Direct numerical simulation of gas transfer through the air-water interface in a turbulent flow environment

在许多环境和工业系统中，弱可溶性气体通过空气-水界面的传递过程起着核心作用。污染河流的再曝气和温室气体的吸收，特别是二氧化碳进入海洋，是环境中气体转移过程的两个重要例子。理解弱可溶性气体（O2、CO2、CO、NO、NO2）的气体传递问题的困难源于该过程集中在液体侧的非常薄的层（10-1000 µm）内。大多数以前的研究与气体传输速率的全球可测量的参数。先进的光学测量技术的最新发展提供了更好的洞察气体传输问题。然而，这些技术在分辨最上面的漫射子层方面仍然具有局限性。本研究的目的是通过采用IfH开发的LESOCC代码的改编版本，使用直接数值模拟（DNS），以提高对湍流环境中气-水界面气体传输物理机制的基本理解。DNS技术非常适合于解决复杂的相互作用之间的分子扩散和湍流过程的界面附近，包括最上面的扩散子层。该项目的重点是通过无剪切界面与远场均匀湍流水环境，如由水流或网格搅拌产生的气体传输过程。建议的DNS研究的结果旨在填补基本理解的差距，即使有先进的实验室实验能力也无法解决。

Transfer processes of weakly soluble gases across the air-water interface plays a central role in many environmental and industrial systems. Reaeration in polluted rivers and the absorption of greenhouse gases, notably carbon dioxide into the ocean are two important examples of gas transfer processes in the environment. The difficulty in understanding the gas transfer problem of weakly soluble gases (O2, CO2, CO, NO, NO2) stems from the fact that the process is concentrated within a very thin layer on the liquid side (10-1000 µm). Most previous studies related the gas transfer rate to global measurable parameters. Recent development of advanced optical measurement techniques have provided better insight into the gas transfer problem. However, these techniques still have limitations in resolving the uppermost diffusive sublayer. The aim of this study is to improve the fundamental understanding of the physical mechanisms of gas transfer across the air-water interface in a turbulent flow environment using direct numerical simulations (DNS) by employing an adapted version of the LESOCC code developed at IfH. The DNS technique is highly suited for resolving the complex interaction between the molecular diffusion and turbulent processes near the interface including the uppermost diffusive sublayer. The project focuses on gas transfer processes across a shear-free interface with far-field homogenous turbulent water environment, such as generated by stream flows or grid-stirring. The results of the proposed DNS study aims to fill the gap in fundamental understanding that can not be resolved even with advanced laboratory experimental capabilities.