This paper is focused on the investigation of the effect of coherence decay on the acoustic field generated by a wavepacket source. Coherence decay, which is the statistical signature of jitter in the time domain, has been identified by several studies as a key parameter for the acoustic efficiency of jet-noise sources.1-3'27 Here we study its effect using the model source proposed by Cavalieri and Agarwal1 which is based on two-point statistics. This source comprises a linear wavepacket with modulated growth and coherence. The wavepacket parameters necessary to estimate the sound pressure levels radiated by the source were educed from a dual-plane-time-resolved PIV experiment. The jet Mach number was Ma = 0.4. The sound pressure levels computed were compared with the acoustic m = 0 mode obtained experimentally and the results show that when coherence decay is correctly accounted, the sound-pressure levels generated are in reasonable agreement with experimentally measured values, especially for low Strouhal numbers. A Proper Orthogonal Decomposition of the model source was also performed motivated by the relationship between POD modes and turbulent forcing and coherence decay established by other studies.~(29'35'36) It is shown that only a few POD modes are necessary to recover acoustically important wavepacket traits.
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