Pressure loss and acoustic models of automotive exhaust silencers: Prediction of mean mass flow impact on silencer acoustic behaviour

Design of automotive silencers relies mainly on a compromise between acoustics and pressure drop. 1D calculation tools (plane wave models for acoustics and 1D network fluid flow tools for pressure drop) allow the designer to assess the performances of a high number of configurations very quickly. Still, the one dimensional hypothesis in flow distribution calculation is not always fulfilled. The pressure loss prediction accuracy is thus affected, but also acoustics results because, in some cases, mean mass flow and its distribution in the silencer internal completely modify the acoustic behaviour. The solution we found is to focus on several standard designs of silencers and to adopt an original semi-empirical approach for flow distribution and pressure loss calculation. With accurate calculation of flow distribution inside the silencers, associated with a refined description of flow impact on perforated pipe acoustics, we are able to predict the impact of mean mass flow on standard silencers acoustic behaviour.