可压缩混合层湍流结构的生成演化机理研究

Coherent structure of mixing layer is very classical in turbulent flow and its generation and evolution mechanism has some universality. In order to understand these mechanisms, a strategy from instability wave to instability structure then to coherent structure has been proposed out and three jobs has been planned in this project. The first job is to study the flow instability of mixing layer from low convective Mach number to high convective Mach number by using linear stability theory. The second job is to simulate the generation process from instability wave to instability structure and the evolution process from instability structure to coherent structure by using numerical method. The last job is obtain some photos of these flow structures with high fidelity by using flow visualization technique, which can be used to validate the prediction results from theory. The intrinsic relation between instability wave and instability structure will be built, and the nonlinear interaction among the instability waves will be used to explain the generation mechanism of coherent structures of mixing layer. Furthermore, the dynamics parameters of these structures can be obtained from numerical and experimental visualization photos.

混合层流动具有非常典型的湍流结构，其生成和演化机制具有一定的普适性。本项目提出从失稳扰动到失稳结构再到湍流结构的研究思路，拟通过三方面的研究来认识混合层湍流结构的生成与演化机制。一是开展宽范围对流马赫数混合层流动的稳定性分析，确定失稳扰动类型与扰动参数；二是通过数值模拟研究不稳定扰动生成失稳结构的过程，以及从失稳结构到湍流结构的演化过程；三是通过流动显示技术给出混合层失稳结构和湍流结构的清晰照片，对理论预测结果进行验证。稳定性分析与数值模拟将建立不稳定扰动与失稳结构的关系，扰动之间的非线性作用将为湍流结构的生成机制提供解释，而数值与实验显示将给出失稳结构和湍流结构的动力学参数。

混合层具有丰富的流动结构，这些结构的产生和演化过程有助于认识湍流结构行为。在本项目资助下，我们研究了宽范围对流马赫数混合层流动的线性稳定性，分析获得了声模态扰动及其空间演化特征，对混合层扰动模态进行了重新分类，消除了概念间的混淆；发现温度比值大于1以后，即使对流马赫数小于0.6，混合层最不稳定波也是三维的；采用数值模拟方法研究了单一扰动和多个扰动演化产生的流动结构，证实扰动增长放大形成失稳结构；通过小扰动理论建立了波纹壁增强混合的控制原理，给出了波纹壁几何参数的设计依据；提出用涡线来辅助识别流动结构，发现混合层经历一次失稳、二次失稳后，在后掠Λ结构的头部出现涡环结构，引起后掠结构的再次失稳，加速进入湍流状态。这些新的认识为湍流结构研究提供了素材。