# Evaluation and Validation of Viscous Oil Cavitation Model Used in Torque Converter
## 6 Conclusions  
The present work investigated the hydrodynamic performance of torque converter and cavitation fluid field by establishing a full 3D steady-state CFD model, and the cavitation effect was also considered. A series of cavitation models were investigated and the influence of empirical parameters on the cavitation model were analyzed. The study made the following conclusions clear:  
1. Cavitation occurred in a high power-weight ratio torque converter, especially under low \(SR\) operating conditions. It has a great change on the hydraulic performance of the torque converter. We should consider the cavitation processes in the analysis of the torque converter to obtain high-precision calculation results. 2. The seven parameters of the cavitation model have different effects on the degree of cavitation. \(NVF\) is the most important factor, \(F_{\rm vap}\) and \(R_{\rm B}\) rank the second, \(MDR\)  
Figure 38: Errors of turbine torque, torque ratio, efficiency, and capacity constant between modified cavitation model and test at various speed ratio under cavitating conditions. Figure 37: Comparison of torque ratio, efficiency, and capacity constant between the original model and modified model and test at various speed ratios under cavitating conditions. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Position on Stator Blade** & **Head of Suction Surface** & **Head of Pressure Surface** & **Tail of Pressure Surface** \\ \hline Simulation average pressure (Pa) & 16,374 & 1,212,461 & 639,934 \\ Test average pressure (Pa) & 17,763 & 1,298,350 & 611,840 \\ Error (\%) & –7.82 & –6.62 & 4.59 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Pressure data at different locations on stator blade. CRRF_, \(P_{\rm v}\), \(F_{\rm cond}\) are among the least influential parameters. Changing the model parameters according to the actual conditions could improve the prediction accuracy of cavitation model. 3. The parameters affect the cavitation hydrodynamic performance and cavitation behaviors in different ways. For instance, \(NVF\) and \(F_{\rm vap}\) are the most influential factors to the capacity constant and mass flow rate of torque converter. However, all parameters have little influence on the stall torque ratio of the converter. 4. The cavitation flow field and bubble distributions in the torque converter are closely related to the cavitation model parameters. \(R_{\rm B}\) and \(NVF\) have great influence on the shape of the cavitation bubble, \(R_{\rm B}\) mainly affects the length and the thickness of bubbles, and \(NVF\) mainly affects the length. \(MDR\) and \(F_{\rm vap}\) have little effect on the bubble shape, but \(R_{\rm B}\) has a great effect on the air content in the bubble. 5. For the base torque converter, the modified cavitation model improved the calculation accuracy under cavitation operating conditions. It is worth noting that this paper only reveals the effects of a single parameter; however, interaction effects are possible between parameters. Further studies are required to comprehensively investigate the effects using more samples. In our future work, we will consider the surface tension of viscous oil and further modify the cavitation model, pay more attention to the prediction of cavitation inception, study the transient cavitation behavior in the torque converter at higher speed by transient calculation and transient measurement technology. Conceptualization, M.G. and C.L. ; Methodology, M.G. and C.L. ; Software, M.G. and Z.K. ; Validation, J.L. and M.G. ; Formal analysis, M.G. and C.L. ; Investigation, J.L. ; Resources, W.W.; Data curation, M.G. and C.L. ; Writing--original draft preparation, M.G., C.L., and W.W.; Writing--review and editing, Q.Y. ; Visualization, M.G. ; Supervision, C.L. ; Project administration, Q.Y. and W.W.; Funding acquisition, C.L., Q.Y., and W.W. All authors have read and agreed to the published version of the manuscript. This work has been funded by the National Natural Science Foundation of China (NSFC) through grant nos.