Design And Optimization Of Acoustic Characteristics Of The Wind Ducts In High-speed Train By Transfer Matrix Method

The interior noise level is a key factor to affect the ride comfort of high-speed train.It can be divided into running noise and stationary noise according to the train status.At present,the researches on the interior noise of rail trains always focus on the running noise,but the stationary noise is also a key indicator viewed from the noise evaluation and the live situation.And in practice,it was found that the noise of the metro air conditioning exceeded the standard and the noise of the high-speed air conditioning was prominent.Air-conditioning noise includes air conditioning unit noise and duct noise.Limited by the level of electrical equipment manufacturing,air conditioning noise control tends to rely more on optimizing airway acoustics,and in other words,that's duct acoustics.For the air-conditioning duct in high-speed trains,traditional finite element method and boundary element method are limited due to the duct's large size and long body length.Therefore,in this paper,the air-conditioning duct system of high-speed train is the object,and its acoustic characteristics are analyzed,and then the optimization design is carried out by transfer matrix method(TMM).The main research is as follows:(1)Based on TMM,the transfer matrix of the straight tube unit and the rectangular expanded gradient cross-section unit is derived,including the one-dimensional plane wave method and the three-dimensional analytical method(modal expansion method and modal matching method).A transfer matrix is derived in which the sound absorbing material is attached around the wind duct of the expanded gradient cross section and the sound absorbing material is attached only to the side of the variable section.(2)For the wind duct structure of the expansion chamber with baffles,the transmission loss of low frequency is calculated by one-dimensional plane wave method,and the influence of resistance and resistivity factors on the acoustic characteristics is discussed.From the perspective of resistance analysis,those factors include the rotation angle,length,width and position of the baffle.From the perspective of resistivity analysis,the flow resistance and thickness of the lining sound absorbing material are analyzed.The results show that the maximum transmission loss and the large sound surface ratio are obtained when the length of the baffle is equal to the width of the wind duct,the width is 0.06 m,and the rotation angle is 80°.The position of the axial direction affects the frequency variation of the low-frequency peaks and valleys,while the position of the radial direction affects the magnitude of the transmission loss.(3)Based on the three-dimensional analytical method,a transfer matrix model is established for the entire wind duct in the air-conditioning system of high-speed train,and the acoustic analysis and optimization scheme design are carried out.The effects on acoustic performance are analyzed from the perspective of resistance and resistivity,including the rotation angle,length,width and position of the sound package,as well as the flow resistance and thickness of the sound absorbing material.The results show that from the perspective of sound field and flow field,the optimal solution for large and small sound absorption packages can improve the transmission loss by 18.0dB,and the optimization scheme with large sound absorption package can improve the transmission loss by 16.4dB.The optimization scheme of the small sound absorption package can improve the transmission loss by 2.5dB,and the comprehensive optimization scheme can improve the transmission loss by 29.4dB.The relevant research results can provide reference for the acoustic design of high-speed train air-conditioning duct system.