Turbulence structure in a shock wave/turbulent boundary-layer interaction

The boundary-layer turbulence structure in a two-dimensional 24-deg compression corner flow was investigated experimentally in the Princeton University 203 × 203-mm supersonic blowdown wind tunnel. The incoming conditions were M_∞ = 2.84, Re_∞/l = 6.5 × 107, and δ₀ = 26 mm. The results show that the maximum mass-flux turbulence intensity is amplified by a factor of about 5, whereas the mean mass flux increases by only 2 through compression. Probability density functions (pfd’s) of the mass-flux fluctuations show that upstream the distributions are Gaussian-like and typical of a fully turbulent boundary layer. Behind the interaction, however, the distributions are bimodal, centering about a level indicative of the freestream mass flux and a lower level indicative of the mass flux near the wall. The unsteady shock motion does not appear to contribute signficantly to the turbulence amplification. It is suggested that the strong, bimodal mixing indicated in the pdf’s is probably caused by the presence of large-scale motions associated with the instability of the inflectional velocity profiles observed downstream of the interaction. Space-time correlations of the mass flux and wall pressure were measured, as well as the level of intermittency of the boundary layer to further characterize the changes in the boundary-layer structure through the interaction.