HIFiRE-1 Ascent-Phase Boundary-Layer Transition

The Hypersonic International Flight Research Experimentation (HIFiRE) program is a hypersonic flight test program. The primary experiment for flight one, launched in March 2010, was to measure boundary-layer transition in hypersonic flight on a nonablating, 7 deg half-angle axisymmetric cone with a small bluntness of 2.5 mm radius. The flight gathered pressure, temperature, and heat transfer measurements during ascent and reentry. Although the vehicle reentered the atmosphere at a higher-than-intended angle of attack, the ascent portion of the flight provided smooth-body boundary-layer transition data at freestream Mach numbers greater than 5, where transition was presumed to be dominated by second-mode instability. The angle of attack during this portion of the flight was less than 1 deg. The end of turbulent-to-laminar transition occurred at Reynolds numbers between 10.3 x 10(6) and 12.2 x 10(6), based on x-location and freestream conditions. Transition was correlated with second-mode N-factors of approximately 14. Smooth-body transition showed good azimuthal uniformity. High-bandwidth transducers indicated some intermittency in the transition process. Fluctuating pressures, relative to the cone mean pressure, were relatively constant beneath the turbulent boundary layer, but peaked in amplitude just before transition. A diamond-shaped trip retained turbulent flow through ascent until reaching a roughness Reynolds number Re-kk = 2200.