Unsteadiness in shock wave boundary layer interactions with separation

Shock/turbulent boundary-layer interactions produce generally unsteadiness of the shock system. This phenomenon is reviewed and analyzed, by evaluating the results of various experiments; in particular results in the case of a shock reflection are presented. It appears that the frequency of the fluctuations produced by the shock motion are much lower than the characteristic frequencies of turbulence in the incoming boundary layers. It is checked that in the supersonic case, a previously proposed scaling provides the correct order of magnitude of the shock motion frequencies. It is suggested from experimental results that the three-dimensional structure of the separated bubble may be at the origin of such unsteadiness.