Fluid dynamics of droplet impact and splitting on superhydrophobic wedges

We report an extensive computational and experimental investigation of droplet impact and subsequent splitting hydrodynamics on superhydrophobic wedges. Using two-dimensional (2D) and three-dimensional (3D) volume-of-fluid (VOF) simulations, supported by high-speed imaging experiments, we predict the impact, spreading, splitting, retraction and daughter droplet lift-off from superhydrophobic wedges. In particular, we examine how the wedge angle ( ϕ ), wedge asymmetry ( ϕ 1 – ϕ 2 ), Weber number ( We ) and normalized Bond number ( Bo * ) influence the post-impact dynamics. We observe that for symmetric wedges, the maximum spread factor ( β ) max of the droplet decreases with an increase in wedge angle ( ϕ ) at a fixed We . At high wedge angles, the sharp steepness of the wedge causes less contact area for the droplet to spread. For the asymmetric wedges, it has been noted that ( β ) max increases with an increase in We owing to the higher inertial forces of the droplet against sliding. Furthermore, ( β) max increases with an increase in Bo * at a fixed We owing to the dominance of the gravitational force over the capillary force of the droplet. It has also been found that at the same Bo * , ( β ) max rises with an increase in We owing to the dominance of inertial forces over capillary forces. We discuss the non-dimensional split volume ( V * ) of daughter droplets during the split-up stage for different symmetric and asymmetric wedge angles. In general, our 2D simulations agree well with the experiments for a major part of the droplet’s lifetime. Further, we have conducted a detailed 3D simulation-based energy-budget analysis to estimate the temporal evolution of the various energy components at different post-impact hydrodynamic regimes.