Hidrofobik hareketli duvarlara damlacık çarpma simülasyonları

Numerical simulations of water drop impact onto hydrophobic surfaces (Wax, Teflon) are carried out through usage of Eulerian multiphase model. Volume of fluid (VOF) model is used to capture the deformation of the water drop interface. Importance of contact angle and viscous flow modeling are shown by taking static contact angle (SCA)/dynamic contact angle (DCA) approaches and laminar/turbulent flow regimes respectively. Two and three dimensional simulations are conducted. Validation of the numerical scheme is done successfully by comparing the results of the simulation of impact to static walls with those from the experiments of R. Rioboo, M. Marengo & C. Tropea, Experiments in Fluids, 33, 112(2002). Internal flow of the liquid during the process of impact to static wall is analyzed, particularly for the case of partial rebound. It is observed that the flow structures in the droplet next to the contact line can prevent total rebound. For the moving wall case, partial rebound, deposition and split deposition phenomena are observed as was documented by the experimental study of R. H. Chen, H. W. Wang, Experiments in Fluids, 39, 754(2005). As expected, at high tangential We numbers, the tangential motion of the wall stretches the droplet in the motion direction and causes splitting. In split deposition case, the role of bubble entrainment in rupturing and splitting was mentioned. Energy profiles in time are plotted for each case to provide insight on the dynamics of impact both for moving or stationary walls. Interestingly, viscous dissipation starts to increase slightly before impact and it shows a sudden increase upon impact in the kinematic phase. In general, the kinetic energy drops first due to dissipation and surface enlargement and, in later stages, it increase as a result of surface motion and droplet retraction. Counter intuitively, as the tangential We is increase, the viscous dissipation attains higher value and shifts the minimum of kinetic energy profile to an earlier dimensionless time but with a higher value. It is found that the dimensionless time where maximum spread of the droplet happens is less influenced by tangential We number.