Analysis Of Acoustics Performance And Flow Field Characteristics For Vehicle Muffler

Exhaust muffler is the most effective way to control vehicle’s exhaust noise. Itsinstallation can reduce the noise of vehicles effectively, but it can also cause the loss ofengine power, thus affecting the dynamic performance and fuel economy of the vehicle.Therefore, it has been an important topic to design exhaust mufflers that have goodattenuation performance and low pressure loss in the field of automobile’s noise control.In this paper, the acoustics and fluid characteristics of the basic anechoic units suchas simple expansion chamber, the expansion chamber with inserted pipe and Helmholtzresonator etc, were analyzed by one-dimensional(1-D) CFD software Gt-power and3-DCFD software Fluent, and the transmission loss(TL), the pressure loss and internal fluiddistribution in muffler were obtained in order to discuss the influence of basic anechoicunit’ s structure parameters on its acoustic performance and aerodynamics performance.A certain car’s muffler with complex structure was taken as the research target,and its three-dimensional model was established in3-D modeling software Catia. Themuffler’s shell with irregular shape should first be imported into the software Gt-powerand the work of shell model transformation was finished, and then, other structures suchas pipe fitting, baffle wall and perforating structure etc, were completed by using thetools in the Gt-power. The completed muffler model should be scattered in order tobuild the transmission loss computing platform and the result of TL was obtained byrunning the transmission loss computing platform. At last, the accuracy of the mufflermodel was verified through comparison with the test result, which showedgood agreement with numerical simulation result.The engine simulation model was established in Gt-power according to thestructural parameters provided by the manufacturer. Then, comparing the engine torqueand power gained by the simulation calculation with the experimental result, thefeasibility of simulated engine model was validated. Finally, the insertion loss (IL) ofmuffler was obtained by conducting the coupling simulation of engine and muffler.For the sake of analysing the influence of inlet velocity on the fluid characteristicsinside the muffler, the3-D muffler model built in Catia was imported into Hypermeshsoftware to mesh the air domain inside the muffler. And then, the finite element modelof muffler was imported into Fluent software and the boundary conditions were loaded.The internal flow field distribution and the pressure loss between inlet and outlet cross-section were obtained finally through operation simulation model.The numerical simulation and calculation of the improved muffler provided by themanufacturer was conducted and the experiment of tail pipe noise for the two mufflerswas conducted in the laboratory. And then the comparison and analysis of the numericalsimulation result and tail pipe’s noise between the two mufflers was made that verifiedthe effectiveness of the proposed scheme. So in this paper, taking acousticalperformance, flow characteristics and tail pipe’s noise into consideration, the feasibilityof improved plan was validated by combining the simulation with experiment.