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

水文系统如海洋、河流、湖泊和含水层的颗粒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，在构成世界饮用水供应的重要部分的断裂含水层和其他地下介质中明显存在微塑料和病原体等固体污染物。理解和预测地下裂缝流中的颗粒输运提出了基本和实际的挑战，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，我们的研究将揭示耦合粒子/流体传输的物理起源及其对大规模粒子传输的影响，通过结合实验室实验，理论建模和计算，在粒子尺度和网络尺度。由此产生的颗粒传输模型将大大提高我们对广泛的地下过程的预测能力，其中包括污染物传输，地质核废料处理，水力压裂和增强地热系统。此外，该项目还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，这些实习生将作为跨学科团队的一部分获得基于项目的经验。研究人员将探索和量化双向耦合颗粒/流体运动对破碎介质中颗粒传输的影响。为此，他们将结合联合收割机详细的实验室实验，以及在单裂缝规模的颗粒分辨模拟，与新的放大方法裂缝网络规模。传统的地下系统中的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，甚至触发流体动力学不稳定性。通过克服传统模型的这一不足，本研究项目将提供下一代大尺度地下颗粒物传输模型。具体而言，他们将解决三个研究问题：1）双向耦合的微观起源; 2）单个裂缝中的流体动力学不稳定性和分散; 3）双向耦合对网络尺度颗粒传输的影响。他们将进行系统的实验室实验，以表征颗粒尺度的不稳定性和集体粒子行为在单一的裂缝规模，这将得到验证和补充的颗粒解析Navier-Stokes模拟粗糙裂缝中的浓缩悬浮液。由此产生的数据将提供有效的分散性和颗粒运动的随机规则，捕获颗粒传输的双向耦合效应。这些来自单一裂缝研究的结果将被纳入裂缝网络模型中，以评估双向耦合对网络尺度颗粒传输的影响，并开发升级的颗粒传输模型。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

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.