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Coherent Structures beneath Wind-Generated Deepwater Waves  

Oh, Sang-Ho (Coastal Engineering Research Department, Korea Ocean Research and Development Institute)
Suh, Kyung-Duck (Department of Civil, Urban and Geosystem Engineering & Engineering Research Institute, Seoul National University)
Mizutani, Natsuki (Department of Civil Engineering, Osaka Sangyo University)
Publication Information
Journal of Korean Society of Coastal and Ocean Engineers / v.19, no.1, 2007 , pp. 16-28 More about this Journal
Abstract
The results of experimental investigation of coherent structures beneath wind-generated waves in deep water are presented. Vorticity fields of deepwater wind waves were visualized by analyzing the velocity fields obtained by PIV measurements under different wind and fetch conditions. In addition, spatio-temporal evolution of the coherent structures and subsequent changes in vertical profiles of the instantaneous vorticity were qualitatively examined. It was found that a coherent structure is formed right underneath the wave crest and traveled in phase with the surface wave. The direction of rotation of the coherent structure was contrary to the wave orbital motion when wind speed is less than 10 m/s, while was same as the wave orbital motion when wind speed is approximately 13 m/s and wave breaking occurs at the wave crest. In the near-surface region, complex vortex-vortex interactions were observed according to the traveling of the coherent structure. In contrast, coherent structures far below the water surface changed little due to weak influence of orbital motion by the surface waves.
Keywords
vorticity; coherent structures; particle image velocimetry; wind waves; turbulent flows;
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