The Effect of Sound Pressure on the Aeroacoustic Sources Around Two Ducted Tandem Cylinders

An empirical investigation of the spatial distribution of aeroacoustic sources around two tandem cylinders subject to ducted flow and forced transverse acoustic resonance is described. The work builds on a previous investigation by the authors and utilises Howe’s theory of aerodynamic sound. The influence of the sound pressure level in the duct on the strength and location of the aeroacoustic sources in the flow was the main focus of the investigation and experiments to resolve the aeroacoustic source distribution were concentrated at a low main-stream flow velocity (before acoustic-Strouhal coincidence), at a medium mainstream flow velocity (just after acoustic-Strouhal coincidence) and at a high mainstream flow velocity (substantially higher than acoustic-Strouhal coincidence). The sound pressure level was found to have a considerable effect on the “lock-in”’ range of the cylinders which widened as the sound pressure level increased. A proposed normalisation of the net acoustic energy transfer per spanwise location appears to show good metric for the distribution of the aeroacoustic sources in the flow field. Using this, it was found that the amplitude of the sound pressure had a negligible influence on the aeroacoustic sources in the wake and the gap region for all the tested cases apart from the lowest flow velocity. This particular case showed indications that the aeroacoustic source strength and location could be altered for certain changes in sound pressure level.