Study On Flow Performance And Acoustic Performance Of Automobile Exhaust System

The sdudy of the engine exhaust system performance is the requirement of automobile's emission control and noise control.It is difficult to obtain accurate calculation results of the flow characteristics and acoustic characteristics of exhaust system by using traditional methods.the finite volume method,acoustic finite element method numerical simulation method were used to sdudy the engine exhaust system,it can simulate the actual flow of gas,but also consider the influence of several factors on the performance of the exhaust system.First,we use fliud-solid coupling method to study the flow performerce of exhaust system.This paper used the 3D numerical simulation to analysis fliud-solid coupling modle of the exhaust system,which can get the pressure field,temperature field and velocity field of exhaust system.On this basis,we analysed pressure loss reasons of the exhaust system,putted forward the necessity analysis of the temperature field,and gave specific flow in system.Secondly,it taken the exhaust gas pressure and exhaust temperature of 6 test points on the exhaust system as comparison object.using the test bench which was built with an enterprise to verify the reliability of the numerical simulation results.Then,establishing the acoustic finite element model in the LMS Virtual.lab and taking transmission loss as the evaluation index,using the finite element method to analyse the acoustic characteristics of front muffler,rear muffler,the overall sound system,respectively which gutted the transmission loss curve of front muffler,rear muffler,the overall muffler system,and gave parts of sound pressure distribution nephogram of some frequency.Finally,we consider the influence of temperature and the flow rate to the acoustic characteristics of the muffler,and get the overall muffler system transmission loss curve.t of coupled temperature and velocity.The results show that after considering the temperature,noise frequency shifts to higher frequency,the first peak of transmission loss curve shifts from 320 Hz to 480 Hz,and the second peak shifts from 400 Hz to670Hz.The average noise elimination quantity of low frequency was reduced by about20 d B,the Noise attenuation characteristic becomes worse.The average noise in themiddle and high frequency band increased by about 15 d B,the Noise attenuation characteristic improved;consideration of the flow factors,the average transmission loss increased slightly compared with not considering the flow rate,increased about 4d B.On the whole,the effect of temperature on acoustic characteristics more obviously than the effect of flow rate on the acoustic characteristics.