Analytical and experimental investigation of the performance of exhaust mufflers with flow

Abstract

A method for evaluating the impedance of an unknown source has been developed. Source impedance including the effect of mean flow was used to predict the attenuation of expansion chamber type exhaust mufflers, with mean .flow in the system. The transfer matrix approach has been used to predict the noise reduction characteristics of various laboratory and two commercial muffler configurations. Mathematical models have been derived for uniform pipe elements with mean flow and damping, and their steady state solutions are transformed into two-by-two transfer matrices. Another muffler performance criterion called noise reduction is used to measure the performance of laboratory mufflers and some simulated configurations of commercial exhaust mufflers. The performance of exhaust muffler systems was then predicted by considering the product of transfer matrices taking into account all the muffler components present in the system. A general algorithm has been developed for an approximate frequency analysis of any complex muffler system. Knowing the relative magnitudes of all the parameters present in a system, various resonant and antiresonant peaks in the performance curves can be predicted using the algorithm. To determine the general properties of commonly used silencer components, some reactive muffler configurations are studied with and without mean flow and the performance of some similar configurations is compared. The transfer matrix of a circumferencially lined pipe element including the effect of mean flow has been derived and used to predict the performance of some expansion chamber type dissipative exhaust mufflers.