This conference paper was submitted for presentation at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

For a complete CFD modeling of jet breakup processes as in atomization followed by spray propagation, a transition model from an interface tracking consideration with the volume of fluid method (VoF) to Lagrangian particles is presented. The model was integrated by the authors into the open-source CFD toolbox OpenFOAM, validated on various benchmarks, and finally used to clarify disintegration processes in molten metal atomization. Modeling approach To represent the interactions between dynamic, viscous and surface forces during the disintegration, the initial fluid dispersion is modelled using a volume-of-fluid approach. Here, adaptive meshes on the liquid-gas interface are used to geometrically resolve the lamellae and ligament structure. If the individual cell regions of disintegrated ligaments form separated and spherical structures, they are converted into Lagrangian particles. The transformation is required, because the many droplets produced during atomization are often too small for a further spray modelling using interface tracking methods. Typical criteria to identify VoF sections valid for a transition to Lagrangian particles are the sphericity, size and position of separated fluid cell regions. After the transformation the mesh is locally coarsened again and the interactions between the droplets and continuous flow are realized via Lagrangian source terms. In the following, the droplets can further disintegrate according to their respective Weber number in a secondary breakup model. The model has been integrated into OpenFOAM as cloud-functions. Thus, it can be used with both incompressible and compressible solvers, with compressible solvers being particularly suitable for twin-fluid atomization at high gas velocities. Validation For validation the fuel jet in cross flow benchmark [1] is set up. A LES model is used to represent the turbulence structure and an iso-advector interface tracking algorithm is applied [2]. The horizontally flowing air atomizes the liquid whereby the final drop sizes at a greater distance are dominated by the secondary break-up of the Lagrange droplets according to the Reitz-Diwakar model. Good agreement with experimental results is achieved for the resulting particle size in the control planes at different distances from the injection nozzle. Another application presented is pressure atomisation from a round nozzle [3]. For this type of atomisation, which is dominated by primary break-up, a good match is also achieved for both droplet sizes and velocities. Application The model is then applied to twin-fluid atomisation of water and metal melts [4]. In this process, a swirl nozzle creates a lamella that breaks into ligaments and is atomized into small particles by high velocity gas jets. References [1] Sekar J, et al, Liquid jet in cross flow modeling. In Proceedings of ASME turbo expo 2014: turbine technical conference and exposition. Düsseldorf, Germany; 2014. [2] Roenby J, Bredmose H, Jasak H. 2016 A computational method for sharp interface advection. R. Soc. open sci. 3: 160405. http://dx.doi.org/10.1098/rsos.160405 [3] Deux, E. Berechnung der turbulenten Zerstäubung von Flüssigkeiten durch Kombination eines Zweifluidmodells mit dem Euler-Lagrange-Ansatz, Dissertation Halle-Wittenberg, 2006 [4] Kamenov, D., et al., Investigating the Atomizer Performance within Aluminium Melt Atomization. The European Conference on Liquid Atomization & Spray Systems (ILASS), 2022