Effect of flow on the drumlike silencer

This study examines the effects of a mean flow and turbulent flow excitation on the performance of the recently conceived device which was tested under the no-flow condition [J. Acoust. Soc. Am. 112, 2014-2035 (2002)]. The silencer consists of two cavity-backed membranes lining part of the duct walls. When a certain optimal tension is applied, the silencer gives a broad stopband in the low-frequency regime. Similar performance is predicted for the condition with a mean flow, and tests conducted for flow speeds from 5 to 15 m/s validated these predictions. The spectrum of transmission loss without flow features three resonance peaks, and the mean flow is found to smooth out all peaks and shift two of them through cross-modal coupling. The silencer was tested in a wind tunnel, and no flow induced flexural instability was found on the membrane in the range of flow speeds tested. Insertion loss measurement was also conducted in a natural ventilation condition where a turbulence intensity of 3% was recorded, and the results were close to those without flow. It is concluded that no noticeable extra sound is produced by the turbulent excitation of the membrane under the optimal tension required by the silencer.