Heaping, Secondary Flows and Broken Symmetry in Flows of Elongated Granular Particles

TL;DR

This study investigates how elongated granular particles create a heap through secondary flows in shear experiments, revealing that particle shape and orientation misalignment drive flow asymmetries.

Contribution

It demonstrates that particle shape anisotropy causes secondary flows and heap formation, a mechanism not present in spherical particles, supported by symmetry analysis and experiments.

Findings

Heap height reaches at least 40% of the filling height.

Secondary flow is absent in spherical particles.

Flow reversal temporarily reverses the secondary flow.

Abstract

In this paper we report experiments where we shear granular rods in split-bottom geometries, and find that a significant heap of height of least 40% of the filling height can form at the particle surface. We show that heaping is caused by a significant secondary flow, absent for spherical particles. Flow reversal transiently reverses the secondary flow, leading to a quick collapse and slower regeneration of the heap. We present a symmetry argument and experimental data that show that the generation of the secondary flow is driven by a misalignment of the mean particle orientation with the streamlines of the flow. This general mechanism is expected to be important in all flows of sufficiently anisometric grains.