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Direct numerical simulation of trapped-phase recirculation at low capillary number
Advances in Water Resources ( IF 4.7 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.advwatres.2020.103717
Amir Hossein Mohammadi Alamooti , Qumars Azizi , Hossein Davarzani

Abstract Understanding multiphase flow in porous media, especially how velocity is distributed at the pore-scale, has been the aim of several studies. However, these studies address the recirculation behavior inside the trapped phase experimentally without any comprehensive numerical study of the impact of different governing mechanisms related to the fluid configurations and properties, including drag force and capillary number analysis at low capillary number regime. In this study, we analyzed the recirculation phenomenon inside the trapped phase for various displacement mechanisms, fluid configurations, and dynamic properties. To simulate the pore-scale displacement at low capillary number, we used a filtered surface-force formulation of volume of fluid method, which was implemented in a separately available solver for OpenFoam package. The results showed that within the ranges of capillary number of invading phase analyzed in this study (in the order of 1 × 10−7 to 1 × 10−2), the recirculation phenomenon exists in trapped phases. During the imbibition mechanism, two stagnant regions are created adjacent to the fluid-fluid interface inside the invading fluid. Drag-force analysis on fluid-fluid interfaces shows that during imbibition the maximum force is exerted near the center of the interface, whereas during drainage more force is applied on two elongated interface tails on a solid surface. The centroids are elongated parallel to the interface during drainage and perpendicularly during imbibition, which is in concordance with drag-force distribution along with the interface. The existence of a solid surface near the fluid-fluid interface affects the recirculation process in a way that one or more centroids can be created depending on displacement mechanisms. When the ratio of trapped-phase radius to cavity depth is lower, two simultaneous recirculation zones are formed inside the invading and trapped phases While the changes in viscosity ratio and interfacial tension shifted the centroid location inside the trapped zone, the center of rotation seems to be independent of injection velocity. The average velocity of trapped phase is individually a logarithmic function of the surface tension and fluids viscosity ratio. The stationariness of centroid results in a linear relationship between the average velocity inside the trapped zone and injection velocity. For all ranges of viscosity ratios, a linear relationship between the capillary number of invading and trapped phase is obtained. The findings of this study lead to a better understanding of trapping and mobilization mechanisms in microchannels where various forces are acting on fluid-fluid interfaces.

中文翻译:

低毛细管数下困相再循环的直接数值模拟

摘要 了解多孔介质中的多相流,尤其是速度在孔隙尺度上的分布方式,一直是多项研究的目标。然而,这些研究通过实验解决了困相内的再循环行为,而没有对与流体配置和性质相关的不同控制机制的影响进行任何全面的数值研究,包括在低毛细管数状态下的阻力和毛细管数分析。在这项研究中,我们分析了各种驱替机制、流体配置和动态特性的困相内的再循环现象。为了模拟低毛细管数下的孔隙尺度位移,我们使用了流体体积法的过滤表面力公式,该公式在单独可用的 OpenFoam 包求解器中实现。结果表明,在本研究分析的侵入相毛细管数范围内(1×10-7~1×10-2),被困相中存在回流现象。在渗吸机制中,在侵入流体内部的流体-流体界面附近会产生两个停滞区域。流体-流体界面的拖曳力分析表明,在吸入过程中,最大的力施加在界面中心附近,而在排水过程中,更多的力施加在固体表面上的两个细长界面尾部。质心在排水过程中平行于界面拉长,在吸液过程中垂直,这与沿界面的阻力分布一致。流体-流体界面附近固体表面的存在以一种可以根据位移机制创建一个或多个质心的方式影响再循环过程。当困相半径与腔深的比值较低时,侵入相和困相内部同时形成两个回流区,而粘度比和界面张力的变化使困相区内的质心位置发生偏移,旋转中心似乎与注射速度无关。被困相的平均速度分别是表面张力和流体粘度比的对数函数。质心的平稳性导致圈闭区域内的平均速度与注入速度之间存在线性关系。对于所有粘度比范围,获得了侵入相和俘获相的毛细管数之间的线性关系。这项研究的发现有助于更好地理解微通道中各种力作用在流体-流体界面上的捕获和动员机制。
更新日期:2020-11-01
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