Atomization of Wall-Bounded Two-Phase Flows (Preprint)

摘要

The current understanding of droplet generation processes from liquid films is reviewed. Films are defined as liquids with one free and one wall-bound surface. In many of the systems where films occur, atomization is an undesirable side-effect of the two-phase flow. The motivation for this study, however, is a process where atomization from the film is the goal--an injector used in a rocket combustion chamber. Because atomization is often unwanted in film configurations, few studies focus on the mechanisms that cause atomization in this set-up. The large body of literature on the atomization of jets and sheets is, therefore, utilized in this review. Similarities and differences between the geometries are discussed when applicable. Generally, the atomization is considered to involve two steps: the creation of a disturbance on the film surface and the breakdown of this disturbance into droplets. Prompt Atomization, where atomization occurs directly at a nozzle exit, is also briefly discussed. Several atomization mechanisms are identified from the literature. Theoretical descriptions are given where available, but, due to limitations in the current understanding and the complexity of the atomization process, these are somewhat incomplete. Consequently, important nondimensional groupings and a selection of empirical correlations are also given to aid in the understanding of film atomization.