汽车发电机冷却风扇旋转噪声预测方法

以汽车发电机冷却风扇为对象,针对其修改叶片分布角度前后的旋转噪声预测问题,提出一套较精确且节约计算机时的预测方法.该方法结合了声类比法和矢量合成方法,首先,用大涡模拟(LES)和Ffowcs-Williams和Hawkings(FW-H)方程相结合的声类比方法对原风扇总噪声和主要阶次旋转噪声幅值进行预测;然后,针对只改变叶片分布角度情况下,提出一种矢量合成方法,用于对修改叶片分布前后主要阶次旋转噪声变化量的预测;最后,得到修改后主要阶次旋转噪声的幅值.计算和实验结果表明,原风扇总噪声最大预测误差4.3dB,第12阶和第18阶主要阶次旋转噪声幅值预测误差为1.24dB和4.26dB;修改后风扇第12阶和第18阶主要阶次旋转噪声分别变小了9.3dB和10.5dB,其变化量预测误差分别为0.36dB和0.43dB.结果表明,这一整套对修改前后风扇旋转噪声进行预测的方法是可行的,且大大节省计算时间,为风扇叶片周向分布角度设计提供了很好的依据.

Prediction method of vehicle alternator cooling fan rotation noise

A set of accurate and time-saving methods were proposed to predict the rotation noise of vehicle alternator cooling fan. First, to predict the overall noise and main order noise magnitudes of the original fan, an acoustic analogy method combined with large eddy simulation (LES) and Ffows-Williams and Hawkings (FW-H) equations was applied. Second, to predict the change of rotation noise caused by blade angle modification, a vector composition method was proposed in case only the blade distribution angle was changed. The main order noise magnitudes of the modified fan were eventually calculated. Calculations and experimental results indicate that the maximum prediction error of the overall noise of the original fan is 4.3dB, and the prediction errors of main rotation noise magnitudes in orders 12 and 18 are 1.24dB and 4.26dB, respectively. The rotation noises of the modified fan in orders 12 and 18 are decreased by 9.3dB and 10.5dB, while the prediction errors of their sound pressure level (SPL) variations are 0.36dB and 0.43dB, respectively. The results show that this set of methods can effectively predict the rotation noise of fan, providing a significant guide to the design of blade distribution angles.