A simple four-pole solution with FEM/BEM validation to estimate the effectiveness of compact resonators in large silencers

Large absorptive silencers are used in the power generation industry to abate intake or exhaust noise. They are very effective at mid to high frequencies; however, low-frequency performance is an area of concern for absorptive silencers. Hybrid baffles and bars with empty space reserved for a quarter wavelength duct design have been used to target low-frequency tonal noise with some success. Although, at times the hybrid baffles or bars themselves are not enough to reduce the low-frequency noise to an acceptable level. Synonymously, the overall high-frequency performance may suffer due to the loss of space that could be used for more dissipative elements such as absorptive baffles or bars. Compact resonators with a tapering neck may then be considered as an add-on to improve the low-frequency performance. In this paper, a simple four-pole solution is utilized to estimate the first natural frequency of a compact resonator. The end correction factor is then empirically correlated to the finite element method (FEM) or boundary element method (BEM) solution. The small compact devices have a potential application to provide engineers with a very flexible design add-on strategy without significantly altering the installed silencer design, and their target frequencies can also be adjusted depending on the situation.