Study On Deformation And Breakup Of Liquid Jet Under The Action Of Radial Electric Field

Instability is an important research aspect of fluid mechanics,and instability of charged liquid jets also falls within the scope of electrohydrodynamics.To date,there have been many reports on the instability of charged liquid jets.However,few reports on the complex singular instability behavior of charged liquid jets under radial electric field can be found in the literature.In this study,we performed an experimental investigation on the deformation and breakup of radially electrified liquid jets.First,we chose ethanol as an lower viscid experimental fluid,and observed that under a sufficiently strong electric field,droplets in an ethanol jet are stretched in the radial direction and form a singular spike or flat plate structure.Moreover,tens of evenly distributed fine jets are possibly emitted from the periphery of each deformed droplet,i.e.the radial multi-cone-jet structure.Due to Rayleigh instability,these fine jets ultimately break up into droplets whose size is much smaller than the jet radius.Later,to examine the effect of viscosity,we chose four mixtures of ethanol and glycerol with different weight ratios and observed the instability phenomena of their jets.Three different groups,i.e.regular jets(RJ),irregular jets(IRJ)and irregular jets with tip-streaming(IRJS)were identified and the borders between them were fitted in the space of the three main nondimensional parameters,i.e.the Ohnesorge number,the Weber number and the electric Bond number.We found that viscosity suppresses the formation of multi-cone-jet structure to a certain extent and that viscosity may result in the decrease in the number of multi-cone-jet structures.The multi-cone-jet structure observed in the experiment is a transient structure,whose lifetime is below l ms.Nevertheless,the instability in it is rich,and to perform relevant theoretical study or numerical analysis will be a big challenge.We also observed some other complicated phenomena during the evolution of multi-cone-jet structures,for instance,the merging of neighbor cone-jet structures,the coexistence of axisymmetric and non-axisymmetric modes,electrospraying under high conductivity etc.All these phenomena need to be further studied.The open source CFD software Gerris under Linux helps us to study this subject numerically.We attempted to use Gerris to perform direct numerical simulation.Unfortunately,we did not solve the problem of charge diffusion into the ambient medium and did not get any reliable result.But according to other researchers' reports,this problem might be solved.