Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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The Flow Field in Steady Breaking Waves
The Flow Field in Steady Breaking Waves
Pages 534-549
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From page 534... ...
mom analysis of several instantaneous flow fields obtained by particle image velocimetry, they were able to verify that the flow in the breaking region was nearly stagnant as was assumed by other investigators. Surface ripples generated by these breaking waves have also been investigated previously.
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From page 535... ...
In the present work, both the surface ripples and flow fields in steady, hydrofoil-produced breaking waves are investigated. The waves are generated by three NACA 0012 hydrofoils with chords (c)
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From page 536... ...
Thus, all measurements were conducted in this region. 2.2 Measurement techniques The measurements reported herein include surface profile histories of the breaking waves, water surface height versus time at a fixed location in the tank as the wave passes by, and velocity field measurements in the breaking region.
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From page 537... ...
1~\ ~ laser light sheet Figure 2: Schematic showing end view of tank with setup for profile measurements.
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From page 538... ...
Between experimental runs, the timing circuit fired the laser system continuously with a 30 Hz repetition rate. During each run, upon the closing of a stationary limit switch actuated by the passing of a spindle attached to the tow cables, the timing box interrupted the laser firing cycle so that the lasers fired a known time later, triggered the camera whose shutter remained open for 1/30 of a second, and started the mirror rotation.
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From page 539... ...
Techniques to deal with this problem are presently under investigation. In the present, preliminary results, bad vectors (a bad vector being defined as a vector exceeding a threshold standard deviation from its nearest neighbors)
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From page 540... ...
The streamwise profiles show an area near the leading edge of the breaking region where the surface fluctuations oscillate upstream and downstream. However, over most of the breaking region it is apparent that the surface height fluctuations propagate downstream and that the wavelength of these fluctuations increases with downstream distance.
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From page 541... ...
0.8 6.7 4.0 0.60 6.91 5.4 3.2 0.59 1.02 7.2 5.0 0.69 3.72 6.8 4.9 0.72 1.10 8.8 6.6 0.75 1.47 7.6 6.0 0.79 1' />o x 105 10.7 5.69 2.12 Table 2: Spectral peaks, dominant disturbance, presented as reciprocal wavenumber (length/cycle) nondimensionalized by the wavelength, frequency, nondimensionalized by the deep water wave frequency, and characteristic velocity.
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From page 542... ...
Each curve is a profile of dimensionless surface height versus dimensionless horizontal distance. The profiles at successive times are displaced vertically upward in the plots for clarity of the presentation.
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From page 543... ...
5 o -5 —10 ... , , ~ ~ -10 0 kx~o 10 20 Figure 6: Wavenumber-frequency spectra from streamwise profile histories for the six Ffoude-scaled conditions.
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From page 544... ...
liar instantaneous flow fields. The reference frame Another interesting parameter describing the chosen is that of the breaking wave crest.
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From page 545... ...
These projections are similar to those shown in Figure 9. Many of the droplets appear to be formed from the jet-like projections 4 Conclusion Surface profile and flow field measurements from a Ffoude-scaled steady breaking wave experiment have been presented.
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From page 546... ...
(c) Figure 8: Particle image velocimetry results, 15-cm foil, d/c = 1.02.
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From page 547... ...
1.00 0.90 0.80 0.70 0.60 lo_ ~ 0.50 _ .
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From page 548... ...
~I- ~ -~-~ @~: `~-~ -- :~:~^ -- a * -- it - -- -`- ~~ ~ -a Figure 10: yes produced by the work boy Britt~ 348
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From page 549... ...
H 1981 An experimental investigation of breaking waves generated by a towed hydrofoil.
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