Boundary Layer Transition Preflight Experiments in a Mach-6 Quiet Tunnel

Experiments on a subscale model of the U.S. Air Force Office of Scientific Research Boundary Layer Transition flight experiment were made in the Boeing/Air Force Office of Scientific Research Mach-6 Quiet Tunnel. Infrared thermography and temperature-sensitive paint were used to measure the surface temperature and heat transfer and provide images of streamwise streaks with the model at 0, 2, and 4 deg angle of attack. Variations in heating patterns were measured for yaw and roll angles. All smooth body cases remained laminar under quiet flow, but symmetric turbulent wedges were seen in noisy flow. Discrete surface pressure sensors measured possible instabilities on the model surface at locations that correspond to computed instability growth. It was discovered that the geometry was sensitive to forward- and rearward-facing steps near the swept leading edges. Controlled forward- and rearward-facing steps were created and tested. No transition was measured under quiet flow for any rearward-facing step at 0 deg angle of attack. Early transition was measured for the forward-facing steps, and correlations were developed for scaling step effects to the flight vehicle.