Direct numerical simulation of high-speed turbulent boundary layers over a backward-facing curved wall

We perform direct numerical simulations (DNS) of turbulent boundary layers over a backward-facing curved wall at free-stream Mach numbers 2, 4, and 6, and a friction Reynolds number Re_τ=1000 upstream of the wall curvature. The effect of wall temperature is also investigated, considering both adiabatic and cold walls. We find that the flow physics differ substantially from those of canonical shock wave/boundary layer interactions. In particular, we do not observe evidence of the typical low-frequency unsteadiness associated with a reattachment shock, despite the presence of Görtler vortices visible in the instantaneous flow field. We also perform Reynolds-averaged Navier–Stokes (RANS) simulations at matched flow conditions using the Spalart–Allmaras model and conduct both a-priori and a-posteriori analyses, focusing on the Reynolds stress tensor and the turbulent heat flux vector. The results show that the baseline Spalart–Allmaras model captures the main flow features, including separation and reattachment. The a-priori study indicates that improved accuracy could be achieved using nonlinear constitutive relations.