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

弱溶性气体在空气-水界面的传递过程在许多环境和工业系统中起着核心作用。污染河流的再生和温室气体的吸收，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。理解弱溶性气体（O2, CO2， CO， NO, NO2）的气体传递问题的困难源于这样一个事实，即该过程集中在液体侧（10-1000µm）的非常薄的层内。以往的研究大多将气体传输速率与全球可测量参数联系起来。近年来先进的光学测量技术的发展为气体传输问题提供了更好的见解。然而，这些技术在分辨最上层的扩散子层时仍然有局限性。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）来提高对湍流环境中气体在空气-水界面上传递的物理机制的基本理解。DNS技术非常适合于解析包括最上层扩散子层在内的界面附近的分子扩散和湍流过程之间的复杂相互作用。该项目的重点是通过无剪切界面与远场均匀湍流水环境的气体传输过程，例如由水流或电网搅拌产生的。提出的DNS研究结果旨在填补即使具有先进的实验室实验能力也无法解决的基本理解空白。

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.