Dynamics of a supersonic boundary layer over a curved compression ramp

Scale-resolved simulations are utilized to study the dynamics of a Mach 3 boundary layer developing under strong mechanical nonequilibrium, over a curved compression ramp of a high-speed mixed compression air intake. The nascent boundary layer trips through bypass mechanisms over the ramp, resulting in a tribalized profile, which rapidly deviates from canonical behavior in the vicinity of the compression zone. Wall spectra indicate three dominant bands of unsteadiness in this zone, and the corresponding dynamically relevant modes are identified: (a) the low-frequency large-wavelength modes which couple the boundary layer unsteadiness with the compression waves extending into the freestream, (b) the intermediate frequencies representing convective vortical structures extending over the outer edge of the boundary layer, and (c) the high-frequency modes representing the fine-scale turbulence within the boundary layer. The expansion fans formed at the ramp exit (at the ramp-isolator junction) effectively attenuate the fine-scale turbulence. However, the intermediate frequencies persist through the expansion fans following the compression ramp and are influential in determining the boundary layer instability entering the isolator of the intake.