高超声速圆锥边界层对平面涡波的感受性研究

边界层的转捩预测是高超声速飞行器设计中需要考虑的重要问题。由于高超声速实验难度大，很难像低速飞行器那样，有足够的实验数据来支撑半经验的预测方法。为此，需要理解转捩过程中的核心科学问题，从机理上完善预测方法。其中，边界层对外界扰动的响应，即感受性问题是必须考虑的关键问题。本项目拟针对自由流平面涡波扰动，开展高超声速圆锥边界层的感受性研究。平面涡波是高空中由大气湍流引起的速度脉动，较过去研究地比较多的声波而言，是更贴近物理现实的自由流扰动。通过理论分析和直接数值模拟相结合的方法，找到直接对感受性起主导作用的激波后的扰动，理解边界层中不稳定波激发的具体路径和内在机理。研究结果将提升对感受性机理的科学认知，完善基于物理机理的转捩预测方法。

Boundary-layer transition prediction is of great importance in designing hypersonic flight vehicles. Due to great difficulties of implementing hypersonic experiments, there is no enough experimental data to realize a semi-empirical method of transition prediction for high-speed flight vehicles as reliably as for their low-speed counterparts. For that purpose, one has to understand the key scientific problems involved in the process of transition, and improve the transition prediction method based on physical mechanism. Among them, the response of a boundary layer to external disturbances, i.e. receptivity is a key problem which must be considered. This project investigates the receptivity of a boundary layer over a cone to a planar free-stream vorticity. A planar vorticity is induced by the velocity fluctuations due to atmospheric turbulence. It is a more common free-stream disturbance at high altitude compared with acoustic disturbances, which have been extensively investigated previously. By means of theoretical analysis and direct numerical simulation, we will find the disturbance which plays a leading role in receptivity behind the shock, and understand the specific route through which the instability wave is excited in the boundary layer and its corresponding mechanism. The outcome of the present study will promote further understanding of receptivity mechanism, and consequently improve the transition prediction method based on physical mechanism.