Acoustic liners are an essential part of noise reduction technologies commonly applied in aircraft turbofan engines. Fan noise suppression can be achieved by selecting an appropriate liner design with optimal acoustic impedance at the blade passing frequency. Great efforts have been made not only to improve experimental characterization and numerical methods for acoustic liners, but also to understand noise generation mechanisms, which ultimately impacts on the liner design itself. To gain confidence in the liner design process, a liner barrel was developed and fabricated for the Fan Noise Test Rig located at the University of São Paulo. To this end, analytical methods were used to determine the optimal acoustic impedance for the Fan Noise Test Rig, and a flat test sample was fabricated for experimental characterization with flow using both in-situ and impedance eduction techniques at the Federal University of Santa Catarina. A liner barrel of same nominal geometry was fabricated and placed at the Fan Noise Test Rig, and a modal decomposition indicated that the Tyler-Sofrin mode has been successfully suppressed at the first blade passing frequency. Numerical predictions of liner transmission loss considering the flat sample impedance showed good agreement with experimental results.

声学衬垫是飞机涡扇发动机常用降噪技术的重要组成部分。风扇噪声抑制可以通过选择合适的衬里设计来实现，在叶片通过频率下具有最佳声阻抗。不仅在改进声学衬垫的实验表征和数值方法方面做出了巨大努力，而且还为了理解噪声产生机制，最终影响衬垫设计本身。为了获得对衬管设计过程的信心，我们为位于圣保罗大学的风扇噪声测试台开发并制造了衬管筒。为此，分析方法用于确定风扇噪声测试台的最佳声阻抗，并且在圣卡塔琳娜联邦大学使用原位和阻抗导出技术制作了一个扁平的测试样品，用于对流动进行实验表征。制造了具有相同标称几何形状的衬筒并将其放置在风扇噪声测试台上，模态分解表明 Tyler-Sofrin 模式已在第一叶片通过频率下成功抑制。考虑到平坦样品阻抗的线性传输损耗的数值预测与实验结果非常吻合。