HIFIRE-5b Heat Flux and Boundary-Layer Transition

Hypersonic International Flight Research Experimentation (HIFiRE)-5 is a hypersonic flight-test experiment designed to investigate the aerothermodynamics of a three-dimensional geometry. The vehicle is a 7 deg minor-axis half-angle elliptic cone with a 2 : 1 aspect ratio and 2.5 mm nose radius. The HIFiRE-5b achieved a Mach number of 7.7-7.9 and a freestream unit Reynolds number of 5. 10(6)-50. 10(6)/m during descent. Heat flux was calculated from thermocouple pairs, and boundary-layer transition locations were identified from these heating rates. A multilobed transition front was observed, with earliest transition at the centerline, on the leading edges, and part way in between. It is suspected that a different mechanism is responsible for each of these lobes. Transition along HIFiRE-5b's leading edges occurred at roughly constant length-based Reynolds numbers, suggesting a different mechanism than the roughness-induced transition suspected for HIFIRE-5a. Transition near the planes of symmetry was found to be less sensitive to attitude variation than elsewhere on the vehicle surface. In particular, hot streaks suspected to be due to stationary crossflow vortices were very sensitive to small changes in attitude (roughly +/- 1 deg angle of attack and yaw). Data from 128 pairs of thermocouples show the overall temperature, heat flux, and boundary-layer state during flight.