Hypersonic vehicles encounter extreme conditions due to increased thermal and pressure loads from shockwaves and friction. This can lead to signifcant damage of aerodynamic surfaces in flight. To better understand these conditions, we perform wind tunnel experiments in a Mach 4 Ludwieg tube in the Tennessee Aerothermodynamics Laboratory (TALon) at the University of Tennessee Space Institute. Herein, we investigate a hollow-cylinder with a 30 degree flare that can be adjusted along the length of the cylinder. We apply fast-response pressure-sensitive paint (PSP) to the flare surface and image at 20 kHz. The oxygen-sensitive molecules in the paint are excited by UV light and emit red light. In the presence of higher concentrations of oxygen, corresponidng to higher pressures, the emission of light from these molecules is quenched resulting in lower intensities in the images. At the start of the flared surface, we see low pressure regions indicating flow separation. We also see the formation of streamwise Görtler vortices where the flow reattaches to the flare surface. Coupling this method with schlieren imaging, we are able to form a broader picture of the flow conditions in the boundary layer and on the surface of our model. Where the boundary layer at the start of the flare transition from a laminar to a turbulent state, an upstream influence shock appears intermittently corresponding with a thickening of the boundary layer. Understanding where this laminar-turbulent transition occurs and the dynamics during transition is a priority to mitigate adverse effects for future hypersonic vehicles.
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