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Journal Articles Boundary-Layer Meteorology Year : 2008

Air flow structure over short-gravity breaking water waves


Despite its importance for momentum and mass transfer across the air-sea interface, the dynamic of the airflow over breaking waves is largely unknown. To fill this gap, velocity and vorticity distributions above short-gravity breaking waves have been measured in a wind-wave tank.A Digital Particle Image velocimetry technique was developed to accomplish these measurements above single breaking waves, propagating in mechanically-generated wave groups and forced by the wind. By varying the wind speed and initial characteristics of the groups, the airflow structure was captured over waves at different stages of the breaking process, and breaking with various intensities.The instantaneous airflow separated from a sharp breaking crest is very similar to that occurs over the backward facing step. The separation bubbles dynamic is however strongly unsteady: the steeper the wave crest and the larger the Reynolds number based on the crest-height, the higher the separated-layer and the farther downwind the reattachment point. Instantaneous flow topology displays specific features of three-dimensional separation patterns. The tangential stress above the wave profile do not exhibits spikes at reattachment but grows progressively downwind from zero at reattachment to a value at the next crest approximately that found at the upwind breaking crest. Static pressure measurements revealed that large pressure drops are generated by vortices in the separated layer, as found in separated flows over solids.This study may provide useful data for theoretical and numerical modeling of the flow and associated phenomena.
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hal-00193129 , version 1 (25-05-2023)




Nicolas Reul, Hubert Branger, Jean-Paul Giovanangeli. Air flow structure over short-gravity breaking water waves. Boundary-Layer Meteorology, 2008, 126 (3), pp.477-505. ⟨10.1007/s10546-007-9240-3⟩. ⟨hal-00193129⟩
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