Dynamics of double-droplet centered impacting a hydrophobic surface featuring a micro-ridge

Upon impact, the droplets undergo spreading and receding phases, with the total duration of these processes defined as the contact time. In this study, the lattice Boltzmann method (LBM) is employed to investigate the dynamics of a centered double-droplet impact on a micro-ridge on a hydrophobic surface. The influences of the Weber number (We), the contact angle (θ), and the droplet spacing (Δx*) on impact dynamics and contact time are systematically examined. Regarding impact dynamics, We plays a dominant role in governing the spreading behavior, while θ exerts a more significant influence on the receding phase. In contrast, Δx* significantly affects both the spreading and receding stages, ultimately determining whether droplet rebound occurs. With respect to contact time, it is primarily governed by We and θ. At low Weber numbers, the contact time remains nearly constant for θ ≤ 135°, but decreases markedly when 135° < θ ≤ 150° due to the “pancake rebound” phenomenon. At high Weber numbers, a sharp reduction in contact time is observed, particularly at larger contact angles of θ = 130°–150°. In conclusion, the presence of a micro-ridge can substantially reduce contact time, especially under conditions of high Weber numbers and large contact angles. This study provides deeper insights into the complex interfacial dynamics of droplet impact and offers valuable guidance for the design of functional surfaces in applications such as anti-frosting/icing, self-cleaning, and water harvesting.