Acoustic Simulation of an Automotive Muffler with Perforated Baffles and Pipes

A complex automotive muffler consisting of multiple chambers, perforated baffles and pipes with perforated sections is simulated with both a linear and non linear solver in regard to duct acoustics. The goal is to be able to predict the acoustic performance of the muffler and correctly assess the effect of any changes to the muffler configuration. The linear solver is a frequency domain code using the transfer matrix method to predict the acoustic performance. The non linear solver is a time domain code using a finite volume method to predict the flow distribution and pressure drop across the muffler. A recently developed linear acoustic model for perforates has been applied to the perforated sections of the automotive muffler. This includes different configurations of the muffler both with and without flow. The perforate model with flow requires the correct flow distribution throughout the muffler in terms of through flow and grazing flow for each perforated section. This flow distribution is determined from the non linear simulation of the different muffler configurations. This same code can also be used to determine the pressure drop across the muffler and thereby assess the effect of the muffler on engine performance. The predicted transmission loss for different muffler configurations, both with and without flow, has been validated against measured data. The predicted pressure drop of the muffler configurations has also been validated against measured data.