Numerical Investigation of Fluid Injection to Reduce Trailing-Edge Noise

欧盟2020远景计划预计每架飞机的运营噪音将减少10分贝。也就是说，在着陆时，除了发动机噪声，特别是由高升力装置和起落架产生的机身噪声必须减少，因为它是同样重要的噪声源。由于代表细长机身的高升力装置和由钝体组成的起落架的流动特性不同，本建议将只考虑细长机身问题的降噪。作为一种通用构型，本文以有限厚度平板的后缘为例，数值分析了在设计“声学柔和”后缘时的降噪潜力。更准确地说，涡流在边缘对流时所经历的不连续性将被降低，以降低边缘散射的强度。这种不连续性的减少是通过在边缘上游注入额外的流体以在接近边缘时产生类似于较软表面的近壁流动结构来实现的，并通过在钝化后缘直接注入流体以降低自由剪切层中的剪应力来实现。采用成熟的混合LES-APE方法进行分析，从而实现了频率和方向性无关的降噪的总体目标。

The EU Vision 2020 expects a 10dB noise reduction per aircraft operation. That is, at landing besides engine noise especially airframe noise generated by high-lift devices and landing gears has to be reduced since it is an equally significant noise source. Due to the disparity of the flow characteristics of high-lift devices, which represent a slender body, and landing gears, which consist of blunt bodies, only the noise reduction of the slender-body problem will be considered in this proposal. As a generic configuration the trailing edge of the flat plate of finite thickness is used to numerically analyze the potential to reduce the noise when an “acoustically soft” trailing edge is designed. To be more precise, the discontinuity experienced by an eddy in convecting over the edge is to be lowered to decrease the intensity of edge scattering. This reduction of the discontinuity is to be realized by injecting an additional fluid upstream of the edge to generate a near-wall flow structure that resembles a softer surface as the edge is approached and by injecting fluid right at the blunt trailing edge to decrease the shear stress in the free-shear layer. The well-established hybrid LES-APE method is applied to analyze the mechanisms such that the overall objective of a frequency and directivity independent noise reduction is achieved.