Experimental study of unsteadiness in supersonic shock-wave/turbulent boundary-layer interactions with separation

Shock-wave/turbulent boundary-layer interactions (SWTBLIs) with separation are known to be inherently unsteady but their physical mechanisms are still not totally understood. An experimental investigation has been performed in a supersonic wind tunnel at a freestream flow Mach number of 2.42. The interaction between a shock wave created by a shock generator (alpha = 3 degrees, alpha = 9 degrees, alpha = 13 degrees and alpha = 15 degrees deflection angles) and a turbulent boundary layer with thickness delta = 5mm has been studied. High-speed Schlieren visualisations have been obtained and used to measure shock wave unsteadiness by means of digital image processing. In the interactions with separation, the reflected shock's unsteadiness has been in the order of 10(2)Hz. High-speed wall pressure measurements have also been obtained with fast-response micro-transducers along the interactions. Most of the energy of the incoming turbulent boundary layer is broadband and at high frequencies (>10(4)Hz). An addition of low-frequency (<10(4)Hz) fluctuation energy is found at separation. Along the interaction region, the shock impingement results in an amplification of fluctuation energy due to the increase in pressure. Under the main recirculation region core there is only an increase in high frequency energy (>10(4)Hz). Amplification of lower frequency fluctuation energy (>10(3)Hz) is also observed close to the separation and reattachment regions.