Dynamics and morphology of displacement fronts across textural and wettability discontinuities

由于结构和结构变化或长相关非均质性，孔隙地层中流动和输运的速率和模式受到优先路径或流动障碍存在的强烈影响。此外，在不饱和B多孔介质中，毛细力、重力和粘性力之间不断变化的相互作用导致了一系列复杂的流动现象，影响了润湿和排水锋面的形态、稳定性和动力学。在这个项目中，我们计划量化当液体-空气置换锋面从细层到粗层，或从可湿域到不可湿域时毛细约束力突变对锋面形态的影响，以及与不稳定发生的极端流动聚焦相关的优先路径的形成。在与P1和内部合作中，我们计划使用晶格玻尔兹曼（LB）和流体体积（VoF）方法来详细描述孔隙和样品尺度上的液体破碎、迁移和夹持。将开发标度定律来描述稳定与不稳定位移情景的流动状态和条件。相对于连接不良或均质介质的预测，流向有限通道的流量集中大大缩短了营养物质和污染物到达地下水的平均时间。该项目的结果将为进行更大规模的现场实验提供指导，并为估计相分布敏感输运性质（气体扩散、水力传导性等）所需的特殊升级考虑提供指导。

Rates and patterns of flow and transport in porous formations are strongly influenced by existence of preferential paths or flow barriers originating from textural and structural changes or long-correlation heterogeneity. Additionally, ever-changing interplay between capillary, gravity and viscous forces in unsaturated B porous media gives rise to a range of complex flow phenomena affecting morphology, stability and dynamics of wetting and drainage fronts. In this project we plan to quantify effects of abrupt changes in capillary restraining forces as a liquid-air displacement front passes from fine to coarse layer, or from wettable to non-wettable domains on morphology of the front and on formation of preferential pathways associated with extreme flow focusing due onset of instabilities. In collaboration with P1 and in house we plan to use lattice Boltzmann (LB) and volume of fluid (VoF) methods to provide detailed account of liquid fragmentation, migration and entrapment at the pore and sample scale. Scaling laws will be developed to characterize flow regimes and conditions for stable vs. unstable displacement scenarios. Concentration of flow to limited pathways significantly shortens mean arrival times of nutrients and contaminants to groundwater relative to predictions for poorly connected or homogenous media. Results of this project will provide guidance for conducting larger scale field experiments and for special upscaling considerations required for estimation of phase distribution sensitive transport properties (gaseous diffusion, hydraulic conductivity, etc).