The clustering morphology of freely rising deformable bubbles

TL;DR

This study uses 3D numerical simulations to analyze how bubble deformation influences clustering patterns during free rise, revealing deformation-dependent clustering types and underlying vorticity mechanisms.

Contribution

It introduces a quantitative Voronoi-based method to distinguish clustering types and links bubble deformation to clustering morphology across various parameters.

Findings

Spherical bubbles tend to form grid-like structures.

Deformed bubbles exhibit preferential clustering.

Clustering behavior is linked to surface vorticity generation.

Abstract

We investigate the clustering morphology of a swarm of freely rising deformable bubbles. A three-dimensional Vorono\"i analysis enables us to quantitatively distinguish between two typical clustering configurations: preferential clustering and a grid-like structure. The bubble data is obtained from direct numerical simulations (DNS) using the front-tracking method. It is found that the bubble deformation, represented by the aspect ratio \chi, plays a significant role in determining which type of clustering is realized: Nearly spherical bubbles with \chi <~ 1.015 form a grid-like structure, while more deformed bubbles show preferential clustering. Remarkably, this criteria for the clustering morphology holds for different diameters of the bubbles, surface tension, and viscosity of the liquid in the studied parameter regime. The mechanism of this clustering behavior is connected to the amount of vorticity generated at the bubble surfaces.