基于模态发生器的进气道风扇噪声及声衬降噪实验

Experiment of intake fan noise and noise reduction of acoustic liner based on mode generator

为研究发动机进气道风扇噪声特性及声衬降噪效果,使用模态发生器提供声源,采用固定麦克风阵列和旋转扫描耙装置测量进气道内噪声信号,进而利用周向和径向模态分解方法得到声模态幅值,对影响模态分解结果的关键因素进行了研究。对周向模态在时域内进行分解,得到幅值和相位的时变特性。最后完成了2套声衬实验件降噪效果测试。结果表明:模态发生器提供的声源可获得风扇噪声的主要模态特征,包括模态幅值、旋转角速度等;满足采样定理条件,径向模态n=0情况下模态发生器产生的主模态和扬声器数量无关;使用旋转扫描耙装置测量声模态,旋转扫描耙的采样位置数对测量结果影响可忽略;在设计频率下,声衬降噪效果良好。模态发生器提供的进气道风扇噪声源可用于对声衬设计方法进一步实验验证。

In order to investigate the characteristics of engine intake fan noise and the noise reduction effect of acoustic liner,the intake fan noise was provided by a mode generator.The noise signal inside the intake was measured by using a fixed microphones array and a rotating microphones rake,and then the amplitude of acoustic mode inside the intake was determinated by using circumferential and radial mode decomposition method.The key factors affecting the results of mode decomposition were investigated.The circumferential mode was decomposed in time domain,and the time-resolved characteristics of amplitude and phase were obtained.Finally,the noise reduction effect of two acoustic liner samples was experimented.The results showed that:the main mode characteristics of fan noise could be obtained by the mode generator,including the mode amplitude and the rotating angular velocity;under the condition of satisfying the sampling theorem,the main mode produced by the mode generator was independent of the numbers of loudspeakers in the case of n=0;the influence of the numbers of sampling position of the rotating microphones rake on the results could be ignored if using the rotating microphones rake to measure the acoustic mode;and at the design frequencies,the acoustic liners had good noise reduction effect.It is concluded that:the intake fan noise source provided by the mode generator can be used for further experimental verification of acoustic liner design method.