Contact Time of a Droplet Off-Centered Impacting a Superhydrophobic Cylinder

Extensive research has shown that a superhydrophobic cylindrical substrate could lead to a noncircumferential symmetry of an impacting droplet, reducing the contact time accordingly. It is of practical significance in applications, such as anti-icing, anticorrosion, and antifogging. However, few accounts have adequately addressed the off-centered impact of the droplet, despite it being more common in practice. This work investigates the dynamic behavior of a droplet off-centered impacting a superhydrophobic cylinder via the lattice Boltzmann method. The effect of the off-centered distance is primarily discussed for droplets taking various Weber numbers and cylinder sizes. The results show that the imposition of an off-center distance can further disrupt the droplet symmetry during the impact. As the off-center distance increases, the droplet movement is gradually tilted toward the offset side until it tangentially passes the cylinder side, resulting in a direct dripping mode. The dynamic features, focusing mainly on maximum spreading in the axial direction and contact time, are specifically explored. A quantitative model of the maximum spreading factor is proposed based on the equivalent transformation from the off-center impact into oblique hitting, considering the full range of off-centered distance. A preliminary contact time model is established for droplet off-centered impacting superhydrophobic cylinders by substituting the maximum spreading and the effective velocity of the liquid moving. This work aims to make an original contribution to the fundamental knowledge of droplet impact and could be of value for related applications.