Effect of angle of attack on hypersonic boundary-layer stability

An experimental investigation of the effects of angle of attack on hypersonic boundary-layer stability on a ¯ ared-cone model was conducted in the low-disturbance Mach-6 Nozzle-Test-Chamber Facility at NASA Langley Research Center. Hot-wire anemometry diagnostics were applied to identify the boundary-layer instability mechanisms that lead to transition. The present results show that the boundary layer becomes more stable on the windward ray and less stableon the leeward ray relative to the zero-degree angle-of-attack case. The second-mode instability dominates the transition process at a 0-deg angle of attack; however, on the windward meridian at an angle of attack this mode was stabilized. On the leeward meridian the frequency of the dominant instability was higher than the estimated frequency of the second-mode disturbance; thus the dominant transition mechanism may beother than a second-modedisturbance. Nonlineareffects, such as growth saturation, harmonic generation,