BOLT-1B Roughness Side Flight Results

A series of flight experiments referred to as BOLT (for Boundary Layer Transition/Turbulence) has been underway since 2017 to study hypersonic transition or turbulence on a geometry with concave surfaces and highly swept leading edges. The most recent flight was with BOLT-1B, which successfully flew from Andøya, Norway, on September 2, 2024. The BOLT geometry provides two independent surfaces that allow for both smooth and rough wall experiments to be flown at the same time. The present report is focused on the BOLT-1B rough wall flight data, which were developed to investigate the effect of nose-joint steps. Details on the as-flown size and locations of joint steps are provided. Comparisons of the boundary-layer transition onset movement between the smooth and rough sides as a function of flight conditions have shown that the flight results behaved as expected, with the rough side having a lower transition Reynolds number than the smooth side. The rough side flight transition data compare favorably to the ground-based step correlation used to design the experiment.