Study on the Finite Element Method for Prediction of Acoustic Characteristics of Exhaust Silencers
|School||Harbin Engineering University|
|Course||Power Machinery and Engineering|
|Keywords||silencer acoustic characteristics finite element method convective effect perforated tube sound-absorbing material experimental measurement|
Silencer is an effective device to reduce the exhaust noise of internal combustion engines. Three-dimensional numerical methods should be used to predict the acoustic performance of silencers in view of the complex sound field inside the silencers. Finite Element Method (FEM) is an effective numerical method which has been widely used to predict the acoustic performance of silencers. However, the conventional FEM can not be applied to calculate the acoustic problems associated with sound field in higher Mach number subsonic flow. In order to solve this problem, the three-dimensional FEM and the two-dimensional axisymmetric FEM are developed in this thesis.The three-dimensional and two-dimensional axisymmetric FEM programs are developed for prediction of the acoustic characteristics of silencers. The basic principle and the numerical procedure of FEM were introduced. Numerical results showed that the present FEM has high accuracy, and is suitable for acoustic characteristic prediction of silencers with the stationary and flowing medium. Computational complexity and computer memory requirements of the conventional FEM limit its application for solving the large-scale or high frequency acoustic problems. In order to solve this problem, substructure FEM was developed.Perforated tube silencers are widely used in the intake and exhaust noise control of internal combustion engines due to their low resistance loss and high noise attenuation. Three-dimensional FEM is developed to predict and analyze the acoustic attenuation characteristics of perforated tube silencers. Comparisons of transmission loss predictions with experimental results for straight-through perforated tube silencer and three-pass perforated tube silencer illustrated that the FEM can predict acoustic characteristics of perforated tube silencers accurately. The FEM is then used to investigate the effects of geometrical parameters on the transmission loss of three-pass perforated tube silencer.Perforated tube dissipative silencers are also widely used to reduce the intake and exhaust noise of fluid machinery. Three-dimensional FEM is developed to predict the acoustic attenuation characteristics of perforated tube dissipative silencers. Comparisons of transmission loss predictions with experimental results for straight through perforated tube dissipative silencer illustrated that FEM can predict acoustic characteristics of perforated tube silencers accurately. The FEM is then used to investigate the effects of porosity, bulk density of sound-absorbing material (or flow resistivity) and thickness of sound-absorbing material.In order to verify the validity of acoustic performance predictions of exhaust silencers from the present FEM, two-load method is used to measure the transmission loss of silencers without flow. Measurement results agree well with FEM predictions, which showed that the measurement method and the numerical method are both valid.