Characteristics of Air Flow Over a Sessile Droplet at the Verge of Shedding

A Particle Image Velocimetry (PIV) study on the air flow over a sessile water droplet exposed to a boundary layer flow was done in a wind tunnel. Reynolds number based on free stream velocity and the height of the droplet was 600<Re1000. The effects of the substrate wettability (PMMA, PEMA, PS, and Teflon) and droplet size (10-30 l) on flow characteristics in the plane that bisects the droplet streamwise were studied. A PIV experimental setup -including the closed wind tunnel- was designed, fabricated and set up. The flow structure was seen to be similar for all cases regardless of the surface wettability and drop size. The order of c_f and c_p is the same for all cases. For all cases, the instantaneous drag coefficient is similar to their average values. The effect of oscillation in flow structure and turbulence statistics is equivalent to the effect of surface roughness for 3D-printed solid mockups of the droplets (for the velocity ramp-up set in the study).