The primary breakup of liquid jets is a major step in many technical and industrial processes, from fuel injection to spray cooling, from ink-jet printing to surface treatment and from spray drying to medical sprays. However, due to the small length scales involved, which determine the size of entrained droplet, a fully resolved numerical simulation of industrial applications is still unfeasible. In this work a numerical model for the coarse-grid simulation of turbulent liquid jet disintegration and primary atomization is developed based on an Eulerian-Lagrangian coupling. To picture the unresolved droplet formation near the liquid jet interface in the case of coarse grids we considered a theoretical model to describe the unresolved flow instabilities leading to turbulent breakup. The generated droplets are then represented by an Eulerian-Lagrangian hybrid concept. On the one hand, we used a volume of fluid method (VOF) to characterize the global spreading and the initiation of droplet formation; one the other hand, Lagrangian droplets are released at the liquid-gas interface according to the theoretical sub-grid model balancing consolidating and disruptive energies. The dynamics of the generated droplets are modelled using Lagrangian particle tracking (LPT). A numerical coupling between the Eulerian and Lagrangian frameworks is then established via source terms in conservation equations.
The presented methodology was tested through sets of validation studies using different test cases and empirical correlations from the literature. As a more sophisticated validation study, the results of an in-house phase-Doppler anemometry (PDA) experiment were used to test the simulation results of three liquid jets at high Reynolds numbers. The droplet properties, such as size distribution, Sauter mean diameter (SMD) and velocity distributions obtained from the simulations are compared with experiment at various streamwise locations with very good agreement.
Finally, the proposed multiscale Eulerian-Lagrangian methodology is further adopted to be used for numerical simulations of the general flow behaviour, jet breakup and surface porosity formation in high pressure die casting process.