Water droplet shedding in a turbulent boundary layer

Removing liquid drops from surfaces is ubiquitous to everyday processes. It is fundamental to drying your vehicle at a car wash, de-icing an airplane, drying your hands, and to a multitude of industrial applications.

Developing a better understanding of the physical mechanisms involved in drop shedding can help to make many industrial processes more energy efficient, reduce process time, and reduce noise. To this end, we are conducting a study of water drops shedding off a smooth surface in a turbulent boundary layer. High speed images of the shedding drops are recorded along with synchronized measurements of the free stream air velocity. These measurements are used to identify at what velocities the droplets begin to shed. The effects of flow and drop characteristics on the critical velocities are of interest. Video 10 is a recording of a drop as it responds to a progressively increased incoming flow velocity. Initially, the drop is static and assumes the shape of a spherical cap. As the air velocity increases, the drop begins to oscillate due to unsteady fluid forcing in turbulent boundary layer. The drop then begins to slide along the surface in a start-stop pattern while continuing to oscillate. At sufficient wind speed, the drop ceases to oscillate and moves nearly continuously along the plate.

 

Video 10. Water drop shedding in turbulent boundary layer. Drop volume = 35μL, played at 1/10th speed.