A Three-Dimensional Numerical Investigation of Taylor Cone Jets Instabilities Using VOF Method

Abstract

Abstract Taylor cone liquid jets occurs when a conductive liquid is placed on a capillary nozzle and a strong electric field is applied. The electric field causes the surface of the droplet to deform into a conical shape, and a liquid jet is ejected from the tip of the cone. This phenomenon has a wide range of applications, such as in inkjet printing, drug delivery, and electrohydrodynamic propulsion. An understanding of the underlying physics of the Taylor cone jet is essential for optimizing the performance of devices that utilize this phenomenon. Computational fluid dynamics (CFD) has become a powerful tool for studying the Taylor cone jet, and in this paper, we propose the utilization of a full three-dimensional model to study the complete dynamics of the Taylor cone jet. These electrohydrodynamic jets are a method to accomplish the controlled emission of microdroplets, with applications from constructing nanofibers to micro-propulsion. For the numerical computations, we use the interIsoFoam solver on OpenFOAM, which resolves an immiscible two-phase flow, and coupled it with a transport equation for the electric charges as well the simplified version of the Maxwell equations for an electrostatic field. The advection equation of the phase fraction is solved by a geometric Volume-Of-Fluid (VOF). Moreover, the hydrody-namic momentum equation incorporates electrically generated body forces using the Maxwell Stress Tensor (MST). While axisymmetric simulations are computationally less expensive, they fail to capture an important behavior of this type of jet, such as the whipping effect and the tiny droplets emitted during the receding of the jet emission cycle. In contrast, the three-dimensional simulations used in this study offer a more accurate representation of the physics involved in the jet formation process, including the formation of instabilities and the resulting complex jet shapes. As we show in our results the droplets are radially scattered on the target collector due to the formation of the ionic wind, which we also show the three-dimensional structures. The current study begins with the numerical validation of the Taylor cone formation, by comparing the cone shape with the experimental results of the literature. Then simulations were performed for different electric potentials and inlet flow rates, which showed that the stable window is narrowed by the applied electric potential. The results revealed that the instability of the jet is due to the concentration of the electric charges, which led to a breakup of the jet into droplets, in the direction of the electric field. Overall, this study emphasizes the value of using three-dimensional numerical simulations to study Taylor cone jet instabilities because they provide a more accurate depiction of the physics at play and can offer useful information for optimizing Taylor cones jet-using equipment like inkjet printers and electrospray systems.