Acoustics of Suction

The sound of suction is characterised by conducting an experimental investigation of the acoustic response from a flow that is sucked into a duct capped by an orifice plate. Dimensional analysis is undertaken to identify the key parameters affecting the frequency response. As the flow is sucked through the orifice plate it separates at the edge of the plate and forms a jet downstream of the plate. It is found that in addition to the broadband noise associated with the jet the acoustic response has a tone produced by the interaction of the jet with the recirculation region behind the orifice plate. For small orifices, the Strouhal number of this tone (based on the bulk jet velocity and duct diameter) is approximately constant and does not depend on the other geometric parameters or the Reynolds number. The tone can be suppressed by using an appropriate insert downstream of the orifice plate.