Effects of wall temperature and acoustic impedance surface on stability of high enthalpy boundary layer

The transition of the boundary layer from laminar flow to turbulence poses a serious challenge to the design of high-speed aircraft. The chemical non-equilibrium processes in the high-speed boundary layer flow make its instability mechanism more complicated, and the under-standing of the fundamental mechanism need to be strenghthened. This work investigates the effects of different wall temperatures and acoustic impedance boundaries on the flow stability using the linear stability analysis method with high-temperature chemical nonequilibrium and acoustic impedance surface taken into account. Research has found that compared to the calorically perfect gas, the high-temperature chemical non-equilibrium effect at the same wall temperature makes the dominant mode more unstable but has a smaller impact on the frequency of the peak mode. In the high enthalpy flow, wall cooling promotes the instability of the second and third modes, which can affect the mode synchronization process in the boundary layer more prominently than the chemical non-equilibrium effect, thus causing the corresponding frequency of the most unstable mode to move to the high frequency. Both the microgrooves and micropores on wall surfaces can significantly inhibit the second and third modes, but the difference between their effects decreases with the rise of wall temperature.