考虑影响声传播因素的车用交流发电机气动噪声预测

Aerodynamic noise prediction of vehicle alternator considering the factors affecting acoustic propagation

为了更准确地预测车用交流发电机的气动噪声,基于计算流体力学及声类比理论,考虑影响声传播的因素,对实验室安装条件下的某型车用交流发电机气动噪声进行研究。利用大涡模拟方法计算了交流发电机内部三维非稳态流场;依据Lighthill声类比思想,将转子表面的压力脉动等效为旋转偶极子源点集;考虑发电机机壳及实验台面对声传播的影响,建立了以机壳内表面为声源边界的半自由声场计算模型,进而预测了发电机的远场气动噪声;最后,利用实测数据对发电机气动噪声仿真结果进行了验证。结果表明:交流发电机气动噪声的辐射声场具有明显的偶极子指向特性;仿真计算结果与实验测试结果具有很好的一致性。所提的研究方法能更准确地预测发电机的气动噪声,同时可为实车安装条件下的车用交流发电机气动噪声预测提供参考。

In order to predict the aerodynamic noise of vehicle alternators more accurately, an approach based on computational fluid dynamics（CFD） and acoustic analogy theory is proposed for aerodynamic noise prediction of a vehicle alternator under the mounted condition in laboratory and considering the factors affecting acoustic propagation. The large eddy simulation（LES） method is adopted to calculate the three-dimensional unsteady flow field inside the alternator firstly. Then the surficial pressure fluctuation of rotating components is equivalent to rotating dipole sources based on Lowson’s fan source theory. After that, a half free field acoustic computational model is established to predict the outer radial acoustic field of the alternator by taking the inner face of alternator enclosure as the boundary of sound sources and considering influences of the enclosure and experimental rig desk on the acoustic propagation. Finally, prediction results are validated by experiment data. It shows that there is an obvious dipole directivity of the radial acoustic field of aerodynamic noise of the alternator, and the prediction results agree with experimental ones quite well. The approach in this work can predict the aerodynamic noise of alternators more accurately. Furthermore, it provides a reference for aerodynamic noise prediction of alternators mounted on vehicles where more obstacles need to be considered.