The common structure of multiple instability patterns on free liquid surfaces induced by charge injection

A previously disregarded electrohydrodynamic (EHD) instability pattern at the gas–liquid interface caused by charge injection is elaborately described and identified as the classical EHD instability. The characteristics and evolutionary processes of three classic EHD instability patterns were meticulously described experimentally. A Taylor cone-like conical structure is proposed as the common basis for the formation of all these patterns. A direct numerical model based on coupled hydrodynamic and electrodynamic equations is developed, and the evolution of the free liquid surface from static to classical EHD instability patterns is obtained from numerical simulations. The simulation results match the experiments, providing details that cannot be observed experimentally and proving the similarity between the conical structure and the Taylor cone. The comprehensive experimental observations and efficient numerical models can serve as a valuable inspiration and foundation for various applications related to EHD surface instability.