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 scale e are 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 k(ini) at which the energy is injected into the system.