SPECTRA OF DECAYING TURBULENCE IN A SOAP FILM

Grid turbulence in a flowing soap film is investigated with ambient pr essure P as one of the control parameters. Reducing P significantly de creases air drag thus minimizing three-dimensional effects on the flow ing film. It was found that while the total kinetic energy 1/2[upsilon (2)] = integral E(k) dk of velocity fluctuations increased noticeably as P was reduced, the energy spectrum E(k) for wave numbers greater th an the injection scale was remarkably insensitive to the pressure chan ge, and obeyed a power law E(k) similar to k(-3.3+/-0.3).