关键词: 声衬, 宽频噪声, 声阻抗, 三维直接提取法, 传声损失

Abstract:

To fulfill the requirements for researching and validating the acoustic characteristics of aviation acoustic liners across a wide frequency range， a flow tube acoustic test bench was developed， employing the three-dimensional straightforward method （3D-SFM） and the pipe acoustic mode decoupling approach. In a grazing flow environment with a maximum Mach number of 0.14， the acoustic performances of single- and double-degree-of-freedom acoustic liners， including acoustic impedance and sound transmission loss， were tested. The maximum test frequency could reach 10 kHz， covering the main noise frequency bands of aeroengines and auxiliary power units. The experimental results demonstrate that the 3D-SFM can effectively educe the acoustic impedance of the acoustic liner in a multi-modal sound field. Furthermore， based on spanwise mode decomposition and the Prony method， the optimization principle and methodology were proposed to optimize acoustic impedance under multiple spanwise modes and scattering modes. The final acoustic impedance outcomes exhibited excellent consistency with the prediction of liner’s impedance model. Sound transmission loss was capable of reflecting the variation law of the noise reduction capability of single/double-degree-of-freedom acoustic liners under different Mach numbers of grazing flow， as well as the advantages of double-degree-of-freedom acoustic liners in broadband noise reduction.

Key words: acoustic liner, broadband noise, acoustic impedance, three-dimensional straightforward method, sound transmission loss