# 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 above research involved the spreading and breakage of the liquid film when the molten metal was spread on the disk surface, but it only studied the influence law of different disk shapes under the working condition of 10,000 rpm. Thus, the key factor of the rotating disk speed was not considered. Therefore, the influence of the disk structure on the liquid film characteristics under different rotation-speed conditions is studied. In the previous study, the VOF method was used to capture the gas-liquid interface of aluminum alloy liquid film formation, but the simulation of the thin liquid film distribution formed by high-speed rotation could not be performed by the VOF method. Because the capture of the liquid film by the VOF method requires that the mesh size is less than 1/5 of the thickness of the liquid film, but the thickness of the liquid film formed by the high-speed atomization disk is at the micron level, the application of the VOF method to capture the liquid film requires a large number of grids, which cannot be achieved using the existing resources. In this case, the Fluid Film model of the STAR-CCM+ 2022.1.0 software is used to capture the micron liquid film of the atomizing disk, in order to study the liquid film characteristics on the surface of the rotating disk at a high speed. However, the Fluid Film model cannot be used alone but should be combined with the VOF model. The VOF model should be used first to capture the initial thick liquid film, which gradually becomes thinner as the liquid film expands, and then the Fluid Film model can be used to further capture the later development characteristics of the thin liquid film. The Fluid Film model was used to simulate and study the characteristics of the liquid film on the surface of the atomizing disk under the rotational speeds of 10,000 rpm, 30,000 rpm, and 60,000 rpm. The obtained calculation results of the liquid film distribution on the surface of the flat disk and the spherical disk are shown in Figures 13 and 14. The liquid film distribution mainly consists of a thick liquid film, including a liquid filament (gray), calculated by the VOF method, and a thin liquid film (color) calculated by the Fluid Film method. In Figures 13 and 14, it can be seen that the characteristics of the molten metal forming a liquid film on the surface of the rotating disk are basically the same at different rotational speeds. First, the molten metal is poured onto the center of the rotating disk through the diversion nozzle, and a continuous thick liquid film is formed within a certain diameter of the central region (the gray circular region of the cloud image), whose diameter is the boundary diameter of the continuous liquid film, defined above. The outside of the gray circular area is a colored region representing the thickness distribution of the liquid film with different colors. In Figures 13 and 14, it can be seen that the liquid film begins to split into liquid bundles when the boundary diameter of the continuous liquid film is exceeded, and when the rotational speed increases from 10,000 rpm to 60,000 rpm, the gray liquid filaments obtained by the VOF method gradually disappear and a liquid filament obtained by the Fluid Film method is gradually formed. The liquid filaments formed by splitting maintain a relatively continuous liquid filament state and move radially in the disk direction, and the motion trajectory is approximately involut  
Figure 12: Velocity distribution cloud diagram of liquid film on the surface of the spherical disk. (a) Liquid film velocity distribution; (b) radial velocity distribution; (c) tangential velocity distribution. Based on the analysis and study of the general characteristics of the liquid film on the surface of the atomizing disk at different speeds, the different characteristics of the liquid film formed by different disk shapes at different speeds were further analyzed.