A study of hypersonic flow control over a curved compression ramp

The experimental study of a curved ramp model was conducted at Mach 6 freestream conditions with a unit Reynolds number of 7.3 × 106 m−1 in the Ludwieg tube at the Hong Kong Polytechnic University. In addition, a two-dimensional numerical flow study was conducted to assist in validating and explaining the phenomena captured in the experiments. The benchmark geometry comprises a 60-mm long flat plate followed by a 16° ramp. Multiple rounding radius configurations of 16° ramp were experimentally and numerically investigated to analyze flow variations. Flow diagnostics included high speed Schlieren imaging, Rayleigh scattering visualization, and infrared thermography. Results indicate that the boundary layer on the flat plate remains laminar up to the separation point. The benchmark compression corner exhibited large-scale separation. The small ramp rounding radii slightly reduce the separation bubble, yielding dimensions comparable to the benchmark case, whereas increasing the radius to a critical value leads to its complete suppression. The suppression of the separation bubble beyond the critical radius eliminates the heating peak associated with reattachment shock, suggesting that the curved compression ramp configuration can effectively mitigate thermal concentration on the ramp surface. The transition location exhibits minimal sensitivity to radius variations below the critical threshold but shifted downstream once this threshold is exceeded. Streamwise streaks with regularly distributed spanwise band structures are observed in all cases, showing radius-dependent spanwise wavelengths variations and delayed distortion and breakdown positions at larger rounding radius. To unravel the underlying instability mechanisms, the resolvent analysis and global stability analysis were applied to identify and validate the dominant instability modes in the flow.