Electrohydrodynamics (EHD) is a branch of science which deals with the coupling of hydrodynamics and electrostatics. Electrospray is a subset of EHD which is a method of liquid atomization by electrical forces. It has a wide variety of applications such as ink jet printing, generating micro and nanoparticles, surface coating and fuel atomization. In this study, the effect of some effective parameters on the deformation of a perfectly conductive and a leaky dielectric liquid from a capillary which protrudes from the top plate of a parallel-plate capacitor into a surrounding insulating gas is studied numerically. An incompressible fluid suspended to air at nozzle outlet shows different dynamic behaviors in an electric field that depends on its physical properties. The phenomenon of fluid deformation under the application of an electric field, in the absence of a net volume charge is simply caused by the surface stresses. Therefore, an accurate method is required for numerical modeling of the electric driving force at the interface to handle all of the discontinuities involved in the model. For this purpose, in this study the level set method is used along with the ghost fluid method to investigate the responses of two types of fluid in the presence of an electric field. The incompressible Navier-stokes equation has been used for modeling the fluid at nozzle outlet and the surrounding fluid. In addition, to calculate the electric potential in the entire domain, the Poisson equation with discontinuous coefficients has been solved using the ghost-fluid method. To demonstrate the accuracy of the method, the dynamics of water drop formation is carefully simulated. Finally, the results of the simulations a re compared with similar numerical and experimental results. The simulation results indicate the accuracy of the method for modeling of the phenomenon. The behavior of perfect conductive and leaky dielectric fluids is studied in electrospray process. For perfect conductive liquid the effect of electrical field, flow rate and viscosity on the size of produced droplets is investigated. It is observed that by increasing electric field, different modes of electrospray such as dripping, jetting and multi jetting are obtained. Particularly, for leaky dielectric fluids, the effect of electrical field, electrical conductivity and electrical permittivity is simulated. In leaky dielectric model, presence of the surface charges leads to produce electrical tangential forces which do not exists in the perfect conductive model. Surface charges and tangential forces create some rotational flows in both fluids and caused the fluid to deform in oblate and prolate shape. In oblate deformation, fluid at nozzle outlet moves toward the high potential electrode (upper electrode) and flows upward. In prolate shape, fluid moves downward and hence jet is produced. Also by enhancing the relative permittivity the amount of surface charges increase and tip streaming deformation is occurred which is the best mode for producing very fine droplets in electrospraying process. Key Words Electrospray, Electrohyrdodynamic, Two phase flows, Level set, Ghost fluid method
