Impact of a shear-thinning droplet on a superhydrophobic cylindrical pillar

Droplet impact dynamics on pillared surfaces are critical for applications in inkjet printing, 3D printing, heat transfer, and surface engineering. This study numerically investigates the dynamic behavior of a shear-thinning droplet impacted on a cylindrical pillar of different diameters for impact Weber numbers ranging from 25 to 100. The droplet exhibits bottom rebound on a flat surface. However, the impact of a droplet on a vertical cylindrical pillar led to its splitting into two portions: a satellite droplet and a remaining volume that either slides along the surface of the pillar or breaks into multiple secondary droplets, depending on the impact conditions. The satellite droplet shows a bottom rebound on the top surface of the pillar, and its size has increased with an increase in pillar to droplet diameter ratio (dp/do). The impact force of the droplet on the pillar shows the highest value near the impact point, and then diminishes for pillared substrates and shows a second peak on a flat substrate. The magnitude of peak force has increased with an increase in dp/do and is highest in the absence of a pillar. The energy budget of the droplet reveals that the rate of dissipation of its initial energy is highest for the flat surface, and the presence of a pillar has slowed the rate of dissipation of energy.