On the stability of rarefied gas flows over a compression corner calculated using kinetic methods*

Two-dimensional supersonic flow over several compression corners have been studied using Direct Simulation Monte Carlo (DSMC) and linear BiGlobal stability analysed. The steady-state base flow is dominated by a large separation bubble, which becomes larger at increasing ramp angles. The maximum recirculation, calculated by reference to the free stream velocity, is found to be around 10% for all cases. Linear stability analysis is performed on the two-dimensional DSMC states by imposing a wide range of spanwise wavelengths in order to understand the transition behaviour of such flows. At long times these flows are shown to be linearly stable despite the high ramp angles used. The dominant stationary least damped mode persists over a range of wavenumbers and its amplitude function is consistent with those shown in many previous separated flow studies. While, at short time behaviour, through the solution of an initial value problem, there are signs of significant energy growth of disturbances that may lead to the bypass of the long-time behaviour causing transition to occur in specific three-dimensional cases. These potential peaks in energy gain are currently being studied more closely to identify the scenarios most at risk of causing a transition to turbulence.