Characterization of Flow under Different Geometric Properties and Reynold Numbers in Y-Junction Bifurcated Fractures

Bifurcated fractures are the basic units of fracture networks. In this paper, a bifurcated fracture model is designed using Fluent software to characterize the fluid flow in a fracture network. The characterization of water flow was investigated by changing the geometrical properties, namely, joint roughness coefficient ($JRC$), angle between two outlet fractures ($\theta$), and the mechanical aperture ($e$) of either outlet fracture. The effect of Reynolds numbers (Re), hydraulic gradient ($J$), flow rate ($Q$), flow velocity ($V$), critical Reynolds numbers (${\mathrm{Re}}_{\mathrm{c}}$), and hydraulic aperture ($E$) on the flow were systematically analyzed. The results showed that (1) given the increase in roughness and $\theta$, the flow ratio in the branches increases nonlinearly, whereas the aperture ratio showed an opposite characteristic; (2) the deflected flow caused by the variation in $\theta$ is mainly attributed to inertial forces, whereas that caused by the change in $JRC$ and the aperture ratio is due to the combination of the viscous and inertial forces; (3) when Re was small, the ratio of $E·e^{-\mathit{1}}$ was slightly lower than 1, and with an increase in Re, the $E·e^{-\mathit{1}}$ strength of the outlet fractures was weak; and (4) the aperture is the most important parameter affecting the deflected flow, followed by $\theta$ and $JRC$.