两种声衬阻抗提取方法的对比

航空发动机短舱声衬是发动机最重要的降噪装置,为建立精确的、关联声衬结构和声学性能的阻抗模型,需要精细化分析声衬声阻抗提取技术。本文对比分析了2种声衬阻抗提取技术——当地阻抗提取方法和直接提取方法——的差异。应用了同一个流管声学试验平台、制造偏差可控的声衬试验件,并进一步通过阻抗测量的重复性试验,保证了两种阻抗提取方法对比的基础。应用两种阻抗测量方法分别提取了单自由度声衬和双自由度声衬的声阻抗。结果表明：2种阻抗提取方法测量结果在中、高频段内相互吻合,在低频范围内存在显著差异。对比分析可见：相比于直接提取方法,当地阻抗提取方法适用的频率范围更宽,能够反应声衬的局域声阻抗特性,对声衬的尺度限制小,但需要破换声衬的物理结构,且适用于传统声衬结构；相比于当地阻抗提取方法,直接提取方法测量了声衬的整体阻抗特性,在中、高频段内能够获得精确的阻抗结果,不需要破换声衬的物理结构,而使用于更为广泛的板型吸声材料。

Comparative Study of Two Kinds of Impedance Eduction Methods

The acoustic liner of the nacelle of an aeroengine is the most important noise reduction device of the engine. In order to establish an accurate impedance model related to the structure and acoustic performance of the acoustic liner, it is necessary to analyze the acoustic impedance eduction technology of the liner. This paper compared and analyzed the difference between two liner impedance eduction techniques-an situ impedance eduction method and straightforward method. The same flow tube acoustic test platform, liners with controllable deviation, and the repeatability test of impedance measurement were used to ensure the basis for the comparison of the two impedance extraction methods. Two impedance measurement methods were used to obtain the acoustic impedance of single-degree-of-freedom acoustic liner and double-freedom liner. The results show that the measurement results from the two impedance eduction methods are consistent with each other in the mid-range and high-range, and there are significant differences in the low-frequency ranges. The comparative analysis shows that compared with the straightforward method, the in situ method is applicable to a wider frequency range, can resist the local acoustic impedance characteristics of the acoustic liner, and has a small limitation on the size of the acoustic liner, but it needs to break the structure of the liner. It is suitable for the traditional liner. Compared with the in situ method, the straightforward method measures the overall impedance characteristics of the acoustic liner. It can obtain accurate impedance results in middle and high frequency range without the need to break the structure, and used in a wider range of plate-type sound-absorbing materials.