The project deals with the transfer of gaseous substances across a gas-liquid interface driven by buoyant-convective instability. The physical mechanisms that play a role in buoyancy-driven convective gas transfer are not well understood, despite of their significant contributions to the global heat budget and environmentally important gas cycles (including green-house gas cycles). Though numerous empirical relations to predict the gas transfer velocity have been reported in the literature, the dynamics of the interaction between the near-surface turbulent field and the interfacial gas flux in buoyancy driven flow are yet to be fully described. As the interfacial mass transfer of such low-diffusive (high Schmidt number) substances is characterized by very thin diffusive layers near the interface and the instantaneous occurrence of steep concentration gradients in other regions, performing detailed laboratory measurements is extremely difficult. At the same time existing direct numerical simulations (DNS) - constrained by the high demand on computational resources needed to resolve all scales of motion - are mostly limited to low Schmidt numbers (typically less than 10) and/or low Reynolds numbers.

In this project, a series of direct numerical simulations of buoyancy-driven gas transfer using a specifically designed numerical code for the discretization of scalar convection and diffusion are performed at realistically Prandtl and high Schmidt numbers up to 500.

Wissink, J.G. and Herlina, H.  2015. Direct numerical simulation of gas transfer across the air-water interface driven by buoyant convection. J. Fluid Mech. [DOI]