Turbulence Level Below the Waves and Its Relation to Absorptionby Jacques Magnaudet, CNRS, Toulouse, France,
Jacques George, CNRS, Toulouse, France,
Lucien Masbernat, CNRS, Toulouse, France,
Bernard Caussade, CNRS, Toulouse, France,
Abstract: A review of recent experimental studies carried out on gas transfer at water surfaces in various situations shows that the absorption coefficient is better related to the turbulence level below the interface than to other classical parameters such as the interfacial friction velocity. When the source of the turbulent motion does not lie in the free surface deformation, usual one-point closure models allow a reasonable prediction of the turbulence level; it is no longer the case when strong wind waves exist. In order to understand the mechanisms occurring at a wavy surface in presence of wind, a theoretical analysis of wave-turbulence interactions is developed, which reproduces correctly the most prominent features observed, especially the level of the turbulent kinetic energy. A similar analysis of the fluctuating concentration budget of any passive scalar is carried out and shows that the turbulent velocity-concentration correlation in the vertical direction represents the entire mean mass flux: there does not seem to exist any direct correlation between the wave motion and the concentration fluctuations.
Subject Headings: Turbulence | Surface waves | Water waves | Water surface | Wind waves | Absorption | Motion (dynamics) | Free surfaces
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