Numerical study on the influence of fluid properties in constant-voltage electrohydrodynamic pulsating jets

The pulsating jet is a common working mode in electrohydrodynamic printing (EHDP), and this process is highly influenced by operating parameters and material properties. In this paper, we investigated the behavior of pulsating jets in liquids with varying physical properties through numerical simulations. We established an electrohydrodynamic (EHD) solver and employed a charge flux restriction step to ensure a realistic distribution of free charges. Our simulations revealed three different ejection regimes: an oscillating cone (OC), a choked jet (CJ), and a stable cone–jet (SJ). We found that the ejection regime is primarily determined by three dimensionless numbers related to liquid properties: the Ohnesorge number, Q0εr/Q, and Q0/(QRe). Based on these dimensionless numbers, we analyzed the influence of liquid properties on pulsating jets in OC and CJ. In OC, the jet's breakage is mainly attributed to the significant oscillation of the Taylor cone, a phenomenon primarily influenced by viscosity and conductivity. In CJ, the emission of the jet is terminated due to the excessive resistant force in the cone–jet transition region. For liquids with low to medium viscosity, the dominant resistant force is either the polarization force or the viscous force depending on whether εrRe is larger or smaller than 1, respectively. In the cases of high viscosity liquids, the viscous force always plays a major role as the primary resistance. These findings provide deeper insight into the physical mechanisms of pulsating jets.