Droplet impact on a heterogeneous wettability wall: a lattice Boltzmann method study

Heterogeneous wettability surfaces can passively direct the motion of impacting droplets without external actuation. However, the mechanisms governing droplet impact across a single planar wettability boundary remain insufficiently understood, particularly when the lamella undergoes perforation and rupture. In this study, the non-orthogonal multiple-relaxation-time lattice Boltzmann method is used to examine the effects of the contact angle theta Subscript upper R θ R $\theta _R$ , Weber number italic We We $\textit{We}$ and dimensionless impact deviation upper D D $D$ . Increasing theta Subscript upper R θ R $\theta _R$ suppresses spreading and advances recoil. The kinetic energy valley time decreases approximately exponentially, whereas the minimum kinetic energy increases nearly linearly. The recoil-stage kinetic energy peak generally increases with theta Subscript upper R θ R $\theta _R$ but drops markedly at theta Subscript upper R Baseline equals 170 Superscript ring θ R = 170 ∘ $\theta _R=170^\circ$ , where lamella perforation disrupts coherent retraction. Increasing italic We We $\textit{We}$ raises the peak effective surface energy, vorticity and wetted area, yet reduces the normalised recoil-stage kinetic energy peak. Perforation and fragmentation redistribute energy into local deformation and viscous dissipation, thereby weakening coherent recoil and lateral migration. Shifting the impact position towards the less-wetting region suppresses spreading but enhances recoil. The recoil-stage vorticity is largest at upper D equals 0