航空发动机三维弯掠叶片与短舱声衬的声学相互影响研究

The bypass-ratio of modern turbofan engine increases constantly, and fan noise is attached more and more significance. Correspondingly, the acoustic design in engine nacelle meets up with challenges. On the one hand, the three-dimensional sound source modeling is needed; On the other hand, the length of nacelle is getting smaller, and this effect on the liner’s optimization should be taken into account. In this application: 1) we use the established three-dimensional sound source prediction models, both for fan discrete and broadband noise, to further study the passive control of fan noise by swept-and-leaned vanes design. 2) by employing the transfer element method, the mutual effects between the swept-and-leaned vanes design and finite nacelle acoustic liners optimization are investigated, to gain larger benefits of noise reduction. 3) the mature numerical calculation methods are used to solve the scattering near the inlet and outlet of the nacelle. With the computation cost considered, the numerical simulation and the internal transfer elements analysis are coupled. In this way, the geometry and the non-uniform mean flow, which are near the inlet and outlet of the nacelle, and more realistic sound source input can be considered at the same time for the finite liners optimization. This application is expected to provide a more favorable guide for the nacelle acoustic design through the study of the fast-running theoretical model and its comparison with the relevant experimental results.

现代民用涡轮风扇发动机涵道比不断增大，风扇/压气机噪声日益凸显，相应的，短舱声学设计面临更高的要求：一方面，需要发展全三维声源预测模型；另一方面，短舱长度减小，声衬设计需要考虑有限长管道的影响。本项申请中：1）首先利用我们已发展的包含离散和宽频干涉噪声的三维声源预测模型，进一步对弯掠叶片被动控制风扇噪声的机理进行研究；2）进而结合传递单元方法，研究叶片弯掠造型和声衬两种不同降噪措施之间的相互影响，期望获得更大的降噪收益；3）将目前较为成熟的数值计算方法用来求解短舱进/出口的散射，同时在尽量节省计算量的前提下，通过界面匹配的方式实现数值模拟与管道内部各声学单元之间的耦合求解，实现即包含真实声源输入、又包含端口几何形状及非均匀流动等因素影响的有限长短舱声衬设计。本项申请期望通过建立快速求解的理论模型，及与相关实验结果的对比验证，为短舱声学设计方案提供更有利的指导。

静子叶片弯掠和短舱声衬分别是从声源和声传播角度控制风扇噪声。随着风扇涵道比不断增大，短舱声学设计面临更高的要求：一方面，需要发展全三维风扇噪声声源预测模型；另一方面，短舱长度减小，声衬设计需要考虑有限长管道的影响。本项目从这两方面入手，并且着重研究声源与声衬的声学相互作用。.本项目完成了航空发动机短舱内三维弯掠叶片与声衬的声学相互作用研究，提出了考虑相互作用时的短舱声学初步设计思路。实现了以下重要结果：验证了管道内声场模态对叶片响应的影响，验证了叶片弯掠设计会改变声衬最优阻抗区间；改进了传递单元界面匹配方式，实现数值模拟方法与内部管道单元之间的耦合求解，包含真实声源输入、端口几何形状及非均匀流动等因素影响；研究了弯掠叶片对宽频噪声控制效果，风扇宽频预测模型为管道内多模态宽频声衬设计提供声源输入条件。未来工作期望进一步通过理论模型的研究，及与相关实验结果的对比，为短舱声学设计方案提供更有利的指导。