Characteristics of the three-dimensional boundary layer over a lifting body at Mach 12

Direct numerical simulation (DNS) is performed to investigate the three-dimensional turbulent boundary layer on the leeward side of a lifting body, the HyTRV model, at Mach number 12 and attack angle $6^\circ$. The complicated interactions involving the transition process and three-dimensional effects induce two distinct regions of enhanced skin friction and wall heat flux: the upstream Region A and the downstream Region B. Results indicate that Region A is dominated by flow acceleration coupled with unsteady separation and reattachment, while Region B is driven by the roll-up and breakdown of quasi-streamwise vortices. Furthermore, the friction Reynolds number $Re_{\tau}$ reaches approximately 3000 in Region A, whereas the momentum thickness Reynolds number $Re_{\theta}$ exhibits an overshoot in Region B. Distinct flow structures are also identified: Region A is characterized by a band structure of quasi-streamwise high-momentum flow, while Region B features fully developed transverse vortical structures. Notably, compressibility effects are significant in these regions, evidenced by a negatively skewed dilatation distribution and shocklets extending into the outer layer. Regarding turbulence statistics, Reynolds stress components in the upstream region exhibit pronounced outer peaks except for Region A, attributed to large-scale structures induced by blowing/suction effects. Conversely, Region B is characterized by intense turbulence production leading to prominent inner peaks. Moreover, Joint Probability Density Functions analysis reveals a characteristic frequency-stress decoupling mechanism: while sweep (Q4) events occur more frequently as diffusive recirculation flows, the Reynolds stress is predominantly generated by intermittent ejection (Q2) events driven by the heads of quasi-streamwise and spanwise vortices.