DNS of Hypersonic Boundary Layer Transition in the BOLT II Side A Descent Trajectory

The BOLT II flight experiment has provided a wealth of data on boundary layer transition on a complex geometry, and offers a unique opportunity to validate direct numerical simulation (DNS) predictions against flight test data. This work investigates boundary layer transition on the BOLT II side A geometry using low-dissipation DNS in the US3D solver. A case at Re_L = 6 × 10⁶ is selected for analysis, as it represents the beginning of centerline transition on BOLT II. Freestream isotropic atmospheric turbulence with dissipation rates based on HYFLITS ballooning data is used to excite the flowfield, and turbulent wall heat fluxes are compared against flight data. It is confirmed that extremely low dissipation numerical simulations allow for the preservation and evolution of small-amplitude noise which is otherwise dissipated out in a standard DNS. We show that grid singularities generate noise, which can initiate boundary layer transition in an unforced DNS. By moving grid singularities away from the upstream of transition regions, we are able to mitigate numerically induced boundary layer transition. We obtain a laminar, low-dissipation, unforced baseflow which will enable us to study the impact of low-amplitude atmospheric turbulence on the sensitive hypersonic flowfield of BOLT II.