Numerical optimization of porous surfaces to reduce trailing-edge noise

在着陆进近时，机体噪声是影响整体噪声水平的主要因素之一。由于尾缘噪声是机体噪声的重要组成部分，因此有必要降低尾缘噪声，以减少飞机噪声排放对机场附近人口的环境影响。在本项目中，采用大涡模拟/计算气动声学（LES/CAA）混合方法，研究了一种被动降噪技术，用于一般后缘的多孔表面。在第一阶段，分析了多孔表面对降低尾缘噪声的影响。对不同尾缘形状和多孔结构的计算表明，它们可以降低湍流涡的相关性，使总声压级降低11dB。通过新开发的LES/CAA方法的伴随配方优化，孔隙度额外降低了4dB。在第二阶段，调查范围将扩大至宽频减低噪音。这种分析的新颖性是由多孔表面形状的展向变化来定义的，即考虑了锯齿形状，以及在流向和展向方向上多孔结构的变化。基于高保真代理优化模型，对多孔表面的形状和结构进行了优化。此外，还考虑了迎角对降噪增益的影响，并研究了高马赫数对后缘声增益的影响，即对声扰动及其对整体空气动力学的影响。简而言之，分析孔隙度对宽带尾缘噪声的影响并降低它是本项目的总体目标。

At landing approach, airframe noise is one of the major contributors to the overall noise level. Since trailing-edge noise defines an essential part of airframe noise, it is necessary to lower it, to reduce the environmental impact of aircraft noise emissions on the population near airports. In this project, a passive noise reduction technology for trailing-edge noise, i.e., porous surfaces applied to generic trailing edges, is investigated by a hybrid large-eddy simulation/computational aeroacoustics (LES/CAA) approach.In the first phase, the impact of porous surfaces to reduce tonal trailing-edge noise has been analyzed. The computations for various trailing-edge shapes and porous structures have shown to reduce the correlation of the turbulent eddies and to lower the overall sound pressure level by 11dB. The tonal noise has been lowered by an additional 4dB for a porosity having been optimized by a newly developed adjoint formulation of the LES/CAA aproach.In the second phase, the investigation will be extended to broadband noise reduction. The novelty of this analysis is defined by a spanwise variation of the shape of the porous surface, i.e., a sawtooth shape is considered, and an alteration of the porous structure in the streamwise and spanwise direction. Based on a high-fidelity surrogate optimization model, the shape and the structure of the porous surface are optimized. Furthermore, the impact of the angle-of-attack on the noise reduction gain is taken into account and the influence of higher Mach numbers on the acoustic gain at the trailing edge, i.e., on the acoustic perturbations and their effect on the overall aerodynamics, is investigated.In brief, it is the overall objective of this project to analyze the impact of porosity on broadband trailing-edge noise and to reduce it.