Measurements of Air Entrainment by Bow Waves

[+] Author and Article Information
T. A. Waniewski

Naval Hydrodynamics Division, Science Applications International Corporation, 10260 Campus Point Dr., M/S C4, San Diego, CA 92121

C. E. Brennen, F. Raichlen

Division of Engineering and Applied Science, California Institute of Technology, Mail Code 104-44 Pasadena, CA 91125

J. Fluids Eng 123(1), 57-63 (Oct 17, 2000) (7 pages) doi:10.1115/1.1340622 History: Received June 04, 1999; Revised October 17, 2000
Copyright © 2001 by ASME
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Cross sectional view of the IVFM probe (not to scale).
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Frames from high speed video of the single bubble tests showing the IVFM probe tip above the tube which released the bubbles. The time is noted beneath each frame.
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Typical IVFM signal from the single bubble tests; the frames from the corresponding high speed video are shown in Fig. 2.
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Typical IVFM signal from the calibration experiments. A voltage of −1.2 V occurs when no air bubbles are touching the probe tip, and each large negative pulse corresponds to an air bubble encounter.
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Calibration data for the IVFM from the bubbly column facility. The different groups of points were produced by processing the same data set using different thresholds; (○) for threshold=−0.50 V, (+) for threshold=−0.75 V, and ( * ) for threshold=−1.00 V. A linear curve fit for the data corresponding to threshold=−0.75 V also is shown.
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Photograph of bubble clouds passing by the IVFM probe, the tip of which is visible in the center. The flow is from right to left with θ=25°,ϕ=0°,U=2.47 m/s,d=7.39 cm, and F=2.90.
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Schematic diagram of the planform of the flow with a typical IVFM traverse (⋯) indicated.
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A typical signal from the IVFM located several centimeters beneath the bow wave plunging jet: θ=26°,U=2.39 m/s,d=6.47 cm,F=3.00, and α=6.5 percent.
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Local, averaged void fractions beneath the bow wave plunging jet for a traverse at x=91.2, and for θ=26°,ϕ=0°,U=2.48 m/s,d=7.89 cm, and F=2.82. The IVFM measurement locations are marked (•) and labeled with the void fraction (percent). Nine equally spaced contour levels (Δα=1 percent) also are shown.
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Local, averaged void fractions for six different traverses: (a), (c), and (e) for the flow conditions specified in Fig. 9 and (b), (d), and (f ) for θ=26°,ϕ=0°,U=2.39 m/s,d=6.47 cm, and F=3.00. Ten equally spaced contour levels (Δα=1 percent) are shown.
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Total volume of air entrained per unit streamwise distance as a function of distance from the origin of the impact line, x*; (•) for the traverses of Fig. 10(a), (c), and (e) and (▴) for those of Fig. 10(b), (d), and (f ). A quadratic curve fit (- -) also is shown.
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Bubble chord histograms from bubble clouds observed at x=75.9 cm for different elevations. Upper: y=66.6 cm. Middle: y=63.5 cm. Lower: y=60.5.
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Detail of signal processing technique. Upper: raw IVFM signal. Lower: cloud detection algorithm output, frequency of individual bubble impacts, from the IVFM signal.
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Schematic diagram of the proposed air entrainment mechanism. A time series of plunging jets and bubble clouds is depicted; (⋯) for t=0, (- -) for t=Δt, and (—) for t=2Δt.




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