Two-point wavepacket modelling of jet noise

Resumo

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.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 effciency 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.