BEM analysis of large tuned dissipative silencers and bar silencers

In this paper, the BEM impedance-to-scattering matrix method is used to predict the transmission loss (TL) of large dissipative silencers with a rectangular cross section. Of particular interest are the tuned dissipative silencers and the bar silencers commonly used in the power generation industry. A tuned dissipative silencer incorporates a mix of lined resonators of various sizes to target certain different frequency ranges. Its internal geometry is quite complex but usually has a certain repeating pattern. On the other hand, the bar silencer has a relatively uniform internal geometry. The direct mixed-body BEM with the substructuring technique can be used for both types of silencers. The impedance-to-scattering matrix method developed recently has the ability to include higher-order propagating modes at the large inlet and outlet for TL computation. Results from the proposed method are compared to the TL curves from a "lumped four-pole matrix" approach, in which simple averages are taken for sound pressures at the inlet and the outlet, respectively, to form an equivalent four-pole matrix for TL computation.