HIGH-ORDER AZIMUTHAL INSTABILITIES ON A CYLINDRICAL LIQUID JET DRIVENBY TEMPORAL AND SPATIAL PERTURBATIONS

A method has been developed to drive a cylindrical liquid jet unstable for deformations with axial wavelengths shorter than the circumferenc e of the jet and azimuthal mode numbers greater than 0. The benefit of this method is that a cylindrical Liquid jet can be broken into a spr ay with an average diameter smaller than the diameter of the initial j et. The higher-order instabilities were created by establishing initia l conditions for the jet in space and time at the nozzle. An electrome chanical transducer creates the applied temporal initial condition whi ch is a sinusoidally varying velocity perturbation added to the steady velocity of the jet. The amplitude of the velocity perturbation can b e as large as the jet's steady velocity and the energy in the applied velocity perturbation drives the instability. The spatial perturbation is created by placing perturbations in the circumference of the nozzl e. As the velocity perturbation travels on the jet, its leading edge s teepens and the trailing edge broadens in a manner analogous to the st eepening of a pressure pulse in a compressible gas. If the driven velo city perturbation is sufficiently large, a shock or jump forms on the leading edge of the velocity pulse and the jet may break up into highe r-order modes. A theoretical analysis of the breakup process, based on an adaptation of compressible fluid shock theory, is used to derive a fundamental lower bound on the spray's Sauter mean diameter as a func tion of the velocity perturbation amplitude. Techniques for approachin g the theoretical minimum spray diameter by using the higher-order mod es to atomize liquid jets are discussed. (C) 1998 American Institute o f Physics.