LAUSR

Surface ablation induced by aerodynamic heating is a common phenomenon for high-speed cruising vehicles, impacting surface geometry, temperature distribution, and mass injection, all of which play crucial roles in the perturbation evolution and boundary-layer transition. This paper presents a high-Reynolds-number asymptotic theory to formulate the impact of a local surface ablation on the Mack-mode evolution in high-enthalpy hypersonic boundary layers. The mean-flow distortion induced by ablation is formulated by the compressible triple-deck formalism, incorporating the chemical non-equilibrium effect. Simultaneously, the distortion of the Mack mode is formulated by the multi-scale analysis, with an amplification factor quantifying the overall impact of the ablation. The asymptotic model distinctly separates the effects of the mean-flow distortion and the Mack instability property. The amplification factor is attributed to two main factors: a local scattering effect at the ablation region, primarily contributed by the indentation, and a successive adjustment of the Mack growth rate, mainly contributed by the temperature distribution. The study reveals that the Mack mode experiences enhancement by ablation when its frequency falls below a critical threshold but is suppressed for higher frequencies. Remarkably, the critical frequency aligns closely with the most unstable frequency within the second-mode frequency band.