Spatial and temporal distributions of turbulence under bichromatic breaking waves

Joep van der Zanden; Dominic A. Van der A; Ivan Cáceres; Bjarke Eltard Larsen; Guillaume Fromant; Carmelo Petrotta; Pietro Scandura; Ming Li

doi:10.1016/j.coastaleng.2019.01.006

Spatial and temporal distributions of turbulence under bichromatic breaking waves

Joep van der Zanden (Corresponding Author), Dominic A. Van der A, Ivan Cáceres, Bjarke Eltard Larsen, Guillaume Fromant, Carmelo Petrotta, Pietro Scandura, Ming Li

Engineering

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Abstract

The present study aims to extend insights of surf zone turbulence dynamics to wave groups. In a large-scale wave flume, bichromatic wave groups were produced with 31.5 s group period, 4.2 s mean wave period, and a 0.58 m maximum wave height near the paddle. This condition resulted in plunging-type wave breaking over a fixed, gravel-bed, barred profile. Optic, acoustic and electromagnetic instruments were used to measure the flow and the spatial and temporal distributions of turbulent kinetic energy (TKE). The measurements showed that turbulence in the shoaling region is primarily bed-generated and decays almost fully within one wave cycle, leading to TKE variations at the short wave frequency. The wave breaking-generated turbulence, in contrast, decays over multiple wave cycles, leading to a gradual increase and decay of TKE during a wave group cycle. In the wave breaking region, TKE dynamics are driven by the production and subsequent downward transport of turbulence under the successive breaking waves in the group. Consequently, the maximum near-bed TKE in the breaking region can lag the highest breaking wave by up to 2.5 wave cycles. The net cross-shore transport of TKE is in the shoaling region primarily driven by short-wave velocities and is shoreward-directed; in the wave breaking region, the TKE transport is seaward-directed by the undertow and the long-wave velocities. Downward transport of TKE is driven by the vertical component of the time-averaged flow. The cross-shore and vertical diffusive transport rates are small relative to the advective transport rates.

Original language	English
Pages (from-to)	65-80
Number of pages	16
Journal	Coastal Engineering
Volume	146
Early online date	29 Jan 2019
DOIs	https://doi.org/10.1016/j.coastaleng.2019.01.006
Publication status	Published - 1 Apr 2019

Bibliographical note

We gratefully acknowledge the suggestions by the three reviewers that helped to improve the manuscript. The work described in this publication was supported by the European Community’s Horizon 2020 Programme through the grant to the budget of the Integrated Infrastructure Initiative HYDRALAB+, Contract no. 654110, and was conducted as part of the transnational access project HYBRID. BEL acknowledges financial support from the Independent Research Fund Denmark project SWASH: Simulating WAve Surf-zone Hydrodynamics and sea bed morphology, Grant no. 8022-00137B. For their contributions to the experiments, we thank fellow HYBRID researchers and the CIEMLAB staff (Oscar Galego, Andrea Marzeddu, and Joaquim Sospedra). We are grateful to Deltares for lending out their ECMs and to dr Jose Alsina for his contributions to the generation of the wave paddle steering signals.

Keywords

Turbulence
breaking waves
surf zone
wave groups
bichromatic waves
wave flume experiment

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Cite this

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title = "Spatial and temporal distributions of turbulence under bichromatic breaking waves",

abstract = "The present study aims to extend insights of surf zone turbulence dynamics to wave groups. In a large-scale wave flume, bichromatic wave groups were produced with 31.5 s group period, 4.2 s mean wave period, and a 0.58 m maximum wave height near the paddle. This condition resulted in plunging-type wave breaking over a fixed, gravel-bed, barred profile. Optic, acoustic and electromagnetic instruments were used to measure the flow and the spatial and temporal distributions of turbulent kinetic energy (TKE). The measurements showed that turbulence in the shoaling region is primarily bed-generated and decays almost fully within one wave cycle, leading to TKE variations at the short wave frequency. The wave breaking-generated turbulence, in contrast, decays over multiple wave cycles, leading to a gradual increase and decay of TKE during a wave group cycle. In the wave breaking region, TKE dynamics are driven by the production and subsequent downward transport of turbulence under the successive breaking waves in the group. Consequently, the maximum near-bed TKE in the breaking region can lag the highest breaking wave by up to 2.5 wave cycles. The net cross-shore transport of TKE is in the shoaling region primarily driven by short-wave velocities and is shoreward-directed; in the wave breaking region, the TKE transport is seaward-directed by the undertow and the long-wave velocities. Downward transport of TKE is driven by the vertical component of the time-averaged flow. The cross-shore and vertical diffusive transport rates are small relative to the advective transport rates.",

keywords = "Turbulence, breaking waves, surf zone, wave groups, bichromatic waves, wave flume experiment",

author = "{van der Zanden}, Joep and {Van der A}, {Dominic A.} and Ivan C{\'a}ceres and {Eltard Larsen}, Bjarke and Guillaume Fromant and Carmelo Petrotta and Pietro Scandura and Ming Li",

note = "We gratefully acknowledge the suggestions by the three reviewers that helped to improve the manuscript. The work described in this publication was supported by the European Community{\textquoteright}s Horizon 2020 Programme through the grant to the budget of the Integrated Infrastructure Initiative HYDRALAB+, Contract no. 654110, and was conducted as part of the transnational access project HYBRID. BEL acknowledges financial support from the Independent Research Fund Denmark project SWASH: Simulating WAve Surf-zone Hydrodynamics and sea bed morphology, Grant no. 8022-00137B. For their contributions to the experiments, we thank fellow HYBRID researchers and the CIEMLAB staff (Oscar Galego, Andrea Marzeddu, and Joaquim Sospedra). We are grateful to Deltares for lending out their ECMs and to dr Jose Alsina for his contributions to the generation of the wave paddle steering signals.",

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doi = "10.1016/j.coastaleng.2019.01.006",

language = "English",

volume = "146",

pages = "65--80",

journal = "Coastal Engineering",

issn = "0378-3839",

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TY - JOUR

T1 - Spatial and temporal distributions of turbulence under bichromatic breaking waves

AU - van der Zanden, Joep

AU - Van der A, Dominic A.

AU - Cáceres, Ivan

AU - Eltard Larsen, Bjarke

AU - Fromant, Guillaume

AU - Petrotta, Carmelo

AU - Scandura, Pietro

AU - Li, Ming

N1 - We gratefully acknowledge the suggestions by the three reviewers that helped to improve the manuscript. The work described in this publication was supported by the European Community’s Horizon 2020 Programme through the grant to the budget of the Integrated Infrastructure Initiative HYDRALAB+, Contract no. 654110, and was conducted as part of the transnational access project HYBRID. BEL acknowledges financial support from the Independent Research Fund Denmark project SWASH: Simulating WAve Surf-zone Hydrodynamics and sea bed morphology, Grant no. 8022-00137B. For their contributions to the experiments, we thank fellow HYBRID researchers and the CIEMLAB staff (Oscar Galego, Andrea Marzeddu, and Joaquim Sospedra). We are grateful to Deltares for lending out their ECMs and to dr Jose Alsina for his contributions to the generation of the wave paddle steering signals.

PY - 2019/4/1

Y1 - 2019/4/1

N2 - The present study aims to extend insights of surf zone turbulence dynamics to wave groups. In a large-scale wave flume, bichromatic wave groups were produced with 31.5 s group period, 4.2 s mean wave period, and a 0.58 m maximum wave height near the paddle. This condition resulted in plunging-type wave breaking over a fixed, gravel-bed, barred profile. Optic, acoustic and electromagnetic instruments were used to measure the flow and the spatial and temporal distributions of turbulent kinetic energy (TKE). The measurements showed that turbulence in the shoaling region is primarily bed-generated and decays almost fully within one wave cycle, leading to TKE variations at the short wave frequency. The wave breaking-generated turbulence, in contrast, decays over multiple wave cycles, leading to a gradual increase and decay of TKE during a wave group cycle. In the wave breaking region, TKE dynamics are driven by the production and subsequent downward transport of turbulence under the successive breaking waves in the group. Consequently, the maximum near-bed TKE in the breaking region can lag the highest breaking wave by up to 2.5 wave cycles. The net cross-shore transport of TKE is in the shoaling region primarily driven by short-wave velocities and is shoreward-directed; in the wave breaking region, the TKE transport is seaward-directed by the undertow and the long-wave velocities. Downward transport of TKE is driven by the vertical component of the time-averaged flow. The cross-shore and vertical diffusive transport rates are small relative to the advective transport rates.

AB - The present study aims to extend insights of surf zone turbulence dynamics to wave groups. In a large-scale wave flume, bichromatic wave groups were produced with 31.5 s group period, 4.2 s mean wave period, and a 0.58 m maximum wave height near the paddle. This condition resulted in plunging-type wave breaking over a fixed, gravel-bed, barred profile. Optic, acoustic and electromagnetic instruments were used to measure the flow and the spatial and temporal distributions of turbulent kinetic energy (TKE). The measurements showed that turbulence in the shoaling region is primarily bed-generated and decays almost fully within one wave cycle, leading to TKE variations at the short wave frequency. The wave breaking-generated turbulence, in contrast, decays over multiple wave cycles, leading to a gradual increase and decay of TKE during a wave group cycle. In the wave breaking region, TKE dynamics are driven by the production and subsequent downward transport of turbulence under the successive breaking waves in the group. Consequently, the maximum near-bed TKE in the breaking region can lag the highest breaking wave by up to 2.5 wave cycles. The net cross-shore transport of TKE is in the shoaling region primarily driven by short-wave velocities and is shoreward-directed; in the wave breaking region, the TKE transport is seaward-directed by the undertow and the long-wave velocities. Downward transport of TKE is driven by the vertical component of the time-averaged flow. The cross-shore and vertical diffusive transport rates are small relative to the advective transport rates.

KW - Turbulence

KW - breaking waves

KW - surf zone

KW - wave groups

KW - bichromatic waves

KW - wave flume experiment

U2 - 10.1016/j.coastaleng.2019.01.006

DO - 10.1016/j.coastaleng.2019.01.006

M3 - Article

SN - 0378-3839

VL - 146

SP - 65

EP - 80

JO - Coastal Engineering

JF - Coastal Engineering

ER -

Spatial and temporal distributions of turbulence under bichromatic breaking waves

Abstract

Bibliographical note

Keywords

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