## 5 Discussion  
The flow region distribution of four kinds of pads is shown in Figure 9. The values of \(\Delta c\) determine the locations of the transition lines, thereby changing the area of the laminar and turbulence flow regions. As a consequence, the cylindrical pad, saddle pad, and spherical pad increase the turbulent flow area. These three kinds of surface topographies will increase the water film thickness and the flow rate. The effect of the saddle pad on improving the lubrication performance was the most obvious. The turbulent flow area was reduced by the transverse pad, which was disadvantageous to the increase in the film thickness.  
The lubrication performance of the six pads is shown in Figure 10. It can be seen that the cylindrical pad, saddle pad, and reverse transverse pad could increase the fulcrum film thickness, and the saddle pad had the most significant effect on the increase in the film thickness. The fulcrum film thickness of the transverse pad was obviously reduced, and the load-carrying capacity was weakened. Although the spherical pad was beneficial to increasing the fulcrum film thickness when \(\Delta c\) was small, with the increase in \(\Delta c\), the fulcrum film thickness decreased to even lower than that of the plane pad. Compared with the other pads, the power loss and maximum film pressure of the spherical pad would be the largest. The power loss and maximum film pressure of the saddle pad were close to those of the plane pad, but the flow increased significantly. The cylindrical pad was found to be mediocre  
Figure 8: Geometries of the pads.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type No.** & \(z_{\theta}\)**, \(z_{r}\)** & **Characteristics of Surface Profile, Crown** & \(\Delta c\)** * & \\ \hline Type 1 & \(z_{\theta}=0\), \(z_{r}=0\) & Plane pad & 0 & 0 \\ \hline Type 2 & \(z_{\theta}>0\), \(z_{r}=0\) & Cylindrical pad, convex crown & \(z_{\theta}/a\) & \(z_{r}=0\) \\ \hline Type 3 & \(z_{\theta}=0\), \(z_{r}>0\) & Transverse pad, convex crown & \(z_{r}/a\) & \(z_{\theta}=0\) \\ \hline Type 4 & \(z_{\theta}>0\), \(z_{r}>0\) & Spherical pad, convex crown & \(z_{\theta}/a\) & \(z_{\theta}=z_{r}\) \\ \hline Type 5 & \(z_{\theta}>0\), \(z_{r}<0\) & Saddle pad, circumferential convex and radial & \\  & & concave crown & \(z_{\theta}/a\) & \(z_{r}=-z_{\theta}\) \\ \hline Type 6 & \(z_{\theta}=0\), \(z_{r}<0\) & Reverse transverse pad, concave crown & \(|z_{r}|/a\) & \(z_{\theta}=0\) \\ \hline \hline \end{tabular}  
* \(\Delta c\) expresses the degree of convexity and concavity and uses relative quantity \(a\) (=20 \(\upmu\)m) to express it.  
\end{table}
Table 3: Definition and classification of the characteristics of the pad surface profile and crown.  
The simulation example shows that it is feasible to adjust the flow pattern by changing the pad shape. The circumferential bulge (\(z_{\theta}>0\)) and radial concave (\(z_{r}<0\)) of the pad's surface are beneficial for increasing the turbulent area, which will obviously improve the load-carrying capacity. In addition, the performance of the six pads changed accordingly with the degree of convexity and concavity. The performance seemed to be related to the fluid property of the pad itself. However, the minimum film thickness of the cylindrical  
Figure 10: Effects of crown parameters on the lubrication performance: (**a**) fulcrum film thickness, (**b**) frictional power loss, (**c**) flow of pad inlet side, and (**d**) maximum film pressure.  
Figure 9: Boundary line of laminar flow mode and turbulent flow mode (\(\Delta c\) changes): (**a**) cylindrical pad, (**b**) transverse pad, (**c**) spherical pad, and (**d**) saddle pad.  
pad showed an extreme fluctuation with the change in \(\Delta c\). When \(\Delta c\) was 0.7, the minimum film thickness was the largest. This means that an excessive value of \(\Delta c\) will hinder the water flow on the pad's surface, thereby affecting the formation of the water film.