Study On Performance Analysis And Test Method For Resonant Muffler

The resonant muffler is often used to reduce the noise of an automobile exhaust system.However,the high-speed and high-temperature airflow exist in the actual working condition of the muffler,which makes the muffler's performance difficult to achieve the desired results.Therefore,it is of practical significance to investigate the sound attenuation performance of a muffler with airflow.Taking an automotive exhaust resonant muffler as the research object,the sound pressure level(SPL)in multi-field coupled by the flow field,the sound field and the temperature field of the muffler is studied based on the combination of numerical simulation and experimental test.An improved resonant muffler is designed and optimized based on above obtained results.Firstly,a simulation model of the muffler is established by combining the Large Eddy Simulation(LES)and Acoustic Analogy(AA)methods.The SPL is taken as an evaluation index to analyze performance of the muffler with airflow.By using the double microphone method,a test bench is built for measuring and analyzing SPL spectrum characteristics of the muffler.Comparisons of the experimental with simulated results show a good accuracy of the established simulation model.Secondly,the influences of flow velocity,temperature and structure on the acoustical attenuation performance of the muffler are analyzed by numerical simulation based on the verified muffler model.The computation results show that the aerodynamic noise and the turbulent kinetic energy(TKE)have higher numerical values at some structural mutations in muffler.And the nephogram distribution of the two parameters is in accordance with each other.The SPL increases with the rising of inlet flow velocity and reversely with the rising of the air flow temperature.But the spectral characteristic is less influenced by flow velocity and temperature.From these findings,it can be seen that appropriate changes to the muffler structure can improve its performance.The results of multi-field coupling can be used as a reference for the resonant muffler design.Finally,according to the above results,the muffler structure is improved on two aspects.On the one hand,a fillet transition structure is added to the end of the inserting tube to reduce the aeroacoustic noise.On the other hand,the aerodynamic performance is improved by improving structure where the TKE distribution is concentrated.The SPL,the TKE and the sound pressure distribution in the cavity before and after the improvement of muffler structure are compared and analyzed.The results show that the SPL at the exhaust pipe under the muffler is reduced by 3-5d B,the TKE is reduced by 10-20%.The muffler performance has been significantly improved.This thesis is to study the muffler performance under multi-field coupling condition.The conclusion can be applied to improve the design of muffler,and has certain theoretical value and practical significance.