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Article Dans Une Revue Journal of Fluid Mechanics Année : 2012

Educing the source mechanism associated with downstream radiation in subsonic jets

Résumé

This work belongs to the ongoing debate surrounding the mechanism responsible for low-angle sound emission from subsonic jets. The flow, simulated by large eddy simulation (Bogey & Bailly, Comput. Fluids, vol. 35 (10), 2006a, pp. 1344-1358), is a Mach 0.9 jet with Reynolds number, based on the exit diameter, of $4\ensuremath{\times} 1{0}^{5} $. A methodology is implemented to educe, explore and model the flow motions associated with low-angle sound radiation. The eduction procedure, which is based on frequency-wavenumber filtering of the sound field and subsequent conditional analysis of the turbulent jet, provides access to space- and time-dependent (hydrodynamic) pressure and velocity fields. Analysis of these shows the low-angle sound emission to be underpinned by dynamics comprising space and time modulation of axially coherent wavepackets: temporally localized energization of wavepackets is observed to be correlated with the generation of high-amplitude acoustic bursts. Quantitative validation is provided by means of a simplified line-source Ansatz (Cavalieri et al. J. Sound Vib., vol. 330, 2011b, pp. 4474-4492). The dynamic nature of the educed field is then assessed using linear stability theory (LST). The educed pressure and velocity fields are found to compare well with LST: the radial structures of these match the corresponding LST eigenfunctions; the axial evolutions of their fluctuation energy are consistent with the LST amplification rates; and the relative amplitudes of the pressure and velocity fluctuations, which are educed independently of one another, are consistent with LST.

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Dates et versions

hal-00759011 , version 1 (29-11-2012)

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Franck Kerherve, P. Jordan, A.V.G. Cavalieri, Joël Delville, Christophe Bogey, et al.. Educing the source mechanism associated with downstream radiation in subsonic jets. Journal of Fluid Mechanics, 2012, 710, pp.606-640. ⟨10.1017/jfm.2012.378⟩. ⟨hal-00759011⟩
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