Detailed SGS atomization model and its implementation to two-phase flow LES

Abstract

A novel turbulent atomization model, which is physically closed itself and free of case-by-case parameter tuning using experimental data, has been formulated and demonstrated in the framework of turbulent spray combustion large-eddy simulation (LES). Based on our accumulated research findings that elementary droplet/ligament generation is a deterministic phenomenon, not something random as considered in the conventional understanding, the model describes two dominant modes of turbulent atomization, i.e. the turbulent resonant mode and the Rayleigh–Taylor (RT) mode, in a physically straightforward manner. Extending the baseline theory proposed in Umemura (2016), to a hybrid turbulent spray LES formulation which includes both an Eulerian liquid jet core and Lagrangian droplets, the subgrid-scale (SGS) atomization characteristics are completely detailed in this study. Using the LES-resolved turbulent Weber and Bond numbers on the liquid core surface, the atomization mode and the SGS atomization characteristics such as droplet size, number, ejection velocity and core regression velocity are all identified locally, and the information is transferred back to the LES code as input information. Test cases of Diesel fuel jets demonstrate that the present formulation well reproduces the turbulent spray behavior. Thanks to the obtained detailed data, the spray formation process can be tracked both temporally and spatially, from the initial head formation with edge atomization to the later core atomization and spray spreading. It is essentially featured that the present turbulent atomization model works well without ambiguous user input, contrary to the conventional way of spray simulation. This is a significant breakthrough to urge paradigm shift in spray simulation, from unclosed/unpredictable to closed/predictable, which enables drastic improvement in the accuracy of spray simulation and may exert a large impact on both research studies and industrial applications.