滴状流条件下非饱和交叉裂隙分流机制研究

Splitting mechanisms of droplets through unsaturated fracture intersections

交叉裂隙作为裂隙网络的基本结构是控制场地尺度非饱和渗流特性的关键。随着流量的减小,交叉裂隙非饱和渗流将从连续、稳定的线状流转变为非连续、非稳定的滴状流,但目前对后者的研究还很少。在滴状流条件下,开展了交叉裂隙非饱和流动特性的理论和试验研究,发现了交叉裂隙滴状流存在毛细力驱动以及重力与毛细力联合驱动两种分流驱动模式。基于瞬态静力平衡方法,提出了一套液滴分流理论及计算模型,实现了动态分流过程的定量化描述与预测。结合模型预测与可视化试验,详细探究了两种模式下液滴的分流过程,阐明了动态分流行为受重力、毛细力、黏滞力共同控制的细观机制,并揭示了液滴长度、裂隙倾角、通道中液体的累积等因素对界面流速、分流体积比例的影响。研究成果为低流量、低饱和度条件下非饱和裂隙岩体渗流的预测与控制提供了理论及试验支撑。

As a key structural element of fracture networks, fracture intersections play an important role in water infiltration in unsaturated fractured rocks. With the decrease in flow rate, the flow mode within intersecting fracture changes from continuous and stable rivulet flow to intermittent and unstable droplet flow. Most studies have focused on the rivulet flow, while less attention has been paid to the droplet flow. In this paper, theoretical and experimental work on the characteristics of droplets flowing through unsaturated fracture intersections is performed. It is found that there are two regimes of droplet splitting: capillary dominated splitting regime and capillary-gravitational splitting regime. Based on force balance analysis, we propose a quasi-static model and a semi-analytical solution approach to predict the dynamic splitting behavior of droplets at fracture intersections. Additionally, by investigating the detailed processes of different splitting regimes, we clarify the microscopic mechanism about the combined influence of gravity, capillary force and viscous force on the dynamic splitting behavior. We elucidate the mechanisms based on the variation of interface velocities and droplet splitting volume ratio under different initial droplet lengths and inclination angles. This work provides a theoretical and experimental basis for prediction of seepage in unsaturated fractured rocks under low flow rate and low saturation conditions.