Numerical and Analytical Modeling of Flow Partitioning in Partially Saturated Fracture Networks
Numerical and Analytical Modeling of Flow Partitioning in Partially Saturated Fracture Networks
复制标题
DOI：
10.1029/2020wr028775
复制
发表时间：
2020-09
影响因子：
5.4
通讯作者：
J. Kordilla;M. Dentz;A. Tartakovsky
中科院分区：
文献类型：
--
作者：
J. Kordilla;M. Dentz;A. Tartakovsky
裂隙-多孔介质中的渗透过程仍然是补给和脆弱性评估的一个重要组成部分，但尚未得到很好的理解。在部分饱和条件下，裂隙中的流动，扩展裂隙网络和断层带有助于通过优先通道获得最快的渗透速度谱。具体而言，在裂缝交叉点的分区动态确定成垂直和水平分量的流量碎片的大小，因此，散装流速度和分散的裂缝网络。在这里，我们推导出一个近似的解析解的分割过程，并验证它使用平滑粒子流体动力学模拟。传递函数的概念是基于模拟结果和实验室实验在以前的作品进行。它允许通过简单的立方结构和任意数量的裂缝和孔径大小的裂缝网络，通过线性响应理论和给定的输入信号的卷积进行有效的流动模拟。我们推导出了无量纲的整体流速（v）和弥散系数（D~）来表征裂缝网络的无量纲水平和垂直时间尺度τm和τ0。弥散系数强烈地依赖于水平时间尺度，在合理的流体和几何参数范围内，弥散系数向0.08的常数值收敛，而无量纲速度则表现出特征性的v~ π τm−1/2标度。考虑到水力信息通常仅在（裂隙-多孔）含水层系统（钻孔或泉水）的有限位置可用，我们的研究旨在提供一种分析概念，以便从外部边界信息（如排水的分散特性（地下水位波动））重建内部裂隙网络几何形状。
Infiltration processes in fractured‐porous media remain a crucial, yet not very well understood component of recharge and vulnerability assessment. Under partially saturated condition flows in fractures, percolating fracture networks and fault zones contribute to the fastest spectrum of infiltration velocities via preferential pathways. Specifically, the partitioning dynamics at fracture intersections determine the magnitude of flow fragmentation into vertical and horizontal components, hence the bulk flow velocity and dispersion of fracture networks. Here we derive an approximate analytical solution for the partitioning process and validate it using smoothed particle hydrodynamics simulations. The transfer function is conceptually based on simulation results and laboratory experiments carried out in previous works. It allows efficient flow simulation through fracture networks with simple cubic structures and an arbitrary number of fractures and aperture sizes via linear response theory and convolution of a given input signal. We derive a nondimensional bulk flow velocity ( v∼ ) and dispersion coefficient ( D~ ) to characterize fracture networks in terms of dimensionless horizontal and vertical time scales τm and τ0. The dispersion coefficient strongly depends on the horizontal time scale and converges toward a constant value of 0.08 within reasonable fluid and geometrical parameter ranges, while the nondimensional velocity exhibits a characteristic v~∼τm−1/2 scaling. Given that hydraulic information is often only available at limited places within (fractured‐porous) aquifer systems (boreholes or springs), our study intends to provide an analytical concept to potentially reconstruct internal fracture network geometries from external boundary information, such as the dispersive properties of discharge (groundwater level fluctuations).