Dynamic behaviors of double droplets undergoing off-center impact on a macro-ridge

This study investigates the dynamic behaviors of vertically aligned double droplets undergoing off-center impact on a macro-ridge situated on a superhydrophobic surface using lattice Boltzmann method simulations. The effects of the dimensionless off-center distance (Δx*), the center-to-center distance between droplets (l*), and the impact Weber number (We) are systematically examined to elucidate their influence on spreading and receding dynamics. The spreading time is independent of Δx*, whereas it increases with l* in the horizontal direction but remains unaffected by variations in the vertical direction. At low and moderate Weber numbers (8 ≤ We < 38), the receding time increases within the range 0 ≤ Δx* < 0.4 but decreases for 0.4 ≤ Δx* ≤ 0.5; at high Weber numbers (38 ≤ We ≤ 58), this trend is reversed. The contact time exhibits a strong dependence on both the off-center distance and the Weber number: it increases monotonically with Δx* at low and moderate Weber numbers, whereas it initially increases and then decreases as Δx* increases at high Weber numbers. These findings enhance the understanding of droplet dynamics on structured superhydrophobic surfaces and provide valuable insights for optimizing surface designs in applications such as anti-icing, spray coating, and self-cleaning technologies.