Author(s): Kohei Kusaba; Xianting Zhao; Yuji Sugihara; Michio Sanjou; Kazumasa Matsumoto; Shun Kaneko

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Keywords: PIV; Turbulence; Wind-driven water surface; Wind wave; Wind-wave tank

Abstract: Laboratory experiments were carried out to clarify turbulent properties in water under the wind-driven water surface. The wind speed, the water surface displacement, and the wind-driven surface flow velocity were measured in a laboratory wind-wave tank. The friction velocity was estimated according to the logarithmic distribution law for the wind speed. The flow velocities in water in the horizontal and vertical directions were measured by means of particle image velocimetry, i. e., PIV. The vertical distributions of the averaged flow velocities, the turbulent intensities, the turbulent kinetic energy and the Reynolds stress in water were evaluated from the PIV-measured velocities. The distributions of the averaged velocities strongly suggest that the Langmuir circulation appear in the case where the wind speed becomes relatively large. Based on the values of the boundary layer thickness and the turbulent quantities at the water surface extrapolated from the deeper layer values, the distributions of the turbulent quantities were normalized. For the turbulent intensities, the boundary layer thickness normalized with the water depth was found to be varied linearly with the windsea Reynolds number in each region before and after large-scale wave breaking occurs. The turbulent intensities at the water surface nondimensionalized by the friction velocity were also empirically described by using the windsea Reynolds number. The dependences of these dimensionless quantities on the windsea Reynolds number were varied around a critical condition associated with the large-scale wave breaking. This suggests that the wave breaking has an important role in characterizing the wind-driven subsurface turbulence.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1995-cd

Year: 2025