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TECHNICAL PAPERS

Surfactant Effects on the Free Surface Thermal Structure and Subsurface Flow in a Wind-Wave Tunnel

[+] Author and Article Information
Supathorn Phongikaroon1

Coastal and Ocean Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375supathorn.phongikaroon@inl.gov

K. Peter Judd2

Coastal and Ocean Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375

1

Present address: Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83403.

2

Present address: Mechanical Engineering, Clemson University, Clemson, SC 29634.

J. Fluids Eng 128(5), 913-920 (Feb 02, 2006) (8 pages) doi:10.1115/1.2234781 History: Received July 15, 2004; Revised February 02, 2006

In this study, the dynamic effects of surfactant (oleyl alcohol) on the surface temperature and the near surface velocity field of a wind driven free surface are investigated. Different surfactant concentrations and wind speeds were examined to elucidate the flow physics. The water surface was imaged with an infrared (IR) detector and the subsurface flow was interrogated utilizing digital particle image velocimetry (DPIV). The IR imagery reveals the presence of a Reynolds ridge that demarcates the boundary between clean (hot) fluid and contaminated (cold) fluid. The clean region was found to be composed of laminae structures known as fishscales. A “wake region” which is an intermediate temperature region resulting from mixing of the near surface fluid layers develops behind the ridge. Experimental results from infrared imagery indicate that the fishscales in the clean region become elongated and narrowed as the wind speed increases. In addition, the results reveal that higher wind speed is required to form a Reynolds ridge in the presence of higher surfactant concentration. The plots of the surface temperature probability density functions reveal that these thermal structures undergo the same evaporative process while the increase in wind speed enhances this process. DPIV results reveal that the growth of a subsurface boundary layer for the contaminated case is more pronounced than that for the clean case.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 4

IR images of the contaminated free surface at a wind speed of (a) 4.4, (b) 5.5, and (c)6.7m∕s; (d) plots of the temperature pdfs; (e) extracted temperature profiles taken through the center of the IR image (vertical line section)

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Figure 6

Streamwise velocity profiles at various downstream distances for the contaminated case. Dashed lines show both the common region and the location of the Reynolds ridge (occurs at about 144mm downstream of the leading edge of the channel).

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Figure 1

The wind-wave tunnel facility, the tunnel dimensions are L=35cm, W=10.4cm, and H=8.9cm: (a) IR camera setup; and (b) DPIV camera and beam orientation

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Figure 2

IR images of the free surface flow at a wind speed of (a) 5.1, (b) 6.7, and (c)8.1m∕s. The image is 10.4cm×12.8cm.

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Figure 3

Plots of (a) temperature pdf and (b) normalized temperature pdf for the extracted IR image at different wind speeds

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Figure 7

Surface velocity vector maps superimposed on IR images for: (a) clean surface at a wind speed of 5.1m∕s, and (b) contaminated case at a wind speed of 6.7m∕s

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Figure 5

Velocity vector plot for the clean case at the wind speed of 5.1m∕s with a corresponding IR image. Dashed lines show the common region of the IR image and the DPIV velocity field.

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