| Nowadays,people are becoming more and more attention to the noise pollution of all kinds of machinery and facility.So the wind tunnel acoustic test has been more and more important for cars,aircrafts,trains,and so on.But the useful acoustical signal of targets will be buried in the stronger background noise.It is difficult to clear the band noise,and the SNR will be reduced in these aero acoustics tests.It is a very important problem to reduce the wind tunnel test background noise.There are some normal methods called passive de-noising such as sound absorption materials,soundproof treatment,reducing reflected sound in acoustic wind tunnel construction.Even the normal methods have a better effect in high-frequency noise reducing;they have no effect in removing low-frequency noise.This thesis applies the active noise control(ANC)technology in aero acoustics tests which has a significant effect in removing low-frequency noise and is improved for wind tunnel.The ANC technology cooperating with traditional methods will reduce wind tunnel background noise further and improve the aero acoustic test accuracy.This thesis proposes a kind of method for secondary sound source layout optimization which can improve the multi-channel ANC system based on Monte Carlo method and acoustic simulation.We also propose a noise control algorithm for improving the system stability and denoising efficiency based on 1D adaptive filter.And a dual-channel ANC test system is built for laboratory test.The results show that an ANC system with secondary sound source optimization layout and noise control algorithm has a better noise reduction efficiency and a wider denoising area than the one without it.Finally,this thesis applies the dual-channel ANC test system in the real acoustic wind tunnel and achieves a good denoising effect with-7dB at target frequency and-1.4dB at the whole band.The test results show the validity and feasibility of the secondary sound source layout optimization method and noise control algorithm which are proposed by this thesis. |
