Hybrid URANS/LES turbulence modeling for spray simulation: A computational study

Turbulence modeling for fuel spray simulation plays a prominent role in the understanding of the flow behavior in Internal Combustion Engines (ICEs). Currently, a lot of research work is actively spent on Large Eddy Simulation (LES) turbulence modeling as a replacement option of standard Reynolds averaged approaches in the Eulerian-Lagrangian spray modeling framework, due to its capability to accurately describe flow-induced spray variability and to the lower dependence of the results on the specific turbulence model and/or modeling coefficients. The introduction of LES poses, however, additional questions related to the implementation/adaptation of spray-related turbulence sources and to the rise of conflicting numerics and grid requirements between the Lagrangian and Eulerian parts of the simulated flow. About the latter, an efficient alternative might be found in hybrid URANS/LES formulations, which are still relatively unexplored for spray modeling applications and for ICE modeling in general. In this work, we conduct a systematic analysis aimed to assess the effects of several URANS, LES and hybrid turbulence modeling formulations on the spray dynamics. The hybrid form is based on a purposely developed version of the k-g URANS closure, and the simulation campaign is focused on a standard n-dodecane evaporating spray case in a constant volume vessel configuration. The spray is modeled within the Eulerian-Lagrangian framework, with primary and secondary breakup taken into account by means of the Kelvin-Helmholtz-Rayleigh-Taylor (KHRT) model. Further, we investigate on the effects due to the Stochastic Turbulence Dispersion (STD) of parcels. Numerical experiments are carried out via the open-source CFD code OpenFOAM. The results are validated against the baseline experimental data for evaporating ECN Spray A and with previous computational findings available in literature.