Abstract The aerodynamic noise of an alternator, which is difficult to predict due to the complex internal flow, has become an issue for vehicles in recent years. To study the acoustic characteristics of the vehicle claw pole alternator, a numerical simulation method is proposed in this paper to predict its aerodynamic noise. First, a Scale Adaptive Simulation (SAS) in the numerical calculation is used to calculate the flow field. Then, the Ffowcs-Williams and Hawkings acoustic model is applied to calculate its acoustic characteristics. Additionally, a series of experiments are performed to verify the accuracy of the simulation method. According to the experimental data, it is determined that the dominant influencing orders for the overall noise are the 8th, 16th and 24th orders. Comparing the simulation results with the experimental results, the prediction errors are −0.67 dBA, −2.9 dBA and −3.22 dBA in the acoustic power levels of the 8th, 10th and 12th orders, respectively, which are all within 4%. Finally, the Vector Composition Method (VCM), considering the mass flow rate and low noise, is applied to ameliorate the distribution of the spectral energy by optimizing the distribution angles of the rear fan. Moreover, a prototype is produced to verify the practical application of this method. After optimization, the numerical results indicate that the mass flow rate of the rear fan is reduced by 5.172%, while the front fan is increased by 5.128%. The experimental results indicate that the maximum increasing overall noise on the 6th order is 4.7 dB and the increasing values of the 10th and 14th orders are all in a limited range. Additionally, the maximum decreasing overall noise amounts of the 8th order and 12th order exceed 5.1 dB and the average decreasing amount exceeds 2.5 dB; that is to say, this method has a remarkable effect on the acoustic noise spectral structure.

中文翻译：

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汽车爪极交流发电机气动噪声的数值方法优化

摘要 交流发电机的气动噪声由于内部流动复杂而难以预测，已成为近年来车辆面临的一个问题。为了研究汽车爪极交流发电机的声学特性，本文提出了一种数值模拟方法来预测其气动噪声。首先，在数值计算中使用尺度自适应模拟（SAS）来计算流场。然后，应用 Ffowcs-Williams 和 Hawkings 声学模型计算其声学特性。此外，还进行了一系列实验以验证模拟方法的准确性。根据实验数据，确定总体噪声的主要影响阶数为8阶、16阶和24阶。将仿真结果与实验结果进行比较，8阶、10阶和12阶声功率级的预测误差分别为-0.67 dBA、-2.9 dBA和-3.22 dBA，均在4%以内。最后，考虑质量流量和低噪声的矢量合成法（VCM）通过优化后风扇的分布角度来改善光谱能量的分布。此外，还制作了一个原型来验证该方法的实际应用。优化后的数值结果表明，后风扇的质量流量降低了5.172%，而前风扇的质量流量增加了5.128%。实验结果表明，6阶的最大增加总噪声为4.7 dB，10阶和14阶的增加值均在有限范围内。此外，8阶和12阶的最大降低总噪声量超过5.1dB，平均降低量超过2.5dB；也就是说，这种方法对声学噪声谱结构有显着的影响。