Development, uniformity and peak heating of a hypersonic laminar near-wake flow

This paper describes visualisation experiments performed using the planar laser-induced fluorescence of nitric oxide. The focus was to investigate the establishment and cross-stream uniformity of the hypersonic separated flow generated in a pulsed free-piston shock tunnel facility. In particular, the laminar Mach 7.5 flow over a step downstream of a wedge was investigated. The ratio of wedge width to total horizontal distance downstream of the leading edge was 0.71 at the furthest downstream measurement point, and model side plates were not used. Flow images were obtained on successive tunnel runs with different delays after flow onset, to identify the nominal flow establishment time. Furthermore, images were obtained at the nominal facility test time using a laser sheet oriented perpendicular to the step, propagating in the spanwise direction at a height equal to half the step height. These images are compared with thermocouple heat flux measurements obtained both with and without the step and show that while the flow downstream of reattachment is uniform in the middle of the model, the separated flow immediately downstream of the step is non-uniform.