Stokes experiment in a liquid foam

TL;DR

This study investigates the steady flow of dry liquid foam around a spherical obstacle, analyzing force dynamics, plastic events, and their correlation with foam structure through experiments and modeling.

Contribution

It provides detailed measurements and a simple elasto-plastic model to understand force fluctuations and plasticity localization in foam flow around an obstacle.

Findings

Force signal exhibits elastic loading and sudden drops.

Plasticity is localized near the bead, with bubble rearrangement size increasing with force jumps.

Scaling laws relate force signals to bubble size.

Abstract

The paper reports on the quasi-static steady flow of a dry liquid foam around a fixed spherical bead, few times larger than the typical bubble size. The force exerted on the bead is recorded with a precision and a time resolution large enough to show the succession of elastic loading of the foam, separated by sudden force drops. The foam structure is observed by direct light transmission, synchronized with the force measurement, thus allowing to correlate the plastic events with the force variations. Scaling laws for the force signal as a function of the bubble size are detailed and interpreted with a simple elasto-plastic model. The spatial distribution of the plasticity is strongly localized in the first bubbles layers around the bead and the average size of bubble rearrangements increases with the corresponding force jump amplitude.