Effective boundary conditions for dense granular flows

TL;DR

This paper develops an effective boundary condition for dense granular flows that accounts for force network heterogeneity, bridging no-slip and Coulomb friction, and relates slip length to particle size.

Contribution

It introduces a novel boundary condition for granular flows that incorporates force network effects and links slip length to particle diameter.

Findings

Derived boundary condition bridging no-slip and Coulomb friction.

Identified functions relating wall stress, velocity, and variance.

Showed slip length depends on particle diameter.

Abstract

We derive an effective boundary condition for granular flow taking into account the effect of the heterogeneity of the force network on sliding friction dynamics. This yields an intermediate boundary condition which lies in the limit between no-slip and Coulomb friction; two simple functions relating wall stress, velocity, and velocity variance are found from numerical simulations. Moreover, we show that this effective boundary condition corresponds to Navier slip condition when GDR MiDi's model is assumed to be valid, and that the slip length depends on the length scale that characterises the system, \emph{viz} the particle diameter.