Re-touch rebound patterns and contact time for a droplet impacting a superhydrophobic cylinder

Background: Droplet impact on a superhydrophobic cylinder differs from that on a flat surface. After bouncing, once re-touch takes place, the contact time τ_c would increase, which is unfavorable for some applications. The increased τ_c may strongly depend on the Weber number and radius ratio, R*, of cylinder to droplet. 
Methods: The impact is investigated via lattice Boltzmann method simulations. The particular emphasis is placed on re-touch rebound patterns and τ_c. 
Significant findings: Rebound patterns and τ_c both strongly depend on a combined parameter, α=We/R*, characterizing the asymmetry of droplet spreading and retraction. As α increases, upward rebound and stretched breakup take place sequentially for the first bouncing, whereas rebound patterns change as intact re-touch rebound and separate re-touch rebound for the second bouncing. Increasing α enhances the asymmetry, which promotes the first rebound, thereby reducing τ_c regardless of rebound patterns. The enhanced asymmetry also accelerates rebound and thus reduces τ_c in the separate re-touch rebound regime, whereas it hinders rebound, leading to a significantly increased τ_c. The power-law correlations of τ_c vs α are developed for the first and second bouncing. Besides, a method is proposed to suppress or prevent the re-touch, which is proven to effectively reduce τ_c.