壁温和声阻抗边界对高焓边界层稳定性影响

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

  • 摘要: 边界层从层流到湍流的转捩是高速飞行器设计面临的重要难题。高速边界层流动中的高温化学非平衡过程使流动失稳机制更加复杂,其机理认识有待深化。通过考虑高温化学非平衡和声阻抗边界的线性稳定性分析方法,研究了不同壁温和不同声阻抗边界对流动稳定性的影响。研究发现,当壁温相同时,与量热完全气体状态相比,高温化学非平衡效应使主导模态更不稳定,但对模态峰值频率的影响较小。在高焓流动中,壁面冷却促进第二、第三模态失稳,该效应比化学非平衡效应更能影响边界层内模态同步过程,从而导致最不稳定模态对应频率向高频移动。微槽和微圆孔壁面均能明显抑制第二、第三模态,但随壁温升高,二者抑制效果的差异减小。

     

    Abstract: 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.

     

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