Experimental and numerical investigation on the deformation and breakup of water droplets in shear airflow

The dynamic behaviors of supercooled large water droplets (SLDs) in airflow involving deformation, breakup, and splash affect the local water collection coefficient, leading to an increase in the complexity of aircraft icing. A parametric study on the influence of deformed water droplets in shear flow is investigated experimentally and numerically. A horizontal refrigerated wind tunnel is used to create the background shear airflow. A high-speed camera records the evolution of cross-stream/streamwise diameters and the breakup process. The level set method is employed to capture the deformation of micrometer-sized supercooled water droplets in continuous airflow. The deformation modes are categorized into five regimes: stabilization, vibration, transition, bag breakup, and bag-stamen breakup. A dimensionless deformation factor L is defined to describe the droplet deformation, which increases with airflow speed, droplet volume, and temperature. Applying the scaling expression Oh4.39We0.85, a normalized acceleration model of water droplets in shear airflow is established. Based on the experimental results, a drag coefficient model for disc-shaped droplets within the transient Reynolds number range of 420–10000 is obtained. As the initial Weber number exceeds 9.5 and the maximum deformation factor exceeds 3.5, the droplet enters the breakup regime. Furthermore, bag-stamen breakup occurs when the initial Weber number exceeds 17.5.