A one-way coupling approach for simulating in-nozzle flow and spray characteristics of a pressure-swirl atomizer

Abstract

This article proposes a model framework coupling in-nozzle flow and external spray and presents its application to the simulation of a commercial pressure-swirl atomizer, focusing on the transient characteristics of the internal flow and subsequently the impact on the spray characteristics. High-fidelity in-nozzle simulation of the liquid–gas interactions is performed using the volume-of-fluid (VOF) method. Then, a corresponding Lagrangian simulation of sprays is performed where the parcels are injected using the information from the VOF predictions instead of phenomenological models. Both the internal flow and the spray are compared to the experimental data that are available in the literature, and satisfactory agreement is obtained in terms of the in-nozzle velocity, film thickness, and Sauter mean diameter. The effect of the different liquid properties and geometric features on the air–core formation, and consequently, on the spray characteristics have been obtained directly through spray simulation coupled with nozzle flow. As indicated by the Eulerian simulation results, the viscosity plays a key role in the formation of the air core, as the hollow-cone shape can degenerate into a solid cylindrical liquid jet under high viscosity conditions. Additionally, significantly distinct spray characteristics in terms of droplet velocity, mean diameter, and penetration were predicted depending on the formation of air core. Even if there is no stable air core in the nozzle, the spray is still discharged in a swirling motion. As opposed to the converging angle and orifice length, the nozzle diameter has a direct correlation with the formation of air core and spray atomization. This study implies that the in-nozzle flow field, which is usually ignored in fuel spray simulation, has a substantial impact on the spray characteristics and should be taken into account for design optimization by applying the developed one-way coupling approach.