Morphology and transport dynamics of droplets through a confining orifice: A numerical study using the lattice Boltzmann method

The passage of droplets through narrow constrictions is a critical phenomenon in enhanced oil recovery (EOR) and geological carbon dioxide storage. This study employs a two-dimensional lattice Boltzmann method coupled with the Cahn–Hilliard phase-field equation to numerically investigate the dynamic behaviors of a droplet passing through a confining orifice-throat structure. The study systematically examines the effects of the Weber number (We), the pore-to-droplet diameter ratio (Rr), and surface wettability on droplet deformation and transport. Under neutral wetting conditions, three distinct flow regimes are identified: complete entrapment, partial passage, and complete passage. Detailed analysis reveals various capture modes, including fore capture, rear capture, and splitting instability, as well as breakup mechanisms driven by inertial stretching. Quantitative analysis demonstrates that the critical Weber number (Wec) for droplet capture exhibits three distinct stages relative to Rr, highlighting the shifting dominance between inertial and capillary forces. Furthermore, the droplet penetration ratio shows a non-monotonic “V-shaped” dependence on the Weber number for certain droplet sizes. When wettability is considered, the interaction becomes more complex; a phase diagram mapping seven dynamic regimes is established. Notably, simulations reveal that high contact angles combined with high Weber numbers can lead to a unique regime where droplets pass the throat but become trapped in downstream recirculation zones. These findings provide theoretical insight into phase distribution and displacement efficiency in porous media.