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Influence of nozzle-exit boundary-layer conditions on the flow and acoustic fields of initially laminar jets

Published online by Cambridge University Press:  04 November 2010

C. BOGEY  and
C. BAILLY
C. BOGEY*
Affiliation:
Laboratoire de Mécanique des Fluides et d'Acoustique, UMR CNRS 5509, Ecole Centrale de Lyon, 69134 Ecully CEDEX, France
C. BAILLY
Affiliation:
Laboratoire de Mécanique des Fluides et d'Acoustique, UMR CNRS 5509, Ecole Centrale de Lyon, 69134 Ecully CEDEX, France Institut Universitaire de France, 103 Boulevard Saint-Michel, 75005 Paris, France
*
†Email address for correspondence: christophe.bogey@ec-lyon.fr
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Abstract

Round jets originating from a pipe nozzle are computed by large-eddy simulations (LES) to investigate the effects of the nozzle-exit conditions on the flow and sound fields of initially laminar jets. The jets are at Mach number 0.9 and Reynolds number 105, and exhibit exit boundary layers characterized by Blasius velocity profiles, maximum root-mean-square (r.m.s.) axial velocity fluctuations between 0.2 and 1.9% of the jet velocity, and momentum thicknesses varying from 0.003 to 0.023 times the jet radius. The far-field noise is determined from the LES data on a cylindrical surface by solving the acoustic equations. Jets with a thinner boundary layer develop earlier but at a slower rate, yielding longer potential cores and lower centreline turbulent intensities. Adding random pressure disturbances of low magnitude in the nozzle also increases the potential core length and reduces peak r.m.s. radial velocity fluctuations in the shear layer. In all the jets, the shear-layer transition is dominated by vortex rolling-ups and pairings, which generate strong additional acoustic components, but also amplify the downstream-dominant low-frequency noise component when the exit boundary layer is thick. The introduction of inlet noise however results in weaker pairings, thus spectacularly reducing their contributions to the sound field. This high sensitivity to the initial conditions is in good agreement with experimental observations.

JFM classification

Acoustics: Jet noise Turbulent Flows: Shear layer turbulence Turbulent Flows: Turbulence simulation
Type
Papers
Information
Journal of Fluid Mechanics , Volume 663 , 25 November 2010 , pp. 507 - 538
Copyright
Copyright © Cambridge University Press 2010

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References

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Supplementary material: File

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File 2.6 MB

Bogey and Bailly supplementary movie

Movie 1. Snapshots in the (z,r) plane of vorticity norm obtained for the jets without inlet noise and with initial boundary layer thickness of δ=0.2r0 (JetD02), δ=0.1r0 (JetD01), δ=0.05r0 (JetD005), and δ=0.025r0 (JetD0025). The color scale ranges from 0 to the level of 6.5uj/r0 (uj and r0: jet velocity and radius). Jets with thinner boundary layer develop erlier but at a slower rate, leading to longer potential cores.

Download Bogey and Bailly supplementary movie(Video)
Video 3.8 MB

Bogey and Bailly supplementary movie

Movie 1. Snapshots in the (z,r) plane of vorticity norm obtained for the jets without inlet noise and with initial boundary layer thickness of δ=0.2r0 (JetD02), δ=0.1r0 (JetD01), δ=0.05r0 (JetD005), and δ=0.025r0 (JetD0025). The color scale ranges from 0 to the level of 6.5uj/r0 (uj and r0: jet velocity and radius). Jets with thinner boundary layer develop erlier but at a slower rate, leading to longer potential cores.

Download Bogey and Bailly supplementary movie(Video)
Video 11 MB

Bogey and Bailly supplementary movie

Movie 2. Snapshots in the (z,r) plane of vorticity norm obtained downstream of the pipe lip for the jets without inlet noise and with initial boundary layer thickness of δ=0.2r0 (JetD02), δ=0.1r0 (JetD01), δ=0.05r0 (JetD005), and δ=0.025r0 (JetD0025). The color scale ranges from 0 to the level of 10uj/r0 for JetD02, but to 20uj/r0 for the other jets (uj and r0: jet velocity and radius). In all jets, the shear-layer transition is dominated by processes of vortex rolling-up and paring.

Download Bogey and Bailly supplementary movie(Video)
Video 4 MB

Bogey and Bailly supplementary movie

Movie 3. Snapshots in the (z,r) plane of vorticity norm obtained downstream of the pipe lip for the jets with initial boundary layer of δ=0.05r0, without inlet noise (JetD005) and with random pressure disturbances in the pipe of maximum amplitude 250 Pa (JetD005p250) and 2000 Pa (JetD005p2000). The color scale ranges from 0 to the level of 20uj/r0 (uj and r0: jet velocity and radius). The introduction of inlet noise results in weaker vortex rolling-ups and pairings.

Download Bogey and Bailly supplementary movie(Video)
Video 2.1 MB

Bogey and Bailly supplementary movie

Movie 3. Snapshots in the (z,r) plane of vorticity norm obtained downstream of the pipe lip for the jets with initial boundary layer of δ=0.05r0, without inlet noise (JetD005) and with random pressure disturbances in the pipe of maximum amplitude 250 Pa (JetD005p250) and 2000 Pa (JetD005p2000). The color scale ranges from 0 to the level of 20uj/r0 (uj and r0: jet velocity and radius). The introduction of inlet noise results in weaker vortex rolling-ups and pairings.

Download Bogey and Bailly supplementary movie(Video)
Video 3.7 MB

Bogey and Bailly supplementary movie

Movie 4. Snapshots in the (z,r) plane of vorticity norm and fluctuating pressure obtained directly from Large-Eddy Simulation, for the jets without inlet noise and with initial boundary layer thickness of δ=0.2r0 (JetD02), δ=0.1r0 (JetD01), δ=0.05r0 (JetD005), and δ=0.025r0 (JetD0025). The color scales range for levels from 0 to 5uj/r0 for vorticity, and from -200 to 200 Pa for pressure (uj and r0: jet velocity and radius). Strong acoustic waves are generated by the turbulent transition of the shear layers. Their frequencies and magnitudes decrease with thinner inlet boundary layer.

Download Bogey and Bailly supplementary movie(Video)
Video 10 MB

Bogey and Bailly supplementary movie

Movie 4. Snapshots in the (z,r) plane of vorticity norm and fluctuating pressure obtained directly from Large-Eddy Simulation, for the jets without inlet noise and with initial boundary layer thickness of δ=0.2r0 (JetD02), δ=0.1r0 (JetD01), δ=0.05r0 (JetD005), and δ=0.025r0 (JetD0025). The color scales range for levels from 0 to 5uj/r0 for vorticity, and from -200 to 200 Pa for pressure (uj and r0: jet velocity and radius). Strong acoustic waves are generated by the turbulent transition of the shear layers. Their frequencies and magnitudes decrease with thinner inlet boundary layer.

Download Bogey and Bailly supplementary movie(Video)
Video 32.4 MB

Bogey and Bailly supplementary movie

Movie 5. Snapshots in the (z,r) plane of vorticity norm and fluctuating pressure obtained directly from Large-Eddy Simulation, for the jets with initial boundary layer of δ=0.05r0, without inlet noise (JetD005) and with random pressure disturbances in the pipe of maximum amplitude 250 Pa (JetD005p250) and 2000 Pa (JetD005p2000). The color scales range for levels from 0 to 5uj/r0 for vorticity, and from -150 to 150 Pa for pressure (uj and r0: jet velocity and radius). The introduction of inlet noise reduces vortex pairing noise.

Download Bogey and Bailly supplementary movie(Video)
Video 5.4 MB

Bogey and Bailly supplementary movie

Movie 5. Snapshots in the (z,r) plane of vorticity norm and fluctuating pressure obtained directly from Large-Eddy Simulation, for the jets with initial boundary layer of δ=0.05r0, without inlet noise (JetD005) and with random pressure disturbances in the pipe of maximum amplitude 250 Pa (JetD005p250) and 2000 Pa (JetD005p2000). The color scales range for levels from 0 to 5uj/r0 for vorticity, and from -150 to 150 Pa for pressure (uj and r0: jet velocity and radius). The introduction of inlet noise reduces vortex pairing noise.

Download Bogey and Bailly supplementary movie(Video)
Video 18.2 MB