  Linear stability of supersonic flow over a short compression corner with ramp
angles 30 and 42 is investigated using Direct Simulation Monte Carlo (DSMC) and
Linear Stability Theory (LST) at Mach number 3, Reynolds number 11,200 and low
Knudsen number, O(10$^{-4}$). The two-dimensional base flows feature nonzero
velocity slip and temperature jump and were found to be steady and laminar at
both ramp angles. Modal analysis revealed a previously unknown traveling
three-dimensional global mode, the amplitude functions of which peak at the
leading-edge and separation shocks and extend within the shear layer of the
large laminar separation bubble formed on the short compression corner. This
mode is linearly unstable at the higher ramp angle and stable at the lower one,
while the known stationary three-dimensional global mode which peaks at the
laminar separation is also present in the spectrum, but is (strongly) damped at
both ramp angles. Three-dimensional DSMC simulations have fully confirmed the
LST results, underlined (again) the significance of modeling the shock
contribution in linear stability analyses of high-speed flow, and predicted the
nonlinear evolution of the flow up to the generation of lambda vortices on the
ramp, for the first time in the context of kinetic theory simulations.
