Wall pressure fluctuations in transonic shock/boundary layer interaction

The structure of wall pressure fluctuations beneath a turbulent boundary layer interacting with a normal shock wave is investigated through direct numerical simulation (DNS). In the zeropressure-gradient (ZPG) region upstream of the interaction pressure statistics well compare with canonical boundary layers in terms of fluctuation intensities and frequency spectra. Across the interaction zone, the r.m.s. wall pressure fluctuations attain large values (in excess of ≈162 dB), with an increase of about 7 dB from the upstream level. The main effect of the interaction on the frequency spectra is to enhance of the low-frequency Fourier modes, while inhibiting the high-frequency ones. Excellent collapse of frequency spectra is observed past the interaction zone when data are scaled with the local boundary layer units. In this region an extended ω7/3 power-law behavior is observed, which is associated with the suppression of mean shear caused by the imposed adverse pressure gradient.