## 4 Methodology
### Numerical Simulation and Result Analysis
#### 4.4.4 Simulation Analysis of Spindle Velocity Change  
The initial rotational velocity of the spindle is set at 20 r/min to analyze the effect of spindle velocity changes on the flow field. Subsequently, the rotational velocity is increased sequentially to 25 r/min, 30 r/min, 35 r/min, and 40 r/min to analyze the impact of drum velocity variations on the flow field and winnowing efficiency within the film stalk separation device. The cross-sectional sampling method remains consistent with the previous approach. The average values of pressure and velocity for each cross-section are calculated. These values are then applied to plot curves illustrating the changes in pressure and velocity distribution within the flow field under different spindle velocities. Figure 15 illustrates the variation in pressure along the length of the cavity when the spindle velocity is altered, while Figure 16 depicts the evolution of fluid velocity across the dimensions of the cavity during the spindle velocity change.  
Figure 14: The change of fluid velocity along the cavity under different drum rotational velocities.  
An analysis of Figure 15 reveals that the average pressure value within the internal section of the initial model is negative. As the spindle velocity increases, the initial pressure gradually transitions into positive territory. When the spindle velocity reaches 35 r/min, all sections exhibit positive pressure values. The negative pressure experiences a notable increase in spindle velocity below 35 r/min. At a spindle velocity of 25 r/min, the flow field exhibits the most significant negative pressure, with a maximum value of \(-\)1 Pa. Conversely, when the spindle velocity is increased to 40 r/min, there is a decrease in the average pressure value within the model. These findings demonstrate the influence of spindle velocity on pressure distribution within the system. As the spindle velocity increases, the pressure values shift towards positive values, indicating improved performance and efficiency. Conversely, at lower spindle velocities, the negative pressures are more pronounced, potentially affecting the overall system operation.  
The analysis of Figure 16 reveals that with an increase in the spindle velocity, the maximum fluid velocity inside the cavity also increases. Additionally, when the spindle  
Figure 16: The change of fluid velocity along the length of the cavity under different spindle velocities.  
Figure 15: The change of flow field pressure along the length of the cavity under different spindle velocities.  
velocity reaches 30 r/min, the velocity model is generally consistent with that of 40 r/min. This implies that the sedimentation zone of the residual film remains relatively stable. At both 30 r/min and 40 r/min spindle velocity, the velocity exceeds 2 m/s, and the velocity fluctuations are not consistent. At a spindle velocity of 35 r/min, the velocity below 2 m/s accounts for 12.5%. The pressure and velocity inside the model exhibit relatively stable characteristics, with moderate fluctuations.  
In summary, when the spindle velocity is set to 35 r/min, the pressure distribution and velocity distribution within the flow field exhibit improved characteristics.