ACOUSTIC MODELLING OF MULTIPLE PATH SILENCERS WITH EXPERIMENTAL VALIDATIONS

Abstract

The results are presented of an investigation to identify and quantify the relative influence of their geometrical features with that of other relevant physical and operational factors on the acoustic behaviour of cross-flow silencers. This was accomplished by comparing the measured with the predicted attenuation performance of a sequence of generic examples of cross-flow and flow-reversing silencing elements. Such silencers are all assembled around a common geometric central feature, consisting of an expansion chamber spanned by the perforated inlet and outlet pipes. The predictive modelling included the simplifying assumption that the wave motion throughout the central element is essentially one-dimensional and directed along the pipe and chamber axes, with radial propagation existing only through walls. The existence of any axial mean velocity gradients was also neglected, so that the mean flow velocity and all the other relevant physical properties of the acoustic medium were represented by their locally space averaged values. Comparisons between measured and predicted performance of some thirty representative models are summarized and discussed in terms of the relative significance of their relevant physical and operational features on their attenuation performance. The subsequent validation of the acoustic, modelling included the identification of those features that required further investigation. Nevertheless, the results demonstrate that the predictive modelling provides adequately realistic predictions of silencer acoustic performance for practical application to exhaust system design.