Solid-fluid transition in a granular shear flow

TL;DR

This study investigates the rheology of granular shear flow in a rotating cylinder, revealing a sharp transition from fluid-like to solid-like behavior characterized by a viscosity change and a Maxwellian to Poisson velocity distribution shift.

Contribution

It identifies a solid-fluid transition in granular flow with a clear viscosity change and velocity distribution shift, analogous to a glass transition, using experimental measurements.

Findings

Sharp viscosity transition at a specific depth

Viscosity scales as u^{-1.5} below the transition

Velocity distribution shifts from Maxwellian to Poisson

Abstract

The rheology of a granular shear flow is studied in a quasi-2d rotating cylinder. Measurements are carried out near the midpoint along the length of the surface flowing layer where the flow is steady and non-accelerating. Streakline photography and image analysis are used to obtain particle velocities and positions. Different particle sizes and rotational speeds are considered. We find a sharp transition in the apparent viscosity ($\eta$) variation with rms velocity ($u$). In the fluid-like region above the depth corresponding to the transition point (higher rms velocities) there is a rapid increase in viscosity with decreasing rms velocity. Below the transition depth we find $\eta \propto u^{-1.5}$ for all the different cases studied and the material approaches an amorphous solid-like state deep in the layer. The velocity distribution is Maxwellian above the transition point and a Poisson velocity distribution is obtained deep in the layer. The observed transition appears to be analogous to a glass transition.