利用轴流机械流动噪声的偶极子特性，把旁通管道置于轴流机械两侧，使其向两侧辐射的同幅反相声波相互抵消，从而降低其流动噪声。用平面波模型对噪声自抵消方法进行了分析，并通过仿真计算和实验研究进行了验证。研究表明：当旁通管有效长度为波长的整数倍时，插入损失最大；为半波长的奇数倍时，插入损失为零。与普通旁通管消声器不同，由于轴流机械辐射噪声主要为偶极子噪声，因此在趋于零的极低频段，旁通管自抵消系统的插入损失并不为零。频率趋于零时的插入损失与主管道和旁通管道的截面积比和有效长度比相关。平面波模型的理论结果与仿真计算结果以及空气管道实验结果在低频部分吻合较好，在中高频段平面波模型的峰值频率与仿真结果和实验结果略有差异。%Ducted fan noise attenuation method using Herschel Quincke tube (HQ tube)placed on both sides of a ducted fan was studied theoretically and experimentally.The results showed that the insertion loss of the system is zero when the effective length of the bypass duct is odd times of half sound wave length;however,the sound attenuation performance is good when it's even times;being different from usual HQ Tube,the insertion loss of the system proposed here is not zero when the frequency is approaching zero because dipole noise is the main part of the ducted fan noise;the insertion loss of the system when the frequency is approaching zero depends on the length ratio and area ratio between bypass duct and main duct;comparing with those of the theoretical method,the results of the simulation method and experimental method are in good agreement with each other at low frequency,but have small difference in middle and high frequency ranges because the plane wave is not the only wave in the duct.
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