<p>The stretch of interfacial flows due to the external application of an electric field has considerable importance in several applications. These range from engineering nanofibres to propulsion, the electrified jets bring us an outstanding technique to perform the emission of microdroplets. The present investigation concerns the resolution of interfacial electrohydrodynamic flows from a numerical standpoint using computational fluid dynamics. The reduced form of the Maxwell equations, for an electrostatic field, and a transport equation for the electric charges are coupled to the standard interFoam solvers on OpenFOAM, which resolves an immiscible two-phase flow. &nbsp;A laminar condition is assumed for the flow thus the laminar incompressible Navier-Stokes’s equations are used to compute the hydrodynamic behavior of the flow and, associated to them, electrically induced body forces are incorporated into the hydrodynamic momentum equation. The Maxwell Stress Tensor (MST) describes electrical surface forces acting on the liquid, making it possible to incorporate that effect on the momentum equation. Although many numerical approaches have been proposed to solve two-phase flows, the capability to capture the interface is still in need for improved simulation methods, in particular for cases with &nbsp;sharper interface edges. Recently, a new efficient geometric Volume-Of-Fluid (VOF) method for general meshes, called isoAdvector, was implemented in OpenFOAM, as a substitute for the Multidimensional Universal&nbsp;Limiter&nbsp;for Explicit Solution (MULES). The open literature on the subject presents quantitative benchmarks that demonstrated a significative improvement on the quality with which we can compute sharper interfaces on immiscible two-phase flows (Gamet, L. <i>et al.</i> 2020). Following this approach, we present here an application of that method to the simulation of the breakup of electrified liquids jets. To validate the implementation of the electric field equations, the order of the accuracy of the spatial and time discretization is herein computed. The validation is accomplished with a planar test case that is considered a benchmark test for this class of flows. The test case showed improved accuracy on the resolution of the electric potential and electric field having lesser than 0.1% of difference against the theoretical solution. Another case of validation is the deformation of liquid droplets. This second case presents errors below 1% for small deformations when compared with analytical solutions. This shows a superior accuracy in the simulation of electrified jets by the proposed model, in particular those produced by Taylor cone jets. This type of jets is at the base of the Electrohydrodynamic sprays (EHDS) physics. These latter operate by a potential difference between a conductive liquid, usually on the tip of a needle, and an extractor electrode. When a certain threshold voltage is reached the electric stress at the apex of the liquid surface overcomes the surface tension and a spray of particles is ejected towards a counter electrode. As a final test case we present a simulation for this type of jet. As expected, the increase in complexity results in an increase on the numerical error. Still the numerical model shows that it can deal with many types of electrohydrodynamic flows with remarkable accuracy.</p>

Numerical Simulation of Electrified Liquid Jets Using a Geometrical VoF Method

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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