The aim of this study is to implement, validate and compare three different dynamic contact angle models for use in the CFD-software IBOFlow, a state-of-the-art multiphase flow solver developed by Fraunhofer-Chalmers research centre. The solver has been successfully used to simulate a number of industrial applications involving free surface flows, but a correct dynamic contact angle model is missing. In IBOFlow the two-phase flow is modeled with the volume-of-fluid method and the surface tension with the continuum surface force method. In this work, three different dynamic contact angle models are implemented, validated and compared.
Dynamic contact angles are implemented as a boundary condition for the continuum surface force method, rotating interface normals in wall boundary cells. Contact line velocity of the spreading liquid is approximated by the cell velocity in the direction of the contact line. Dynamic contact angle models are only applied on advancing contact lines and a static model is used for receding contact lines. The implementations are validated with grid and time step convergence studies on simulations of glycerol droplets impacting a solid surface. The different dynamic contact angle models are compared and validated against experimental data for a number of test cases where glycerol droplets with alternating viscosity are impacting solid surfaces at low impact velocities.
The implementation shows time step convergence but some dependency on the grid size, because the no-slip condition at the wall affects the contact line velocity if the grid is too refined. Of the three different models implemented, two are truly dynamic and one is quasi-dynamic. The truly dynamic models performs best in almost all test cases simulated, and the results agree very well with experimental data. Two situations where a truly dynamic contact angle model is of great importance are distinguished, namely impacts at very low velocities and impacts on hydrophilic surfaces.