Turbulent atomization subgrid model for two-phase flow large eddy simulation (theoretical development)

Current spray combustion simulators work when an initial spray (consisting of point droplets) is prescribed as input data to the spray equation. Two-phase flow Large Eddy Simulation (LES), combined with such a reactive system treatment, could be a promising tool for simulating industrial spray combustion, if a subgrid model describing local turbulent atomization from any possible bulk liquid surface element could be incorporated. In the present study, theoretical considerations were made to develop a turbulent atomization subgrid model, which comprises the following two models. (i) Interfacial turbulence model compatible with the isotropic turbulence concept adopted in LES. Using local interfacial shear stress and liquid inertia force determined from LES, this model characterizes unresolved liquid- and gas-phase turbulent states realizable in each interfacial LES grid cell. (ii) Turbulent atomization model, which judges the occurrence of local atomization based on the interfacial turbulence model data and predicts the mean diameter, ejection velocity and number density of resulting atomized droplets. Thus, the proposed subgrid model provides instantaneous input data to the spray equation where atomization is judged to occur, and recedes the resolved interface by the volume corresponding to the locally atomized droplets.