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Experimental Study of Turbulence and Entrained Air Characteristics in a Plunging Breaking Solitary Wave

State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, Sichuan, P. R. China

E-mail Address: tanglian@scu.edu.cn

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Yun-Ta Wu

Department of Hydraulic and Ocean Engineering, National Cheng Kung University, Tainan 70101, Taiwan

E-mail Address: ytwu@mail.ncku.edu.tw

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Onyx. W. H. Wai

Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

E-mail Address: onyx.wai@polyu.edu.hk

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, and

Pengzhi Lin

State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, Sichuan, P. R. China

E-mail Address: cvelinpz@scu.edu.cn

Corresponding author.

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https://doi.org/10.1142/S2529807020500013Cited by:4 (Source: Crossref)

Abstract

The entrained air and turbulence characteristics under a breaking solitary wave on a 1:20 sloping beach are investigated through laboratory measurement. Free surface elevation is obtained from wave gauge measurements. Wave breaking process is captured in detail by a high-speed camera. The bubble image velocimetry (BIV) is used to measure the velocity and the fiber optic reflectometer (FOR) is used to capture instantaneous void fraction in the aerated region. The mean void fraction and velocities in the aerated region are obtained by ensemble averaging over 22 repetitions. Results show that the maximum mean void fraction is 0.6 in the collapsing cavity region and is 0.35 in the splash up region. The time series of the mean void fraction has good synchronization with the instantaneous images taken by high-speed camera. The maximum horizontal velocity occurs in the splash up region and reaches 1.17C shortly after the plunging jet hits the water surface, with C being the phase speed of the primary wave. The turbulence intensities over the entire aerated region are presented and discussed. The measured data can be used for the calibration and verification of the numerical model for aerated flows simulation under breaking waves in the surf zone.

Keywords:

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