Hypersonic Boundary Layer Transition of BOLT-1B at Flight Conditions

The recent BOLT-1B flight experiment collected a high-quality dataset of surface pressure and heating measurements that capture the onset of boundary-layer transition under hypersonic flight conditions. Consistent with earlier BOLT-2 observations, the data show a marked rise in surface heating, accompanied in this case by distinct spectral peaks in pressure data near the centerline and midspan regions at slightly higher Reynolds numbers. These features suggest the presence of significant instability mechanisms that precede transition and motivate the present computational investigation. This study analyzes the BOLT-1B transition process using a combination of high-fidelity baseflow solutions, stochastically forced direct numerical simulation (DNS), and plane-marching parabolized stability equation (PPSE) analysis. The forced DNS is employed to model receptivity and nonlinear disturbance amplification within the boundary layer, supported by a modal analysis of the resulting transition process. Complementary PSE calculations provide linear growth predictions for comparison with the DNS and to establish a baseline consistent with linear stability theory. Together, these methods yield a comprehensive interpretation of the instability mechanisms that likely govern transition on BOLT-1B and provide a validated reference framework for future transition modeling efforts under realistic hypersonic flight environments.