Flow of wet granular materials

TL;DR

This paper investigates the transition from frictional to lubricated flow in dense suspensions of non-Brownian particles, identifying a critical shear rate and universal velocity profiles, with implications for understanding flow in wet granular materials.

Contribution

It introduces the Leighton number as a key parameter for the transition and characterizes the flow regimes, revealing universal velocity profiles and flow inhomogeneity.

Findings

Critical shear rate defines flow transition

Universal velocity profile in both regimes

Flow inhomogeneity indicated by viscosity discrepancy

Abstract

The transition from frictional to lubricated flow of a dense suspension of non-Brownian particles is studied. The pertinent parameter characterizing this transition is the Leighton number $Le = \frac{\eta_s \dot{\gamma}}{\sigma}$, which represents the ratio of lubrication to frictional forces. The Leighton number $Le$ defines a critical shear rate below which no steady flow without localization exists. In the frictional regime the shear flow is localized. The lubricated regime is not simply viscous: the ratio of shear to normal stresses remains constant, as in the frictional regime; moreover the velocity profile has a single universal form in both frictional and lubricated regimes. Finally, a discrepancy between local and global measurements of viscosity is identified, which suggests inhomogeneity of the material under flow.