Transversal modes and acoustic attenuation performance of a perforated tube dissipative silencer

The two-dimensional finite element method was used to calculate the transversal modes of a perforated tube dissipative silencer, and the numerical mode matching method was developed to predict its acoustic attenuation performance. The corresponding formulation was derived and the computational code was written. For a circular concentric configuration, the transmission losses achieved using the numerical mode matching method, the three-dimensional finite element method and tests agreed well. This fact demonstrated the correctness of the 2-D finite element method to calculate the transversal modes and that of the numerical mode matching method to predict the transmission loss of a perforated tube dissipative silencer, respectively. The numerical mode matching method was then used to investigate the effects of hole diameter, porosity, density of sound-absorbing material and offset of a perforated tube on the transversal modes and acoustic attenuation characteristics of the circular straight-through perforated tube dissipative silencer. The results showed that smaller hole diameter or higher porosity or bigger offset of perforated tube may lead to wider effective frequency range of plane wave domination, better acoustic attenuation performance in a high-frequency range, and worse acoustic attenuation performance in a middle-frequency range; increasing the filling density of sound-absorbing material may improve the acoustic attenuation of the silencer in a mid to high frequency range.