Three-dimensional foam flow resolved by fast X-ray tomographic microscopy

TL;DR

This study uses ultra-fast X-ray tomography to visualize and analyze the 3D flow and deformation of foam around an obstacle, revealing new insights into bubble dynamics and plastic rearrangements.

Contribution

It provides the first detailed 3D visualization of foam flow around an obstacle, highlighting differences from 2D flow and identifying triggers for bubble rearrangements.

Findings

Velocity field is axisymmetric with recirculation zone.

Bubble deformations are smaller than in 2D due to azimuthal variations.

Plastic rearrangements occur when film faces fall below a critical area.

Abstract

Thanks to ultra fast and high resolution X-ray tomography, we managed to capture the evolution of the local structure of the bubble network of a 3D foam flowing around a sphere. As for the 2D foam flow around a circular obstacle, we observed an axisymmetric velocity field with a recirculation zone, and indications of a negative wake downstream the obstacle. The bubble deformations, quantified by a shape tensor, are smaller than in 2D, due to a purely 3D feature: the azimuthal bubble shape variation. Moreover, we were able to detect plastic rearrangements, characterized by the neighbor-swapping of four bubbles. Their spatial structure suggest that rearrangements are triggered when films faces get smaller than a characteristic area.