# Identification and Optimization Study of Cavitation in High Power Torque Converter
## 4 Optimized Design of Cavitation in High Power Torque Converter
### Analysis of Cavitation Mechanism of Hydraulic Torque Converter  
The pressure surface is defined as the side of the stator facing the impact of the liquid flow, while the suction surface is defined as the other side. A simulation calculation was performed on the research object with an input speed of 1700 r/min and a speed ratio of 0 for the pump wheel. After the calculation was completed, the pressure and velocity cloud diagram of the stator was extracted, as shown in Figure 7.  
Under the initial conditions, negative pressure was observed on the surface of the stator blades due to the lack of consideration of cavitation. The lowest negative pressure on the stator blade surface \(P_{lowest\_D}\) was \(-2.76\) MPa as shown in Figure 7a. The negative pressure region was mainly located at the starting position of the suction surface of the stator blades, specifically the side of the suction surface at the nose of the stator. Meanwhile, a  
Figure 6: Performance of the stall test was evaluated at various pump input speeds.  
low-pressure region, which is a localized vortex region as shown in Figure 7d, is distributed above the front suction surface at the peak bending position of the stator. The lowest pressure, denoted as \(P_{lowest\_D}\) of the stator occurs in the nose region of the stator, specifically located on the pressure surface side of the nose region. This region is directly impacted by the turbine hydrodynamics.  
The velocity cloud diagram shows that the flow velocity near the stator blade region is nearly zero due to the viscous effect of the liquid flow near the wall. Some of the liquid flow moves towards the pressure surface of the stator, while another part of the velocity increases rapidly after skimming over the nose region of the stator. The velocity then levels off after entering the middle region of the blade. Regions of low-velocity flow with varying degrees can be observed above the front suction surface at the peak position of stator bending. Figure 7c shows that the liquid flow impacts the pressure surface adjacent to the stator blades after skimming the nose of the stator. The flow then folds back to form a vortex, which is the main factor causing the emergence of local negative pressure and local low-speed flow region above the front suction surface at the peak position of the stator bending.  
As shown in Figure 8, the angle between the turbine liquid flow outflow direction vector and the rotation direction vector of the impeller in the stall condition is defined as the stator liquid flow incidence angle \(\beta_{inci}\), and the angle between the stator liquid flow incidence angle \(\beta_{inci}\) and the stator blade streamlined inlet angle \(\alpha_{inD}\) is defined as the liquid flow incidence deviation angle \(\Delta\beta_{Dif}\).  
\[\Delta\beta_{Dif}=\beta_{inci}-\alpha_{inD} \tag{10}\]  
Figure 7d shows the partial diagram of the stator streamline. In stall conditions, the \(\Delta\beta_{Dif}\) formed by the turbine outlet angle and the inlet angle of the stator nose is larger, resulting in high-speed liquid flow being swept over the stator nose flow to the suction surface of the liquid flow being greater. In the stator nose and the stator, bending the peak position of the front of the suction surface over the formation of a localized negative pressure zone, respectively, is the cause of the occurrence of cavitation in the torque converter.  
Figure 7: Simulation cloud map of the original scheme: (**a**) stator pressure cloud map; (**b**) stator velocity cloud map; (**c**) streamline diagram of stator flow direction; (**d**) localized view of the stator streamline.