风扇后传声降噪声衬设计方法及实验验证

针对航空发动机风扇后传声降噪问题，开展了外涵道降噪声衬设计方法研究。将声衬设计过程分为两步，通过采用基于半经验声阻抗模型的声衬设计方法针对给定的声源频率进行初步设计，获得较优的声阻抗及相应的声衬几何参数。之后在初步设计结果的基础上，利用基于高精度计算气动声学的声传播计算软件对声阻抗进行优化，并得到最终的优化方案。为验证提出的设计方法，在全消声室内的风扇后传声降噪声衬测试台分别对初步设计声衬和优化声衬进行了实验验证。实验中采用扬声器模拟风扇声源，给定声源模态为(1，0)，频率为3150Hz，内涵出口马赫数为0.8，外涵出口马赫数为0.6。结果表明:在给定的声源模态和频率下，初步设计的声衬可以取得10dB的降噪效果。优化设计的声衬相较于初步设计声衬，远场噪声可以再降低3~4dB。 

Design method of acoustic liner applied toaft-fan noise reduction and experimental validation

Liner design method applied to aft-fan noise reduction was implemented.The design phases were separated into two parts. In the first phase, an empirical impedance model was adopted to get the preliminary design. In the second phase, an optimization procedure was performed by numerical simulations based on high-order computational aeroacoustic method to achieve the optimal acoustic impedance and corresponding geometry parameters.In order to validate the method, an experimental investigation of aft-fan noise was carried out in the anechoic chamber of Beijing University of Aeronautics Astronautics.The fan noise source was modeled by a mode source generated by speakers.The circumferential mode was 1 and the radial mode was 0, the frequency was 3150Hz.The Mach numbers were 0.8 and 0.6 for the core and bypass ducts respectively. Experimental results showed that the preliminary design had 10dB insertion loss and the optimized liner achieved 3-4dB more attenuation.