Shock/boundary-layer interactions: Possible sources of unsteadiness

In shock induced separation, the question of the origin of the low frequency motions affecting the shock waves remains controversial. According to the situations, it may be argued that upstream or downstream flow conditions can provide a likely explanation. A short review of this question is proposed, mainly based on the analysis of existing experimental work. One of the recent interpretations is the role which can be played by the long turbulent superstructures of the incoming boundary layer. This is shown to be a valid interpretation in a limited number of cases. An experiment in which perturbations of the same type are formed is shown to bring no modification to an oblique shock reflection interaction. The different cases are discussed and an assessment of the generality of their results is proposed.