Structure-Acoustic Coupling Characteristic Of Expansion Chamber Muffler

The expansion chamber muffler withstands the impact of airflow while eliminating noise.The interaction between the internal air flow and the external thin shell structure will change the inherent acoustic properties and structure regeneration noise of the muffler,which seriously reduce its actual noise reduction effect.Therefore,it is of great practical significance to explore the transmission loss and the structural acoustic radiation change influenced by the structureacoustic coupling effect to improve the actual use effect of muffler.Firstly,the basic theory of the muffler is given,the acoustic and aerodynamic performance of muffler is discussed.It is shown that the structural parameters of the muffler have an effect on the acoustics,aerodynamic performance,cavity velocity and turbulent kinetic energy distribution.The transmission loss and resistance loss changes under different intubation combinations were obtained.A structure of single-inlet and double-outlet resistant exhaust muffler is proposed.Then,a theoretical analysis model of the structure-acoustic coupling of the muffler was constructed.Based on the modal analysis,the modal superposition method is used to consider the structure-acoustic coupling effect,and the transmission loss under the influence of the coupling is calculated and compared.The results show that: the transmission loss will change abruptly in different degrees under the coupling action,which will affect the use stability of muffler.The aspect ratio becomes smaller and the temperature increases to reduce the coupling effect on the transmission loss;the formation of mutation is mainly affected by the structural mode.The effect of the state can be improved by reinforcing the structural mode through reinforcement.Furthermore,the FEM-BEM method is used to analyze the structural acoustic radiation of the expansion chamber muffler.Comparing the influence of the flow velocity,installation constraints and shape structure of the muffler on its sound radiation.The results show that: the increase of the flow velocity will increase the radiation noise;the simultaneous restriction of the inlet and outlet can reduce the total sound power level;the minimum radiation noise is produced by the circular section expansion cavity and the inner tube type muffler;the radiated sound field of the muffler is mostly symmetrically distributed;total sound power level of the overall radiation of the muffler can be effectively reduced by thickening or external reinforcement at the large wall surface.Finally,in order to further improve the performance of the muffler,the CFD method was used to investigate the resistance loss of the multi-input and multi-output muffler.The influence of structural parameters on the resistance loss is analyzed.The results show that the resistance loss of double in and single out muffler is the largest;the change of the relative angle of the inlet pipe and the outlet pipe has a great influence on the cross muffler;with the increase of the distance between the outlet pipe and the diameter of the expansion cavity,the resistance loss of the coaxial muffler and the cross muffler decreases and increases respectively;increasing the length of the expansion cavity increases and decreases the resistance loss of the coaxial and cross-type mufflers,respectively;the resistance loss of both mufflers decreases as the diameter of the inlet and outlet pipes increases;the resistance loss of muffler can be reduced by adding inner tube and transition structure.Through the combination optimization of the original design of the exhaust muffler,such as end openings and the transition structure,the aerodynamic performance of the muffler is improved by 21.8% without affecting the acoustic performance.The optimization effect is obvious.