Experimental evidence of flow destabilization in a 2D bidisperse foam

TL;DR

This study experimentally demonstrates flow destabilization caused by large bubbles in 2D bidisperse foam flows, revealing new instabilities, segregation, and organized structures that influence foam dynamics.

Contribution

It provides the first experimental evidence of flow destabilization and segregation phenomena in 2D bidisperse foam flows, with analysis of large bubble behavior.

Findings

Large bubbles migrate faster above a size-dependent velocity threshold.

Large bubbles induce flow instability and segregation in bidisperse foam.

Large bubbles organize into flow-aligned columns due to attractive interactions.

Abstract

Liquid foam flows in a Hele-Shaw cell were investigated. The plug flow obtained for a monodisperse foam is strongly perturbed in the presence of bubbles whose size is larger than the average bubble size by an order of magnitude at least. The large bubbles migrate faster than the mean flow above a velocity threshold which depends on its size. We evidence experimentally this new instability and, in case of a single large bubble, we compare the large bubble velocity with the prediction deduced from scaling arguments. In case of a bidisperse foam, an attractive interaction between large bubbles induces segregation and the large bubbles organize themselves in columns oriented along the flow. These results allow to identify the main ingredients governing 2D polydisperse foam flows.