Plug flow and the breakdown of Bagnold scaling in cohesive granular flows

TL;DR

This study uses discrete element simulations to show that Bagnold scaling, valid for noncohesive granular flows, breaks down in cohesive granular flows on inclined planes, leading to a generalized constitutive relation.

Contribution

The paper introduces a generalized Bagnold relation to describe cohesive granular flows, revealing differences from noncohesive flow behavior.

Findings

Bagnold scaling does not hold for cohesive granular flows.

A generalized constitutive relation is proposed for cohesive media.

Physical mechanisms underlying the different laws are discussed.

Abstract

Cohesive granular media flowing down an inclined plane are studied by discrete element simulations. Previous work on cohesionless granular media demonstrated that within the steady flow regime where gravitational energy is balanced by dissipation arising from intergrain forces, the velocity profile in the flow direction scales with depth in a manner consistent with the predictions of Bagnold. Here we demonstrate that this Bagnold scaling does not hold for the analogous steady-flows in cohesive granular media. We develop a generalization of the Bagnold constitutive relation to account for our observation and speculate as to the underlying physical mechanisms responsible for the different constitutive laws for cohesive and noncohesive granular media.