The impact of a spherical water droplet onto a stationary sessile droplet lying on a solid wall is studied numerically using the volume-of-fluid methodology. The governing Navier-Stokes equations are solved both for the gas and liquid phase coupled with an additional equation for the transport of the liquid interface. An unstructured numerical grid is used along with an adaptive local grid refinement technique, which enhances the accuracy of the numerical results along the liquid-gas interface and decreases the computational cost. The stationary sessile droplet has been created from the prior impact of one or two water droplets falling onto the solid wall, while two solid walls have been studied−an aluminum substrate and a glass substrate. The material of the wall plays an important role because it has an impact on the droplet's wetting behavior. The numerical model is validated against corresponding experimental data presented in the first part of the present work (Nikolopoulos et al., 2010), showing good agreement. Furthermore, the numerical investigation sheds light on the governing physics of the phenomenon.

Keywords: VOF, droplet, impact onto a sessile droplet