# Numerical Simulation of Liquid Film Characteristics during Atomization of Aluminum Alloy Powder
## 3 Simulation Results and Discussion
### Liquid Film Characteristics with Disk Structure at Different Speeds
The mesh model is shown in Figures 17 and 18, and its boundary conditions are shown in Figure 19.  
The results obtained from the above simulation research, which aimed to capture the liquid film on the surface of the rotating disk, and the liquid film splitting to form liquid filaments and finally breaking into droplets, are shown in Figures 20 and 21. According to the cloud image of the evolution process of the separation and fragmentation of the liquid film in the small-angle atomization of the rotating disk in Figure 20, it can be seen that the liquid in the small-angle fluid domain is poured onto the surface of the rotating disk and gradually spread on the surface of the atomization disk to form a continuous liquid film with a free surface. When the liquid film spreads and moves a certain distance, local bulges begin to form and the initial shape of the liquid filament is formed, as shown in Figure 20b; t = 2.2 s. After the initial liquid filament is formed, the liquid filament gradually expands and extends, and the diameter of the tip gradually shrinks. At this time, interface stress (such as surface tension, etc.) has a significant impact on the liquid filament, and the tip begins to shrink, as shown in Figure 20c; t = 2.4 s. Because of the influence of surface tension, the tip of the liquid filament shrinks. The R-T interface becomes unstable due to the interaction of the gas-liquid two-phase interface, and an interfacial wave along the liquid column is generated [34]. The disturbance of the interfacial wave is formed along the tip and spreads upstream. The tip absorbs upstream fluid through contraction, and it begins to grow and forms large droplets at the end of the liquid filament, as shown in Figure 20d; t = 2.6 s. When the diameter of the necking area of the liquid filament shrinks to a certain extent, the tip separates from the main liquid filament to form discrete droplets under the influence of circumferential surface tension, as shown in Figure 20e; t = 2.8 s. After the tip of the liquid filament is broken and formed into small droplets, the liquid flow at the back of the liquid filament is continuously supplied, and the tip droplets are continuously broken and dispersed to form atomized droplets. The atomized droplets move away from the atomization zone along the movement track and gradually evolve into spherical droplets under the action of surface tension; finally, spheroidal droplets are formed, as shown in Figure 20f; t = 3.2 s.  
Figure 19: Boundary conditions. Figure 18: Global fluid domain meshing. The evolution processes of atomization to form a single liquid filament and breakage to form a droplet have been analyzed. The global motion characteristics of the liquid film on the rotating disk and the evolution process of the separation liquid filament breaking into droplets are shown in Figure 21. Based on the cloud image of the evolution process of global liquid film formation, separation, and crushing in Figure 21, it can be seen that the liquid is poured from the nozzle onto the rotating disk to form a circular, continuous liquid film at the center of the disk, as shown in Figure 21a; t = 0.3 s. With the gradual growth of the liquid film, the continuous liquid film gradually expands on all sides and forms a local bulge at the front end of the liquid film, as shown in Figure 21b; t = 1.2 s. The thickness of the local liquid film at the convex vertex will gradually increase, and the adjacent area will become thinner. The mass of the local liquid film and the centrifugal force will gradually increase. Finally, the liquid film will break at the local liquid film under the influence of the liquid film on the rotation of the liquid film. Figure 14:0 Cloud image of the evolution of liquid film separation and fragmentation during atomization.