Collaborative Research: Two-way Coupled Fluid/Particulate Transport in Fractured Media - Bridging the Scales from Microscopic Origins to Macroscopic Networks

海洋、河流、湖泊和含水层等水文系统受到颗粒物污染已成为当今最紧迫的环境问题之一。最近的实地数据表明，在裂缝性含水层和其他地下介质中明显存在固体污染物，如微塑料和病原体，而裂缝性含水层占世界饮用水供应的很大一部分。理解和预测地下裂缝流动中的颗粒输运既面临着基础挑战，也面临着实际挑战，因为它需要定量理解从单个颗粒到裂缝网络的许多长度尺度上的颗粒/流体输运。为了克服这些挑战，我们的研究将通过实验室实验、理论建模和粒子尺度和网络尺度的计算相结合，揭示粒子/流体耦合输运的物理起源及其对大尺度粒子输运的影响。由此产生的颗粒输送模型将极大地提高我们对广泛的地下过程的预测能力，包括污染物输送、地质核废料处理、水力压裂和增强型地热系统。此外，该项目将为来自不同背景的研究生和博士后提供培训机会，并为高中暑期实习生提供合作教育活动，他们将作为跨学科团队的一部分获得基于项目的经验。研究人员将在大范围内探索和量化颗粒/流体双向耦合运动对裂缝介质中颗粒输运的影响。为此，他们将结合详细的实验室实验以及单裂缝尺度上的颗粒解析模拟，以及裂缝网络尺度上的新型升级方法。传统的地下系统颗粒输运模型将颗粒视为不影响周围流场的被动标量，尽管他们的初步实验表明，颗粒可以主动改变流体流动，甚至引发流体动力不稳定。通过克服传统模型的这一缺陷，本研究项目将提供下一代大尺度地下颗粒输运模型。具体来说，他们将解决三个研究问题：1)双向耦合的微观起源；2)单个裂缝的水动力不稳定性和分散性；3)双向耦合对网络尺度颗粒物输运的影响。他们将进行系统的实验室实验，以表征单个裂缝尺度下的颗粒尺度不稳定性和集体颗粒行为，并通过粗糙裂缝中集中悬浮物的颗粒解析Navier-Stokes模拟来验证和补充。所得到的数据将提供有效的色散和粒子运动的随机规则，这些规则捕获了粒子输运的双向耦合效应。这些来自单一裂缝研究的结果将被纳入裂缝网络模型，以评估网络尺度上双向耦合对颗粒输运的影响，并开发更大规模的颗粒输运模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The contamination of hydrologic systems such as oceans, rivers, lakes, and aquifers with particulates has emerged as one of the most urgent environmental issues of today. Recent field data suggests a clear presence of solid contaminants, such as microplastics and pathogens, in fractured aquifers which make up a significant portion of the world's drinking water supply and in other subsurface media. Understanding and predicting particulate transport in subsurface fracture flows poses both fundamental and practical challenges, as it requires a quantitative understanding of particle/fluid transport across many length scales that range from individual particles to a network of fractures. To overcome these challenges, our research will uncover the physical origin of the coupled particle/fluid transport and its effects on the large-scale particle transport, by combining laboratory experiments, theoretical modeling, and computations both at the particle scale and the network scale. The resultant particulate transport models will greatly improve our predictive capabilities for wide-ranging subsurface processes, which include contaminant transport, geological nuclear waste disposal, hydraulic fracturing, and enhanced geothermal systems. In addition, this project will provide training opportunities for graduate students and post-docs from diverse backgrounds, as well as collaborative educational activities for high school summer interns who will gain project-based experience as part of interdisciplinary teams.The investigators will explore and quantify the effects of two-way coupled particle/fluid motion on particulate transport in fractured media, across a wide range of scales. Towards this end, they will combine detailed laboratory experiments as well as particle-resolving simulations at the single-fracture scale, with novel upscaling approaches to the fracture network scale. Traditional particulate transport models in subsurface systems treat particles as passive scalars that do not affect the surrounding flow field, although their preliminary experiments demonstrate that particles can actively modify the fluid flow and even trigger hydrodynamic instabilities. By overcoming this deficiency of traditional models, this research project will provide the next generation of large-scale subsurface particulate transport models. Specifically, they will address three research questions: 1) the microscopic origins of the two-way coupling; 2) the hydrodynamic instabilities and dispersion in a single fracture; 3) the effects of two-way coupling on network-scale particulate transport. They will conduct systematic laboratory experiments to characterize particle-scale instabilities and collective particle behavior at the single fracture scale, which will be verified and supplemented by particle-resolving Navier-Stokes simulations of concentrated suspensions in rough fractures. The resulting data will provide effective dispersivities and stochastic rules of particulate motion that capture the two-way coupling effects on particulate transport. These results from the single fracture study will be incorporated into fracture network models, in order to assess the influence of two-way coupling on particulate transport at the network scale and to develop upscaled particulate transport models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.