Laser based tomographic measurement of the local acoustic impedance of overflowed liners (TOMLIM)

基于激光断层扫描测量溢出内衬的局部声阻抗 (TOMLIM)

• 批准号: 408927635
• 负责人: Professor Dr.-Ing. Jürgen W. Czarske
• 金额: --
• 依托单位: Abteilung Triebwerksakustik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/408927635?language=en
• 关键词: Laser; based; tomographic; measurement; local

The increasing growth of air traffic demands highly efficient noise reduction measures especially addressing the noise emitted from aero-engines. Common applications for noise attenuation are acoustically lined surfaces, called liner, placed along the flow pass in the engine nacelle. Liners consist basically of perforated walls with a cavity structure behind. Up to now the design of these liners for an optimal performance under flow conditions is based on heuristic and empirical methods due to the lack of sufficiently describing, fully analytical models. The applicants could even show in previous projects that under certain circumstances lined surfaces can contribute to noise generation instead of attenuation. This demonstrates the need for improved liner model descriptions which allows a liner design optimization with robust prediction ability.A key quantity in describing the liner performance is the acoustic impedance, the ratio of the pressure fluctuations to the wall-normal velocity fluctuation of the sound field. This liner impedance is commonly determined globally, homogenously distributed over the line surface, by indirect methods. However, due to the lack of corresponding measurement techniques the local distribution of the impedance and its correlation with the global impedance is still unknown.This will be addressed in the present application. A novel non-intrusive impedance measurement technique, a combination of tomographic acoustic pressure measurements and Doppler Global Velocimetry based acoustic particle velocity measurements, will be developed, validated and applied on liner setups under realistic grazing flow conditions. Therefore, the optical setups as well as the post-processing algorithms need to be developed to facilitate the application with limited optical access to the liner section in a flow duct test rig.

日益增长的空中交通需要高效的降噪措施，特别是解决航空发动机发出的噪音。噪声衰减的常见应用是声学内衬表面，称为衬垫，放置在发动机机舱内的流动通道上。衬垫基本上由穿孔的壁和后面的空腔结构组成。到目前为止，由于缺乏充分描述、充分分析的模型，这些尾管的设计都是基于启发式和经验方法来实现流动条件下的最佳性能。申请人甚至可以在以前的项目中证明，在某些情况下，内衬表面可能会产生噪音，而不是衰减噪音。这表明需要改进线性模型描述，使线性设计优化具有鲁棒预测能力。描述衬垫性能的一个关键指标是声阻抗，即声场的压力波动与壁向速度波动的比值。这种线性阻抗通常是通过间接方法全局均匀分布在线路表面上确定的。然而，由于缺乏相应的测量技术，阻抗的局部分布及其与全局阻抗的相关性仍然未知。这将在本申请中解决。一种新型的非侵入式阻抗测量技术，结合层析声压测量和基于声波粒子速度测量的多普勒全球测速技术，将被开发、验证并应用于实际掠流条件下的尾管装置。因此，需要开发光学设置和后处理算法，以方便在流动管道测试台中光学通道有限的尾管部分的应用。