Heterogeneity and macroscopic anisotropy of porous media play an important role for dilution and reaction enhancement of conservative and reactive plumes. In this study, we perform numerical simulations to investigate steady-state flow and transport in three-dimensional heterogeneous porous media. We consider two macroscopic anisotropic inclusions resulting in helical flows with twisting streamlines in a three-dimensional flow-through domain. The inclusions are obtained by alternating two layers of angled slices of coarse and fine porous media with different hydraulic conductivity. We investigate flow and transport scenarios considering different geometry and relative position of the two anisotropic inclusions yielding helical flow fields with different extent of interaction. We use metrics of stretching and folding to characterize the flow field and entropy-based metrics for the analysis of the conservative and reactive transport problems. The outcomes show that the two helices result in different patterns of twisting streamlines, which cause distinct deformation of the plumes. However, mixing and reaction enhancement could not be directly related to the extent of the flow field deformation: Configurations with strong deformation can result in only moderate mixing enhancement, whereas configurations with limited deformation of the flow field can lead to significant mixing of the solute plume. Finally, we explore the impact of different degradation rates on reactive transport and the role of reaction kinetics on the entropy balance for a reactant undergoing transport and mixing-controlled degradation in the twisting flow fields. The results show that strong mixing enhancement due to helical flow increases the importance of the reaction kinetics that becomes the rate-limiting process for solute reactive transport.

中文翻译：

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羽流变形，混合和反应动力学：三维多孔介质中相互作用的螺旋流的分析。

多孔介质的非均质性和宏观各向异性对稀释和反应性羽流的稀释和反应增强起着重要作用。在这项研究中，我们进行数值模拟以研究三维异质多孔介质中的稳态流动和传输。我们考虑了两个宏观的各向异性包裹体，它们在三维流域中产生带有扭曲流线的螺旋流。夹杂物是通过交替使用两层具有不同水力传导率的粗糙和精细多孔介质的成角度的切片来获得的。我们研究了考虑两种各向异性夹杂物的不同几何形状和相对位置的流动和运输情景，产生了相互作用程度不同的螺旋流场。我们使用拉伸和折叠度量来表征流场，并使用基于熵的度量来分析保守和反应性运输问题。结果表明，这两个螺旋导致扭曲流线的模式不同，这导致羽流明显变形。但是，混合和反应的增强与流场变形的程度没有直接关系：具有强烈变形的构型只会导致中等程度的混合增强，而具有有限的流场变形的构型可能导致溶质羽流的显着混合。 。最后，我们探索了不同降解速率对反应性传输的影响，以及反应动力学在扭曲流场中经历传输和混合控制降解的反应物的熵平衡中的作用。结果表明，由于螺旋流动而引起的强混合增强增加了反应动力学的重要性，这成为了溶质反应性传输的限速过程。