Sound Produced by Vortex Pairing: Prediction Based on Particle Image Velocimetry

In some cases, the prediction of the sound generated by flows is impaired by inaccuracies in the available flow data. These inaccuracies can be due to the degree of approximation of a flow model, or to the uncertainty of a measurement technique. A particular crucial point for sound prediction is the conservation of the flow invariants. The sound radiated by vortex pairing in a subsonic excited jet is deduced from experimental data obtained by particle image velocimetry. The performance is compared of different formulations of vortex sound theory to predict the corresponding sound production. It is shown that assuming several times the conservation of the momentum and kinetic energy in the implementation of the vortex sound theory improves considerably the robustness of the prediction. In fact, a prediction in good agreement with both a theoretical model of leapfrogging and numerical simulations of merging is obtained, although the basic data do not respect precisely these conservation laws.