近轴对称超声速管内激波汇聚特征和机理

A convergent axisymmetric shock wave will face a problem of focusing and strength enhancement. It was found that a transition to Mach reflection and formation of Mach disk will occur at the center part and therefore an infinite increment to the center is terminated. However, if there exists a deviation away from the axisymmetric condition, the circular Mach disk can no longer be maintainable since the convergence is non-uniformly distributed along the circumferential direction. How the wave structure develops is an unknown subject to the best of the applicant's knowledge. On the other hand, from an engineering point of view, such kind of near-axisymmetric supersonic flows can be easily found in hypersonic airbreathing propulsion system, particularly an inward turning hypersonic inlet. Therefore, an investigation on near-axisymmetric shock wave interaction is important not only for academic interests, but also for engineering applications. Based on the above considerations, this proposal is concentrated on the shock enhancement process during the convergence, with special care about the shock instable development that caused by small non-axisymmetric deviations. At the same time, the quality of the flowfield, the loss caused by the severe interactions at the center part, as well as the performance of the channel flow are going to be evaluated, and possible optimizations and improvements are also planned to be challenged. We hope that the achievements of the proposed project will become a useful reference for the design and development of the new-generation hypersonic vehicle, as well as enriching the knowledge of shock wave interaction phenomena.

圆截面超声速内压缩流道产生的轴对称激波在向内传播过程中将面临汇聚增强的问题。前人已认识到此类激波汇聚终将通过马赫反射，即转变为马赫盘从而终止向轴心汇聚的无限增强问题。但一旦轴对称条件不能严格保证而出现偏离，则激波汇聚中周向不平衡发展会颠覆圆形马赫盘赖以存在的前提，此时波系如何演变尚未见有针对性的研究报道。而工程应用中，以高超声速内转式进气道为代表的内流道通常都是以接近轴对称的超声速流动形式存在。可见，近轴对称管内流动激波演变及相互作用研究的学术和应用价值都较高。本项目申请拟以内转式进气道为代表的近轴对称超声速管内流动为背景，重点关注其中的激波汇聚增强过程，小幅非轴对称条件引起的激波演变不稳定发展特征和规律，考察汇聚中心附近参数显著变化对流道性能的影响，尝试探索抑制流场恶化和提高效能的途径，在丰富相关的机理和规律认识的基础上，为新一代吸气式高超声速飞行器研制提供概念支撑和理论参考乃至指导。

针对以高超声速内转式进气道为代表的近圆形截面内收缩管道产生的激波及相互作用问题，提出激波汇聚演变的近轴对称流动模型，采用椭圆内锥和非轴向来流内锥构型，从几何和来流偏轴对称两个方面，突出近轴对称的重点，并分解表征三维激波的难点，高效揭示激波周向不均匀演化与不稳定发展的核心机制。研究表明，轴对称内锥激波汇聚增强必然会形成马赫反射，马赫盘位置不仅受激波自身强度约束，还与马赫盘下游形成的声速喉道密切相关；而几何或来流偏轴对称带来的初始激波横向曲率或强度的非均匀性，在激波汇聚过程中都会被放大，导致原本光滑的激波面上出现拐折点，被拐折点分割的激波趋于扁平化，为汇聚中心发生规则反射创造了关键条件。利用高超声速等价原理进行空间降维并结合几何激波动力学，构建了波面扰动追踪法，不仅快速预测了近轴对称条件下的激波汇聚演化过程，而且阐明了激波面不稳性发展并形成拐折点的机制。进一步地，明晰了椭圆内锥激波汇聚演化主要呈现马赫反射、临界反射和规则反射三种类型，在不同长短轴比和前缘压缩角下揭示了反射类型的转变规律；而非轴向来流内锥流动存在马赫反射和规则反射两种类型，揭示了来流攻角、马赫数对激波不稳定性发展的影响规律。此外，还发现斜切内锥兼具几何和来流偏轴对称的特征，揭示了斜切角对激波汇聚并产生马赫反射或规则反射的影响规律。研究成果可为革新高超声速内转式进气道设计提供概念支撑和理论方法参考，在国内外重要学术期刊发表论文11篇，其中Journal of Fluid Mechanics 3篇，Physics of Fluids、AIAA Journal、Chinese Journal of Aeronautics各1篇，《航空学报》等中文期刊5篇；发表会议论文4篇；出版学术专著1部。项目负责人杨基明教授在第32届国际激波学术会议上作大会邀请报告。本项目共培养毕业博士生5人，在读博士生4人，在读硕士生1人。