An evaluation of drop size and injection angle in near-field spray calculations

A common feature in Lagrangian-Eulerian spray models is the prediction of droplet size and the initial spreading angle of the spray at the nozzle exit. In the present work, the importance of drop size and spreading angle are evaluated by employing high-fidelity atomization simulations using an algebraic VoF approach (interFoam). The process begins by extracting an axial drop size profile (D32VoF) from VoF results and imposing this profile directly on LE calculations, thereby excluding all breakup models and isolating the effect of the LE calculations on the accuracy of the spray predictions. This LE accuracy is evaluated based on comparisons to projected mass density maps generated by the VoF calculations. The results show that, even with the imposition of the D32VoF profile, the LE calculations exhibit significant errors in comparison to VoF results. This discrepancy emphasizes that having the correct breakup model in LE computations can still lead to substantial difficulties. Additionally, the spreading angle is found to play a much more critical role in the prediction of spray mass distribution in comparison to drop size. A key ingredient missing in LE calculations, which is primarily responsible for the errors observed, is the ability of the LE spray model to replicate the axially developing spreading angle, which we believe is partially based on the complex momentum transfer between the gas phase and a large population of dynamically evolving and highly non-spherical liquid elements.