Analysis and design of composite/folded variable area perforated tube resonators for low frequency attenuation

Abstract

Variable area concentric-tube-resonator mufflers may be used effectively for attenuating the odd harmonics. This ensures a broad-band transmission loss (TL) spectrum. In this paper, configurations that consist of variable area resonators within a uniform area muffler shell for enhancing the low-frequency noise attenuation are investigated. The variable area resonator elements within a muffler allow multiple elements, where the sum of their acoustic lengths is more than the geometric length of the muffler. This shifts the overall TL spectrum toward lower frequency. The underlying idea of incorporating the extended inlets and outlets in these resonators, is to reproduce the broadband attenuation. It has the effectiveness of dissipative ducts without the use of any absorptive materials. The results have been validated by means of three-dimensional finite element analysis.