Effect of swirl on jet atomization

Abstract

Introduction B ECAUSE of its practical significance, the subject of jet atomization has been given considerable attention in the literature.' However, the number of published investigations on the problem of the effect of swirl on the atomization of a liquid jet has been very limited. The most comprehensive theoretical treatment of the problem is that of Ponstein. More recently, Kang and Lin studied the spatial instability of a swirling liquid jet, including the effect of nonaxisymmetric disturbances in their analysis. Lian and Lin investigated the convective instability of a viscous liquid jet emanating into a swirling in viscid gas. All of the previous studies of the effect of swirl on liquid jet atomization were conducted via the linear theory of hydrodynamic stability. The problem with the linear stability analysis is the assumption that the perturbations are infinitesimally small, since, after a finite interval of time, unstable perturbations will have grown to finite quantities. Because of the limitations of the linear stability theory, alternative methods of analysis have been sought. These include the method of strained coordinates. Direct numerical solution of Navier-Stokes equations in their axisymmetric form was attempted by Shokoohi and Elrod. Bogy used the Cosserat theory developed by Green. A weakly nonlinear instability analysis was advanced by Ibrahim and Lin. Though mathematically or computationally elegant, all of the aforementioned methods suffer inherent complexity. Lee developed a one-dimensional nonlinear direct-simulation technique that proved to be a simple and practical approach to investigate the nonlinear instability of a liquid jet. Lee's direct-simulation approach formed the basis of a comprehensive treatment of the jet instability and atomization presented by Chuech et al. In the present work we shall extend the direct-simulation analysis of Chuech et al. to include the effect of swirl on jet atomization.