Surface band segregation and internal convection in rotating sphere densely filled with granular material: Experiments

TL;DR

This study investigates granular segregation and convection in a densely filled rotating sphere, revealing stable surface band segregation, butterfly-shaped convection patterns, and layered internal structures, advancing understanding of granular dynamics in confined geometries.

Contribution

It provides new experimental insights into granular behavior in densely filled rotating spheres, including internal layering and unique convection patterns, which were not previously characterized.

Findings

Granular convection forms butterfly-shaped structures with alternating bead layers.

Two concentric interfaces divide the sphere into three distinct layers.

Convection patterns are stable and independent of sphere size.

Abstract

While granular segregation in partially filled containers has been studied extensively, granular dynamics in densely filled spheres is not fully understood. Here, surface band segregation and granular convection are reported in a rotating sphere of highly compacted glass beads. Distinct from Rayleigh-Benard convection, granular convection has a butterfly-shaped structure with vortexes of alternating layers of small/large beads, which is stable and independent of the sphere size. Two concentric interfaces at the zero tangential/norm flux are discovered, which divide the sphere into three layers from the surface to the core. The law that governs the jamming dynamics in rotating spheres remains an open question.