On the Unsteadiness and Three Dimensionality of a Laminar Separation Bubble for a Supersonic Flow over a Compression Corner

Two-dimensional supersonic flow over several compression corners are computed by Direct Simulation Monte Carlo (DSMC) and their linear global stability are analysed by solution of the compressible BiGlobal eigenvalue problem on generalized coordinates. The base flow features a large separation bubble, while time resolved DSMC data shows that the flow reached a steady state at the parameters examined. The maximum recirculation, calculated as the ratio of maximum negative streamwise velocity to free stream velocity, is found to be around 10% for all cases. Linear stability analysis performed confirms this prediction, yielding a globally stable solution for a wide range of spanwise wavenumbers. The two-dimensional (spanwise wavenumber B= 0) limit is found to be the least stable, an increase of leading to more stablespectra while retaining the same leading stationary mode. Higher scaled ramp angles, creating substantially higher recirculation levels, are currently being analyzed.