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Structure of the turbulent flow field under breaking waves in the surf zone

Published online by Cambridge University Press:  26 April 2006

Kazuo Nadaoka ,
Mikio Hino  and
Yoshiji Koyano
Kazuo Nadaoka
Affiliation:
Tokyo Institute of Technology, 2–12–1, O-okayama, Meguro-ku, Tokyo 152, Japan
Mikio Hino
Affiliation:
Tokyo Institute of Technology, 2–12–1, O-okayama, Meguro-ku, Tokyo 152, Japan
Yoshiji Koyano
Affiliation:
Tokyo Institute of Technology, 2–12–1, O-okayama, Meguro-ku, Tokyo 152, Japan
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Abstract

The structure of turbulence and its role in the breaking wave dynamics within the surf zone have been investigated through laboratory experiments using several flow visualization techniques and a fibre-optic LDV system. The results indicate that there exists a characteristic structure of large-scale eddies referred to here as ‘horizontal eddies’ and ‘obliquely descending eddies’, which has a significant role in the generation of Reynolds stress and thus affects the deformation of the mean flow field. The experiments also reveal that these eddies caused by the wave breaking bring a large amount of vorticity (with non-zero average) into otherwise almost irrotational velocity fields, resulting in the generation of vorticity-related mean flow fields as well as turbulence (vorticity-containing velocity fluctuation). This means that the breaking waves in the surf zone can be regarded as pseudowaves which consist of irrotational velocity components as ‘wave motion’ and appreciable amounts of rotational mean velocity components as ‘eddying motion’ (with non-zero mean vorticity) together with turbulence. It is found that the generation of the mean rotational velocity component due to wave breaking causes considerable increase in mass and momentum transport, as compared with ordinary non-breaking waves, and thus a decrease in wave height.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 204 , July 1989 , pp. 359 - 387
Copyright
© 1989 Cambridge University Press

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