Laboratory Observation of Turbulence and Wave Shear Stresses Under Large Scale Breaking Waves Over a Mild Slope

Wen Yang Hsu, Zhi Cheng Huang, Byoungjoon Na, Kuang An Chang, Wei Liang Chuang, Ray Yeng Yang

研究成果: Article同行評審

摘要

Laboratory measurements of turbulent flow and shear stresses in a surf zone under monochromatic breaking waves in a large-scale wave flume are presented. Waves with various surf similarity parameters were generated to break at nearly identical water depths over a 1/100 mild slope. Free surface elevations were measured along the plane beach. Velocities in a water column located at the breaking region were measured by acoustic Doppler velocimeters. Results from wave shoaling coefficient, breaking index, and images are inconsistent with the breaker type categorizations from the surf similarity parameter. This suggests that a modification of the surf similarity parameter for very mild slopes may be necessary. For the plunging breakers, the ensemble-averaged results indicate that intense turbulence kinetic energy was initially generated by large eddies at the surface then transported to the bottom frequently. The instantaneous results demonstrate that the intermittency of turbulence kinetic energy near the bed was caused by large eddies generated by wave overturning and relatively smaller obliquely descending eddies. Moreover, the magnitude of the wave shear stress (WSS) is one order of magnitude larger than that of the turbulent shear stress, indicating that the effects of the bottom slope, wave breaking, and bed friction are significant in the surf zone. The sign of the time-averaged WSS switched between positive and negative, depending on the occurrences of phase lag and phase lead of the vertical coherent velocity. It suggests that a change may be required in Zou et al.'s (2006, https://doi.org/10.1029/2005JC003300) theory on the formulation of wave-breaking induced WSS.

原文English
頁(從 - 到)7486-7512
頁數27
期刊Journal of Geophysical Research: Oceans
124
發行號11
DOIs
出版狀態Published - 2019 十一月 1

All Science Journal Classification (ASJC) codes

  • 地球化學與岩石學
  • 地球物理
  • 地球與行星科學(雜項)
  • 空間與行星科學
  • 海洋學

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