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Wake Dynamics During Aerodynamic Fragmentation of Liquid Drops

Wake Dynamics During Aerodynamic Fragmentation of Liquid Drops

Deutscher Luft- und Raumfahrtkongress, Berlin, September 2012




An experimental investigation to resolve the interaction between a liquid droplet and its surrounding air flow field is discussed. Ethanol droplets are injected into an air flow field, resulting in aerodynamic forces which cause deformation and fragmentation of the droplet. This process is sometimes referred to as secondary atomization. Some typical applications are: pharmaceutical sprays, diesel injectors and air assisted fuelatomizers in gas-turbines. In this investigation two conditions are considered: one which leads to breakup rith bag-type morphology and one in the sheet-thinning regime. The morphology of the atomizing droplet is acquired with High-Speed Shadowgraphy (HSS). From the shadowgraph pictures, the droplet average trajectory, velocity as well as acceleration and spatial extent is obtained. Particle Image Velocimetry (PIV) techniques are used to record 2000 realizations of the gas-phase flow at multiple locations along the drop trajectories. The resulting ensemble average velocity fields reveal vortical wake structures and regions of persistent backflow. These results provide new insight into the physics of secondary atomization and will be useful for the validation of numerical simulations.