On the rising and sinking of granular bubbles and droplets

TL;DR

This paper introduces an analytical model that predicts the behavior of granular bubbles and droplets, explaining their rising and sinking motions in vibrated granular beds and identifying five distinct motion regimes.

Contribution

The paper presents the first analytical model for the coherent motion and transition of granular bubbles and droplets, enhancing understanding of their dynamics.

Findings

Model accurately predicts neutral buoyancy limit

Regime map with five distinct motion regimes

Provides insight into transition between rising and sinking

Abstract

Recently, the existence of so-called granular bubbles and droplets has been demonstrated experimentally. Granular bubbles and droplets are clusters of particles that respectively rise and sink if submerged in an aerated and vibrated bed of another granular material of different size and/or density. However, currently there is no model that explains the coherent motion of these clusters and predicts the transition between a rising and sinking motion. Here, we propose an analytical model predicting accurately the neutral buoyancy limit of a granular bubble/droplet. This model allows the compilation of a regime map identifying five distinct regimes of granular bubble/droplet motion.