在全球能源转型和温室气体减排的背景下，增强型地热系统（EGS）作为一种可持续清洁能源解决方案，受到国际社会的广泛关注。EGS技术的核心是提高地热能开发效率，尤其是通过人工增强地下岩石渗透性来实现高效热能提取。然而，由于天然岩石裂隙几何形态和粗糙特征的复杂性，现有数值模拟研究中常采用简化的裂隙数值模型，可能导致模拟结果与实际情况存在偏差。为了更准确地揭示EGS中干热岩(HDR)裂隙内的流体渗流和热传递机制，本研究围绕单裂隙粗糙度和交叉裂隙几何形态对渗流和传热特性的影响开展了深入的理论分析和不同物理场的数值模拟分析。研究成果将为EGS的优化设计和高效开发提供重要的理论依据。

本研究基于数字扫描技术获取的真实岩石裂隙三维数据，构建了包括三维、二维平面和二维中面粗糙裂隙在内的多种几何裂隙模型，并通过引入表面粗糙放大系数M(1~2.5)和多个参数对裂隙粗糙度进行细致表征。通过对特征参数统计发现，中面粗糙度特性参数通常低裂隙表面参数，尤其是Z₂参数存在显著差异。同时，研究评估了二维平面裂隙和粗糙中面裂隙在模拟三维裂隙流动过程中的差异，结果表明，相较于二维平面裂隙，二维粗糙中面裂隙能够更好地捕捉弯曲流动路径，从而更准确地预测裂隙传导率，更接近三维裂隙中的实际流动过程。此外，研究还发现裂隙中面的粗糙度参数T_or(w)和Z₂(w)与渗透率偏差密切相关，当其小于阈值0.32和1.08时，中面粗糙度的影响可以忽略。

在单裂隙的传热特性研究中，本文采用了稳态和瞬态数值模拟方法，对比分析了不同维度和粗糙度条件下裂隙表面温度分布特征和对流换热系数（HTC）。结果表明，相比于二维平面裂隙模型，二维中面粗糙裂隙结构模型能更准确地预测裂隙的渗透率和捕捉弯曲流动路径。此外，裂隙表面粗糙度通过改变内流场和速度分布，显著影响流体的热交换效率。粗糙的裂隙增加了流体与岩石的接触时间和面积，有助于提高水温和热传递效率。三维裂隙的换热系数显著高于二维裂隙，且中面裂隙在模拟裂隙传热过程中表现更接近实际情况。

本文进一步地探讨了“X”与“V”型交叉裂隙在不同工况下对流体渗透和热传递特性的影响。结果表面“X”型裂隙的传热性能优于“V”型裂隙，裂隙开度的增加和交叉裂隙的几何特征显著改变了渗流场和温度场的分布，调整裂隙开度和注入流速可有效控制热交换效率。交叉裂隙的连通作用导致局部区域流速增强。裂隙开度和注入流速是影响裂隙出口温度和热衰退阶段的关键因素，合理调整这两个参数可以有效控制地热开采过程中的热交换效率。

In the context of global energy transition and greenhouse gas emission reduction, the Enhanced Geothermal System (EGS), as a sustainable and clean energy solution, has received extensive attention from the international community. The core of EGS technology is to improve the efficiency of geothermal energy development, especially through artificially enhancing the permeability of subsurface rocks to achieve efficient thermal energy extraction. However, due to the complexity of natural rock fracture geometries and roughness characteristics, simplified numerical models of fracture are often used in existing numerical simulation studies, which may lead to the deviation of simulation results from the actual situation. To more accurately reveal the fluid seepage and heat transfer mechanisms within dry hot rock (HDR) fractures in EGS, this study carries out in-depth theoretical and numerical simulation analyses centered on the effects of single-fracture roughness and cross-fracture geometries on seepage and heat transfer characteristics. The research results will provide an important theoretical basis for the optimal design and efficient development of EGS.

In this study, multiple geometric models including 3D, 2D planar, and 2D mid-surface roughness fractures were constructed based on real rock fracture 3D data obtained by digital scanning, and the fracture roughness was meticulously characterized through the introduction of amplification coefficients M(1~2.5), and multiple parameters. It is found that the characteristic parameters of mid-surface roughness are usually significantly different from the low fracture surface parameters, especially the Z₂ parameter. Meanwhile, the study evaluates the difference between 2D planar and rough mid-surface fractures in simulating the 3D fracture flow process, and the results show that the 2D rough mid-surface fracture can capture the curved flow paths better than the 2D planar fracture, which leads to a more accurate prediction of the fracture conductivity and a closer approximation to the actual flow process in the 3D fracture. It is also found that the roughness parameters T_or(w) and Z₂(w) of the fracture mid-surface are closely related to the permeability deviation, and the effect of mid-surface roughness can be neglected when they are smaller than the thresholds 0.32 and 1.08.

In the study of heat transfer characteristics of a single fracture, steady state, and transient numerical simulation methods are used in this paper to compare and analyze the characteristics of temperature distribution and convective heat transfer coefficients (HTC) on the fracture surface under different dimensionality and roughness conditions. The results show that the 2D mid-surface roughness fracture structure model can more accurately predict the permeability of the fracture and capture the curved flow paths than the 2D planar fracture model. In addition, fracture surface roughness significantly affects the heat exchange efficiency of the fluid by changing the internal flow field and velocity distribution. Rough fracture increases the contact time and area between the fluid and the rock, which contributes to the water temperature and heat transfer efficiency. The heat transfer coefficients of the three-dimensional fracture are significantly higher than those of the two-dimensional fracture, and the mid-surface fracture performs more closely to the actual situation in the simulated fracture heat transfer process.

In this paper, the effects of "X" and "V" cross-fractures on the fluid permeability and heat transfer characteristics under different working conditions are further investigated. As a result, the heat transfer performance of the "X" type fracture is better than that of the "V" type fracture. The increase of fracture opening and the geometrical characteristics of the cross-fracture significantly change the distribution of the seepage and temperature fields, and the adjustment of the fracture opening and the injection flow rate can effectively control the heat exchange efficiency. The connectivity effect of cross-fracture leads to the enhancement of flow velocity in the local area. Fracture opening and injection flow rate are the key factors affecting the exit temperature and thermal recession stage of the fracture, and reasonable adjustment of these two parameters can effectively control the heat exchange efficiency in the process of geothermal mining.