Correlations of strain and plasticity in flowing foam

TL;DR

This study uses simulations to explore how elastic correlations influence flow behavior in foam across different densities, revealing persistent correlations below the jamming point and their role in flow organization.

Contribution

It provides a unified microscopic picture linking elastic correlations to flow organization in foam from above to below jamming.

Findings

Elastic correlations cause spatial flow organization above jamming.

Below jamming, elastic correlation length diminishes but correlations persist.

Flow field arises from superposition of quadrupolar strain fields.

Abstract

Via simulations of flowing foam, we connect the high and intermediate density regimes of complex fluid flows into a consistent microscopic picture of deformation. While at and above the jamming transition, elastic correlations lead to strong spatial organization of the flow field, below jamming, the slowly diminishing elastic correlation length leads to slowly ceasing spatial organization, which is nevertheless still present down to densities far below jamming. We show that the long-range correlated flow field arises from the superposition of quadrupolar strain fields of shear zones with highly correlated positions, strengths and orientation. These interactions are still pertinent below jamming, where they systematically weaken with the slowly diminishing elastic correlation length. These results demonstrate the ubiquity and importance of elastic correlations in the flow of complex fluids even below the jamming transition, and motivate a scale-bridging description of their flow over wide ranges of density from solid to fluid.