Impingement of a water droplet onto a superhydrophobic rotational surface

This study experimentally examined how a water droplet impacted a superhydrophobic rotational surface. The effects of the surface rotational speed and the droplet impact Weber number on the contact time, rebound behavior, spreading morphology, and wetting area were systematically studied. The results indicated that, at a constant impact Weber number, contact time decreased with increasing rotational speed, while spreading time remained unchanged. This suggested that changes in contact time were primarily governed by the retraction stage. A functional formula for the contact time was established based on the inertial-capillary timescale, and the prediction agreed well with the experimental results. In terms of rebound, increasing the rotational speed reduced the restitution coefficient and weakened the maximum rebound height. The linear dissipation model was used to characterize the rebound height, and the additional dissipation due to rotation was introduced to explain its attenuation law. The spreading and wetting results showed that the surface rotation enhanced the dimensionless angular wetting length. At high impact Weber number, the dimensionless radial wetting length curves under different rotational speeds tended to converge, and the maximum radial spreading was mainly dominated by the normal inertia. Moreover, new correlation formulas for the spreading ratio, dimensionless excess spread area, and maximum wetting area were proposed in this study.