Orbiter BLT Flight Experiment Wind Tunnel Simulations: Nearfield Flowfield Imaging and Surface Thermography

This paper reports a series of wind tunnel tests simulating the near-field behavior of the Space Shuttle Orbiter Boundary Layer Transition Detailed Test Objective (BLT DTO) flight experiment. Hypersonic flow over a flat plate with an attached BLT DTO-shaped trip was tested in a Mach 10 wind tunnel. The sharp-leading-edge flat plate was oriented at an angle of 20 degrees with respect to the freestream flow, resulting in post-shock edge Mach number of approximately 4. The flowfield was visualized using nitric oxide (NO) planar laser-induced fluorescence (PLIF). Flow visualizations were performed at 10 Hz using a wide-field of view and high-resolution NO PLIF system. A lower spatial resolution and smaller field of view NO PLIF system visualized the flow at 500 kHz, which was fast enough to resolve unsteady flow features. At the lowest Reynolds number studied, the flow was observed to be laminar and mostly steady. At the highest Reynolds number, flow visualizations showed streak instabilities generated immediately downstream of the trip. These instabilities transitioned to unsteady periodic and spatially irregular structures downstream. Quantitative surface heating imagery was obtained using the Temperature Sensitive Paint (TSP) technique. Comparisons between the PLIF flow visualizations and TSP heating measurements show a strong correlation between flow patterns and surface heating trends.