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An experimental study has been conducted to investigate unsteady flow phenomena observed within various two-dimensional configurations of shock/boundary layer interactions. Six configurations have been tested in Mach 2 flow: ϕ1 = 14 • and 20 • compression ramps, and incident shock reflections from ϕ1 = 7 • , 8 • , 9 • , and 10 • shock generators; Reynolds numbers in each case are Re θ ≈ 8350. The flow is assessed using an array of fast-response pressure transducers in conjunction with a high-repetition rate PIV system. Development of the mean flow structures early in each interaction is observed to be consistent with the Free Interaction concept. Unsteady wall-pressure energy content at frequencies above those associated with the characteristic low-frequency shock motion also show significant similarities in the vicinity of the shock foot. Results confirm that this low-frequency peak is not associated with a narrow-band forcing mechanism from either upstream or downstream, but rather a characteristic frequency that varies with interaction strength, which describes the flow's dynamic response. These findings support various models published in literature that have sought to explain the source of low-frequency unsteady shock motion.

The effects of interaction strength and configuration generality are the subject of an experimental investigation to assess the low frequency unsteadiness typically observed in Shock Wave Boundary Layer Interactions (SWBLIs). The core dominant mechanisms responsible remain disputed due to the lack of a broad approach for understanding what drives each mechanism across a range of interaction types. This paper forms the first part of an investigation to observe various interactions in a well characterized baseline environment. Experiments have been conducted in the Imperial College London supersonic wind tunnel where three configurations of SWBLI have been tested, each with a strength of interaction designed to result in incipient separation: a) 14 • compression ramp interaction (Mach 2.0), b) 8 • incident shock reflection interaction (Mach 2.0), and c) normal shock interaction (Mach 1.4). Analysis has been conducted using high-speed planar two-component particle image velocimetry and schlieren photography to characterize the baseline flow and inspect shock unsteadiness. Each configuration exhibits similar levels of incipient separation with probabilities of reversed flow between 12% and 26% in each frame. Significant energy content has been observed within the interactions at frequencies far lower than typically witnessed in a supersonic boundary layer, providing agreement with results in literature.