Yield drag in a two-dimensional foam flow around a circular obstacle: Effect of liquid fraction

TL;DR

This study investigates how liquid fraction affects the yield drag in a two-dimensional foam flow around a circular obstacle, using experiments and simulations to reveal a linear relationship with obstacle size and a strong increase with decreasing liquid content.

Contribution

It provides a comprehensive analysis of the liquid fraction's impact on foam yield drag, combining experimental and simulation approaches with a unified liquid fraction definition.

Findings

Yield drag is linear with obstacle-to-bubble size ratio.

Yield drag is independent of channel width.

Decreasing liquid fraction significantly increases yield drag.

Abstract

We study the two-dimensional flow of foams around a circular obstacle within a long channel. In experiments, we confine the foam between liquid and glass surfaces. In simulations, we use a deterministic software, the Surface Evolver, for bubble details and a stochastic one, the extended Potts model, for statistics. We adopt a coherent definition of liquid fraction for all studied systems. We vary it in both experiments and simulations, and determine the yield drag of the foam, that is, the force exerted on the obstacle by the foam flowing at very low velocity. We find that the yield drag is linear over a large range of the ratio of obstacle to bubble size, and is independent of the channel width over a large range. Decreasing the liquid fraction, however, strongly increases the yield drag; we discuss and interpret this dependence.