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.