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Research Papers: Techniques and Procedures

# Hydrodynamics and Sound Generation of Low Speed Planar Jet

[+] Author and Article Information
Victoria Suponitsky

Department of Engineering,  Queen Mary, University of London, London, E1 4NS, UKv.suponitsky@qmul.ac.uk

Department of Engineering,  Queen Mary, University of London, London, E1 4NS, UKe.avital@qmul.ac.uk

Mike Gaster

Department of Engineering,  Queen Mary, University of London, London, E1 4NS, UKm.gaster@qmul.ac.uk

J. Fluids Eng 130(3), 031401 (Mar 03, 2008) (8 pages) doi:10.1115/1.2844581 History: Received March 16, 2007; Revised October 03, 2007; Published March 03, 2008

## Abstract

Hydrodynamics and sound radiation of a low speed planar jet with $Re=3000$ have been studied by large eddy simulation combined with Lighthill’s acoustic analogy. Jets evolving from both well-developed (parabolic) and undeveloped (top-hat) mean velocity profiles have been simulated. The results showed the following: (i) initial domination of a symmetrical mode for jets evolving from top-hat profiles and prevailing of an antisymmetrical mode resulting in a sinuous distortion of the potential core for jets evolving from parabolic profiles, and (ii) shape of a mean velocity profile has some effect on mean flow characteristics; however, the major differences were observed in the development of the fluctuations. Velocity fluctuations were significantly higher for jets evolving from a parabolic profile in the region beyond the end of the potential core before the flow reached a self-preserving state. To calculate the basic sound radiation, the sources in Lighthill’s equation were treated either as compact in all directions or as noncompact in the spanwise direction. The spanwise length of the computational domain was found to have a little effect on the results obtained with compact in all directions solution provided that spanwise length exceeds the correlation length. Results showed that the majority of sound was generated by the region beyond the end of the potential core.

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## Figures

Figure 1

Instantaneous flow field shown by the contours of the passive scalar at the midplane of the computational domain

Figure 2

Jet mean flow characteristics: (a) centerline mean velocity decay; (b) downstream growth of the jet’s half-width

Figure 3

Normalized mean velocity profiles for a parabolic (hollow symbols) and top-hat (full symbols) inflow profiles. (a) u velocity; (b) v velocity. Experimental data obtained by Bradbury (8) are shown by the thick solid lines.

Figure 4

rms values of velocity fluctuations at the jet centerline (black lines) and along the nozzle lip line y=±h∕2 (gray lines). (a) streamwise velocity fluctuations; (b) transverse velocity fluctuations.

Figure 5

Normalized profiles of rms values of velocity fluctuations for a parabolic (hollow symbols) and top-hat (full symbols) inflow profiles. (a) u-velocity fluctuations; (b) v-velocity fluctuations. Experimental data by Bradbury (8) are shown by the thick solid lines.

Figure 6

Spanwise correlation coefficient calculated from u fluctuations at the jet centerline for the parabolic inflow profile

Figure 7

Time-correlation function (a) and coherence spectra (b) calculated from the v-velocity fluctuations for the points on the opposite sides of the jet (y∕b≈1) in the case of a parabolic inflow profile

Figure 8

Acoustic power spectral density obtained in the case of a parabolic inflow profile (compact solution)

Figure 9

Intensity spectra obtained for ϕ=90deg (compact solution)

Figure 10

Direcivities of OASPL’s for the case of the parabolic inflow profile (compact solution)

Figure 11

Spanwise averaged contours of rms values of Qxx quadrupole obtained from the compact source solution for a parabolic inflow profile

Figure 12

Spectra of Qxx (a) and Qzz (b) quadrupoles for the noncompact in the spanwise direction solution at several wave numbers kz(Lz∕h=8)

Figure 13

Acoustic power P (Eq. 6) obtained from the noncompact in the spanwise direction solution. Results are shown for M=0.35.

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