Coupled Vibro-Acoustic and CFD Modeling Solution for Complex-Shaped Mufflers Subject

Flow within a duct strongly affects the propagation of acoustic waves. This effect must be addressed by the vibroacoustic modeling of duct systems that are subject to flow. The effective sound propagation speed in a duct is changed and the sound is refracted towards or away from the duct walls depending on flow direction. Narrowband acoustic sources from the engine must be attenuated by the muffler system. Because flow will shift the frequencies of the muffler system acoustic resonances, accurate modeling of acoustic propagation within a duct is crucial for design and “tuning” of muffler systems. For many actual muffler systems which have arbitrary or complex geometry, flow patterns do not have an analytical solution and must be determined through computational fluid dynamics (CFD) simulations. This paper describes an automated process for coupling an acoustic finite element (FE) muffler vibroacoustic design to an open source computational fluid dynamics (CFD) solver to obtain noise attenuation predictions accounting for flow effects, saving test effort and time. A validation case study showing the ability for a non-CFD expert modeler to obtain accurate muffler predictions for cases of uniform and non-uniform flow is presented. Limitations and future steps for this modeling approach are discussed.