Spectra of Decaying Turbulence in a Soap Film

Grid turbulence in a flowing soap film is investigated with ambient pressure $P$ as one of the control parameters. Reducing $P$ significantly decreases air drag thus minimizing three-dimensional effects on the flowing film. It was found that while the total kinetic energy $\frac{1}{2}〈v^2〉=\int E\left(k\right)\mathrm{dk}$ of velocity fluctuations increased noticeably as $P$ was reduced, the energy spectrum $E\left(k\right)$ for wave numbers greater than the injection scale was remarkably insensitive to the pressure change, and obeyed a power law $E\left(k\right)\sim k^{-3.3\mathrm{}\pm 0.3}$.