Unsteady Flow Features Across Different Shock/Boundary-Layer Interaction Configurations

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:phi(1)=14 and 20 degrees compression ramps, and incident shock reflections from phi(1)=7, 8, 9, and 10 degrees shock generators; Reynolds numbers in each case are Re-theta approximate to 8350. The flow is assessed using an array of fast-response pressure transducers in conjunction with a high-repetition rate particle image velocimetry 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 shows 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 the literature that have sought to explain the source of low-frequency unsteady shock motion.