Transition to turbulence in hypersonic flow over a compression ramp due to intrinsic instability

In this work, a transition process in hypersonic flow over cold-wall compression ramp is studied using direct numerical simulation (DNS) and global stability analysis (GSA). The free-stream Mach number the Reynolds based on flat-plate length are 7.7 $8.6 \times 10^5$ , respectively. shock-induced pressure rise causes boundary layer to separate flat plate, forming separation bubble around corner. Without introducing any external disturbances, DNS captures turbulence downstream of reattachment. results agree well with experimental data as theoretical predictions. To uncover intrinsic instability system, GSA employed investigate three-dimensionality two-dimensional base flow. Several stationary oscillatory unstable modes revealed, which result spanwise periodicity inside bubble. indicate that system triggers formation streamwise counter-rotating vortices boundary-layer streaks near starts from breakdown streaks. Moreover, second harmonic most mode broadband low-frequency unsteadiness occur saturated flow, has significant influence process. summary, present study demonstrates compression-ramp system.