Flowing soap films: a laboratory for studying two-dimensional hydrodynamics

We present the results of recent experiments in a vertically flowing soap film in which the turbulence is produced by a comb that penetrates the film. After an abbreviated review of the theory of turbulence in two and three dimensions, we discuss two experiments performed in this quasi-two-dimensional system. The first experiment concentrates on measurements of the probability density function for velocity differences on various spatial scales. Special attention is given to the third moment. In the second experiment von Karman vortices are bathed in a background of turbulence, which results in enhanced diffusion-like spreading of the vortex street. A turbulent diffusivity is thereby measured.