PARAMETRIC-INSTABILITY OF DIELECTRIC, SLIGHTLY VISCOUS-LIQUID JETS UNDER AC ELECTRIC-FIELDS

The ac electric fields longitudinally tangential to a dielectric liqui d column are able to excite capillary waves on the cylindrical surface . The phenomenon is theoretically predicted using a Lagrangian formula tion of the dynamics of small amplitude perturbations of the free surf ace. As in the de case, dielectric forces tend to stabilize those pert urbations affected by the capillary instability, but if the field is p eriodic parametric resonance takes place for perturbations of shorter wavelength, otherwise stable with de fields. A detailed description of the stability spectrum is included and the role of field intensity an d frequency in the parametric resonance phenomenon is discussed. Non a xisymmetric modes are also excited but they are always dominated by th e axisymmetric one. The effect of a small viscosity is to diminish or even suppress unstable regions. The field necessary to observe paramet ric resonance is calculated. (C) 1997 American Institute of Physics.