Effects of pore scale on the macroscopic properties of natural convection in porous media
Effects of pore scale on the macroscopic properties of natural convection in porous media
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DOI：
10.1017/jfm.2020.164
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发表时间：
2020-03
影响因子：
3.7
通讯作者：
S. Gasow;Zhe Lin;Hao Zhang;A. Kuznetsov;M. Avila;Yan Jin
中科院分区：
文献类型：
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作者：
S. Gasow;Zhe Lin;Hao Zhang;A. Kuznetsov;M. Avila;Yan Jin
多孔介质中的自然对流是深层咸水层中长期储存二氧化碳的基本过程。通常，多孔介质中传质的细节是从体积平均达西-奥伯贝克-布辛涅斯克 (DOB) 方程的数值解推断出来的，即使这些方程没有考虑多孔介质的微观特性。根据 DOB 方程，多孔介质中的自然对流由瑞利数唯一确定。然而，与实验相比，对于高 $Ra$ 值 ( $Ra\gg 1300$ )，DOB 模拟产生了舍伍德数与瑞利数 ( $Ra$ ) 的线性缩放。在这里，我们进行直接数值模拟（DNS），完全解析孔隙内的流场。我们表明，边界层厚度是由孔径决定的，而不是如之前假设的瑞利数。巨型羽流和原始羽流尺寸随着孔径的增加而增加。我们的 DNS 结果显示出高孔隙率下舍伍德数的非线性缩放，并且对于相同的瑞利数，DNS 在较低孔隙率下预测较高的舍伍德数。可以得出结论，舍伍德数的标度取决于孔隙率和孔隙尺度参数，这与实验研究一致。
Natural convection in porous media is a fundamental process for the long-term storage of CO2 in deep saline aquifers. Typically, details of mass transfer in porous media are inferred from the numerical solution of the volume-averaged Darcy–Oberbeck–Boussinesq (DOB) equations, even though these equations do not account for the microscopic properties of a porous medium. According to the DOB equations, natural convection in a porous medium is uniquely determined by the Rayleigh number. However, in contrast with experiments, DOB simulations yield a linear scaling of the Sherwood number with the Rayleigh number ( $Ra$ ) for high values of $Ra$ ( $Ra\gg 1300$ ). Here, we perform direct numerical simulations (DNS), fully resolving the flow field within the pores. We show that the boundary layer thickness is determined by the pore size instead of the Rayleigh number, as previously assumed. The mega- and proto-plume sizes increase with the pore size. Our DNS results exhibit a nonlinear scaling of the Sherwood number at high porosity, and for the same Rayleigh number, higher Sherwood numbers are predicted by DNS at lower porosities. It can be concluded that the scaling of the Sherwood number depends on the porosity and the pore-scale parameters, which is consistent with experimental studies.