Rebound dynamics of two droplets asymmetrically impacting single-ridge superhydrophobic surfaces

On a single-ridge superhydrophobic surface, the rebound dynamics of double droplet impacts is investigated via lattice Boltzmann method (LBM) simulations, where one droplet is on the left of macro-ridges, whereas the other droplet being on the top of macro-ridges, leading to the asymmetrical impact of double droplets. The simulation results show that under different impact conditions of various Weber numbers, that is, at low, moderate and high Weber numbers, the rebound regime of double droplet impacts always consists of the complete-coalescence-rebound (CCR), partial-coalescence-rebound (PCR) and coalescence-split-rebound (CSR) regimes. Under these three rebound regimes, the contact time of double droplet impacts is always reduced by the increased We, as the center-to-center distances in the horizontal and vertical directions, L_x and L_z, are constant. At constant L_x and We, the contact time of double droplet impacts on single-ridge superhydrophobic surfaces is increased by the increased L_z because of the earlier formation of liquid bridges at larger L_z. But under different impact conditions of various center-to-center distances in the horizontal direction, that is, at the increased L_x, the rebound regime of double droplet impacts is not always composed of the CCR, PCR and CSR regimes at low, moderate and high Weber numbers. At constant We and L_z, both coalescence strength and rebound regime are significantly affected by the increased L_x for double droplet impacts. So that the contact time of double droplet impacts on singe-ridge superhydrophobic surfaces depends on the center-to-center distance in the horizontal direction, that is, in the x- direction. © 2023 Elsevier B.V.