| 基于计算流体力学的寒区土壤水热耦合模型研究 |
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| 引用本文： | 胡锦华,陆峥,仝金辉,李小雁,刘绍民,杨晓帆.基于计算流体力学的寒区土壤水热耦合模型研究[J].冰川冻土,2021,43(4):948-963. |
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| 作者姓名： | 胡锦华 陆峥 仝金辉 李小雁 刘绍民 杨晓帆 |
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| 作者单位： | 1.北京师范大学 地理科学学部 地表过程与资源生态国家重点实验室, 北京 100875;2.北京师范大学 地理科学学部 自然资源学院, 北京 100875 |
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| 基金项目： | 国家自然科学基金项目(42077172);第二次青藏高原综合科学考察研究项目(2019QZKK0306) |
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| 摘 要： | 土壤水文过程（水分运移和传热）及其对气候变化的响应是寒区水文学的前沿问题。然而，冻土的存在使得寒区土壤水文过程变得极其复杂。此外，寒区自然环境恶劣，较难获取长时间序列和高分辨率的野外观测资料。近年来，充分利用已有的观测数据，构建寒区土壤水热耦合模型，并开展相应的数值模拟研究，已成为理解寒区土壤水文物理过程，揭示其动力学机制的重要途径。基于寒区土壤水文物理过程和计算流体力学方法，构建了高分辨率、适用于完全饱和状态下的寒区土壤水热耦合模型，且自主研发了相应的数值求解器和软件包。随后，通过一系列完全饱和状态下的验证算例，如经典的一维传热方程解析解、被广泛应用的二维基准测试算例和室内土柱冻结实验等，对已构建的模型进行了系统的检验。模型模拟结果与解析解、基准算例的结果以及实验数据相比，均有较好的一致性，表明该模型较为准确且高效地模拟了寒区土壤在完全饱和状态下的水分运移和传热过程，尤其能够精细刻画冻土水-冰相态变化等关键过程，有望成为研究寒区土壤水文过程的有力工具。
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| 关 键 词： | 寒区水文学 地下水模型 水热耦合过程 计算流体力学 基准测试算例 |
| 收稿时间： | 2021-02-08 |
| 修稿时间： | 2021-06-20 |
Simulating thermo-hydrologic processes in cold region soil system:a computational fluid dynamics study |
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| HU Jinhua,LU Zheng,TONG Jinhui,LI Xiaoyan,LIU Shaomin,YANG Xiaofan.Simulating thermo-hydrologic processes in cold region soil system:a computational fluid dynamics study[J].Journal of Glaciology and Geocryology,2021,43(4):948-963. |
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| Authors: | HU Jinhua LU Zheng TONG Jinhui LI Xiaoyan LIU Shaomin YANG Xiaofan |
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| Institution: | 1.State Key Laboratory of Earth Surface Processes and Resource Ecology，Faculty of Geographical Science，Beijing Normal University，Beijing 100875，China;2.School of Natural Resources，Faculty of Geographical Science，Beijing Normal University，Beijing 100875，China |
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| Abstract: | Cold regions， which supply freshwater to downstream communities， have been significantly disturbed by anthropogenic climate change that is pronounced to continue in future. As unique and critical elements of the cold regions， frozen soil plays a vital role in cold region hydrology. Although frozen soil is considered relatively impermeable to groundwater flow， the freezing and thawing of the frozen soils under seasonal and climate change may influence the hydrologic components such as surface water infiltration， groundwater recharge， and hydrogeologic connectivity that are important for water resources. Under the pronounced climate warming， increased soil temperature expedites the thawing of frozen soil in cold regions. Therefore， understanding the complex thermo-hydrologic processes in frozen soils is one of key issues in studying cold region hydrology. However， due to the harsh environment， it is difficult to conduct hydrometeorological and geophysical field observations yet collect gap-free， high-resolution datasets. With the recent development of computational methods and resources and based on the observational data in recent decades， it is essential to enable modeling and simulation of the thermo-hydrologic processes in frozen soils to study cold region hydrology. The thermo-hydrologic processes in frozen soils is fundamentally interpreted into multi-phase flow and heat transfer in porous media with phase change. The current challenges in simulating such processes， especially in cold regions include but not limited to the interactions among liquid water， vapor， ice and soil grains and the phase change between ice and liquid water， which introduce high non-linearities and uncertainties in the processes. However， traditional distributed or hydrogeological models were limited in terms of resolution， accessibility and capability of solving the coupled thermo-hydrologic processes with high fidelity. To account for these feedbacks as far as possible， a physically-based， massively-parallel， fine-resolution and fully-saturated cryo-hydrogeological model was in-house developed in OpenFOAM? （http：//www.openfoam.com）， an open-source computational fluid dynamics （CFD） solver， which has been widely used in groundwater modeling and computational hydrology. The cryo-hydrogeological model， named darcyTHFOAM， was formulated by mass conservation， Darcy’s law， energy conservation and soil freezing function. To ensure the convenience and joy for users， an interface-based software was developed correspondingly using Python 3.5 （www.python.org） and designed with QT Designer （www.qt.io） in Linux environment. In general， rigorous validation and benchmarking of the numerical models are prerequisites and critical for their validation and applications. Hence， a series of benchmarking simulations under fully-saturated condition were performed to validate the current model， including the classical analytical solution of Stefan’s equation， two community-recognized benchmark cases （under thawing） using synthetic porous media samples in the Interfrost Project （wiki.lsce.ipsl.fr/interfrost） and laboratory freezing experiment with a 25 cm-long soil column. Simulated results include the evolution of temperature， liquid water content and ice content. Frozen depth， temperature profiles at fixed points or lines， the minimum of the temperature field were selected for quantitative comparisons. Simulated results were in excellent agreements with those obtained from the analytical solution， other cryo-hydrogeological models and experimental data， respectively， which demonstrated the reliability and accuracy of the current model. The study revealed that the proposed model is capable of simulating coupled thermo-hydrologic processes under fully-saturated condition in cold regions with high spatial resolutions and efficiency. Overall， the in-house developed cryo-hydrogeological model is expected to serve as a powerful tool for studying subsurface hydrology in cold regions. Further code developments involve coupling the surface processes， especially snow， and transport processes （e.g. contaminants） for studying groundwater-surface water interactions and hydro-biogeochemical processes in cold regions. |
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| Keywords: | cold region hydrology groundwater model coupled thermo-hydrologic processes computational fluid dynamics benchmark case |
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