Mechanism Of Break-up Of Pneumatic Induced Conical Liquid Sheet

Numerical simulations have been performed to study the formation and disintegration of liquid sheets formed by pressure swirl atomizer using volume-of-fluid(VOF)method augmented with adaptive mesh refinement(AMR)techniques.Attention was paid to the interaction between air and liquid in the external flow field of the nozzle and the mechanism of air-induced primary break-up of hollow conical liquid sheet.The phenomena of oscillation,deformation and fragmentation of conical liquid sheet induced by the flow field at the nozzle outlet were observed under various working conditions.Detailed characteristic parameters and break-up mechanism associated with the temporal evolution and primary break-up of the liquid sheets formed by dual-orifice pressure swirl nozzle are explored over a range of fuel pressure drop,Reynolds and Weber numbers.Special attention is paid to the primary break-up pattern,break-up distance and radius,droplet size and droplet size distributions.The changes of the pattern of conical liquid sheet break-up and the characteristic parameters described above are also investigated under the conditions of dual-orifice swirl nozzles with different air flow velocities and single-orifice swirl nozzles with different air flow velocitiesThe results show that with the increase of pressure drop,the break-up distance,break-up radius and uniformity decrease,while the droplet reference diameter barely changes.In particular,when the fuel pressure drop exceeds a threshold,the interior and exterior liquid sheets generated from atomizer will not merge.At this time,the break-up distance and break-up radius will suddenly increase,while uniformity and reference diameter will not be evidently affected.With the increase of air velocity,the break-up radius and reference diameter of the dual-orifice pressure swirl nozzle decrease,while the break-up distance and uniformity almost remain unchanged.With the influence of air flow,the prismatic liquid bulk can be observed within the liquid sheet produced by single-orifice swirl nozzle,which will affect the mode of disintegration.With the increase of air velocity,the breaking distance,breaking radius and uniformity all decrease.In addition,the influence of liquid velocity fluctuation in the dual-orifice pressure swirl nozzle on the atomization has also been studied.The results show that the axial velocity fluctuation and radial velocity fluctuation will reduce the break-up distance and radius,and increase the uniformity and reference diameter.The circumferential rotation fluctuation has little effect on the break-up distance,break-up radius and uniformity,but increases the reference diameter.