Instability and Transition Research in a Mach-6 Quiet Tunnel

Abstract

Pitot-probe measurements were made to determine the spatial extent of the uniform quiet flow core for the laminar nozzle-wall boundary layer. The uniformity of the flow for a turbulent nozzle-wall boundary layer was determined as well. The nozzle was re-polished in August, and quiet flow is currently being achieved at higher stagnation pressures, around 162 psia. The laser perturber system for the BAM6QT is being re-established. The laser used for this system performs as in previous experiments and a new optical system has been designed for the BAM6QT. Tests were conducted to characterize the effect of suction downstream of the nozzle exit on starting larger blunt models in hypersonic flow. Pressure measurements were made in the upstream pipe-insert section and found that suction levels were highest with a 0.375-in. gap. Models of the Crew Exploration Vehicle (CEV) with diameters of 1.000 and 1.250 in. started regardless of model positioning and gap suction. A 1.500-in. model started in quiet flow, but did not start in noisy flow with pipe-insert suction alone. The 1.500-in. CEV model did, however, start in noisy flow with bleeds open above the maximum quiet pressure. Another project looked at the effect of nosetip roughness on the crossflow instability with a 7-deg half-angle cone at 6-deg angle of attack. When the average roughness of the nosetip was varied by an order of magnitude, the temperature-sensitive paint data showed no effect on the stationary vortices. It appears that the paint step at the nosetip-frustum junction was dominating the generation of the stationary vortices. Lastly, measurements upstream of a cylindrical roughness have confirmed the existence of an absolute instability in the separation region, as suggested by computations. A second absolute instability was also detected at lower Reynolds numbers.