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Title: Spilling breakers and surfactants - 2008 DFD

Description: This video shows how surfactants affect short-wavelength spilling breaking water waves. The waves are generated by a programmable wave maker in a wave tank that is 12.8 m long and 1.2 m wide with a water depth of 0.91 m. Fluorescent dye is mixed with the water at a low concentration and the waves are illuminated with a laser light sheet that is attached to an instrument carriage that moves along the tank with the crest of the breaker. The movies shown here were taken with a high-speed digital camera that is attached to the carriage [the framing rate is 300 pictures per second (pps) and the movie is shown at 10 pps]. In clean water, as the waves approach breaking, the crest forms a rounded bulge on its upstream (left) face and capillary waves form upstream of the leading edge (toe) of the bulge. Under low surfactant concentrations, due to the viscoelastic properties of the surface film, the crest bulge becomes flattened and the capillary waves are diminished. When the surfactant concentration is increased further, beyond the critical micelle concentration, the viscoelastic effects of the surfactant become negligible, and a small plunging jet forms at the wave crest. In this case, the wave behaves as though it were in a pure liquid, but with a lower surface tension than water. At this high surfactant concentration, decreasing the wavelength of the breaking wave causes the crest to take on its shape in clean water, i.e., with a rounded bulge and capillary waves upstream of the toe. The size of these features scales with the surface tension.

Credits: Xinan Liu, James D. Diorio, and James H. Duncan University of Maryland

References:

Web Page: http://pof.aip.org/pof/gallery/2008-Duncan.jsp#video

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