Investigating the dynamics of droplet spreading on a solid surface using PIV for a wide range of Weber numbers

The investigation of the underlying physical processes involved in the impact of droplets has various practical applications in engineering and science. In this research, the spreading velocities within droplet impingement on a sapphire glass were investigated for a wide range of Weber numbers using particle image velocimetry (PIV), which involves tracking the movement of polymeric fluorescent particles (6 mu m) within the droplet. The experiments were carried out at room temperature, and the droplets had impact velocities ranging from 0.41 to 2.37 m/s, which corresponded to Weber numbers of 5-183. The results showed that the radial velocity was generally linear over a wide range of spreading radius but the velocity at the exterior radial positions became nonlinear over time due to the influence of capillary and viscous forces. This nonlinearity was more pronounced for lower Weber numbers because the viscosity effects in the droplet were more significant compared to the inertia forces. As the Weber number decreases, the spreading and receding of the droplets are completed faster, leading to different trends in the radial velocity profiles.