Experimental study on plunging breaking waves in deep water

Ho Joon Lim, Kuang An Chang, Zhi Cheng Huang, Byoungjoon Na

Research output: Contribution to journalArticlepeer-review

51 Scopus citations

Abstract

This study presents a unique data set that combines measurements of velocities and void fraction under an unsteady deep water plunging breaker in a laboratory. Flow properties in the aerated crest region of the breaking wave were measured using modified particle image velocimetry (PIV) and bubble image velocimetry (BIV). Results show that the maximum velocity in the plunging breaker reached 1.68C at the first impingement of the overturning water jet with C being the phase speed of the primary breaking wave, while the maximum velocity reached 2.14C at the beginning of the first splash-up. A similarity profile of void fraction was found in the successive impinging and splash-up rollers. In the highly foamy splashing roller, the increase of turbulent level and vorticity level were strongly correlated with the increase of void fraction when the range of void fraction was between 0 and 0.4 (from the trough level to approximately the center of the roller). The levels became constant when void fraction was greater than 0.5. The mass flux, momentum flux, kinetic energy, potential energy, and total energy were computed and compared with and without the void fraction being accounted for. The results show that all the mean and turbulence properties related to the air-water mixture are considerably overestimated unless void fraction is considered. When including the density variation due to the air bubbles, the wave energy dissipated exponentially a short distance after breaking; about 54% and 85% of the total energy dissipated within one and two wavelengths beyond the breaking wave impingement point, respectively.

Original languageEnglish
Pages (from-to)2007-2049
Number of pages43
JournalJournal of Geophysical Research: Oceans
Volume120
Issue number3
DOIs
StatePublished - 1 Mar 2015

Keywords

  • energy dissipation
  • laboratory experiment
  • particle image velocimetry
  • turbulent kinetic energy
  • Wave breaking

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