Allam S., Åbom M.

The perforated muffler is very often to be used by exhaust system manufacturers to improve the attenuation at low frequencies. In this study different existed models for hole impedance calculation have been tested using a 3D FEM Software and measured data for simple through and cross flow mufflers. The effect of flow is included in the perforation hole impedance and the convective effects are neglected. A modified model presented by Bauer 1977 was found to be the best and applied to analyse a complex muffler with multiple perforated elements. The flow distribution through the muffler was determined using a simple 1-D flow model. The calculated mean flow from this model was used to calculate the perforation impedance and used as input to the FEM code. The model gives an excellent agreement with the measured results for complex muffle without flow. With flow the result is quit satisfactory and the deviations are believed to be related to the simple 1-D flow model used, which only approximately describes the correct flow distribution.