航空发动机声衬降噪与散射试验研究

Experimental Investigation of Turbofan Engine Acoustic Liner Noise Reduction and Mode Scattering

目的研究声衬的吸声效果和声模态散射现象。方法针对飞机短舱进气道声衬开展噪声试验。以缩比尺度进气道试验台为基础,单级轴流风扇为噪声源,通过10倍进气道直径的远场测点,获取固壁条件和声衬作用下的管道声模态和远场指向性,分析不同转速下各远场测点在声衬作用下的吸声效果。结果在三种不同转速工况下,得到前三阶叶片通过频率下声衬上游、下游的管道声模态分布、远场频谱和指向性分布,并以此得出声衬在不同转速、不同噪声频率、不同流速下的降噪效果。在2973 r/min转速下,(1,0)声模态的声功率级降低达24.3dB。(±3,0)模态处,声衬靠近声源一侧的声功率反而升高。结论声衬在设计频率和模态处,吸声效果最明显。随着模态阶数的升高,声衬的降噪能力有所提升。偏离设计频率时,高阶声模态在阻抗交界面发生散射。

The work aims to study the sound absorption and acoustic model scattering phenomenon of acoustic liner. Noise experiment was conducted on the liner of nacelle inlet of an airplane. Based on the scaled test bench, the single stage axial fan was taken as the noise source. Through the far-field measuring points of 10 times the diameter of the inlet, acoustic modal and far-field directivity under the action of solid wall and liner were obtained to analyze the sound absorption effect of each far-field measuring point at different speeds under the action of liner. At three different rotating speeds, the acoustic modal distribution, far-field spectrum and directivity distribution of the pipeline upstream and downstream of the acoustic liner under the first three-order blade passing frequencies were obtained. And on this basis, the noise reduction effect of the acoustic liner at different rotating speeds, noise frequencies and flow rates were obtained. At 2973 rpm, the sound power level of modal(1,0) was reduced to 24.3 d B. Under modal(±3,0), the sound power level near the sound source increased unexpectedly. Under design frequency and modal, the liner has the best sound absorption effect. With the increase of the modal order, the noise reduction capacity of the liner decreased. When deviating from design frequency, acoustic model scattering occurs at the impedance interface.