## 5 Results and Discussion
### Effects of Rotor Speed on Sealing Performance
#### 5.2.2 Changes in Outer Rotor Speed  
Figure 11 shows the effects of the changes to the counter-rotation speed of the outer rotor within 5000-10,000 rpm when the inlet differential pressure is 80 kPa and the inner rotor speed is 10,000 rpm on the seal's leakage rate and friction power consumption. For easy analysis, changes in the minimum film thickness and eccentricity are included in Figure 11. Since the two rotors are in counter-rotation with a stable inner rotor speed of 10,000 rpm, as the outer rotor's speed increases, the relative movement speed of the gas film decreases, and the effects of dynamic pressure on the gas lubrication state gradually weaken. When the speed of the inner and outer rotors is 10,000 rpm, the minimum film thickness approaches zero, indicating maximum leak and friction power consumption.  
As outer rotor speed increases, the leakage rate of the seal increases because, with the relative speed of the gas film decreasing, the gas film's dynamic pressure effect and resistance to axial movement weaken. The minimum film thickness increases then decreases before the outer rotor speed increases to 8000 rpm (the critical speed); the relative movement speed of the gas film is sufficiently high, and the gas film's dynamic pressure is sufficient to support the sealing ring for full fluid lubrication. Although the increase in the outer rotor's speed weakens, the dynamic pressure effect, the speed and the centrifugal expansion of the sealing ring also increase. Therefore, the minimum film thickness increases slightly (Refer to the schematic diagram for the effects of the centrifugal expansion of the sealing ring on the minimum film thickness shown in Figure 12. Position 1 is the initial position of the sealing ring when there is no speed. Position 2 is the position of the sealing ring with speed.) Once the outer rotor speed reaches the critical speed of 8000 rpm, the relative movement speed of the gas film decreases, and the dynamic pressure effect weakens with further increases in sealing ring speed (despite increases in the sealing ring's centrifugal expansion) and the minimum film thickness decreases. The friction power consumption increases first and then increases since, before the outer rotor speed reaches the critical speed (about 8000 rpm), the dynamic pressure effect of the gas film is sufficient. The sealing ring and the inner rotor are fully fluid-lubricated (the minimum film thickness exceeds the critical value). The friction power consumption is mainly related to the gas film's relative  
Figure 11: Effects of outer rotor speed on sealing performance.  
speed. As the outer rotor speed increases, the relative speed of the gas film decreases, and friction power consumption decreases slightly. When the outer rotor speed exceeds the critical speed, the minimum gas film thickness is smaller than the critical value of film thickness. The sealing ring and the inner rotor are in a mixed lubrication state, and solid contact occurs. As the outer rotor speed increases, the minimum film thickness further decreases, mixed lubrication becomes more obvious, and friction power consumption increases significantly.