Experimental study of fluid-particle flow characteristics in a rough fracture

Rough fractures can significantly affect particle-fluid flow in a stratum, but particle transport characteristics are still not fully understood. This paper proposes a novel method to combine three-dimensional laser scanning and casting technology for making rough transparent panels based on rock fractures. A large model with two-sided rough surfaces is constructed, and the inner sizes are 2 m x 0.3 m x 3 mm. The particle image velocimetry method is used to analyze slurry flow. The experimental results show that distorted irregular streamlines, vortexes, sand settling, and dispersion are primary characteristics of particles transported by low-viscosity fluid. Shear flow can induce prominent vortexes around the inlet and the fracture top. With the increase in fluid viscosity, sand-fluid flow along preferential flow paths, and particle clusters are easily formed due to sand aggregation in tortuous pathways. Increasing the fluid velocity avoids particles plugging around the inlet, and there is a threshold velocity. The vortex number has a negative relationship with fluid viscosity. With the dune accumulation, the vorticity intensity is significantly increased, and discrete vortexes are connected into a large vorticity region, which collapses sand aggregation along the whole fracture. Increasing fluid velocity and viscosity and reducing particle diameter are more effective ways to improve particle distribution than increasing particle concentration. The combination of multiple factors can enhance the more even distribution of particles in rough fractures. The investigation provides a fundamental understanding of slurry flow behaviors in fractured media and is a valuable reference for the simulation of particle-fluid flow.