Universal and wide shear zones in granular bulk flow

TL;DR

This study investigates slow granular flows in a modified Couette setup, revealing universal, wide shear zones that scale with layer height and follow a particle-independent error function profile.

Contribution

It demonstrates the creation of wide, tunable shear zones away from sidewalls and establishes a universal scaling law and velocity profile for these zones.

Findings

Shear zones grow wider with increasing layer height.

Velocity profiles collapse onto a universal error function curve.

Shear zone width and shape are independent of particle specifics.

Abstract

We present experiments on slow granular flows in a modified (split-bottomed) Couette geometry in which wide and tunable shear zones are created away from the sidewalls. For increasing layer heights, the zones grow wider (apparently without bound) and evolve towards the inner cylinder according to a simple, particle-independent scaling law. After rescaling, the velocity profiles across the zones fall onto a universal master curve given by an error function. We study the shear zones also inside the material as function of both their local height and the total layer height.