Numerical contact line behavior prediction for droplet-wall impact by the modified Hoffman-function-based dynamic contact angle model

The droplet-wall impact phenomenon is observed in numerous applications such as spray cooling, coatings, wetting, and inkjet printing. To date, there are still unresolved issues related to the effect of wettability and hysteresis on droplet spreading along a wall and rim fingering. This research deals with the effects of dynamic and static contact angles on droplet spreading evolution, as well as with droplet rim fingering characterization. Experiments and direct numerical simulations are performed in a wide range of Weber numbers (We = 1–375). At high We numbers, the droplet rim loses stability and begins to deform, forming fingers. The critical disturbances resulting in the formation of fingers occur in times of around 1 ms, which are significantly smaller than those typical of maximum droplet spreading. Moreover, a certain shape of the droplet meniscus is shown to be necessary for the growth of fingers. When the contact line receding takes place, the contact angle depends only on the initial contact line acceleration. Considering the contact angle hysteresis and its dependence on We ensures a better agreement with experimental data during the droplet advancing-to-receding transition and the receding phase.