Wind and current effects on extreme wave formation and breaking

Qingping Zou, Haifei Chen

Research output: Contribution to journalArticle

Abstract

Wind and current effects on the evolution of a two-dimensional dispersive focusing wave group are investigated using a two-phase flow model. A Navier-Stokes solver is combined with the Smagorinsky subgrid-scale stress model and volume of fluid (VOF) air-water interface capturing scheme.Model predictions compare well with the experimental data with and without wind. It was found that the following and opposing winds shift the focus point downstream and upstream, respectively. The shift of focus point is mainly due to the action of wind-driven current instead of direct wind forcing. Under strong following/opposing wind forcing, there appears a slight increase/ decrease of the extreme wave height at the focus point and an asymmetric/symmetric behavior in thewave focusing and defocusing processes. Under a weak following wind, however, the extreme wave height decreases with increasing wind speed because of the dominant effect of the wind-driven current over direct wind forcing. The vertical shear of the wind-driven current plays an important role in determining the location of and the extreme wave height at the focus point under wind actions. Furthermore, it was found that the thin surface layer current is a better representation of the wind-driven current for its role in wind influences on waves than the depth-uniform current used by previous studies.Airflow structure above a breakingwave group and its link to the energy flux from wind to wave as well as wind influence on breaking are also examined. The flow structure in the presence of a following wind is similar to that over a backward-facing step, while that in the presence of an opposing wind is similar to that over an airfoil at high angles of attack. Both primary and secondary vortices are observed over the breaking wave with and without wind of either direction. Airflow separates over the steep crest and causes a pressure drop in the lee of the crest. The resulting form dragmay directly affect the extreme wave height. The wave breaking location and intensity are modified by the following and opposing wind in a different fashion.

Original languageEnglish
Pages (from-to)1817-1841
Number of pages25
JournalJournal of Physical Oceanography
Volume47
Issue number7
Early online date7 Jul 2017
DOIs
Publication statusPublished - Jul 2017

Fingerprint

wind-driven current
wave height
wind forcing
airflow
effect
wave group
breaking wave
wave breaking
flow structure
wind wave
two phase flow
pressure drop
energy flux
vortex
surface layer
wind velocity
fluid
air
prediction
water

Keywords

  • Air-sea interaction
  • Atmospheric
  • Currents
  • Oceanic
  • Waves
  • Wind
  • Wind effects

ASJC Scopus subject areas

  • Oceanography

Cite this

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title = "Wind and current effects on extreme wave formation and breaking",
abstract = "Wind and current effects on the evolution of a two-dimensional dispersive focusing wave group are investigated using a two-phase flow model. A Navier-Stokes solver is combined with the Smagorinsky subgrid-scale stress model and volume of fluid (VOF) air-water interface capturing scheme.Model predictions compare well with the experimental data with and without wind. It was found that the following and opposing winds shift the focus point downstream and upstream, respectively. The shift of focus point is mainly due to the action of wind-driven current instead of direct wind forcing. Under strong following/opposing wind forcing, there appears a slight increase/ decrease of the extreme wave height at the focus point and an asymmetric/symmetric behavior in thewave focusing and defocusing processes. Under a weak following wind, however, the extreme wave height decreases with increasing wind speed because of the dominant effect of the wind-driven current over direct wind forcing. The vertical shear of the wind-driven current plays an important role in determining the location of and the extreme wave height at the focus point under wind actions. Furthermore, it was found that the thin surface layer current is a better representation of the wind-driven current for its role in wind influences on waves than the depth-uniform current used by previous studies.Airflow structure above a breakingwave group and its link to the energy flux from wind to wave as well as wind influence on breaking are also examined. The flow structure in the presence of a following wind is similar to that over a backward-facing step, while that in the presence of an opposing wind is similar to that over an airfoil at high angles of attack. Both primary and secondary vortices are observed over the breaking wave with and without wind of either direction. Airflow separates over the steep crest and causes a pressure drop in the lee of the crest. The resulting form dragmay directly affect the extreme wave height. The wave breaking location and intensity are modified by the following and opposing wind in a different fashion.",
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Wind and current effects on extreme wave formation and breaking. / Zou, Qingping; Chen, Haifei.

In: Journal of Physical Oceanography, Vol. 47, No. 7, 07.2017, p. 1817-1841.

Research output: Contribution to journalArticle

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AB - Wind and current effects on the evolution of a two-dimensional dispersive focusing wave group are investigated using a two-phase flow model. A Navier-Stokes solver is combined with the Smagorinsky subgrid-scale stress model and volume of fluid (VOF) air-water interface capturing scheme.Model predictions compare well with the experimental data with and without wind. It was found that the following and opposing winds shift the focus point downstream and upstream, respectively. The shift of focus point is mainly due to the action of wind-driven current instead of direct wind forcing. Under strong following/opposing wind forcing, there appears a slight increase/ decrease of the extreme wave height at the focus point and an asymmetric/symmetric behavior in thewave focusing and defocusing processes. Under a weak following wind, however, the extreme wave height decreases with increasing wind speed because of the dominant effect of the wind-driven current over direct wind forcing. The vertical shear of the wind-driven current plays an important role in determining the location of and the extreme wave height at the focus point under wind actions. Furthermore, it was found that the thin surface layer current is a better representation of the wind-driven current for its role in wind influences on waves than the depth-uniform current used by previous studies.Airflow structure above a breakingwave group and its link to the energy flux from wind to wave as well as wind influence on breaking are also examined. The flow structure in the presence of a following wind is similar to that over a backward-facing step, while that in the presence of an opposing wind is similar to that over an airfoil at high angles of attack. Both primary and secondary vortices are observed over the breaking wave with and without wind of either direction. Airflow separates over the steep crest and causes a pressure drop in the lee of the crest. The resulting form dragmay directly affect the extreme wave height. The wave breaking location and intensity are modified by the following and opposing wind in a different fashion.

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KW - Atmospheric

KW - Currents

KW - Oceanic

KW - Waves

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