Direct numerical simulation of turbulent scalar transport across a flat surface
Direct numerical simulation of turbulent scalar transport across a flat surface
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平面上湍流标量输运的直接数值模拟
DOI：
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发表时间：
2014
影响因子：
3.7
通讯作者：
J. Wissink
中科院分区：
文献类型：
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作者：
H. Herlina;J. Wissink
摘要为了阐明大气气体向水中界面传递的物理机制，在不同的湍流雷诺数（$R_T=84,195,507$）条件下，对由下向扩散的各向同性湍流驱动的空气-水界面传质进行了一系列直接数值模拟。为了对标量扩散的瞬时效应进行直接（无偏）比较，在每个DNS中，最多可同时求解六个具有不同施密特数的标量平流扩散方程。据作者所知，这是第一个能够准确解析现实的施密特数的模拟，$\mathit{Sc}=500$，这是典型的大气气体（如水中的氧气）的传输。对于考虑的湍流雷诺数和施密特数范围，发现归一化传递速度$K_L$与$R_T^{-{1/2}}$和$\mathit{Sc}^{-{1/2}}$成比例，这表明在计算域底部引入的各向同性湍流中存在的最大涡流倾向于决定传质。当使用0.525的比例常数时，也发现$K_L$结果与McCready， Vassiliadou & Hanratty （AIChE J., vol. 32, 1986, pp. 1108-1115）的表面散度模型很好地一致。虽然靠近表面的大涡流负责大部分的气体传递，但也观察到，对于较高的R_T$，较小的涡流的影响变得更加重要。
Abstract To elucidate the physical mechanisms that play a role in the interfacial transfer of atmospheric gases into water, a series of direct numerical simulations of mass transfer across the air–water interface driven by isotropic turbulence diffusing from below has been carried out for various turbulent Reynolds numbers ( $R_T=84,195,507$ ). To allow a direct (unbiased) comparison of the instantaneous effects of scalar diffusivity, in each of the DNS up to six scalar advection–diffusion equations with different Schmidt numbers were solved simultaneously. As far as the authors are aware this is the first simulation that is capable to accurately resolve the realistic Schmidt number, $\mathit{Sc}=500$ , that is typical for the transport of atmospheric gases such as oxygen in water. For the range of turbulent Reynolds numbers and Schmidt numbers considered, the normalized transfer velocity $K_L$ was found to scale with $R_T^{-{1/2}}$ and $\mathit{Sc}^{-{1/2}}$ , which indicates that the largest eddies present in the isotropic turbulent flow introduced at the bottom of the computational domain tend to determine the mass transfer. The $K_L$ results were also found to be in good agreement with the surface divergence model of McCready, Vassiliadou & Hanratty (AIChE J., vol. 32, 1986, pp. 1108–1115) when using a constant of proportionality of 0.525. Although close to the surface large eddies are responsible for the bulk of the gas transfer, it was also observed that for higher $R_T$ the influence of smaller eddies becomes more important.