Design Of Folded Lumen Pipe Muffler And Analysis Of Its Acoustic Characteristic

Since the 21 st century,as one of the four major pollution problems in the world,noise pollution has seriously affected people’s work and life,and has caused great negative impact on human physical and mental health.Traditional acoustic materials are limited by the law of mass density in controlling low-frequency noise,and can only be used to achieve low-frequency noise reduction by increasing the volume of the material,which has limitations in practical applications.The emergence of acoustic metamaterials provides a new way of thinking for achieving low-frequency noise reduction.Among them,the Helmholtz resonator can realize the control of low-frequency noise in a small structural size.In this paper,a folded tube cavity structure muffler is designed based on Helmholtz resonance theory and its acoustic performance is analyzed computationally,with the main research contents as follows:(1)Based on the Helmholtz resonance theory,finite element analysis is carried out for the traditional Helmholtz resonator and the folded pipe cavity structure muffler.The results show that the resonant frequency of the folded pipe cavity structure muffler is basically the same as that of the classical Helmholtz resonant cavity after straightening the folded channel in the same size;then the size and structure parameters of the folded pipe cavity structure muffler are optimized,and by optimizing the design unit parameters Then the size and structure parameters of the folded cavity structure muffler are optimized.The designed multi-unit parallel coupling structure can achieve effective absorption in the range of 450 Hz-600 Hz,and the average transmission loss in the muffling bandwidth exceeds 35 d B and the maximum transmission loss exceeds 60 d B.The final experimental results are consistent with the overall trend of the simulation results.(2)Filling the cavity inside the folded pipe cavity structure muffler with porous material,so that the designed composite structure has certain sound absorption effect at low frequency.The influence of the basic parameters of porous materials(flow resistance,viscous characteristic coefficient,thermal characteristic coefficient,etc.)and the percentage of porous materials on the absorption coefficient of the composite structure is investigated by using the control variable method,and several units of different frequencies are arranged periodically in the axial direction to broaden the absorption bandwidth based on the determination of the parameters of porous materials,so as to achieve effective absorption in the range of 90 Hz-500 Hz.(3)In analogy with an electronic diode,a double-ended open asymmetric absorber is constructed,and the finite element simulation results show that the absorption coefficient of the acoustic wave entering the system from the left side is 84.6% and the reflection coefficient is12.6%;the absorption coefficient of the acoustic wave entering the system from the right side is only 8.8% and the reflection coefficient is 95.3%.It shows that two different absorption effects occur when the sound waves are incident from different directions.Based on the singleband asymmetric absorber,a broad-band asymmetric absorber is designed by arranging units with different resonant frequencies,and the rationality of the design is proved,and the overall ventilation performance of the structure is ensured while achieving the goal of acoustic modulation.