In internal combustions engines and in systems for exhaust gas aftertreatment, sprays interact with liquid wall films. The impact of fuel drops, for instance, may release oil from the lubricating wall film into the combustion region causing pre-ignition. Fundamental understanding of this interaction and its proper modelling are essential to increase efficiency while reducing emissions. In this study we have investigated the silicone oil drop impact onto liquid film of the same liquid without generation of secondary droplets using Direct Numerical Simulation with a diffuse interface phase-filed interface capturing method. Due to rotational symmetry of the impact process we used an axisymmetric computational domain and utilized Adaptive Mesh Refinement technique for resolving the diffuse interface with sufficient number of cells.
We used the diffuse interface phase-field interface capturing method where the two-phase flow is governed by the coupled Cahn-Hilliard-Navier-Stokes equations developed and implemented by us in the open source C++ library OpenFOAM (code phaseFieldFoam).
The results of the numerical investigation were compared with high quality time-resolved experimental data for three different Weber numbers and a fixed film thickness. Impact outcomes with characteristic morphologies of deposition, crown formation including the formation of a dome-like structure or a Worthington central jet were observed and the evolution of the crown top diameter, base diameter and height were measured and compared with the experimental data.
The numerical investigations were performed for low to high energy drop impact process onto thin liquid films using the diffuse interface phase-field method. It was found that accurate calculation of the interfacial energy plays a significant role in correct prediction of the impact process particularly for moderate to high energy impact. Therefore, an effective formulation for the interfacial energy term was proposed and tested. The numerical results were in a good agreement with the experimental data.