  Prefilming airblast atomization is widely used in aero engines. Fundamental
studies on the annular configuration of airblast atomizers are difficult to
realize. For this reason, researchers focused on planar configurations. In this
regard, the Karlsruhe Institute of Technology (KIT) developed a test rig to
conduct experimental activities, conforming a large database with results for
different conditions. Such data allow validation of two-phase flow calculations
concerning primary atomization on these devices. The present investigation
proposes a Direct Numerical Simulation (DNS) on the KIT planar configuration
through the Volume of Fluid (VOF) method within the PARIS code. The novelty
compared to DNS reported in the literature resides in the use of a boundary
condition that accounts not only for the gas inflow turbulence but also for the
spatio-temporal evolution of the liquid film thickness at the DNS inlet and its
effect on turbulence. The proposed methodology requires computing precursor
single-phase and two-phase flow Large-Eddy Simulations. Results are compared to
DNS that only account for a constant (both timewise and spanwise) liquid film
thickness at the domain inlet, validating the workflow. The proposed
methodology improves the qualitative description of the breakup mechanism, as
its different stages (liquid accumulation behind the prefilmer edge, bag
formation, bag breakup, ligament formation and ligament breakup) coexist
spanwise for a given temporal snapshot. This implies more continuous
atomization than the one predicted by the constant film thickness case, which
showed the same breakup stage to be present along the prefilmer span for a
given instant and led to a more discretized set of atomization events. The
proposed workflow allows quantifying the influence of the liquid film flow
evolution above the prefilmer on primary breakup frequency and atomization
features.
