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Research Papers: Fluid-Structure Interaction

Experimental Investigation of the Acoustic Power Around Two Tandem Cylinders

[+] Author and Article Information
S. L. Finnegan1

Department of Mechanical and Manufacturing Engineering, Trinity College Dublin, Dublin 2, Irelandfinnegsl@tcd.ie

C. Meskell

Department of Mechanical and Manufacturing Engineering, Trinity College Dublin, Dublin 2, Ireland

S. Ziada

Department of Mechanical Engineering, McMaster University, Hamilton, ON, Canada

1

Corresponding author.

J. Pressure Vessel Technol 132(4), 041306 (Jul 23, 2010) (12 pages) doi:10.1115/1.4001701 History: Received October 28, 2009; Revised April 29, 2010; Published July 23, 2010; Online July 23, 2010

Aeroacoustic resonance of bluff bodies exposed to cross flow can be problematic for many different engineering applications and knowledge of the location and interaction of acoustic sources is not well understood. Thus, an empirical investigation of the acoustically coupled flow around two tandem cylinders under two different resonant conditions is presented. It is assumed that the resonant acoustic field could be decoupled from the hydrodynamic flow field, resolved separately, and then recoupled to predict the flow/sound interaction mechanisms using Howe's theory of aerodynamic sound. Particle image velocimetry was employed to resolve the phase-averaged flow field characteristics around the cylinders at various phases in an acoustic wave cycle. It was found that the vortex shedding patterns of the two resonant conditions exhibit substantial differences. For the first condition, which occurred at low flow velocities where the natural vortex shedding frequency was below the acoustic resonance frequency, fully developed vortices formed in both the gap region between the cylinders and in the wake. These vortices were found to be in phase with each other. For the second resonant condition, which occurred at higher flow velocities where the natural vortex shedding frequency was above the acoustic resonant frequency, fully developed vortices only formed in the wake and shedding from the two cylinders were not in phase. These differences in the flow field resulted in substantial variation in the flow-acoustic interaction mechanisms between the two resonant conditions. Corresponding patterns of the net acoustic energy suggest that acoustic resonance at the lower flow velocity is due to a combination of shear layer instability in the gap and vortex shedding in the wake, while acoustic resonance at the higher flow velocity is driven by the vortex shedding in the wake of the two cylinders.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Conceptual approach used to predict the aeroacoustic sources

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Figure 2

Schematic of the experimental test section

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Figure 4

Schematic of the PIV setup showing the orientation and the angle of incidence between the laser and the test section

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Figure 5

Normalized pressure contours of the first transverse acoustic mode

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Figure 6

Contours of the acoustic particle velocity normalized by the mainstream velocity, Ua/V∞, at precoincidence resonance: ϕ=180 deg and V∞=25 m/s

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Figure 7

Phase averaged hydrodynamic flow characteristics at precoincidence resonance, fa/fv=1.2, Re=22,308. (Left) Velocity contours and streamlines. (Right) Vorticity contours.

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Figure 13

Contours of the net acoustic energy for coincidence resonance, fa/fv=0.8

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Figure 14

Comparison of the net energy transfer per spanwise location for the two acoustic resonance regimes: (∗) precoincidence (fa/fv=1.2); (—) coincidence resonance (fa/fv=0.8)

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Figure 15

Contours of the net acoustic energy for precoincidence resonance, fa/fv=1.2 including both the cylinder gap region and the far wake

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Figure 16

The net energy transfer per spanwise location for a secondary test to include both the cylinder gap region and the far wake for precoincidence resonance, fa/fv=1.2

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Figure 17

Decay of the acoustic particle velocity away from the cylinders in the normalized x-direction along the centerline of the test section for precoincidence resonance, fa/fv=1.2, ϕ=180 deg, V∞=25 m/s

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Figure 3

Aeroacoustic characteristics measured by microphone M1: (○) 142 dB; (*) no applied sound.

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Figure 8

Phase averaged hydrodynamic flow characteristics at coincidence resonance, fa/fv=0.8, Re=33,462. (Left) Velocity contours and streamlines. (Right) Vorticity contours.

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Figure 9

Histogram of the PIV particle displacements in the u velocity component direction for precoincidence resonance, ϕ=90 deg. ζ=0.0085. Histogram bin-width=0.05 pixel.

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Figure 10

Time-resolved acoustic power. (Left) Precoincidence resonance, fa/fv=1.2. (Right) Coincidence resonance, fa/fv=0.8.

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Figure 11

A schematic explanation for the positive acoustic power located in the wake region near x/D=−2 during precoincidence resonance based on the integrand of Eq. 1: (a) ϕ=45 deg and (b) ϕ=225 deg

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Figure 12

Contours of the net acoustic energy for precoincidence resonance, fa/fv=1.2

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