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Advanced modeling of active control of fan noise for ultra high bypass turbofan engines.

机译：用于超高旁通涡扇发动机的风扇噪声主动控制的高级建模。

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An advanced model of active control of fan noise for ultra high bypass turbofan engines has been developed. This model is based on a boundary integral equation method and simulates the propagation, radiation and control of the noise generated by an engine fan surrounded by a duct of finite length and cylindrical shape, placed in a uniform flow. Control sources, modeled by point monopoles placed along the wall of the engine inlet or outlet duct, inject anti-noise into the duct to destructively interfere with the sound field generated by the fan. The duct inner wall can be lined or rigid. Unlike current methods, reflection from the duct openings is taken into account, as well as the presence of the evanescent modes. Forward, as well as backward (i.e., from the rear of the engine), external radiation is computed.; The development of analytical expressions for the sound field resulting from both the fan loading noise and the control sources is presented. Two fan models are described. The first model uses spinning line sources with radially distributed strength to model the loading force that the fan blades exert on the medium. The second model uses radial arrays of spinning point dipoles to simulate the generation of fan modes of specific modal amplitudes. It is shown that these fan models can provide a reasonable approximation of actual engine fan noise in the instance when the modal amplitude of the propagating modes or the loading force distribution on the fan blades, is known.; Sample cases of active noise control are performed to demonstrate the feasibility of the model. The results from these tests indicate that this model (1) is conducive to more realistic studies of active control of fan noise on ultra high bypass turbofan engines because it accounts for the presence of evanescent modes and for interference between inlet and outlet radiation, which were shown to have some impact on the performance of the active control system; (2) is very useful because it allows monitoring of any region of the acoustic field; (3) is computationally fast, and therefore suitable to conduct parametric studies.; Finally, the potential that active noise control techniques have for reducing fan noise on an ultra high bypass turbofan engine is investigated. Feedforward control algorithms are simulated. Pure active control techniques, as well as hybrid (active/passive) control techniques, are studied. It is demonstrated that active noise control has the potential to reduce substantially, and over a relatively large far field sector, the fan noise radiated by an ultra high bypass turbofan engine. It is also shown that a hybrid control system can achieve significantly better levels of noise reduction than a pure passive or pure active control system, and that its optimum solution is more robust than the one achieved with a pure active control system.; The model has shown to realistically predict engine acoustic behavior and is thus likely to be a very useful tool for designing active noise control systems for ultra high bypass turbofan engines.
机译：已经开发了一种用于超高旁通涡扇发动机的主动控制风扇噪声的先进模型。该模型基于边界积分方程法，模拟了由有限长度和圆柱形，均匀流动的风管围绕的发动机风扇产生的噪声的传播，辐射和控制。控制源由沿着发动机进气管或排气管壁放置的点单极子模拟，将抗噪声注入到导管中以破坏性地干扰风扇产生的声场。管道内壁可以是带衬里的或刚性的。与当前的方法不同，考虑了导管开口的反射以及渐逝模式的存在。向前和向后（即从发动机后部）计算外部辐射。提出了由风扇负载噪声和控制源产生的声场解析表达式的发展。描述了两种风扇型号。第一个模型使用具有径向分布强度的旋转线源来模拟风扇叶片施加在介质上的加载力。第二个模型使用旋转点偶极子的径向阵列来模拟特定模态振幅的风扇模式的生成。结果表明，在已知传播模式的模态振幅或风扇叶片上的加载力分布的情况下，这些风扇模型可以合理地逼近实际的发动机风扇噪声。进行了主动噪声控制的示例，以证明该模型的可行性。这些测试的结果表明，该模型（1）有助于对超高旁路涡轮风扇发动机的风扇噪声进行主动控制的更现实的研究，因为它考虑了渐逝模式的存在以及入口和出口辐射之间的干扰，这是证明对主动控制系统的性能有一定影响； （2）非常有用，因为它可以监视声场的任何区域; （3）计算速度快，因此适合进行参数研究。最后，研究了主动噪声控制技术对于降低超高旁通涡扇发动机的风扇噪声的潜力。模拟了前馈控制算法。研究了纯主动控制技术以及混合（主动/被动）控制技术。事实证明，主动噪声控制有可能在相对较大的远场扇区中大幅降低超高旁通涡轮风扇发动机辐射的风扇噪声。还表明，混合控制系统可以比纯被动或纯主动控制系统实现更好的降噪水平，并且其最佳解决方案比纯主动控制系统所实现的解决方案更强大。该模型已显示出可以现实地预测发动机的声学特性，因此可能是用于设计超高旁通涡扇发动机主动噪声控制系统的非常有用的工具。

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