The introduction of quiet short take-off and landing for civil aircraft operations in close proximity to the population poses important technological challenges. One critical aspect is the realization of extreme lift augmentation at low acoustic emissions. The aircraft concept selected to achieve this goal is a high-lift system equipped with an active flow-control non-slotted flap and a droop nose. For this specific configuration, trailing edge noise becomes a dominant noise source. Porous materials as a passive means for trailing-edge noise reduction are selected and characterized. Results of extensive experimental investigations in the acoustic wind tunnel Braunschweig are presented and discussed to point out the potential and limitations of the selected porous devices. Practical issues related to material manufacturing and integration into the wind tunnel model are addressed. The noise reduction potential of passive porous trailing-edge devices is found to strongly depend on both these aspects. Issues related to the characterization of the porous materials properties are described. Although porous materials are found to be successful at reducing trailing-edge noise emissions, the results indicate that there is still a need for more generic investigations to further clarify the parametric dependencies between noise reduction and material properties.

中文翻译：

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多孔材料后缘降噪的实验研究

为靠近人口的民用飞机操作引入安静的短距起降带来了重要的技术挑战。一个关键方面是在低声发射下实现极大的升力增强。为实现这一目标而选择的飞机概念是配备主动流量控制无缝襟翼和下垂机头的高升力系统。对于这种特定配置，后缘噪声成为主要噪声源。选择并表征了多孔材料作为用于降低后缘噪声的被动手段。介绍并讨论了布伦瑞克声学风洞中广泛实验研究的结果，以指出所选多孔设备的潜力和局限性。解决了与材料制造和集成到风洞模型中相关的实际问题。发现被动多孔后缘装置的降噪潜力在很大程度上取决于这两个方面。描述了与多孔材料特性表征相关的问题。尽管发现多孔材料在减少后缘噪声排放方面是成功的，但结果表明，仍然需要进行更通用的研究，以进一步阐明降噪和材料特性之间的参数依赖性。