Boundary-Layer Transition Over a Smooth Circular Cone at Non-Zero Angle of Attack in a Mach 8 Digital Wind Tunnel

This paper presents a three-dimensional direct numerical simulation (DNS) of hypersonic boundary-layer transition over a sharp, 7-degree half-angle cone at an 8-degree angle of attack subjected to tunnel-like freestream acoustic disturbances. The flow conditions and geometry match those of experiments conducted in the Sandia Hypersonic Wind Tunnel at Mach 8 (Sandia HWT-8). The DNS captures all stages of the transition process driven by tunnel noise, including the propagation of broadband acoustic fluctuations through the bow shock; boundary-layer receptivity; the generation and amplification of Mack's second-mode and crossflow waves and the unsteady shear-layer instability of the leeward vortex; the nonlinear growth and breakdown of disturbances; and the subsequent development of a fully turbulent boundary layer. The inflow acoustic disturbances were reconstructed from acoustic radiation generated by the turbulent boundary layer over the Sandia nozzle wall, a methodology previously validated in DNS of the same cone at zero degrees angle of attack. The present study extends this framework to a nonzero angle of attack and provides a characterization of the resulting asymmetric transition on the cone in a Mach 8 ``noisy'' environment. The results reveal a strongly asymmetric transition pattern induced by the angle of attack. On the leeward side, the mushroom-shaped vortex experiences early distortion and breakdown, leading to localized shocklet formation and transition to turbulence upstream of the windward side. In contrast, the windward side remains laminar over a longer streamwise distance, with transition dominated by second-mode instabilities that develop later along the cone. Analysis of (synthetic) Schlieren, vorticity, and divergence fields indicates that the interactions with freestream acoustic disturbances play a key role in the complex three-dimensional transition process. The wall-pressure spectra across all azimuthal locations in the turbulent regions of the cone compared well with those measured in the Sandia HWT-8.