Vorticity Dynamics in Soap Films*

Fast flowing soap films offer an experimental realization of two-dimensional flow that allows studies of fluid-structure interaction and vortex shedding mechanisms. The thickness of a gravity driven soap film can undergo significant variations in experiments but most modeling work in the past has focused on incompressible results that correspond to constant thickness films. We discuss a viscous compressible model of soap film flow that is equivalent to the Navier-Stokes equations with a film thickness dependent viscosity. A new vorticity transport equation for compressible soap film flow suggests effects unique to soap films and not predictible by a constant density incompressible theory. New exact solutions for the soap film model will be presented. Numerical simulations are shown to illustrate vortex shedding in soap film experiments.