Direct Numerical Simulation of Gas Transfer at the Air-Water Interface

Abstract

A direct numerical simulation is made to investigate the gas transfer at the air-water interface in an open channel flow. The numerical results show the interfacial gas flux to increase intensively in large positive surface divergence regions. This means that the surface divergence model is effective for evaluating the gas transfer velocity at the air-water interface. Scaling relations for turbulence controlling the gas transfer are examined from view points of the surface divergence model. The scale of the surface divergence can be expressed by the Taylor microscale, not macro turbulent scales. We found a dimensionless gas transfer velocity to depend on the -1/4 power of a turbulent Reynolds number. The divergence model shows formally the same Reynolds number dependence as the small eddy model based on the Kolmogorov scaling.