Simulation And Experimental Investigation On Acoustic Attenuation Performance Of Resonnat Muffler

Resonant muffler is used to reduce the low frequency noise of automobile exhaust system. The characteristics of low frequency noise of exhaust system are not ideal due to simple structure and narrow frequency band. The key of muffler designing is to reduce low frequency noise, broaden resonance frequency band and estimate natural frequency of the resonant muffler accurately. A vehicle exhaust muffler is considered in this thesis. Simulation and experiment test is conducted. Furthermore, the influence of structure parameters of muffler on acoustic attenuation performance are analyzed. Resonant muffler structures is designed and optimized.Firstly, acoustic attenuation performance of the muffler is analyzed by experiment and simulation. Experiment bench is built to measure transmission loss on the basis of two method of load. The results show that the muffler has poor acoustic performance on low frequency. Acoustic model is established to calculate transmission loss by finite element method, which is verified through experiment results.Secondly, single cavity resonant muffler model is established. Numerical simulation is employed to analyze the acoustic attenuation performance which is affected by resonance structure parameters. The resonant frequency and transmission loss which is influenced by structure parameters of resonant cavity such as cavity volume, connecting pipe, connecting length and intubation length are studied. Multi degree of freedom spring oscillator formula of series, parallel and mixed cavity resonant muffler is proposed on the basis of the mechanical-acoustic analogy model, which is verified through simulation. This formula is established to predict resonant frequency and corresponding transmission loss of resonant muffler. The influence of structure parameters such as aperture, porosity of the plate, distance of between cavity and plate and etc. are investigated. Through the analysis of structure parameters of resonant muffler, it can be acted as the basis of muffler design.Finally, according to the above results, two optimization methods are proposed. On one hand, improving the performance of low frequency by changing the cavity volume, the distance between cavity and plate and aperture of holes. On the other hand, double plates are effective to enhance the acoustic performance. The acoustic performance enhance significantly and the band width of low frequency band is becoming broader.This thesis aim to analysis a vehicle experiment and optimization design of resonant muffler, which can improve the performance of the muffler and provide technical support for muffler design.