Oscillation characteristics of low Weber number impinging micro-droplets

Oscillation characteristics of micro-droplets, when in partial contact with a dry and homogeneous substrate, are investigated using a volume of fluid (VOF) numerical method. Water is used as a fluid in both numerical and experimental studies. The velocity vectors are plotted along the phase boundary line, i.e. along the droplet interface, to show how the contact angle impacts the droplet shape during the entire oscillation process. It has been predicted that when the surface/liquid combination is of larger contact angle, the water droplet tends to spread partially as the contact velocity dynamics dominate over inertia, thereby restricting the change in shape, i.e. resulting in lesser mode of oscillations. However, all droplets that are considered here show a damped harmonic motion with the amplitude gradually decreasing to zero. Particularly, at a lower Weber number impact, it is predicted that both the height and spreading dynamics exhibit a unique decaying function for each droplet size considered.