Effects of deflection flow on solute mixing and partitioning at rough-walled fracture intersections

Fracture intersections are an important formation for solute mixing and partitioning in fractured rock, which is crucial for accurate prediction of solute transport in fracture networks. This study investigates the effects of deflection flow on solute mixing and partitioning through numerical simulations and experiments of solute transport at two-dimensional rough-walled fracture intersections. The results show that deflection flow occurs in the case of larger Re. Re and roughness exacerbate the deflection flow effect. The magnitude of the deflection flow intensity decreases, then increases, and then decreases again as the intersecting angle increases. It is not the deflection flow effect that determines mixing at fracture intersections, but rather Pe and the streamlines' contact area. As Pe increases and the contact area of the streamlines decreases, the mixing degree decreases. The mixing ratio reflects the partitioning of solutes at the fracture intersections. It is the deflection flow effect that determines the partitioning of solutes at fracture intersections. The mixing ratio decreases as the deflection flow intensity increases. When the deflection flow intensity is greater than zero, the solute flux at the low-concentration outlet is all from diffusion, and when the deflection flow intensity is less than zero, the solute flux at the low-concentration outlet is obtained from both advection and diffusion. This study emphasizes the effects of deflection flow on the mixing and partitioning of solutes in rough-walled fracture intersections, which is important for deepening the understanding of these complex processes.