Modelling of sprays from high-pressure swirl atomizers

Abstract

Aspects of the modelling and experimental validation of transient sprays injected from high-pressure swirl atomizers are presented. The spray model is based on the Lagrangian particle tracking approach where phenomenological submodels are used in order to resolve the various subgrid scale physical processes. Particular attention is given to the effect of the nozzle flow exit conditions on the atomization process of the injected liquid film. This is addressed by employing a linear instability analysis, describing the formation and growth of waves developing on the surface of the liquid, combined with a film movement model which is active until the film's disintegration into ligaments and droplets. The transient variation of the film thickness and its axial and swirl velocity components required as input to the spray model have been estimated from the solution of the flow inside the pressure swirl atomizer using a two-phase computational fluid dynamics (CFD) model. Model predictions are compared with phase Doppler anemometry measurements of the temporal and spatial variation of the droplet size and velocity as well as high-resolution charge coupled device (CCD) spray images. The results confirm that accurate estimation of the nozzle flow exit conditions plays a dominant role in the prediction of sprays injected from pressure swirl atomizers, while the proposed submodels seem to offer significant improvements on the calculated spray structure.