The observed aeroacoustic behaviour of some flow-excited expansion chambers

Expansion chambers are often installed in flow duct systems to reduce press ure pulsations and to act as silencers. However, in certain circumstances t hey can become flow-excited sound generators rather than attenuators. The p hysics of the flow acoustic interactions responsible for this are examined in detail. They are then illustrated by a systematic sequence of sound powe r flux measurements in the downpipe, expansion chamber and tailpipe of some representative examples. These measurements then identify both the positio n and spectral characteristics of the sources of sustained excitation by th e flow in its relation to the local geometry and its associated reverberant acoustic behaviour. (C) 2001 Academic Press.