During high-speed flight, the aircraft can utilize its own propellant to cool through the micro-hole jet to achieve active thermal protection. However, under high-temperature non-equilibrium conditions, the interaction between the compressible external flow and micro-jets involves complex processes including jet extrusion, mixing, and reactions, making the dominant mechanisms and influencing factors of micro-jet cooling highly intricate. In this study, a viscous wall boundary model for micro-jets was established, and numerical simulations of high-temperature non-equilibrium flow fields under micro-jet effects were conducted. The influence of jet hole diameter, velocity, and spacing on cooling performance were investigated. The simulations reveal the impact mechanisms of micro-jets on chemical reaction boundary layers, wall heterogeneous catalysis, and aerodynamic heating characteristics. The findings indicate that propellant micro-jet cooling under high-temperature non-equilibrium flow conditions is dominated by two key processes: boundary layer crowding and heterogeneous catalytic weakening. Specifically, the low-temperature micro-jet ejection crowds the boundary layer, altering its profile and reducing the temperature gradient near the wall, thus decreasing wall-normal heat conduction and achieving cooling. Additionally, the crowding-out effect of the low-temperature micro-jet promotes the outward displacement of near-wall O atoms, weakening the oxygen catalytic effect and reducing catalytic heat. Further parametric study shows that when the mass flow rate is constant, the heat reduction rate and cooling range decrease with the increase of jet hole size. When the area of the jet hole is constant, the micro-jet velocity is increased, and the heat reduction rate and cooling range are increased. When the mass flow rate is constant and the hole spacing is reduced, the peak value of the spanwise average heat reduction rate decreases, but the cooling range downstream of the hole increases, showing a more uniform cooling effect. These findings provide crucial theoretical support and technical guidance for the design and optimization of active thermal protection systems utilizing micro-jet cooling in future high-speed vehicles.

Advanced thermal protection system is an important part for safe flight of high-speed aircraft. With the development of composite material system for thermal protection, functional gradient composite materials with integrated thermal protection/insulation have been gradually applied to realize on-demand customization and collaborative design of thermal protection and thermal insulation properties. A tight coupling computation method for high Mach number aerothermal environment and thermal response of functionally gradient structure was developed for integrated thermal insulation composite structures. High-speed compressible flow/heat transfer coupling simulation of composite thermal structures with functionally gradient materials embedded was carried out under typical conditions. The infrared heating experiment of quartz lamp was carried out by testing functional gradient material with embedded layered temperature sensors. The influence of coupled heat transfer characteristics of composite thermal structures was obtained. The regulation mechanism of structural gradient characteristics on aerodynamic thermal load of aircraft was analyzed. It was found that under the condition of high Mach number air flow, the thermal insulation gradient material can better regulate the heat transport process inside the thermal insulation structure, which can not only prevent the instantaneous surface from exceeding the temperature limit to cause thermal damage, but also achieve uniform changes in the internal temperature of the structure to avoid thermal mismatch.