Characterization of spray atomization for liquid jets in swirling crossflows

Since the modern low-emission aircraft engine combustors have widely adopted jet-in-swirl-flow injector, it is important to understand the underground physics of the interaction between liquid and air during the liquid injecting the swirling airflow. The present study investigates the swirling flow and spray atomization characteristics of a jet-in-swirl-flow injector. Various optical diagnostics, including particle image velocimetry, shadowgraph, and laser particle size analyzer were employed to provide detailed flow field, liquid jet breakup process, and spray droplet size information. The jet-in-swirl-flow injectors with swirl numbers (0.55 < SN < 1.3) were investigated over relative air pressure drops ranging from 0.5 to 5% and the liquid jet exit velocities ranging from 0.5 to 11 m/s. The results showed that the swirl number altered the positions where the maximum Weber number (We) and the air to liquid momentum ratio (q) occurred within the flow channel by changing the flow velocity distribution. As a result, the spray angle, Sauter mean diameter (SMD), and breakup length were modified by the swirl number. We also found that, under the lower relative air pressure drop conditions, there was an optimal liquid injection velocity that resulted in a smaller SMD for the liquid atomization, while this optimal liquid inject velocity was not shown in the higher relative air pressure drop conditions. The present study provides the mechanism of how the swirling flow breakup the liquid jet, which, to the best of our knowledge, has not been thoroughly discussed before.