Impact and spreading of a rotating droplet on solid surface

The phenomena associated with the impacting liquid droplet on a solid surface are ubiquitously encountered in diverse practical applications for surface cleaning, printing, coating, spray cooling, and so on. In this work, we experimentally investigate the falling behaviors (e.g., influence of rotation speed on inner circulation and its interaction with surface rotation) of a rotating water droplet and their influences on the spreading patterns after the collision with a solid soda lime glass surface. To intentionally control the rotation speed of falling drop, the plate was tilted differently while varying the height. Particle image velocimetry was used to measure the velocity field inside the rotating droplet and the high-speed shadowgraphy was used to visualize the spreading pattern. The results reveal that the flow induced inside the droplet varies from being concentrated at the center to moving towards the surface with increasing angular velocity. Furthermore, the rotating motion of the droplet causes the asymmetric spreading pattern after the impact, which is attributed to the orientation (pre-impact shape) of the droplet.