Jet noise from instability mode interactions

航空旅行的数量继续增加，飞机喷气发动机的噪音干扰对那些在机场附近生活和工作的人来说是一个持续的问题。发动机制造商在降低发动机噪音方面有着出色的记录，但进一步的进展取决于对声音产生机制的更好理解。这个项目将发展一个最近提出的想法，一些最重要的噪音可能来自不稳定模式之间的非线性相互作用，传播沿着射流。以前的研究只考虑了直线机构，对于高速喷气的成功有限。由于不稳定模式本身可以有效地计算与众所周知的技术稳定性分析，所有的二次非线性相互作用，原则上可以计算相对较快。该项目将通过稳定性模式的组合将基流与声场耦合来开发该技术。将进行一系列直接数值模拟，以便在一系列试验情况下评估该技术的准确性，包括二元模式相互作用、过渡到湍流和完全湍流的情况，其中可以包括喷嘴唇缘的影响。已发表的实验室数据也将用于参考。这些测试将确定非线性相互作用机制是重要声源的方向和频率范围。了解这一机制，就可以隔离其他来源。

Air travel continues to expand in volume and noise disturbance from aircraft jet engines is a continuing issue for those living and working near airports. Engine manufacturers have an excellent tack record of reducing the noise from engines, but further progress depends on better underdstanding of the mechanisms of sound production. This project will develop a recently-proposed idea that some of the most important noise may come from nonlinear interactions between instability modes that propagate along the jet. Previous research has only considerd a linear mechanism, with limited success for high speed jets. Since the instability modes themselves can be efficiently computed with well-known techniques of stability analysis, all the quadratic nonlinear interactions can in principle be computed relatively quickly. This project will develop the technique by coupling a base flow with the acoustic field via combination of stability modes. A series of direct numerical simulations will be run so that the technique can be evaluated for accuracy over a range of test cases, including binary mode interactions, transition to turbulence and fully turbulent cases where the effect of the nozzle lip can be included. Published laboratory data will also be used for reference. The tests will determine direction and frequency ranges in which the nonlinear interaction mechanism is an important source of sound. Understanding this mechanism should then allow other sources to be isolated.