Modeling of Silencers for I.C. Engine Intake and Exhaust Systems by Means of an Integrated 1D-multiD Approach

This paper describes the development of a fully 1D and of a 1D-multiD integrated approach for the simulation of complex muffler configurations. The fully 1D approach aims to model the muffler recurring to an equivalent net of 1D pipes. An expansion chamber with offset inlet and outlet pipes was modeled with this preocedure and the resuts compared to CFD simulations, pointing out some critical aspects in the TL prediction. The HLLC Riemann solver and its extension to the second order were implemented both in the 1D and multiD models and exploited to handle the interface between the calculation domains. The integrated 1D-multiD approach was used afterwards to predict the transmission loss of more complex geometries such as series chambers with extended inlet and outlet pipes and with flow reversals. A new procedure has been adopted to calculate the transmission loss, imposing a pressure impulse at the inlet and evaluating the response of the muffler. This method, along with the adoption of more accurate numerical schemes improved considerably the accuracy of the result and shortened the comuptational time. The results pointed out a better prediction of the coupled approach if compared to the results of the 1D simulations. Moreover, a real engine configuration has been adopted to predict the acoustic performance of the reverse chamber under realisic operating conditions, in which pressure perturbations have finite amplitude and mean flow is present.