Linear instability analysis of an electrified coaxial jet

A temporal linear instability analysis of an electrified coaxial jet inside a coaxial electrode is carried out in this paper. The analytic dispersion equation is derived. The characteristic of the temporal instability is investigated and effects of the parameters, including the dimensionless electrostatic force, the dimensionless velocity difference, the density ratio, the inner and the outer diameter ratios, and the Weber numbers, are discussed systematically. The axisymmetric and the helical modes are both considered. Two independent unstable modes, mode 1 and mode 2, are identified. Among all the parameters the dimensionless electrostatic force has remarkable influence on mode 1. It can change mode 1 from the Rayleigh regime to the wind induced regime, and to the atomization regime by increasing the electric-field intensity. Nevertheless, the dimensionless electrostatic force has no apparent effect on mode 2. The behaviors of mode 2 resemble those of a coaxial jet not having electric field. The surface tensions on the inner and the outer interfaces induce instability of the inner and the outer interfaces in the region of long wavelength and suppress the growth rate in the region of short wavelength. (c) 2005 American Institute of Physics.