Hindawi Publishing Corporation Advances in Acoustics and Vibration Volume 2013, Article ID 546120, 10 pages http://dx.doi.org/10.1155/2013/546120 Research Article A Nonlinear Quasi-3D Approach for the Modeling of Mufflers with Perforated Elements and Sound-Absorbing Material G. Montenegro, 1 A. Della Torre, 1 A. Onorati, 1 and R. Fairbrother 2 1 Department of Energy, Politecnico di Milano, Via Lambruschini 4, 20156 Milano, Italy 2 AVL LIST GMBH, Advanced Simulation Technologies, Hans-List-Platz 1, 8020 Graz, Austria Correspondence should be addressed to G. Montenegro; gianluca.montenegro@polimi.it Received 31 August 2012; Revised 21 November 2012; Accepted 7 December 2012 Academic Editor: Luis M. C. Godinho Copyright © 2013 G. Montenegro et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Increasing demands on the capabilities of engine thermo-�uid dynamic simulation and the ability to accurately predict both performance and acoustics have led to the development of several approaches, ranging from fully 3D to simpli�ed 1D models. e quasi-3D approach is proposed as a compromise between the time-demanding 3D CFD analysis and the fast 1D approach; it allows to model the acoustics of intake and exhaust system components, used in internal combustion engines, resorting to a 3D network of 0D cells. Due to its 3D nature, the model predicts high-order modes, improving the accuracy at high frequencies with respect to conventional plane-wave approaches. e conservation equations of mass and energy are solved at cell centers, whereas the momentum equation is applied to cell connections including speci�c source term to account for the of sound-absorbing materials and perforated elements. e quasi-3D approach has been validated by comparing the predicted transmission loss to measured data for a number of standard con�gurations typical of internal combustion engine exhaust systems: a reverse-�ow chamber and series chambers with perforates and resistive material. 1. Introduction Internal combustion engines are the source of mechani- cal, combustion, and gas dynamic noise. In particular, gas dynamic or pulse noise is related to the unsteady �ows in the intake and exhaust systems, induced by the cylinder gas exchange process [1]. e level and quality of noise radiated from the open ends can be controlled by different arrangements of pipe systems and silencers to achieve the required vehicle exterior and interior sound characteristics by attenuating or enhancing certain spectral components. Today numerical simulation codes are very useful during the design and optimization process of both intake and exhaust manifolds and mufflers to quickly de�ne the best geometries which can be �nally re�ned experimentally. e attenuation features of simple and complex acoustic �lters can be pre- dicted by 1D and 2D-3D �uid dynamic/acoustic simulation codes with different levels of complexity, both in the time and frequency domain. On one hand, 1D linear/nonlinear codes are nowadays widely used to calculate the acoustic performances of mufflers [2, 3]. Certainly 1D linear acoustic codes are mainly applied for this purpose [4–6] due to their simplicity, accuracy, and very short computational times. However, as the �ow speed becomes not negligible and the sound pressure level of the signal reaches values of 160 dB, as it can happen inside a muffler for internal combustion engines, the magnitude of the incident pressure perturbation makes the linear approximation not valid anymore [7, 8]. erefore, when the dynamics of the system is nonlinear, time domain simulation tools become attractive. For instance, in the case of perforated tube silencers, the �uid dynamics of the holes exhibit nonlinear features when exposed to sound pres- sure levels typical of internal combustion engines. For this reason, time-domain simulation tools are preferably applied to better reproduce complex pulsating �ows associated with mean velocity, since they directly account for these features in the fundamental equations they are based on [7, 9]. erefore, in the last decade 1D nonlinear, time domain models have become preferential tools for the simulation of the high amplitude wave motion in the silencer ducts with