The internal flow behaviors during Taylor cone formation of pulsating electrohydrodynamic jet printing

The toroidal vortex inside the Taylor cone is one of the most interesting features in electrohydrodynamic (EHD) jet printing. However, due to the considerable difficulty in capturing the microscopic internal fluid flow from the experiment, many aspects of the printing process are still not fully understood. Here, we present a numerical study on the Taylor cone formation process of pulsating EHD jet printing under the variations of several key operational parameters and liquid properties, namely, electric voltage, nozzle height, liquid surface tension coefficient, and liquid dynamic viscosity. In addition to the electrohydrodynamic motion of the liquid–gas interface, we focus our attention to the time evolution of the liquid flow and vortex inside the Taylor cone. The intensity of the vortex is evaluated by analyzing the absolute value of the swirling strength throughout the formation process. By virtue of examining the electric field distribution, interface charge density, velocity field, and the absolute value of the swirling strength from the numerical data, we elucidate the influences of the aforementioned parameters on Taylor cone formation and internal flow behaviors. Eventually, a scaling law of λ2max∝Boe/Ca2 between the maximum absolute value of the swirling strength and the dimensionless variables electric bond number Boe and capillary number Ca is proposed, which applies to all the parameters investigated in this work.