The concentration and distribution of dissolved oxygen (DO) are critical to the self‐purification capacity of water and the survival of aquatic organisms, and they are important factors considered in the ecological balance system of water resources. In this work, the high‐Schmidt number DO transfer phenomenon in open channel flows with anisotropic sediment beds is studied using large eddy simulation. The volume‐averaged Navier‐Stokes equations coupled with the Monod equation is used to describe the in‐sediment flow and the sediment oxygen demand of micro‐organisms, so as to examine the transport characteristics of DO inside and outside the sediment layer. The effects of various permeable conditions of sediments (characterized by the anisotropy index of permeability, i.e., λ) on the distribution of DO concentration and flux, penetration depth, and mass transfer processes is studied by means of the time‐averaged statistics variations in flow and scalar fields. A larger anisotropy index λ is found can enhance the transport of DO from the water flowing into the sediment layer, which is caused by turbulent diffusions and turbulence bursting events. It suggests that the λ‐dependent distributions of the DO fluctuations and fluxes are highly correlated with the coherent structures in the turbulence over the sediment‐water interface (SWI). A key relationship between the Sherwood number and the anisotropy index is found by means of the current simulations and also is verified by our theoretical analysis. The dependence of λ on DO penetration depth is consistent with the hypothesis that coherent turbulence in the water column drives mass transport across the SWI.

中文翻译：

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湍流中各向异性沉积物层对溶解氧迁移的影响

溶解氧（DO）的浓度和分布对于水的自净能力和水生生物的生存至关重要，是水资源生态平衡系统中考虑的重要因素。在这项工作中，使用大涡模拟研究了具有各向异性沉积床的明渠高Schmidt数DO迁移现象。体积平均的Navier-Stokes方程和Monod方程用于描述微生物的沉积物流量和沉积物需氧量，从而研究DO在沉积物层内外的传输特性。沉积物的各种渗透条件（以渗透率的各向异性指数，即λ为特征）对DO浓度和通量分布，渗透深度，通过流场和标量场的时间平均统计变化来研究传质过程。发现较大的各向异性指数λ可以增强DO从水流到沉积物层的传输，这是由于湍流扩散和湍流爆发事件引起的。这表明DO涨落和通量的λ依赖性分布与沉积物-水界面（SWI）湍流的相干结构高度相关。通过当前的模拟发现舍伍德数和各向异性指数之间的关键关系，并且也通过我们的理论分析得到了验证。λ对溶解氧渗透深度的依赖性与水柱中相干湍流驱动整个SWI传质的假设相一致。