| The complicate internal structure and the multi-scale characteristic of the fractured-vuggyporous media improve the difficulty in accurately describing and simulating the fluid flow inthe media, which is significant and challenging. The main problem lies in the coexistence ofthe seepage in the porous medium and the free flow in the open space, i.e., the free/porouscoupling flow. Firstly, we carried out experimental research on the free/porous coupling flow.The analytical solution acquired using the Beavers and Joseph boundary condition can well fitthe experiment data measured using LDA; at the free/porous interface, there exists the slipvelocity, which is much larger than the Darcy velocity. The two-phase coupling flowexperiment also confirmed the existence of the fluid exchange and the complicate fluid flowand distribution situations at the free/porous interface. Then we studied the single-phasefree/porous coupling flow in three scales: the microscopic scale, the mesoscopic scale and themacroscopic scale. Owing to the inertial effect, there is fluid exchange at the free/porousinterface; because the slip velocity is very sensitive to the interface position and thedetermination of the slip coefficient needs the knowledge of the exact interfacial location; theslip coefficient depends on the permeability (internal structure) and the surface structureinstead of the porosity. It is necessary to specifically model the macroscopic parameters alongthe noticeable transition region and it is the description of the permeability variation in thetransition layer that causes the discrepancy in the velocity profile. Next, we conduted the directnumerical simulation on the oil-water two-phase coupling flow and found that the water-waterinterface, water-oil interface and the oil-oil interface may coexist at the free/porous interface.Due to the large value of the permeability of the staggered cylindrical arrangement, the drivingprocess in this structure would be more stable and uniform. Base on consistentphenomenological explanations and under the premise of mechanical equilibrium, weanalyzed the coupling concept for two-phase coupling flow. The problem of the dispersedparticulate-fluid two phase flow in a channel with permeable walls under the effect of theBeavers and Joseph slip boundary condition is concerned at the macroscopic scale. It is shownthat the sinusoidal channel, accompanied by a higher friction factor, has higher pressure drop than that of the parallel-plate channel under fully developed flow conditions due to thewall-induced curvature effect. The slip boundary condition and the volume fraction of theparticle phase would notably influence the fluid flow. |
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