Stability analysis of hypersonic flow over a backstep in chemical equilibrium

Abstract

The purpose of this work is to shed light on the role of chemical equilibrium in the global instabilities that arise in hypersonic non-parallel flows. For this end, the stability of temporal evolving disturbances on a hypersonic flow over a backstep are examined by the linearized Navier-Stokes equations. The flow conditions are unit Reynolds number equal to 6.6 x 10^6 1/m, boundary-layer edge temperature 350 K and freestream Mach number 10. The step height is equal to the local displacement thickness. For these conditions the two-dimensional laminar base flow is computed with the full Navier-Stokes solver TAU software. The results for a given wave number of the perturbations in the homogeneous direction shows that the leading linear mode located around the recirculation bubble is unstable in both cases. The real gas effects increase the temporal growth rate of the leading mode. This instability corresponds to a zero-frequency global linear instability. The spectrum and the structure of the leading mode for real and perfect gas are presented and compared.