Noise from sub-boundary layer steps

Flow-induced noise data has been obtained under a wide range of conditions for a forward-backward sub-boundary layer steppair, using both hydroacoustic and aeroacoustic experimental facilities. The unscaled noise data show that sound generation behaves similarly in air and water. A non-dimensional analysis was used to develop scaling laws of the noise generation process. Appropriate scaling shows the results from each facility collapse when the wavelength of sound is approximately lower than the dimensions of the hydroacoustic facility test section. Noise was found to radiate in both cross-stream and streamwise directions, thus suggesting that a new noise generation model is required for these types of steps. Noise scaled with velocity raised to a power of seven, in agreement with previous forward facing sub-boundary layer step experiments.