Study On The Acoustic And Flow Field Characteristics Of Self-adjusted Dual Mode Exhaust Mufflers

Exhaust mifflers are widely used to control the internal combustion engine exhaust noise.The main performance criteria of exhaust mufflers are the acoustie attenuation performance and aerodynamic performance.In order to meet both requlrements and balance the conflicts between them in muffler design process,many automotive companles developed the dual mode mufflers in exhaust systems,and received good effects.Though the duel mode mufflers have been used for a long time, however,there are only a few related publieations and only experimental methods are used,and many unknown acoustic and aerodynamic characteristics still need to be investigated at the present tiom.As a result,the feasibility and accuracy of two numerical methods:finite element mothed(FEM) and finite volume method(FVM) are demonstrated by numerieal examples at first.Then, the resonance mechanism of the doal mode muffler that appears at low frequenciexs with no flow is studied in detail by using the acoustic finite element software Sysnoise;fluid flow with different flow velocities in the inlet and valve open angles inside the muffler is amply presented by using the CFD software Fluent.Based on the foregoing analysis,the influences of different flow velocities and valve open angles on the acoustic attenuation performance of the muffler are discussed in the paper.The effects of the geometrical parameters on the acoustic performance and pressure loss are also investigated,which is beneficial to the optimum design of practical mufflers.Based on the study of dual mode muffler with butterfly valve, a kind of piston controlled dual mode muffler is'presented,and the acoustic and aerodynamic performance is studied preliminarily,which illustrates that this muffler may perform the dual mode functions too.