A Lattice Boltzmann Based Model for Predicting Unsaturated Flow through Soil Macropores and Capillary Pores

该项目的主要目标是耦合理查兹方程为基础的非饱和流在毛细孔的土壤与流动通过大孔使用Navier-Stokes方程求解使用格子玻尔兹曼（LB）方法的两相流（液体和气体）。 由于计算效率高的机械模型不存在，地下水补给，或深排水的估计，或从垃圾填埋场的气体排放量往往是通过忽略优先流或通过模拟经验。 双渗透率模型通过对微观孔隙和宏观孔隙指定单独的非饱和性质来模拟大孔隙流动。 然而，通过大孔的流动并不遵循达西流动，而是假设所有的大孔作为连续体连接，而大孔通常是离散和断开的。 在这个项目中开发的模型背后的中心思想是，通过大孔的流动类似于具有不规则形状的管道中的流动，因此Navier Stokes方程更合适，并且在使用Lattice-Boltzmann方法求解时数值稳定。 随着数字化X射线CT成像技术的发展，现在可以相对快速和经济地表征土壤的孔隙结构。 因此，可以利用这种高分辨率孔隙结构数据的模型可以彻底改变我们估计长期液体渗透到垃圾填埋场或垃圾填埋场气体排放的方式。 土壤系统中的宏观孔隙和微观孔隙结构将被数字化输入到模型中，使用X射线计算机断层扫描（CT）图像数据从现场规模的粘土帽收集的土壤样品，以验证建模方法。 高分辨率的水平衡数据已收集了为期三年的两个领域规模的粘土盖测试部分位于底特律的垃圾填埋场。传统的基于物理的数值模型可以相对准确地捕捉通过毛细管或微孔的非饱和流。 然而，它们不能模拟通过大孔的流动，大孔是由于压实不充分、干燥开裂、冻/融、根部渗透和啮齿动物活动而形成并不断演变的。 将要开发的模型将克服模拟通过大孔隙的液体或气体流动的挑战。一个数值模型，利用最新进展的X射线成像的土壤结构模拟通过土壤的流动将提供从业者和监管机构的工具，以准确地预测长期深排水到地下水系统的环境意义或温室气体排放的垃圾填埋场。 将为本科生垃圾填埋场设计课程准备一个关于废物场液体和气体迁移的课程模块，并将在研究生课程中准备和介绍一个包含理论和实验室实验的课程模块，以证明优先流过土壤。在夏季训练营期间，将在密歇根州立大学通过实际操作示范向高中生进行宣传。

The key objective of this project is to couple the Richards Equation based unsaturated flow in capillary pores of soils with flow through macropores using the Navier-Stokes Equations solved using the Lattice-Boltzmann (LB) Method for two phase (liquid and gas) flow. Because computationally efficient mechanistically-based models do not exist, groundwater recharge, or deep drainage estimates, or gas emissions from landfills are often carried out by ignoring preferential flow or by modeling it empirically. Dual permeability models simulate macropore flow by specifying separate sets of unsaturated properties to the micro and macro pores. However, the flow through macropores does not follow Darcian flow and assumes all macropores are connected as a continuum while often macropores are discrete and disconnected. The central idea behind the model to be developed in this project is that flow through macropores is similar to flow in conduits having irregular shapes and hence Navier Stokes equations are more appropriate and are numerically stable when solved using the Lattice-Boltzmann method. With the advances in digital X-ray CT imaging techniques, it is now possible to have pore structure of soils characterized relatively quickly and economically. Hence, a model that can take advantage of such high resolution pore structure data can revolutionize the way we estimate long-term liquid percolation into landfills or gas emissions from landfills. The macro pore and micro pore structure in the soil system will be digitally input to the model using X-ray Computed Tomography (CT) image data for soil samples collected from instrumented field-scale clay caps to validate the modeling approach. High-resolution water balance data has been collected over a period of three years from two field-scale clay cap test sections located at a landfill in Detroit. The conventional physically-based numerical models can capture the unsaturated flow through capillary or micropores relatively accurately. However, they cannot model flow through macropores which are formed and continuously evolve due to inadequate compaction, desiccation cracking, freeze/thaw, root penetration, and rodent activity. The model that will be developed will overcome the challenge of modeling liquid or gas flow through macropores. A numerical model that takes advantage of recent advances in X-ray imagining of soil structure for modeling flow through soils will provide practitioners and regulators a tool to accurately predict long-term deep drainage into ground water systems of environmental significance or green-house gas emissions from landfills. A course module on migration of liquids and gases from waste sites will be prepared for an undergraduate landfill design class and a course module containing theory and lab experimentation to demonstrate preferential flow through soils will be prepared and introduced in a graduate level course. Outreach to high school students during summer training camps will carried out with hands-on demonstrations at Michigan State University.