Development and Application of 3D Generic Cells to the Acoustic Modelling of Exhaust Systems

The acoustic simulation of internal combustion engine exhaust systems is an important aspect to meet customer expectations and legislation targets. One dimensional gas dynamic simulation tools are used for the calculation of the exhaust orifice noise in the early stages of the engine development process. This includes the prediction of the acoustic performance of individual components in the exhaust line. One common element used in exhaust systems to increase the acoustic damping is the plug flow muffler. This study looks at the prediction of acoustic performance of various plug mufflers at different flow velocities. These include a single plug muffler, a double plug muffler and an eccentric plug muffler with different porosities for the perforated sections. To this purpose a generic 3D cell approach was developed and applied. It is based on the solution of the mass, momentum and energy equations for non viscous flows over clusters of cell elements arbitrarily connected among each other. In each case a suitable mesh of 3D cells is created to model the geometry of the muffler. Particular attention is required in meshing the cross section of the mufflers. The models include perforated connections between cells to which appropriate numerical methods are applied to provide a stable solution. This includes the application of a flux limiting technique for the momentum equation for each connector. The models provide accurate prediction of the acoustic behaviour with and without flow as well as the pressure drop across the muffler. The results are validated against experimental measurements of the transmission loss and pressure drop.