Estimating acoustic transmission loss of perforated filters using finite element method

Abstract

Finite element method is well established in estimating acoustic transmission loss (TL) of passive reactive acoustic filters. However, the acoustic impedances derived from the established empirical models are being used to model the perforated elements present in these acoustic filters. Such empirical models have been established with known restrictions such as position, shape, size, orientation and evenness of the perforations. In the present work, finite element analysis in frequency domain has been demonstrated to circumvent the necessity of such empirical models in estimating acoustic TL of reactive filters having perforated elements at zero mean flow condition. In order to achieve so, a three-pole measurement based simulation has been carried out which exactly replicates the experimental transmission-loss tube test setup. The essential necessity of simulating anechoic termination to perform three-pole measurement and the associated complexity has been resolved. The constraint of desired meshing for estimating the acoustic TL of a perforated plate has been quantified. The strength of the proposed methodology has been exploited by analyzing reactive acoustic filters with various shapes of perforated components. Further, the challenge of analyzing the reactive filters with external perforation has been considered. In order to simulate the perforation facing to atmosphere, an additional domain or volume with non-reflecting boundary attached to perforation, has been proposed. The proposed methodology has been verified by evaluating the TL of a Helmholtz resonator with a leak and of a perforated tube. Summarizing above, the proposed three-pole based finite element methodology can be used for acoustic analysis of any shape and size of perforated components and reactive filters with perforated elements.