Interaction between droplet and airflow during aerodynamic breakup of droplet

The process of droplet deformation and fragmentation into finer fragments in an airflow involves complex aerodynamic interaction between the droplet and the surrounding air. Previous experimental studies on the aerodynamic breakup of droplets mostly measured the flow field and captured the droplet morphology separately, leaving the spatiotemporal correlation between droplet deformation and flow field evolution still unclear. In this study, the interaction between the droplet and the surrounding airflow is investigated by measuring the rapidly evolving droplet morphology and the flow field around the droplet simultaneously with laser-induced fluorescence and high-speed particle image velocimetry. By combining a continuous laser with a high-speed camera, the temporal resolution of flow field measurement is significantly enhanced, enabling the time-resolved, quantitative measurement of the flow field around rapidly deforming droplets. The temporal evolutions of the flow field are analyzed across different breakup modes. The results reveal that the mode transitions are featured by changes in backflow intensity, wake vortex size, and vortex evolution time. The frequency of vortex shedding in the droplet wake is analyzed, and two dominant frequencies are identified based on the initial diameter and the flattened diameter of the droplet. Finally, the flow field in the shear-stripping mode suggests that the stripping of liquid from the droplet periphery can be induced by the rapid shedding of local vortices.