Experiments and Modeling of the Breakup Mechanisms of an Attenuating Liquid Sheet

We present a combined experimental-numerical study of the primary breakup of a single-phase attenuating liquid sheet emerging from a flat fan nozzle. An experimental setup has been built to produce flat fan liquid sheets/sprays at near industrial conditions, i.e. high pressure and turbulent. The process of sheet disintegration, for a transitional and a turbulent sheet, is visualized using high-speed shadowgraphy. The shadowgrams resolve features of the primary breakup at very fine spatial and temporal resolutions, revealing new information about attenuating liquid sheets. Three breakup mechanisms are identified in the central region of the sheet; two of these, aerodynamic instability and disruption by perforations, are well known. The third mechanism, bag breakup, appears not to have been previously reported in the context of flat fan sprays. Highly resolved Computational Fluid Dynamics (CFD) is employed to model the phenomena of sheet breakup. Features of the attenuating liquid sheet are computed and compared with experimental measurements where strong agreement is found. Breakup mechanisms similar to those observed experimentally are resolved in the CFD simulations, confirming the ability of the simulation methodology to extend studies to scales that are not achievable via laboratory experiments. The mechanisms of holes nucleation and growth are studied, we find that hole nucleation in a turbulent single-phase liquid sheet is due to the growth of local surface disturbance which is initiated by nozzle turbulence.