Aerofoil broadband noise reductions through double-wavelength leading-edge serrations: a new control concept
Aerofoil broadband noise reductions through double-wavelength leading-edge serrations: a new control concept
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DOI：
10.1017/jfm.2018.620
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发表时间：
2018-09
影响因子：
3.7
通讯作者：
P. Chaitanya;P. Joseph;S. Narayanan;J. W. Kim
中科院分区：
文献类型：
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作者：
P. Chaitanya;P. Joseph;S. Narayanan;J. W. Kim
在湍流中运行的翼型通过将涡量散射到前缘处的声音中而产生宽带噪声。以前的工作已经证明了锯齿，或起伏，引入到前缘，可以大大减少宽带前缘噪声的有效性。所有这些工作都集中在正弦（单波长）前缘锯齿轮廓。在本文中，提出了一种新的前缘锯齿的几何形状，它提供了显着更大的降噪相比，相同幅度的单波长锯齿可实现的最大降噪。这是通过机翼前缘不同部分之间的相消干涉来实现的，因此涉及与传统单波长锯齿根本不同的降噪机制。新的前缘锯齿轮廓简单地包括不同波长、振幅和相位的两个单波长分量的叠加，目的是形成两个足够靠近并在流向方向上分开的根部。位于这些根部位置的紧凑源然后干扰，导致比单波长几何结构更低效率的辐射。一个详细的参数研究实验进行调查的灵敏度的降噪轮廓的几何形状。提出了一个简单的模型来解释这些双波长锯齿轮廓的降噪机制，并显示出与测量的降噪光谱密切一致。该研究主要是在理想化的湍流平板上进行的。本文最后通过在10%厚的翼型上引入双波长锯齿来得出结论，与平板相比，获得了几乎相同的降噪效果。
Aerofoils operating in a turbulent flow generate broadband noise by scattering vorticity into sound at the leading edge. Previous work has demonstrated the effectiveness by which serrations, or undulations, introduced onto the leading edge, can substantially reduce broadband leading-edge noise. All of this work has focused on sinusoidal (single-wavelength) leading-edge serration profiles. In this paper, a new leading-edge serration geometry is proposed which provides significantly greater noise reductions compared to the maximum noise reductions achievable by single-wavelength serrations of the same amplitude. This is achieved through destructive interference between different parts of the aerofoil leading edge, and therefore involves a fundamentally different noise reduction mechanism from conventional single-wavelength serrations. The new leading-edge serration profiles simply comprise the superposition of two single-wavelength components of different wavelength, amplitude and phase with the objective of forming two roots that are sufficiently close together and separated in the streamwise direction. Compact sources located at these root locations then interfere, leading to less efficient radiation than single-wavelength geometries. A detailed parametric study is performed experimentally to investigate the sensitivity of the noise reductions to the profile geometry. A simple model is proposed to explain the noise reduction mechanism for these double-wavelength serration profiles and shown to be in close agreement with the measured noise reduction spectra. The study is primarily performed on flat plates in an idealized turbulent flow. The paper concludes by introducing the double-wavelength serration on a 10 % thick aerofoil, where near-identical noise reductions are obtained compared to the flat plate.