Curvature effect on low-frequency unsteadiness on shock-turbulent boundary layer interaction

The effect of ramp curvature on shock–turbulent boundary layer interaction (STBLI) at Mach 2.9 is investigated using direct numerical simulations (DNS). As the corner radius increases, the strength and extent of mean flow separation progressively decrease, while the skin friction coefficient and heat transfer rate increase downstream of the ramp corner. When mean separation is absent, the flow statistically remains attached to the wall. In this case, the characteristic low-frequency unsteadiness is suppressed, although a mid-frequency peak remains. This observation indicates that the emergence of characteristic low-frequency unsteadiness requires the presence of a mean separation bubble. In the highly curved ramp, the reattachment shock appears as a fan of compression waves, inducing strong compressibility effects within the boundary layer, especially downstream of the ramp corner. Instantaneous flow fields and vortex transport analysis reveal the presence of Görtler-like streaks, in which the vortex cores align in the streamwise direction with decreasing radial extent and shift closer to the wall in the downstream of the ramp corner as the curvature increases.