Direct numerical simulation techniques (DNS) have been developed for investigations of transport processes between turbulent gas and liquid streams separated by a wavy interface. The results indicate qualitative similarity between turbulence structures, in the vicinity of a continuous interface, to those in wall turbulence―if the shear rates correspond. There are detailed differences, however, primarily on the liquid side. The liquid-side tangential velocity fluctuations peak right at the interface, whereas on the gas side they peak a small distance away―much like in wall turbulence. The interfacial shear stress pattern correlates with gas-side sweeps and ejections, whereas it does not correlate with liquid-side structures. Heat and mass transfer mechanisms are primarily controlled by the sweeps on each side. Simple parameterizations of the scalar transfer velocity are developed based on these mechanisms and compare well with experiments and DNS. Capillary waves appear to have little effect on scalar transfer.
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