  Spray impacts occur in several environmental and technical applications. The
impact of droplets at different angles onto walls covered with a thin film of
the same liquid can be regarded as an elementary process here. Direct Numerical
Simulations (DNS) provide an important contribution to the understanding and
modeling of the impact outcome, which might be associated with the formation of
a crown and ejection of secondary droplets. Thus, we gain detailed information
about, e.g. the flow field and shape of the interface, which are not accessible
in experiments. This chapter presents a DNS study of the early crown formation
mechanisms present at an oblique droplet impact on a thin film, as well as a
grid study showing the resolution required to resolve the impact's details.
Highly resolved simulations in large domains require continuous development of
the numerical solver's efficiency. The performance of different cycles of the
multigrid (MG) solver for the solution of the pressure Poisson equation was
compared, and a F-cycle was added. Furthermore, we implemented a hybrid MPI and
OpenMP parallelisation, which both increases the scaling limit further.
Additionally, studies on the strong and weak scaling are conducted. The choice
of the F- and V- cycle in the MG-solver and the additional hybrid
parallelisation increased the achieved computed cycles per hour (CPH) by a
factor of 12.4 compared to the formerly employed setup. The nodes efficiently
usable were increased by a factor of 16. Both, the close to linear scaling
regime for the strong scaling and the almost constant performance regime for
the weak scaling were increased by this factor.
