Abstract
KEYWORDS – exhaust, muffler, acoustics, aeroacoustics, thermal
ABSTRACT - Exhaust and muffler aeroacoustics predictions using Lattice Boltzmann Method have been performed and published for several designs at the SAE Noise and Vibration Conference (NVC) in 2015. While the predictions showed excellent accuracy and an innovative methodology for the aeroacoustics design of mufflers was presented, the results were obtained with a cold steady flow inlet boundary condition, similar to a cold bench flow experiment. The goal of this paper is to extend this study and present a similar methodology for hot engine flow realistic conditions, including the modeling of porous material such as glass wool roving within the muffler. The flow conditions at the inlet of the engine-mounted muffler are predicted by GT-Power for a given combustion engine, including temperature and mass flow fluctuations from the periodic engine cycle. First, a steady hot inlet flow boundary condition simulation coupled with PowerTHERM is performed in order to predict the temperature on the walls of the muffler. A second simulation, using the unsteady flow conditions predicted by GT-Power and the wall temperature predicted by PowerTHERM, is performed to predict the aeroacoustics performance of the muffler in engine-mounted conditions. Acoustic and flow results for the engine-mounted muffler design are presented, including the identification of the design features responsible for noise generation. Acoustic and flow results are also presented for an adiabatic wall case in order to assess the importance of the wall temperature modeling. Finally, acoustic and flow results for designs including a vehicle rear geometry with and without an internal glass wool roving are presented in order to illustrate the necessity of the modeling of these components for an accurate prediction of flow and aeroacoustics performance of mufflers.