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The influence of angle patterns of intersecting fractures is crucial for a profound understanding of the flow characteristic of fractured rock masses. This study employs hydraulic and visualization experiments to investigate macroscopic nonlinear flow behavior and local flow field characteristics of a "one inlet two outlet" fracture intersection with varying angle patterns. The angle pattern exerts a significant influence on the morphology of the intersection, leading to enhanced nonlinear flow and altered flow rate distribution. Both the nonlinear coefficient (b) and the ratio of flow rate distribution (ɛ) exhibit a Gaussian distribution pattern with respect to the angle patterns. By observing the intersection morphology and local flow fields under different angle patterns, it was found that the protrusion caused by the inlet and outlet fractures significantly impacts the fluid flow entering the outlet fractures, particularly under high Reynolds number (Re) conditions. Using a machine learning algorithm based on neural networks, the flow rate distribution at the outlet of the intersection fracture under different Re values and angle patterns is predicted. The model demonstrated accurate predictions of the outlet flow rate distribution for intersection fractures under diverse conditions. Additionally, by analyzing the flow velocity and flow characteristics at different positions within the intersection, the relationship between the macroscopic flow rate distribution and the flow field characteristics at the intersection has been clarified. These results will aid in the study of groundwater flow behavior, fluid flow in microfluidic chips, and seepage heat transfer. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the effects of contact rate on fluid flow through rock fractures. Different contact rate fracture models are constituted by changing the relative position of the upper and lower fracture surfaces, which is realized with the three-dimensional scanning technology. The results indicate that the generation of contact area and the increase of contact rate will enhance the nonlinearity of fracture fluid flow, and the influence of inertial force in fluid will be more obvious, under which the regime of fracture fluid flow will turn from linear to nonlinear earlier. The entire pressure field and velocity field in fracture are obviously affected by the contact rate. An obvious pressure dividing line appears near the contact area, and the pressure gradient and velocity increase significantly across the dividing lines. The phenomenon of groove flow exists between the contact areas, and eddy is generated on the back flow area of the contact area. The eddy area increases with the Re, the effective flow aperture is further compressed, and the local velocity increases. In the three-dimensional view, it is discovered that the streamline in the double eddy system is distributed in an "8″ shape, and there is flow exchanges between the two eddies. [ABSTRACT FROM AUTHOR]

• The generation and development of eddy in fracture was observed using PIV. • The relationship between macroscopic nonlinearity and eddies was investigated. • The shrinking of effective aperture and losing of kinetic energy make flow nonlinear. The understanding of nonlinear flow in rough-walled rock fractures is critical for underground engineering and geological sciences. The macroscopic behavior and microfluidic field of flow in rough-walled artificial fracture models was investigated through microscopic visualization of hydraulic experiment. The results indicate that there are three states of flow regime in fracture, namely linear, weak inertial and strong inertial. In linear flow regime, the relationship between pressure drops and flow rate is linear, and all the streamlines in the microfluidic field are parallel. In weak inertial flow regime, pressure drop and flow become nonlinear, and the inertial pressure loss is less than the viscous pressure loss. Moreover, backflow occurs near the tortuous wall in the microfluidic field. In strong inertial flow regime, the inertial pressure loss is greater than viscous pressure loss, and the backflow begins to detach from the wall and eventually develop into a significantly large eddy far away from the wall. However, the flow in the mainstream remains laminar rather than turbulent in this experiment. This result indicates that the main cause of the nonlinearity of flow in fracture is eddies due to the increase of the inertia term and the variation of aperture. The shrinking of effective channel and losing of kinetic energy caused by eddies make fluid flow nonlinear. Moreover, the area and number of eddies depend on the fracture roughness and the Reynolds number. [ABSTRACT FROM AUTHOR]