Droplet impingement on nano-textured superhydrophobic surface: Experimental and numerical study

The impact characteristics of liquid droplet on the nano-textured superhydrophobic surface have been investigated experimentally and numerically to understand the underlying mechanism and select appropriate models to describe them. The evolution of impact process with droplet impact velocity varied form 0.11-3.9m/s (or Weber number ranging from 0.3 to 421.4) was recorded and analyzed. Besides, a conservative level set method coupled with dynamic contact angle models was developed to track the phase interface and made a comparison with the experiment. During the spreading and receding phases, the numerical simulation results showed good agreement with the experiment. The impact of droplet satisfied the energy conservation between kinetic and surface energy, and the maximum spreading factor (beta max) can be well correlated by a scaling law of beta max similar to We(0.52). Both of the contact time and non-dimensional contact time of bouncing droplets were independent of Weber number in the range of 1.5 to 121. The predicted non-dimensional contact times were in good agreement with the reference value of 2.6 +/- 0.1 at low and medium Weber numbers. The dynamic contact angle models derived from the hydrodynamic theory and molecular-kinetic theory, respectively, can mainly apply to the advancing and receding phases of droplet impact on nano-textured superhydrophobic surfaces.