Boundary-layer flow of air over a falling soap film*

A falling soap film is a well-known experimental setup to realize two-dimensional flows in a laboratory. The soap film is invariably embedded in ambient air, which, in turn, is set to motion due to the falling film. We experimentally measure the velocity profile in the air using Particle Tracking Velocimetry (PTV). We find that the measured velocity profile conforms well to theoretical predictions using boundary-layer approximation. We discuss some implications of our results on the modeling of geophysical flows.