Experimental and Modeling Studies of Episodic Air-Water Two-Phase Flow in Fractures and Fracture Networks

Effect of Unsaturated Flow Modes on Partitioning Dynamics of Gravity‐Driven Flow at a Simple Fracture Intersection: Laboratory Study and Three‐Dimensional Smoothed Particle Hydrodynamics Simulations

“…While these results already highlight the importance of flow modes for percolation dynamics through fracture networks, the high variance of the results, especially for lower flow rates in the droplet flow regime (see Wood & Huang, ), makes it difficult to compare results to simulation data and obtain an analytical solution. Therefore, in the following section, we extend our laboratory experiments and SPH simulations to include a larger number of inlets.…”

“…For the given fluid‐solid combination, the whole spectrum of flow modes (droplets, mixed droplets/rivulet, and rivulets) can be observed (Figure ). Due to environmental “noise,” such as slight impurities on the PMMA surfaces and/or tiny air pressure or flow rate variations (Dragila & Weisbrod, ; Wood & Huang, ), it is nearly impossible to establish a perfect droplet regime, i.e., a stream of individual droplets moving at the exact same velocity down the surface. Such interferences commonly induce mixed flow regimes, e.g., merging droplets that temporarily form partial rivulets or larger droplets traveling at high velocities and emitting smaller droplets.…”

“…The accumulation and release of water results in pulsating flows with magnitudes of temporal outflow fluctuations much higher than dripping dynamics in individual fractures alone can explain (Su et al, ), highlighting the importance of fracture intersections (specifically the subvertical fractures) as potential storage zones. Furthermore, the partitioning process at fracture intersections leads to flow focusing or splitting (Wood et al, ; Wood & Huang, ), which essentially controls the lateral and vertical dispersion characteristics of preferential flow paths (zones) (Glass & LaViolette, ). Hence, the analysis of flow partitioning at fracture intersections can ultimately lead to the interpretation and understanding of large‐scale vertical flow structures.…”

Analogue Fracture Experiments and Analytical Modeling of Unsaturated Percolation Dynamics in Fracture Cascades

“…Different flow regimes, e.g., droplet, rivulet, and film flow, can coexist even in controlled settings and are difficult to cast into unified conceptual frameworks (Ghezzehei, 2004). In well-controlled analog percolation experiments, the fracture-specific formation of flow modes and instabilities (Jones et al, 2018;Li et al, 2018) and the role of unsaturated fracture intersections on partitioning behavior has been investigated (e.g., Ji et al, 2006;Kordilla et al, 2017;LaViolette et al, 2003;Nicholl and Glass, 2005;Wood et al, 2002Wood et al, , 2005Wood and Huang, 2015), where the applied flow rate controls the stability of a desired flow regime (Towell and Rothfeld, 1966;Schmuki and Laso, 1990). These studies emphasize the importance of fracture intersections as capillary barriers (until steady-state conditions are established), which may induce pulsating flows and act as important integrators for dispersion and recharge processes.…”

Numerical and Analytical Modeling of Flow Partitioning in Partially Saturated Fracture Networks

“…In order to shed light on the complex infiltration processes, laboratory scale experiments have been a promising addition to the former investigation methods as they allow to isolate important processes under well controlled conditions that are often impossible to observe in-situ. Small-scale laboratory experiments for gravity-driven partiallysaturated flow often exhibit erratic or chaotic flow dynamics (Su et al, 2001;Dragila & Weisbrod, 2004;T. Wood & Huang, 2015).…”