Boundary-Layer Instability Measurements in a Mach-6 Quiet Tunnel

Several experiments have been performed in the Boeing/AFOSR Mach-6 Quiet Tunnel at Purdue University. A 7 degree half angle cone at 6 degree angle of attack with temperature-sensitive paint (TSP) and PCB pressure transducers was tested under quiet flow. The stationary crossflow vortices appear to break down to turbulence near the lee ray for sufficiently high Reynolds numbers. Attempts to use roughness elements to control the spacing of hot streaks on a flared cone in quiet flow did not succeed. Roughness was observed to damp the second-mode waves in areas influenced by the roughness, and wide roughness spacing allowed hot streaks to form between the roughness elements. A forward-facing cavity was used for proof-of-concept studies for a laser perturber. The lowest density at which the freestream laser perturbations could be detected was 1.07 x 10(exp -2) kilograms per cubic meter. Experiments were conducted to determine the transition characteristics of a streamwise corner flow at hypersonic velocities. Quiet flow resulted in a delayed onset of hot streak spreading. Under low Reynolds number flow hot streak spreading did not occur along the model. A new shock tube has been built at Purdue. The shock tube is designed to create weak shocks suitable for calibrating sensors, particularly PCB-132 sensors. PCB-132 measurements in another shock tube show the shock response and a linear calibration over a moderate pressure range

Techniques for application of roughness for manipulation of second-mode waves on a flared cone at Mach 6

Experimental validation of physics-based transition models is essential to improving the state of the art of hypersonic vehicle design. This research focuses on one aspect of this problem, which is the effect of surface roughness on the non-linear breakdown of second-mode waves in hypersonic boundary layers. A flared cone was designed to allow non-linear growth of second-mode waves to sufficient amplitudes to lead to transition under quiet flow in the Boeing/AFOSR Mach 6 Quiet Tunnel. The non-linear breakdown process is characterized by a set of streamwise streaks of increased heating, followed by the onset of turbulence. The location of the streaks is related to small amounts of upstream surface roughness. Techniques for applying and fabricating surface roughness were developed. These are to be used to manipulate this breakdown process. While certain types of roughness have been used to introduce streamwise vorticity in other flows at low speeds, it was unknown what types of roughness would work in the present case. The effects of the new roughness types were analyzed through pressure measurements and global heat transfer visualization using temperature sensitive paint. None of the new roughness types was able to directly control the spanwise periodicity of the streaks, but two types were identified as good candidates for future testing. More work is required to develop a suitable technique for fabricating and applying small roughness