Time and length scales of pressure fluctuations in supersonic flow over swept ramps

We perform direct numerical simulations (DNS) of fully turbulent flow at an x-projected Mach number of 2.9 over a 24° compression ramp to investigate shock wave–boundary layer interactions (SBLI) with flow separation. By imposing a crossflow velocity corresponding to sweep angles of 0∘, 15∘, and 30∘, we reproduce three-dimensional interactions under cylindrical symmetry. Our study focuses on the wall pressure structure within the separated region, which is observed to enlarge under swept conditions. Increasing the sweep angle results in pressure fluctuations characterized by longer length scales and enhanced spatial coherence. Spectral analysis of wall pressure signal reveals large-scale disturbances with spanwise wavelength comparable to the separation length, which appear as coherent corrugations along the separation line associated with distinct dominant frequencies. In the unswept case, a low-frequency peak is observed at a separation length-based Strouhal number of 0.05, which shifts to higher frequencies and grows in amplitude with increased sweep. Spatio-temporal diagnostics further elucidates a dual mechanism driving pressure disturbances in the separated zone, comprising a two-dimensional ‘breathing’ motion of the separation bubble coupled with a spanwise drift at approximately 70% of the crossflow velocity. Last, we wind that the scaling law for the typical frequency of the shock motion developed by Ceci et al. [1] for swept interactions also works well for compression ramp flow upon suitable recalibration of the coefficients, as supported by existing experimental data.