关键词: 旋流, 油水分离, 油滴, 粒子图像测速, 变形特性

Abstract: Cyclonic separation technology is widely employed in oilfield produced water treatment. The kinematic behavior and morphological evolution of discrete-phase media in swirling flow fields provide a critical theoretical basis for guiding the design and parameter optimization of separation equipment. To further elucidate the cyclonic separation mechanisms of oil-water two-phase media and characterize the motion and deformation patterns of oil droplets within three-dimensional (3D) swirling flow fields, this study adopts a combined approach of numerical simulation and particle image velocimetry (PIV) experiments, while focusing on a 3D swirling flow field generated by a dual-tangential inlet configuration; the transport behavior and deformation characteristics of discrete oil droplets are investigated under varying droplet diameters, viscosity ratios, and inlet Reynolds numbers. Results indicate that the constructed 3D swirling flow field exhibits an overall centrosymmetric distribution, within which moving oil droplets undergo processes such as tensile deformation and shear fragmentation while experiencing centripetal migration. During the tensile deformation stage, oil droplets exhibit typical ellipsoidal, rod-shaped, arched, and spiral morphologies. Notably, droplet fragmentation occurs predominantly during the spiraling stage within the axial region of the flow field. As oil droplet diameter increases from 1 mm to 6 mm, the tangential offset angle relative to the axis of the flow field decreases, while the susceptibility to fragmentation enhances. Increased droplet diameter elevates deformation magnitude, fragmentation degree, and mean particle size, consequently reducing the droplet separation time from 1.19 s to 0.58 s. The viscosity ratio exerts a significant effect on oil droplet migration:at low viscosity ratios, droplets migrate toward the axis more readily; conversely, at high viscosity ratios, radial migration capacity is weakened, potentially leading to droplet-wall impingement and adhesion. As the inlet Reynolds number increases from 2×10³ to 1×10⁴, the tangential offset angle of oil droplets relative to the flow field axis increases, accompanied by an enhanced susceptibility to fragmentation. Simultaneously, the deformation magnitude, fragmentation degree, and mean particle size all exhibit upward trends, while the oil droplet separation time is reduced from 2.304 s to 0.342 s. Furthermore, results demonstrate that with increasing inlet Reynolds number, the critical Weber number for droplet breakup increases, while the critical breakup diameter decreases.

Key words: swirling flows, oil-water separation, oil droplet, particle image velocimetry, deformation characteristics