Optimizing the aerodynamic noise of an automobile claw pole alternator using a numerical method

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.