Chemical non-equilibrium effects on entropy-layer stabilities over blunt cones

High-temperature gas effects from bow shock compression and flow friction complicate the transition process. In high-speed flows, a quasi-normal shock and substantial shock angle gradients near the leading edge form an entropy layer. This inviscid, high-vorticity layer overlies the boundary layer. In the region adjacent to the leading edge where the high-temperature gas effects are particularly intense, these effects may strongly affect the entropy-layer stability. Further downstream, the entropy layer will be swallowed by the developing boundary layer, and the perturbations within the entropy layer can propagate into the boundary layer, thereby inducing further instability. However, research on the influence of high-temperature gas effects, particularly chemical non-equilibrium effects, on entropy-layer stability remains limited. In this study, based on the linear stability theory that takes chemical non-equilibrium effects into account, the unstable modes of chemical non-equilibrium entropy layers are computed. The influence of chemical non-equilibrium effects on the entropy-layer stability is explored, along with the effects of Mach number, ionization, and surface catalysis. The findings reveal that in the chemical non-equilibrium entropy layer, there exist inviscid modes with low frequency and low growth rate. Chemical non-equilibrium effects lead to lower growth rates and a narrower instability range. Increasing the Mach number suppresses the entropy-layer mode, whereas the ionization effect promotes it; in contrast, the surface catalysis exerts a relatively minor influence. Additionally, numerical simulations of the evolution of entropy-layer modes were performed, indicating that the entropy-layer mode can excite the unstable mode of the boundary layer in chemical non-equilibrium flows.