Granular Convection in Microgravity

TL;DR

This study experimentally examines how gravity influences convection in dense granular flows, revealing that secondary convective flows diminish in microgravity and intensify with increased gravity, while primary flows remain unaffected.

Contribution

It provides the first experimental evidence that gravity modulates secondary convection in granular shear flows, highlighting frictional interactions as a key factor.

Findings

Secondary convection is near zero in microgravity.

Secondary convection increases with gravity.

Primary flow fields are unaffected by gravity.

Abstract

We investigate the role of gravity on convection in a dense granular shear flow. Using a microgravity modified Taylor-Couette shear cell under the conditions of parabolic flight microgravity, we demonstrate experimentally that secondary, convective-like flows in a sheared granular material are close to zero in microgravity and enhanced under high-gravity conditions, though the primary flow fields are unaffected by gravity. We suggest that gravity tunes the frictional particle-particle and particle-wall interactions, which have been proposed to drive the secondary flow. In addition, the degree of plastic deformation increases with increasing gravitational forces, supporting the notion that friction is the ultimate cause.