Numerical investigation of droplet impingement onto hydrophobic and super-hydrophobic solid surfaces. The effect of Weber number and wettability

In this study, a new model for the wetting interaction between a liquid droplet and a solid surface is presented. Based on this model, a force which acts on the contact line is incorporated as a source term in the Navier-Stokes momentum equation. The advantage of the new model in comparison with the widely-used Brackbill’s model is that the contact angle is not inserted as a boundary condition, but is derived by the induced fluid flow and the adhesion physics of the liquid-surface combination. For the interface tracking, the Volume of Fluid (V.O.F) method is used, accompanied by an automatic local grid refinement technique in order to minimize the arithmetic diffusion of volume fraction and thus acquire more representative physical results. The new model is validated against experimental data for low and moderate We numbers both for hydrophilic and superhydrophobic surfaces. Results of the model are also compared against the standard Brackbill’s model for the implementation of the wetting force. The apparent contact angle during droplet spreading and recoiling is plotted in order to gain insight on the dynamic angle temporal evolution during the impingement process