Simulations of Two-Dimensional Foam under Couette Shear

The flow of two-dimensional aqueous foams in the Couette geometry highlights the shear-response of this complex fluid. Quasistatic simulations using the Surface Evolver software are described which allow the calculation of shear stress, bubble velocity, torsion and the location of topolgical changes in the foam. It is shown that the torsion on the inner cylinder decreases with increasing liquid fraction. After an initial transient the topological changes are located in a region close to the inner cylinder; the width of this region increases with liquid fraction, but is independent of bubble size.