Boundary-Layer Transition Experiment During Reentry of HIFiRE-1

Abstract

The Hypersonic International Flight Research Experimentation program is a hypersonic flight test program. It successfully measured the three-dimensional transition front on a cone at angle of attack in hypersonic flight during its reentry. The test article consisted of a nonablating, 7 deg half-angle, axisymmetric cone with a small bluntness of 2.5 mm radius. During transition, angle of attack dropped from 13 to 5 deg and freestream unit Reynolds number increased from to . Mach number during this time was approximately seven. Earliest transition, determined from fluctuating pressures, occurred on the leeward meridian, at , , and . Attachment line transition occurred at , , and . The latest transition occurred off the windward meridian at and and 280 deg. Transition occurred at lower Reynolds numbers than the transition measured during ascent ( at ). The azimuthally averaged transition Reynolds number determined from thermocouples was . Away from the windward meridian, wind-tunnel transition occurred at lower Reynolds numbers than in flight. However, the decrement in transition Reynolds number due to wind-tunnel noise was not as severe as at zero angle of attack. Wind-tunnel windward transition occurred at a higher Reynolds number than in flight. It is posited that the destabilizing effects of wall cooling, which was higher in flight () than in ground test (), outweighed the effect of wind-tunnel noise on the windward transition. High-bandwidth instrumentation recorded periodic pressure fluctuations approximately midway between the windward and leeward meridians before transition. However, they could not be positively identified as a crossflow instability.