Turbulent flow field and air entrainment in laboratory plunging breaking waves

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

Research output: Contribution to journalArticlepeer-review

22 Scopus citations

Abstract

This paper presents laboratory measurements of turbulent flow fields and void fraction in deep-water plunging breaking waves using imaging and optical fiber techniques. Bubble-size distributions are also determined based on combined measurements of velocity and bubble residence time. The most excited mode of the local intermittency measure of the turbulent flow and its corresponding length scale are obtained using a wavelet-based method and found to correlate with the swirling strength and vorticity. Concentrated vortical structures with high intermittency are observed near the lower boundaries of the aerated rollers where the velocity shear is high; the length scale of the deduced eddies ranges from 0.05 to 0.15 times the wave height. The number of bubbles with a chord length less than 2 mm demonstrates good correlation with the swirling strength. The power-law scaling and the Hinze scale of the bubbles determined from the bubble chord length distribution compare favorably with existing measurements. The turbulent dissipation rate, accounting for void fraction, is estimated using mixture theory. When void fraction is not considered, the turbulent dissipation rate is underestimated by more than 70% in the initial impinging and the first splash-up roller. A significant discrepancy of approximately 67% between the total energy dissipation rate and the turbulence dissipation rate is found. Of this uncounted dissipation, 23% is caused by bubble-induced dissipation.

Original languageEnglish
Pages (from-to)2980-3009
Number of pages30
JournalJournal of Geophysical Research: Oceans
Volume121
Issue number5
DOIs
StatePublished - 1 May 2016

Keywords

  • air entrainment
  • bubble-size distribution
  • turbulent dissipation rate
  • void fraction
  • wave breaking

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