Influence of Environmental Disturbances on Hypersonic Crossflow Instability on the HIFiRE-5 Elliptic Cone

Crossflow instabilities on a 2:1 elliptic cone in hypersonic flow have been investigated in the M6QT and ACE wind tunnels at the Texas A&M National Aerothermochemistry and Hypersonics Laboratory. Experiments on a PEEK 38.1% scale model of the HIFiRE-5 flight test geometry were conducted to investigate the development of crossflow instabilities as well as to characterize the freestream and surface conditions responsible for their initial amplitudes. The freestream environment was varied not only by testing the model in both quiet and conventional tunnels but also by passively changing the fluctuation levels experienced in the conventional facility through systematic model placement. ACE freestream measurements, using a Kulite pressure transducer mounted in a pitot probe configuration and a hot-wire anemometer, indicated that fluctuation levels at the upstream model station were half those at the downstream stations. Fast-response PCB and Kulite surface mounted pressure transducers allowed examination of pressure fluctuation amplitudes and spectra within the model boundary layer. Kulite transducer data show evidence of traveling crossflow in the M6QT and a lower frequency disturbance in ACE. In all cases, frequencies near the expected second mode and secondary instability were observed in data from PCB transducers mounted in the shoulder region. IR thermography measurements examined surface heating levels, indicative of transition onset location and spatial extent. Surface heating magnitude and spatial extent were seen to vary with freestream disturbance level. Under quiet flow, narrow streaks of elevated heating, believed to be evidence of stationary crossflow vortices were observed. Under conventional noise levels, the heating front presents as more diffuse lobes of elevated heating covering a large portion of the cone shoulder and occurs at a much lower freestream Re. Moving the model nosetip to a lower disturbance streamwise station results in more distinct streaks of elevated heating. Results are presented and discussed in context of computations and experimental data from the literature