Computational study of electrohydrodynamic regimes on planar films

Two-phase flow can be affected under sufficiently strong electric fields, giving rise to various electrohydrodynamic (EHD) regimes. Among these, the formation of Taylor cones at curved (meniscus) interfaces is one of the most prominent and well-studied phenomena. However, EHD regimes emerging from planar interfaces remain less explored, particularly in liquid-liquid systems, where interfacial deformations become significantly more complex. In these systems, cone structures form along dimple rims, and Rayleigh-Taylor instabilities occur under specific conditions. This work presents a numerical investigation of the diverse structures formed at planar liquid-liquid interfaces under varying conditions. Numerical results reveal that viscous forces initially dominate the interface deformation; however, as the Taylor cone elongates, inertial forces become significant, indicating that EHD shear stress alone cannot deform the liquid film interface. Instead, the normal EHD force is primarily responsible for the observed deformation. Moreover, this study revealed that onset voltage and conductivity ratio are critical factors influencing interfacial deformation. Higher electric fields accelerate the development of Rayleigh-Taylor instabilities, leading to more pronounced surface perturbations. Conversely, elevated conductivity in the suspending medium facilitates the formation of dimples at the interface. These findings shed light on the intricate interplay between electric fields, fluid properties, and interfacial dynamics, contributing to a deeper understanding of EHD-flow behaviors at planar interfaces.