A time-domain simulation method to predict insertion loss of a dissipative muffler with exhaust flow

Abstract

Insertion loss (IL) is a more useful acoustic index than noise reduction and transmission loss for muffler design, but it is harder to predict because the prediction of IL requires knowing the characteristics of the muffler itself and the acoustic source. A muffler with porous material and complex meanflow makes the prediction even more challenging. Although calculation of noise reduction and transmission loss with the transient computational fluid dynamics (CFD) can naturally solve the flow–acoustic interaction problem, the published CFD methods have not been adopted to evaluate the IL of the dissipative muffler with exhaust flow. In this paper, a time-domain simulation method is developed to predict the IL of a complex engine muffler with porous material. The noise reduction and load impedance of the muffler were first calculated using a three-dimensional CFD model, in which the porous material was simulated by the governing equations modified with the material porosity and flow resistivity. The IL was then predicted from the noise reduction, the load impedance, and the engine source extracted from the measured exhaust noise. This developed method explores the application of the three-dimensional CFD method in calculating noise reduction, load impedance, and insertion loss of complex dissipative mufflers with exhaust flow.