EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION OF THE EFFECTS OF CAVITATION REGIME ON SPRAY PARAMETERS OF STEPPED PLAIN ORIFICE ATOMIZERS

Abstract

An experimental/computational study is presented to investigate the global spray characteristics of a stepped plain orifice atomizer composed of a small orifice upstream, a large orifice downstream coaxial with the small orifice, and a sharp transition between the small and large orifices. We explore a series of five different stepped geometries that gives rise to different two-phase flow patterns within the injector that translate to differences in spray angle, discharge coefficient, and droplet statistics. It was discovered that the stepped geometry operates in four distinct regimes that are controlled by the two-phase flow regime at the exit plane of the injector. Unlike conventional injectors, spray angle, discharge coefficient, and droplet size vary dramatically across the operating regimes for these injectors. An axisymmetric computational model was exercised across relevant operating conditions, and calculated turbulence quantities were compared to measured spray angles and droplet sizes across all operating regimes. It was found that the spray angle is strongly proportional to the turbulence intensity at the exit plane of the injector, and the average droplet size is strongly inversely proportional to the turbulent kinetic energy at the exit plane of the injector.