other granular flow configurations (GDR MiDi 2004), gives predictions in quantitative agreement with the measurements. This result gives new insights in our understanding of free surface granular flows and strongly supports the relevance of the constitutive law proposed.