Collaborative Research: Coupled Numerical and Laboratory Investigations of Chaotic Advection to Enhance Spreading and Reaction in Three-Dimensional, Heterogeneous Porous Media

修复受污染地下水的一种方法是引入一种化学溶液，它可以与污染物发生反应并降解污染物。如果将引入的化学溶液扩散到整个污染区域，这种修复方法是最成功的。地下水流经的多孔材料自然是不均匀的，这意味着水更容易通过某些部分，而更不容易通过其他部分。这种不均匀性自然导致化学溶液向受污染的地下水中扩散，称为被动扩散。额外的扩散，称为主动扩散，可以通过在污染区域诱导某些随时间变化的地下水流动模式来发生。某些时变气流，被归类为混沌平流，已知可以大大增强主动扩散。被动扩散和主动扩散都能增强污染物的降解；然而，主动传播和被动传播的联合效应尚不清楚。在本项目中，将采用一系列实验室实验和数值模拟(1)研究被动和主动扩散之间的相互作用以及它们在增强退化中的作用；(2)制定针对不同异质性模式的混沌平流模式设计策略。实验室实验将使用新的基于激光的光学技术来可视化和量化被动和主动扩散对污染物降解的综合影响。诸如污染地下水的修复、地热能的开采和某些类型的金属开采等活动都依赖于化学溶液在多孔地质材料中的扩散。由于地质材料的天然非均质性，了解非均质性与混沌平流之间的关系及其对扩散的影响对这些应用的成功至关重要。该项目还将开发新的实验室技术，为多孔介质中反应输运的测量提供突破。

One method for remediating contaminated groundwater is to introduce a chemical solution that will react with and degrade the contaminant. This remediation method is most successful if the introduced chemical solution is spread throughout the contaminated area. The porous materials through which groundwater flows are naturally heterogeneous, meaning that water flows more easily through some parts and less easily through others. This heterogeneity naturally causes some spreading, called passive spreading, of the chemical solution into the contaminated groundwater. Additional spreading, called active spreading, can occur by inducing certain time-varying patterns of groundwater flow in the contaminated area. Certain time-varying flows, classified as chaotic advection, are known to substantially enhance active spreading. Both passive and active spreading lead to enhanced degradation of the contaminant; however, the combined effect of active and passive spreading is not well understood. In this project, a suite of laboratory experiments and numerical simulations will be used (1) to investigate the interplay between passive and active spreading and the role that each plays in enhancing degradation, and (2) to develop strategies for designing chaotic advection patterns for different patterns of heterogeneity. The laboratory experiments will be conducted using novel laser-based optical techniques to visualize and quantify the combined effects of passive and active spreading on contaminant degradation. Activities such as remediation of contaminated groundwater, extraction of geothermal energy, and certain types of mining of metals all rely on spreading of chemical solutions in porous geological materials. Because of the natural heterogeneity of geological materials, an understanding of the relationship between heterogeneity and chaotic advection and their effects on spreading is critical to the success of these applications. This project will also develop new laboratory techniques that could provide a breakthrough in measurement of reactive transport in porous media.