Understanding the impact dynamics of droplets on superhydrophobic surface

The dynamics of droplets impacting superhydrophobic surfaces is investigated using experiments and numerical simulations. The superhydrophobic surface is fabricated by growing the carbon nanotube forest on stainless steel mesh in order to perform experiments. To numerically model the surface, Kistler dynamic contact angle model is used. Depending on different physical properties such as drop Weber number, the inclination of the surface and Ohnesorge number, the impact outcomes are categorized into symmetric bouncing, asymmetric bouncing, breakup, and tail impingement. It is observed that with the increase in the inclination angle of the surface, the contact time of droplets on the surface decreases drastically. The energy budget of impacting drops is analyzed for the entire evolution cycle to delineate the process of drop deformation and its bouncing. It is observed that the droplets bouncing off the inclined surface carried more kinetic energy compared to those of their counterparts on horizontal surfaces. To address the bouncing phenomena, co-efficient of restitution of the drop is also explored. The inclination of the substrate is found to increase the co-efficient of restitution of the drop, which is directly related to the energy budget of the bouncing drop. Furthermore, the force exerted by a drop on such surfaces is also analyzed, showing two peaks, making superhydrophobic surfaces more prone to damage in comparison to hydrophilic surfaces, which showed only a single peak. It is observed that the magnitudes of the peak forces are smaller for oblique impact as compared to horizontal impact.