NUMERICAL STUDY ON THE EFFECTS OF DUAL-LAYER LIQUID SHEETS MERGING ON PRIMARY BREAKUP IN DUAL-ORIFICE NOZZLES

Primary breakup during atomization is governed by complex mechanisms and is not well understood. Detailed numerical simulations using the volume-of-fluid method augmented with adaptive mesh refinement techniques were performed to study the formation and disintegration of liquid sheets produced from a dual-orifice pressure-swirl atomizer. The calculated atomization characteristics agree with the experimental results given a maximum relative error for the spray cone angle of 4.9% and maximum relative error for the Sauter mean diameter of 7.4%. For the five considered cases, changes in the pressure drop over a certain range do not affect the final spray angle size, but larger pressure drops will cause the liquid sheet to open faster while delaying the merger of the liquid sheets. The perturbation wave that causes the primary breakup of the dual-layer liquid sheets consists of two parts: the initial perturbation wave and the perturbation wave originating from the merger of the dual-layer liquid sheets, which dominates their primary breakup but whose generation is delayed by an increased pressure drop. The axial position when the disturbance wave first grows to its maximum amplitude matches well with the liquid sheet breakup length with a maximum error of 11.9%. Research on the merger of liquid sheets helps to further study the mechanisms of dual-layer liquid sheet primary breakup and guide the understanding of atomization in dual-orifice pressure-swirl atomizers.