Experimental investigation of shock train behavior in a supersonic isolator

For a better understanding of the shock train structure and its dynamic oscillation features, wind tunnel experiments with linear and stepwise increase backpressure were conducted with supersonic isolator flows at Mach 1.85 and 2.70. High-frequency wall static pressure measurements were performed along the primary and corner regions to capture the behavior of the primary and corner shock train. The fine structures of the shock train were recorded using schlieren visualization with circular, horizontal, vertical, and color knife edges. The pressure results show that the shock train leading shock at Mach 2.70 is more three-dimensional. The flow field exhibits the following features near the corner: the pressure fluctuation amplitude is smaller, the shock train leading shock is closer to the upstream regions, and the oscillation of the shock train leading shock can propagate a longer distance downstream. Schlieren snapshots obtained using horizontal and vertical knife edges show shock train structures with alternating distributions of the vertical and horizontal density gradients. Further application of color knife edges clearly distinguishes these regions. The power spectra analysis of a series of schlieren snapshots was performed to characterize the dominant oscillation structures in the flow field with different visualization variables, and the motion relationship between the structures in the shock train was clarified based on the coherence and phase analyses of the schlieren images. The disturbance downstream first causes the movement of the shock train leading shock, and the closer the downstream shock is to the shock train leading shock, the earlier it moves.