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Noise radiation from instability waves in subsonic coaxial jets

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Classical aeroacoustic theory for free shear flows often relies on quadrupole point-sources to represent the sound sources originating from an unsteady flow field. However, because of almost complete mutual cancellation of the sources [1], such a point-wise analysis of the flow field is usually neither practical for numerical analysis nor does it provide good insight into the noise generation mechanisms induced by large-scale instability waves which are responsible for the dominant downstream noise radiation in subsonic jets. We model such instability waves in coaxial jets using linear stability theory and show that frequency-specific sound radiation patterns can be explained by this simplified approach.

Author(s):

Michael Gloor    
Institute of Fluid Dynamics, ETH Zurich
Switzerland

Dominik Obrist    
Institute of Fluid Dynamics, ETH Zurich
Switzerland

Leonhard Kleiser    
Institute of Fluid Dynamics, ETH Zurich
Switzerland