This paper reports the progress of three projects in the Boeing/AFOSR Mach-6 quiet tunnel at Purdue University. The first project used a 7-deg half-angle cone at 6-deg angleof-attack with temperature-sensitive paint applied to the frustum and small roughness dots added near the nosetip. Depending on the spacing of the roughness, the spacing and breakdown of the stationary vortices was altered. The second project looked at modifications to a pulsed jet perturber to reduce the perturbation duration. This was accomplished through both electronic and physical modifications to the perturber system. Shorter duration perturbations were achieved, but further progress is required. The third project measured low-frequency disturbances in the first-mode instability frequency range with Kulite pressure transducers on the surface of a cone-ogive-cylinder model. Initial measurements show that the magnitude of the low-frequency disturbance on the cone-ogive-cylinder is greatest outside the boundary layer, which may indicate an entropy-layer instability.

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Several experiments have been performed in the Boeing/AFOSR Mach-6 Quiet Tunnel at Purdue University. A 7• half angle cone at 6• 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 × 10 −2 kg/m 3 . 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. Nomenclature

This paper details five different projects in the Boeing/AFOSR Mach 6 Quiet Tunnel (BAM6QT) at Purdue University. In the first project, a highly swept fin on a 7 • half-angle cone was examined. Temperature sensitive paint and pressure fluctuation measurements showed the presence of an instability near 200 kHz. In the second, the effect of roughness on the stationary and travelling crossflow instabilities was investigated on a cone at an angle of attack. It was found that when the roughness generated larger stationary waves, the travelling waves were damped. In the third, discrete roughness elements made of epoxy were applied to a flared cone. The roughness elements were sized to interact with the second-mode waves without becoming a trip. Using this technique, the spacing of streaks of increased heating was controlled. The fourth project involves improving the current pulsed jet perturber used to study nozzle-wall boundary-layer perturbations. Two improvements have been designed and have undergone preliminary testing. Finally, a new model was designed to measure what appears to be an entropy-layer instability at Mach 6. Surface pressure measurements and hot-wire data are used to investigate the entropy layer.