Dynamics of water droplet on a flat plate with airflow*

In this study, water droplet removal on the plates with different wettability is experimentally investigated in a wind tunnel. The droplets (5-20 μl) are placed on PET (hydrophilic) and PTFE (hydrophobic) plates, over which the air flows with different flow speed (up to 20 m/s) and acceleration (3.3-8 m/s²), and their dynamics are recorded with high-speed cameras. It is found that the droplets show different behaviors depending on the distance from the edge of the plate, droplet volume, flow acceleration, and plate wettability. In most cases, the oscillation of the droplet begins at the low velocity regime, and then droplet shedding occurs to the downstream direction with a specific shape at higher air velocity. In some cases, however, e.g., droplet placed very near the leading edge of plate, the droplet tends to move upstream or it is trapped at a specific position while oscillating, and satellite drops are separated and shed to downstream from the original one. This phenomenon is closely related to the boundary layer developments over the plate, and we would discuss the relation between the droplet dynamics and the flow over and around the plate and droplet.