THE INTERNAL FLOW AND EXIT CONDITIONS OF PRESSURE SWIRL ATOMIZERS

Abstract

A computational fluid dynamics model and experiments are used to obtain information on the internal flow of pressure swirl atomizers and their outlet conditions. At the Reynolds numbers typical of many applications, fully turbulent flow is not expected internally so that a time-stepping laminar-flow solution procedure is used. The computed air-core topology, atomizer discharge coefficient, and spray angle agree well with measurements for several internal geometry shapes. The computed velocity distributions generally agree with published laser Doppler anemometer measurements. In a manner dependent on Reynolds number and internal geometry, the velocity fields differ significantly from those assumed in approximate inviscid analyses of swirl atomizers. The most obvious differences are preferences for the flow through the atomizer to concentrate either near the air core or near the wall, and also the occurrence of secondary motion, particularly Görtler vortices near the swirl chamber wall. The modeling technique is particularly useful for predicting the velocity profiles in the liquid sheet at the atomizer exit. Although atomizer discharge coefficient may not vary greatly for variation of the atomizer convergence geometry, these velocity profiles do vary. Viscous losses in the atomizer, for a given Reynolds number, are related to changes in the internal velocity distribution. Air-core surface waves are noted in the experiments and these waves influence the sheet and its breakup downstream. The secondary motion predicted in the liquid inside the atomizer may be a source of perturbation for these waves.