Near-Bed Turbulent Kinetic Energy Budget Under a Large-Scale Plunging Breaking Wave Over a Fixed Bar

Joep Van Der Zanden, Dominic A Van der A, Ivan Cáceres, David Hurther, Stuart J. McLelland, Jan S Ribberink, Tom O'Donoghue

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Abstract

Hydrodynamics under regular plunging breaking waves over a fixed breaker bar were studied in a large-scale wave flume. A previous paper reported on the outer flow hydrodynamics (van der A et al., 2017, J.Geoph.Res. 122(4)); the present paper focuses on the turbulence dynamics near the bed (up to 0.10 m from the bed). Velocities were measured with high spatial and temporal resolution using a two-component laser Doppler anemometer. The results show that even at close distance from the bed (1 mm), the turbulent kinetic energy (TKE) increases by a factor five between the shoaling and breaking regions because of invasion of wave breaking turbulence. The sign and phase behaviour of the time-dependent Reynolds shear stresses at elevations up to approximately 0.02 m from the bed (roughly twice the elevation of the boundary layer overshoot) are mainly controlled by local bed-shear-generated turbulence, but at higher elevations Reynolds stresses are controlled by wave breaking turbulence. The measurements are subsequently analysed to investigate the TKE budget at wave-averaged and intra-wave time scales. Horizontal and vertical turbulence advection, production, and dissipation are the major terms. A two-dimensional wave-averaged circulation drives advection of wave breaking turbulence through the near-bed layer, resulting in a net downward influx in the bar trough region, followed by seaward advection along the bar's shoreward slope, and an upward outflux above the bar crest. The strongly non-uniform flow across the bar combined with the presence of anisotropic turbulence enhances turbulent production rates near the bed.
Original languageEnglish
Pages (from-to)1429-1456
Number of pages28
JournalJournal of Geophysical Research: Oceans
Volume123
Issue number2
Early online date24 Feb 2018
DOIs
Publication statusPublished - Feb 2018

Keywords

  • breaking waves
  • turbulence
  • wave bottom boundary layer
  • surf zone
  • wave flume experiment

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    SINBAD fixed bed experiment

    van der Zanden, J. (Creator), Van der A, D. (Creator), Ribberink, J. S. (Creator), O'Donoghue, T. (Creator), Cáceres, I. (Creator) & Hurther, D. (Creator), 4TU.Centre, 8 Feb 2018

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