Theoretical/empirical prediction and measurement of the sound produced by vortex pairing in a low Mach number jet

The sound produced by vortex pairing in a Mach 0.1, acoustically excited air jet is considered. The sound produced by vortex pairing is predicted on the basis of an experimental description of the flow field and using an aeroacoustical analogy. The experimental data is provided by particle image velocimetry. The aeroacoustical analogy is a conservative formulation of the vortex sound theory that has been developed in a previous work. This formulation has been shown to be robust when the flow data contains approximations or experimental uncertainties, as is the case here. The prediction is compared to measurements of the sound produced by the excited jet. The spectrum exhibits frequency components that are associated to the pairing, an intermittent second pairing, and the acoustical excitation. The agreement between the sound prediction and the acoustical measurements is good for the first two harmonics related to the first pairing. This demonstrates that the authors' conservative formulation of the vortex sound theory allows a correct sound prediction in spite of the uncertainties on the flow data.