大钝度钝锥高超声速边界层转捩机理数值模拟研究

Hypersonic boundary layer transition is a complex fluid process involving many kinds of influence factors and physical mechanisms. Despite more than half a century of extensive researches, many problems in transition process are still not well understood. Among them, “transition reversal” phenomenon observed in the boundary layer of circle cone with large nose bluntness, is not explained with any mechanisms. This problem produces certain indeterminacy for prediction of hypersonic boundary layer transition, and increases difficulties for advanced vehicles as well. Around the problems of large bluntness cone transition, the more real or more close to wind tunnel experimental conditions, including freestream disturbance parameters and surface roughness, will be investigated by system direct numerical simulations of hypersonic boundary layer on large bluntness cone. It is hoped that large bluntness transition mechanisms will be understood deeply and the reasons leading to “transition reversal” will be explained by analyzing the production and evolution process of disturbances within hypersonic boundary layer. These studies will provide fundamental theories for prediction and control of boundary layer transition on hypersonic vehicles with large nose bluntness.

高超声速边界层转捩是一个包含多种影响因素和物理机制的复杂流动过程。尽管相关研究已经进行了半个多世纪，但对转捩过程的认识仍不完全清楚，其中大钝度钝锥边界层“转捩逆转”现象至今其没有得到解释，这给高超声速边界层转捩预测带来一定的不确定性，增加了先进飞行器设计的困难。本项目拟围绕大钝度钝锥边界层转捩开展研究，拟采用更加真实、接近于风洞实验条件的自由流扰动参数和壁面粗糙度，对高超声速大钝度钝锥边界层转捩过程开展系统的数值模拟研究。希望通过对边界层中扰动波产生和演化过程的细致模拟和分析，深入了解大钝度转捩的物理机制，探寻“转捩逆转”现象发生的根源，为高超声速钝头体飞行器边界层转捩预测及控制提供理论依据。

头部钝度是影响高超声速飞行器边界层转捩位置的重要影响因素，但钝度影响转捩的物理机制尚不完全清楚，其中在大钝度时发生的“转捩逆转”的现象至今没得到合理的解释，本项目针对大钝度钝锥高超声速边界层转捩过程进行了数值模拟研究，同时开展了相关的风洞实验和线性稳定性理论分析研究，目前已完成相关研究内容。根据项目内容安排，针对钝度Rn=5、25、40mm的半锥角7度钝锥进行了单频、多频多幅的自由流快/慢声波的感受性过程直接数值模拟，并对比了头部粗糙度的影响，另外在Mach6高超声速风洞中对钝锥进行了边界层转捩位置和壁面脉动压力测量。数值模拟和风洞实验结果都表明，大钝度钝锥（Rn=25、40mm）边界层中没有明显的第二模态波，与线性稳定性分析结果一致，即大钝度钝锥边界层转捩不是由第二模态波导致，但是在边界层中存在一簇较宽频带的扰动，尽管该类扰动较弱，但在风洞实验中最终导致转捩发生。本项研究通过对大钝度钝锥边界层自由流声波感受性过程的模拟和不稳定波的测量，为最终完全揭示大钝度钝锥边界层转捩机理奠定了基础，同时为下一步工作确立了研究方向。