Shock oscillations in a supersonic flow due to downstream pressure perturbations

Shock oscillations are observed in various components of a high-speed vehicle, such as supersonic inlets, transonic airfoils, and high-speed compressors. Such unsteadiness of shock waves can lead to engine unstart in supersonic inlets and buffeting on transonic airfoils, while in gas turbine compressors, it can cause severe issues like flutter. Motivated by the above problems, we study in the present work, the response of a normal shock in a supersonic flow subjected to downstream pressure perturbations, generated by rotating a triangular cross-sectional shaft or oscillating a blade, both being downstream of the shock. In both cases, the normal shock is induced and stabilized at a Mach number of 1.3 within a supersonic wind tunnel, and the shock dynamics in response to the downstream pressure perturbations are visualized using high-speed shadowgraphy. Measurements with perturbations from the downstream triangular shaft show large streamwise motions of the shock, with distinct differences in the shock structure and velocity during its upstream and downstream motions. In the other case of pressure perturbations from a heaving blade downstream of a shock, unsteady force measurements have been carried out to understand the influence of shock oscillations on blade flutter.