Lattice Boltzmann simulation of droplet impacting on the superhydrophobic surface with a suspended octagonal prism

Abstract

The contact time of a droplet impacting on a superhydrophobic substrate is demonstrated to be reduced via adding a macro-wire or a rectangular ridge, which is achieved by triggering the asymmetric feature during the spreading/retraction processes. Here, we use the lattice Boltzmann method to study the droplet impacting dynamics on a superhydrophobic surface with a suspended octagonal prism. We reveal that the asymmetric retraction of the impacting droplet strongly depends on the combined effect of Weber number and the suspended height. The falling droplet is split into two sub-droplets and shows growing asymmetry with increasing Weber number on the surface, during which the contact time reduces because the asymmetry results in an uncompleted retraction process only perpendicular to the prism of the sub-droplets. The study also shows that the prism suspension height remarkably affects the droplet dynamic behavior. A non-bouncing region is found at h/D0 (h is the prism height, and D0 is the initial diameter of droplet) in the range of 0.3–0.8 where the split droplets merge again and wrap the prism so that the attenuation in upward and transverse velocity is unable to tear up the liquid bridge beneath the prism. The prism height larger than ∼0.75 is shown to have limited influence on the contact time variation. Our study shows that at high We = 103.3, the ratio of prism height to the droplet diameter h/D0 is 0.2 or larger than 0.75 and the contact time significantly reduces by ∼59% compared to the flat surface.