Study on effect of absorbent on acoustic damping of duct

Abstract

The acoustic material has been used inside ducts as a countermeasure of the self-sustained tone generated from heat exchangers and boilers. However the effects of the amount of acoustic material and its patching position in a lined duct on the acoustic damping in its duct have not been established. It can be expected that we can suggest the guideline of absorbing treatment at the design stage to avoid the generation of the self-sustained tone. In this study, the experiment and the analysis are carried out to clarify the problems mentioned above. First the usefulness of the analytical method by BEM is shown by comparing experimental results referring to the acoustic damping in the duct. Next, the effects of the amount of acoustic material and its patching position relative to the noise source on the acoustic damping in the duct are examined by BEM analysis. As a result, it was confirmed that the analytical method due to BEM was useful to predict the acoustic damping because the analytical results of acoustic damping were in good agreement with the experimental ones. And the acoustic damping was also clarified to be affected strongly by the positional relation between the noise source and the acoustic material. In addition, it was effective to patch the acoustic material near the noise source.