Measurements of Boundary-Layer Transition During the BOLT-1B Flight Experiment

The Boundary-Layer Transition (BOLT) series of flight experiments was designed to study hypersonic boundary-layer transition and turbulence on a geometry with low-curvature concave surfaces and highly-swept leading edges. The BOLT-1B flight experiment successfully flew on September 2nd, 2024 and a rich data set on Mach 7 boundary-layer transition was collected. Detailed spanwise heat transfer profiles were combined with computational fluid dynamics to study the origin of laminar heating streaks and variations due to Reynolds number. A quantitative methodology to extract transition fronts for BOLT-1B was developed and found Re_Tr = 6−7×10^6, depending on spanwise location. High-frequency pressure sensors measured multiple potential boundary-layer instabilities with peak frequencies between 90 and 300 kHz. The growth and breakdown of these potential instabilities were measured. The BOLT-1B flight data was shown to be heavily influenced by angle of attack and side slip with oscillations in the payload attitude greatly altering the flow field.