Sound Radiated by Large-Scale Wave-Packets in Subsonic and Supersonic Jets

A wave-packet Ansatz is used to model jet noise generation by large-scale turbulence. In this approach, an equivalent source is deflned based on the two-point space-time correlation of pressure on a conical surface surrounding the jet plume. The surface is su‐ciently near the jet to be dominated by pressure signatures of large-scale turbulence, yet su‐ciently far that linear behavior can be assumed in extending the near-fleld pressure to the acoustic fleld. In the present study, a rotating near-fleld microphone array is used to measure multipoint pressure statistics on the conical surface in order to identify model parameters, and a Green’s function based method is used to project the near-fleld pressure to the acoustic fleld. It is shown that the near-fleld pressure signatures are well-represented by a Gaussian wave-packet model for both subsonic and supersonic jets. The acoustic fleld re-constructed from the near-fleld data is shown to compare very well with far-fleld measurements. Results suggest that the source of low-frequency aft-angle sound in subsonic jets is dynamically similar to that in supersonic jets.