# Evaluation and Validation of Viscous Oil Cavitation Model Used in Torque Converter
## 4 Parameter Study Results and Discussion
### Analysis of the Influence of Significant Cavitation Parameters
#### 4.3.2 Cavitation Vaporization Coefficient--\(F_{\rm vap}\)  
The performance of torque converter under various \(F_{\rm vap}\) is shown in Figure 18. Cavitation vaporization coefficient also has a significant influence on the performance. The increase of \(F_{\rm vap}\) will decrease capacity constant, torque ratio and mass flow rate of the torque converter.  
Figure 16: Oil vapor volume fraction distribution on stator blades at stall under various nuclei volume fractions.  
Figure 14: Bulk interphase mass transfer rate on stator blade at stall under various nuclei volume fractions.  
Figure 15: The 10% vapor volume fraction distribution in stator domain at stall under various nuclei volume fractions.  
The absolute pressure distribution diagram of the middle streamline on stator blade surface (Figure 19) shows that with the increase of \(F_{\rm vap}\), the differential pressure between the two sides of stator blade decreases gradually, which leads to the reduction of mass flow rate, capacity constant, and torque ratio of torque converter.  
Figures 20 and 21 depict the oil vapor volume fraction and the bulk interphase mass transfer rate on the middle streamline of stator blade under various \(F_{\rm vap}\). We found that the oil vapor volume fraction and the mass transfer rate of the head and tail on blade surface increase gradually with an increasing \(F_{\rm vap}\), indicating that the increase of \(F_{\rm vap}\) will aggravate the cavitation.  
Figure 19: Absolute pressure on stator blade at stall under various cavitation vaporization coefficients.  
Figure 20: Oil vapor volume fraction on stator blade at stall under various cavitation vaporization coefficients.  
Figure 18: Capacity constant, torque ratio, and mass flow rate of torque converter at stall under various cavitation vaporization coefficients.  
The 10% vapor volume fraction distribution in stator domain and the oil vapor volume fraction distribution on stator blades under various \(F_{\text{vap}}\) are shown in Figures 22 and 23. The influence of \(F_{\text{vap}}\) is similar to that of \(NVF\). Increasing \(F_{\text{vap}}\) leads to more and higher density oil vapor volume fraction.  
The volume of bubbles around blade head increases with the increase of \(F_{\text{vap}}\). To be more specific, the area with high gas content grows and expands, and the length of the oil vapor bubble also increases as \(F_{\text{vap}}\) increases (Figure 24). The reason is straight forward--the increase of the vaporization coefficient indicates quicker vaporization process, consequently leading to more bubbles generation and lower torque converter capacity and mass flow rate. In conclusion, the increase of \(F_{\text{vap}}\) will promote the cavitation process.  
Figure 21: Bulk interphase mass transfer rate on stator blade at stall under various cavitation vaporization coefficients.  
Figure 22: The 10% vapor volume fraction distribution in stator domain at stall under various cavitation vaporization coefficients.