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Subgrid-scale Capillary Breakup Model for Liquid Jet Atomization

ABSTRACT A subgrid-scale capillary breakup model has been developed by coupling a Eulerian interface-capturing approach to a Lagrangian point particle method. At the fully resolved scale, the evolution of phase interface is captured by the Refined Level Set Grid method (RLSG), while the under-resolved, small-scale liquid structures are represented by Lagrangian point particles. To couple the level-set method with the Lagrangian approach, a numerical algorithm is developed to identify the under-resolved structures and compute their shape metric. The capillary instability theory is then applied to predict the sizes and number of post-breakup drops needed to replace them with Lagrangian drops. The secondary atomization of the Lagrangian drops is modeled by the stochastic breakup model. To validate the present model, numerical simulations are performed for the breakups of a single liquid filament and a round liquid coaxial jet. Grid-convergence studies for the drop-size distribution of the resulting spray are conducted and compared to the experimental data. The numerical results show good agreement with the experimental data. The present subgrid-scale capillary breakup model reduces the computational cost by relaxing the stringent grid resolution required for multi-scale atomization simulations.