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Proposing Institution

Institut für Hydromechanik, Universität Karlsruhe
Project Manager

Dr.-Ing. Herlina Herlina
Kaiserstr. 12
76131 Karlsruhe
The present numerical work considers the case of gas transfer across the air-water interface driven by either isotropic turbulence diffusing from below or buoyant convective instability. Applications include, for example, the transfer process of oxygen from the atmosphere into natural water bodies, which is an essential pathway for e.g. rivers to overcome dissolved oxygen deficits. Oxygen and many other atmospheric gases have low-diffusivity (high Schmidt number) in water. For such gases, the interfacial mass transfer is marked by a very thin concentration boundary layer and occurrencesof steep concentration gradients in other regions of the fluid domain. To accurately resolve the physical mechanisms of the turbulent mass transfer at high Schmidt (Sc) numbers, an extremely fine grid resolution is needed. To mitigate this, we employ a specifically designed numerical scheme capable of resolving details of the mass transfer on a computationally feasible mesh size while avoiding spurious oscillations of the scalar quantity. The setup of the present simulations was similar to the gas transfer experiments performed at KIT. Despite the advanced measurement techniques used in the experiments, they still faced accuracy limitations when elucidating the Batchelor sublayer as well as capturing minute fluctuations of the turbulent Transport in the deeper bulk region. Compared to previous simulations that were limited to low Schmidt numbers, thepresent DNS allow us to obtain high quality data for Schmidt numbers that are typical for environmental gases like oxygen (Sc=500). In this way, many experimentally inaccessible aspects of the gas-transfer problem can now be addressed. The present project focuses on the effect of surface contamination which is known to reduce the transfer velocity significantly when compared to the gas transfer across perfectly clean water surfaces.

Impressum, Conny Wendler