Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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Hydrofoil Near-Wake Structure and Dynamics at High Reynolds Number
Hydrofoil Near-Wake Structure and Dynamics at High Reynolds Number
Pages 177-191
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From page 177... ...
Presented here are observations of the hydrofoil's unsteady near-wake and the unsteady surface pressures on the trailing edge for both a baseline and a modified trailing edge configuration. The results include PIV-acquired vector fields, surface dynamic pressure spectra, and LDV-acquired velocity spectra from the separating boundary layer and near wake.
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From page 178... ...
Aspects of boundary layer growth, separation, and shear layer development are potentially Redependent. Thus, significant changes in Reynolds number may lead to significant changes in the near wake shedding.
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From page 179... ...
In addition, a separate investigating team measured the streamwise velocity statistics of the suction side boundary layer at x/C = 0.43 using a miniaturized 1-component LDV probe housed within the hydrofoil body (Fourguette, et al., 2001~. The external 2-component LDV system uses Dantec FO probes with 111-mm beam spacing and 1600-mm (in air)
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From page 180... ...
Presented here are results for test speeds from 0.5 to 18.3 m/s, 0° angle of attack, un-tripped boundary layers, and both the baseline and modified trailing edge geometries. In order to depict the dependence of the vortex shedding on trailing edge geometry and Rec.
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From page 181... ...
the measured normalized boundary layer momentum thickness, 8/C vs. flow speed, Uref, for the modified trailing edge geometry.
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From page 182... ...
Average contours and vector profiles of normalized streamwise velocity, u—/Uref, for the modified trailing edge at Uref = l.Sm/s . (320 averages)
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From page 183... ...
This condition and geometry was the strongest shedding condition tested as determined by surface pressure spectra, and was of equivalent strength to 1.0 m/s modified trailing edge condition as determined by velocity spectra. By comparison the vertical structures are largely absent for the baseline trailing edge in Fig 7.
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From page 184... ...
Normalized power spectrum of vertical velocity component, 0) v, at varying flow speed, Uref, for modified trailing edge.
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From page 185... ...
, indicating no shedding detectable above the turbulence of the separated shear layers. Further discussion of the baseline trailing edge pressure spectra at speeds 3.0 m/s and above, including comparison with historical data, is provided in (Bourgoyne, et.
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From page 186... ...
Comparison of normalized mean streamwise velocity profiles, ~/Uref, for the baseline and modified trailing edges at x/C=1.002 and Uref = l Sm/s RESULTS- DEPENDENCE OF SHEDDING ON REYNOLDS NUMBER In addition to showing dependence of vortex shedding on trailing edge geometry, Figs. 10 and 12 demonstrate a clear dependence in the velocity and pressure spectra on flow speed.
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From page 187... ...
Comparison of normalized mean streamwise velocity profiles, U/Uref ~ for varying flow speed, Uref ~ at x/C=1.002 on the modified trailing edge .
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From page 188... ...
The influence of the location of transition on the shedding strength raises practical questions concerning tripping practices in model testing and the appropriate application of those results to the full scale. ACKNOWLEDGEMENTS The authors of this paper wish to the acknowledge the contributions of Shiyao Bian and Kent Pruss of the University of Michigan; William Blake, Ken Edens, Bob Etter, Ted Farabee, Jon Gershfeld, Joe Gorski, Tom Mathews, David Schwartzenberg, Jim Valentine, Phil Yarnall, Joel Park, and the LCC technical staff from the Naval Surface Warfare Center - Carderock Division; and Ki-han Kim, Pat Purtell and Candace Wark from the Office of Naval Research In addition, the authors wish to thank the Office of Naval Research for supporting this research effort under contract nos.
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From page 189... ...
The BSA Flow software allows for three user inputs for the power spectra: spectral samples, maximum frequency, and filter settings. The spectral-samples input determines the number of discrete frequencies at which the power spectral density is estimated.
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From page 190... ...
Comparison of normalized power spectra ~ of surface pressure, 1) p, and normalized power spectra of foil acceleration, ~ a ~ for the pressure side sensor H- 1 at x/C=0.99 and nearby accelerometer A2, at flow speed Uref = 18.3 m/s on the modified trailing edge.
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From page 191... ...
Comparison of normalized power spectra ~ of surface pressure, ~ p, and normalized power spectra of foil acceleration, ~ a ~ for the pressure side sensor H-1 at x/C=O.99 and nearby accelerometer A2, at flow speed Uref = 1.5 m/s on the modified trailing edge. At this flow speed fs = 11 Hz.
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