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Wavepackets in the velocity field of turbulent jets

Cavalieri, André V. G. and Rodríguez, Daniel and Jordan, Peter and Colonius, Tim and Gervais, Yves (2013) Wavepackets in the velocity field of turbulent jets. Journal of Fluid Mechanics, 730 . pp. 559-592. ISSN 0022-1120.

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We study the velocity fields of unforced, high Reynolds number, subsonic jets, issuing from round nozzles with turbulent boundary layers. The objective of the study is to educe wavepackets in such flows and to explore their relationship with the radiated sound. The velocity field is measured using a hot-wire anemometer and a stereoscopic, time-resolved PIV system. The field can be decomposed into frequency and azimuthal Fourier modes. The low-angle sound radiation is measured synchronously with a microphone ring array. Consistent with previous observations, the azimuthal wavenumber spectra of the velocity and acoustic pressure fields are distinct. The velocity spectrum of the initial mixing layer exhibits a peak at azimuthal wavenumbers ranging from 4 to 11, and the peak is found to scale with the local momentum thickness of the mixing layer. The acoustic pressure field is, on the other hand, predominantly axisymmetric, suggesting an increased relative acoustic efficiency of the axisymmetric mode of the velocity field, a characteristic that can be shown theoretically to be caused by the radial compactness of the sound source. This is confirmed by significant correlations, as high as 10 %, between the axisymmetric modes of the velocity and acoustic pressure fields, these values being significantly higher than those reported for two-point flow–acoustic correlations in subsonic jets. The axisymmetric and first helical modes of the velocity field are then compared with solutions of linear parabolized stability equations (PSE) to ascertain if these modes correspond to linear wavepackets. For all but the lowest frequencies close agreement is obtained for the spatial amplification, up to the end of the potential core. The radial shapes of the linear PSE solutions also agree with the experimental results over the same region. The results suggests that, despite the broadband character of the turbulence, the evolution of Strouhal numbers 0.3 ≤ St ≤ 0.9 and azimuthal modes 0 and 1 can be modelled as linear wavepackets, and these are associated with the sound radiated to low polar angles.

Item Type:Article
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URLURL TypeDescription DOIArticle ItemConference Paper
Cavalieri, André V. G.0000-0003-4283-0232
Jordan, Peter0000-0001-8576-5587
Colonius, Tim0000-0003-0326-3909
Additional Information:© 2013 Cambridge University Press. Received 30 November 2012; revised 10 May 2013; accepted 1 July 2013; first published online 2 August 2013. We thank C. Fourment-Cazenave, P. Braud and Dr J. Delville for their work during the experiments. We also thank Drs K. Gudmundsson, A. Samanta and A. Sinha for their contributions on the development of the PSE code. This work was supported by CNPq, National Council of Scientific and Technological Development, Brazil, and through the EU–Russian programme ORINOCO (FP7-AAT-2010-RTD-Russia; project number 266103). D.R. acknowledges funding by the EU Marie Curie COFUND programme. T.C. acknowledges support from the US Navy Naval Air Systems Command (NAVAIR) with Dr J. Spyropoulos as technical monitor.
Funding AgencyGrant Number
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNSPECIFIED
European Research Council (ERC)266103
Marie Curie FellowshipUNSPECIFIED
US Navy Naval Air Systems Command (NAVAIR)UNSPECIFIED
Subject Keywords:absolute/convective instability, hydrodynamic noise, jet noise
Record Number:CaltechAUTHORS:20131010-095128306
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Official Citation:André V. G. Cavalieri, Daniel Rodríguez, Peter Jordan, Tim Colonius and Yves Gervais (2013). Wavepackets in the velocity field of turbulent jets. Journal of Fluid Mechanics, 730, pp 559-592 doi:10.1017/jfm.2013.346
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41862
Deposited By: Tony Diaz
Deposited On:10 Oct 2013 18:24
Last Modified:09 Mar 2020 13:18

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