地下水流与气流、热流的典型耦合问题及解耦条件研究

发布时间：2018-07-21 16:29

【摘要】：传统水文地质学关注的是地下水本身的运动及其水文地球化学背景,对于地下水与地质环境中其它因素的动力学耦合行为,往往采取忽略或简化的办法进行处理。然而,与地下水有关的耦合过程在自然界普遍存在,且对于地质环境的塑造或起到关键的作用。其中,地下水流与空气流的耦合动力学过程、地下水流场与温度场的耦合,已经成为现代地下水动力学和地质环境领域的热点研究课题。与经典地下水动力学相比,耦合问题的理论描述一般具有较为复杂的数学形式,难以获得解析解,需要通过数值模拟的方法对特例进行观察。由于没有解析解来清楚明了的揭示不同要素之间的相互关系,人们对耦合问题的特征和规律往往并不十分清楚,对物理机理也不能得到清晰的认识。实际上在很多情况下地下水流场具有主控意义,而其它因素对地下水流场的反作用相对比较小,因此地下水流问题可以通过解耦的方法近似获取。这是经典地下水动力学所能立足的基础。只有在满足解耦条件的情况下,才能有效地应用经典地下水动力学。什么情况下可以解耦处理、什么情况下不能忽略耦合作用?这正是本论文试图要回答的问题。本论文主要围绕含水层地下水-空气流耦合问题,以及盆地中地下水流与热流的耦合问题开展研究,模拟分析这2类典型动力学问题的耦合特征及解耦条件。研究成果可以归纳为以下2点：(1)建立了包含少量无量纲参数的径向地下水流-空气流耦合模型,抓住了这一耦合问题最主要的控制因素,比前人的动力学描述更加简洁明了。通过对解耦条件下地下水位计算结果的误差分析,发现在一般情况下空气流对地下水流的影响很弱,具有比较宽松的解耦条件。然而,空气流对地下水流很敏感,解耦的地下水流计算结果并不能有效的解决空气流问题。(2)基于Comsol有限元模型研究了盆地尺度地下水流场与温度场的耦合特征,发现Domenico和Palciauskas(1973)关于单元盆地温度场的对称型解析解可能会产生显著误差,证明地下水的强对流作用可以显著破坏温差分布的对称性。通过对耦合解和解耦条件地下水头计算结果的误差分析,证明在一般情况下(平均大地热流)单元盆地的水-热耦合问题满足解耦条件,且解耦的地下水流场可有效的用于计算温度场的分布。这些研究结果加深了对水文地质过程中多相流耦合问题和水热耦合问题的机理认识,为地质工程和环境工程领域合理利用经典地下水动力学提供了理论指导。本论文研究的概念模型仍然采取了很多简化假设,结论因此也存在一定的局限性,有待于进一步扩展和完善。
[Abstract]:The traditional hydrogeology focuses on the movement of groundwater itself and its hydrogeochemical background. The dynamic coupling behavior between groundwater and other factors in geological environment is often ignored or simplified. However, the coupling process associated with groundwater exists widely in nature and plays a key role in shaping the geological environment. Among them, the coupling dynamic process of groundwater flow and air flow, the coupling of groundwater flow field and temperature field has become a hot research topic in the field of modern groundwater dynamics and geological environment. Compared with the classical groundwater dynamics, the theoretical description of the coupled problem generally has a more complex mathematical form, so it is difficult to obtain an analytical solution, so it is necessary to observe the special case by numerical simulation. Because there are no analytical solutions to reveal the relationship between different elements clearly, the characteristics and laws of coupling problems are often not very clear, and the physical mechanism is not clearly understood. In fact, in many cases, the groundwater flow field has the main control significance, but the other factors have relatively little reaction to the groundwater flow field, so the groundwater flow problem can be obtained by the decoupling method. This is the basis on which the classical groundwater dynamics can be based. Only when the decoupling condition is satisfied, can the classical groundwater dynamics be applied effectively. Under what circumstances can the coupling be decoupled, and under what circumstances can the coupling be ignored? This is exactly the question this thesis tries to answer. In this paper, the coupling problem between groundwater and air flow in aquifer and the coupling between groundwater flow and heat flow in basin are studied, and the coupling characteristics and decoupling conditions of these two typical dynamic problems are simulated and analyzed. The research results can be summarized as follows: (1) the coupling model of radial groundwater flow and air flow with a small number of dimensionless parameters is established, which captures the most important control factor of this coupling problem and is more concise and clear than the previous dynamical description. Through the error analysis of the results of groundwater level calculation under the decoupling condition, it is found that the influence of air flow on groundwater flow is very weak in general, and there are relatively loose decoupling conditions. However, air flow is very sensitive to groundwater flow, and decoupling results of groundwater flow can not effectively solve the problem of air flow. (2) based on Comsol finite element model, the coupling characteristics of basin scale groundwater field and temperature field are studied. Domenico and Palciauskas (1973) may have significant errors in the symmetric analytical solution of the temperature field in the unit basin. It is proved that the strong convection of groundwater can significantly destroy the symmetry of the temperature difference distribution. Through the error analysis of the coupling solution and the calculation result of the groundwater head under the decoupling condition, it is proved that the water-heat coupling problem of the unit basin (mean geothermal flux) satisfies the decoupling condition under general conditions. And the decoupled groundwater flow field can be used to calculate the distribution of temperature field. These results deepen the understanding of the mechanism of multi-phase flow coupling and hydrothermal coupling in hydrogeological processes and provide theoretical guidance for the rational use of classical groundwater dynamics in geological engineering and environmental engineering. The conceptual model of this paper still adopts a lot of simplified hypotheses, so the conclusion has some limitations and needs to be further expanded and improved.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P641.2

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