Abstract
AbstractThe airflow separation from the water surface strongly impacts the coupling between wind and waves. To visualize the airflow and quantify the potential airflow separation's effect on the momentum transfer from wind to the wave, we conducted colocated sampling of air pressure, airflow, and water elevation under a range of wind and wave conditions in the laboratory. The experiments were conducted in the SUrge‐STructure‐Atmosphere INteraction (SUSTAIN) facility at the University of Miami. Three background wave conditions were subjected to wind forcing ( 5–16 m ) to investigate the effects of wave amplitude, frequency, and wind forcing on the airflow regime and momentum transfer. We found the wind forcing shifts the phase of the wave‐induced pressure fluctuations, enhancing the momentum transfer. An increase in wave amplitude or frequency also enhances the aerodynamic sheltering and the momentum transfer. The airflow‐derived pressure based on the nonseparated sheltering (NSS) hypothesis accounts for more than 90% of the momentum transfer until potential airflow separation. We found that the potential airflow separation over the waves' leeward face, which is not accounted for by the NSS hypothesis, leads to an underestimate in momentum transport of more than 30% than the actual value of momentum transport obtained from pressure measurements. Our wave growth rate is consistent with the revisited Miles theory that incorporates the wave‐induced Reynolds stress. The results of this work help explain the wave growth mechanism and inform the development of wind input functions for numerical wave models that account for airflow separation.
Published Version
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