Effect of Freestream Noise on Roughness-Induced Transition for the X-51A Forebody

A 20%-scale X-51A forebody model was tested in the Boeing and U.S. Air Force Office of Scientific Research Mach-6 Quiet Tunnel. The effect of a smooth blank and two different trip strips on windward-forebody transition was measured using temperature-sensitive paint and hot-wire anemometry. Reducing freestream noise from conventional to quiet levels increased the smooth-wall transition Reynolds number by a factor of at least 2.2. In addition, the transition Reynolds number based on the distance from the trips increased by a factor of 2.4 for the smaller trips and by a factor of 1.7 for the larger trips. Thus, tunnel noise had a substantial effect on roughness-induced transition.