Preflight ground test analyses of the boundary layer transition (Bolt) flight geometry

Abstract

Wind-tunnel experiments were performed to quantify boundary-layer instabilities both on and off the surface of a 33% scale model of the U.S. Air Force Research Laboratory/U.S. Air Force Office of Scientific Research Boundary Layer Transition (BOLT) flight geometry. Measurements were obtained in the Mach 6 Quiet Tunnel and Actively Controlled Expansion (ACE) tunnel located at the Texas A&M University National Aerothermochemistry and Hypersonics Laboratory. Surface heating was quantified using infrared thermography. Under quiet conditions, heat flux was characterized by a streak structure with no transition observed. Transition was observed within the conventional noise ACE facility in two regions: 1) in the vicinity of a mixed-mode structure and 2) in an outboard traveling crossflow region. The flow structure within a coherent vortex rollup located off centerline was further characterized under quiet flow conditions with constant-temperature hot-wire anemometry and high-frequency surface-pressure spectra. The measured mean and disturbance flow structure were in qualitative agreement with the simulations. The hot-wire spectral content showed growth in the 25–40 kHz range, which also agreed with the simulations. Surface-pressure spectral results showed similar growth in the 25–50 kHz range observed under both quiet and conventional freestream conditions.