Real-Gas and Surface-Ablation Effects on Hypersonic Boundary-Layer Instability over a Blunt Cone

There has been little research into surface-ablation effects on hypersonic boundary-layer instability, and the current understanding of real-gas effects on hypersonic boundary-layer instability still contains uncertainties. The objective of the current work was to analyze the hypersonic boundary-layer transition process using linear-stability theory, inwhich surface ablation, aswell as real-gas effects, is present, and the secondmode is the dominant instability mode. A thermochemical nonequilibrium linear-stability-theory code with a gas-phase model that includes multiple carbon species, as well as a linearized surface graphite-pseudoablation model, is developed and validated. It is validated with previously published linear-stability analysis and direct-numerical-simulation results. A high-order method for discretizing the linear-stability equations is used, which can easily include high-order boundary conditions. The developed linear-stability code, with mean-flow solutions produced from a high-order shock-fitting direct-numerical-simulation method for hypersonic flows with thermochemical nonequilibrium and surfacechemistry boundary conditions for graphite pseudoablation, is used to study hypersonic boundary-layer instability for a 7 deg half-angle blunt cone at Mach 15.99 and the Reentry-F experiment at 100 kft. Multiple mean-flow simulations are obtained with the same geometry and freestream conditions to help separate real-gas, blowing, and carbon-species effects on hypersonic boundary-layer instability. For the case at Mach 15.99, anN factor comparison shows that real-gas effects significantly destabilize the flowwhencompared to an ideal gas.Blowing is destabilizing for the real-gas simulation, and has a negligible effect for the ideal-gas simulation due to the different locations of instability onset. Notably, carbon species resulting fromablation are shown to slightly stabilize the flow for both cases. It is also found that ablating nose-cone effects may safely be excluded when determining theN factor at transition for Reentry-F at 100 kft.