On linear global instability at the leading edge of a short compression corner with large ramp angle

Abstract Global linear stability analysis of Mach 3 flow over a short compression corner is investigated at Reynolds number 11200 and Knudsen number O(10−4), for the first time using both kinetic theory direct simulation Monte Carlo (DSMC) and continuum Navier–Stokes–Fourier (direct numerical simulation (DNS)). In two dimensions, discrepancies emerged in the shock layer and at the wall, where kinetic simulations resolve the internal shock structure and capture velocity slip and temperature jumps. The BiGlobal eigenvalue analysis using these steady states as base flows yielded qualitatively identical spectra, except for one unstable global mode. This instability appears only in spectra obtained from DSMC base flows, confirmed by three-dimensional unsteady DSMC simulations in both amplification rate and spanwise extent, and persists across a wide range of spanwise wavelengths. The amplitude functions of the leading-edge (LE) global mode peak at the LE and separation shocks, extending into the shear layer of the separation bubble, where DSMC- and DNS-obtained flows differ. Three-dimensional DSMC simulations were continued past the stage of linear amplification into the nonlinear regime, documenting the evolution of the unstable flow up to the generation of λ-vortices, seen for the first time in a kinetic simulation.