Experiments on turbulence in soap films

Grid turbulence in a freely suspended soap film is investigated. The energy spectrum and the velocity difference on a given scalelare examined by fiber velocimetry and by homodyne photon-correlation spectroscopy. While the velocity field shows self-similarity over many different length scales, the energy spectrum, E(k), deviates strongly from the k−5/3 law, which is predicted for the energy inverse cascade in two dimensions. Our experimental data can be satisfactorily fit to k−3 over a range of wave numbers that are smaller than the wave number kinj, at which the energy is injected into the system.