Electric field-induced droplet deformation and breakup in three-dimensional oscillatory shear flow

This study presents a three-dimensional numerical investigation into the deformation and breakup behavior of a single leaky dielectric droplet in an oscillatory confined shear flow under a uniform electric field. A coupled lattice Boltzmann model incorporating the conservative Allen–Cahn phase-field method and the leaky dielectric framework is adopted to simulate the complex electrohydrodynamic (EHD) interactions. Model validation is performed through benchmark comparisons against theoretical predictions and experimental data for droplet deformation in both shear flow and uniform electric fields. The effects of electric field strength, shear frequency, hydrodynamic capillary number (Ca), and electric capillary number (CaE) are systematically explored. Results show that increasing CaE significantly enhances interfacial Maxwell stresses, promoting earlier and more intense droplet breakup. Longer shear periods allow greater droplet elongation within each cycle, increasing the likelihood of breakup. A parametric phase diagram is constructed to classify four distinct breakup modes based on droplet count. Notably, in high CaE and low Ca regimes, irreversible breakup is observed where daughter droplets remain permanently separated despite oscillatory flow reversals. Force and energy analyses reveal that electric field-induced elongation and anisotropic alignment play a critical role in maintaining this non-coalescent state. These findings offer new insights into the control of droplet morphology and fragmentation in microfluidic EHD systems.