# Optimal Design and Fish-Passing Performance Analysis of a Fish-Friendly Axial Flow Pump
## 4 Optimal Design and Hydraulic Performance Analysis of a Fish-Friendly Axial Flow Pump  
### Optimal Design of the Leading-Edge Thickness of Blade  
Previous studies have shown that the part of the runner structure that causes cutting damage to fish is located at the leading edge of the blade. The leading-edge structure of the blade is used to reduce the de-flow of the blade facing the incoming flow and reduce the hydraulic loss. From a fish-friendly point of view, increasing the thickness of the leading edge of the blade can avoid direct cutting when it hits the fish. However, the thickness of the leading edge of the blade is not better when bigger. On the one hand, the greater thickness increases the possibility of de-flow and hydraulic loss, on the other hand, it also increases the probability of hitting fish. Therefore, the choice of the leading-edge thickness of the blade needs to be analyzed. Three runner schemes with different blade leading-edge thicknesses were designed for the prototype axial flow pump, as shown in Figure 7.  
We used the comparative analysis method to comprehensively analyze the operation characteristics and flow field characteristics of the axial flow pump under different blade leading-edge thickness schemes and determine the better blade leading-edge thickness. According to Table 5, the head of the axial flow pump decreases with the increase in the leading-edge thickness of the blade. This shows that the mechanical energy obtained per unit fluid mass was reduced. The inlet and outlet pressure of the blade decreased by about 1.5 kPa with the thickening of the leading edge of the blade, and the decrease in the total pressure at the outlet was slightly larger than that at the entrance. On the one hand, this shows that the internal hydraulic loss of the runner increases with the thickening of the leading edge of the blade; on the other hand, for the pressure difference between the front and rear of the impeller shifts, although increasing the leading-edge thickness makes the suction chamber obtain a lower negative pressure and improve the suction lift, the lower negative pressure also increases the possibility of pressure damage to the upstream fish body. With the increase in the blade leading-edge thickness, the shaft power, runner efficiency, and machine efficiency decreases to a certain extent. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \begin{tabular}{c} **Leading-Edge** \\ **Thickness of Blade** \\ \end{tabular} & **Discharge** & **Head** & \begin{tabular}{c} **Average Pressure at Inlet and** \\ **Outlet of Runner** \\ \end{tabular} & \begin{tabular}{c} **Shaft** \\ **Power** \\ \end{tabular} & \
\begin{tabular}{c} **Runner** \\ **Efficiency** \\ \end{tabular} &
\begin{tabular}{c} **Machine** \\ **Efficiency** \\ \end{tabular} \\ \hline
**Thk (mm)** & **Q (m\({}^{3}\)**-s\({}^{-1}\))** & **H (m)** & **P1 (kPa)** & **P0 (kPa)** & **\(\Delta\)P (kPa)** & **N (kw)** & **H (\%)** & **H (\%)** \\ \hline
5.6 & 8.01 & 6.01 & \(-\)44.5 & 14.3 & 58.8 & 523.4 & 90.12 & 75.68 \\
11.4 & 8.02 & 5.91 & \(-\)45.9 & 11.9 & 57.9 & 518.8 & 89.38 & 74.50 \\
17.4 & 8.02 & 5.83 & \(-\)47.3 & 9.8 & 57.1 & 514.8 & 88.87 & 73.59 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Operating parameters of axial flow pump with different leading-edge thickness of blade. Figure 7: Different leading-edge thicknesses of blade. The cross-section pressure distribution of the axial flow pump under different blade leading-edge thickness schemes is shown in Figure 8. As can be seen from the pressure distribution map, with the thickening of the leading edge of the blade, the area lower than \(-40\) kPa gradually increases. Too large a negative pressure area causes irreversible negative pressure damage to the fish. From the velocity distribution map, it can be seen that in the case of \(5.6\) mm, the velocity gradient at the leading edge of the blade and the guide vane region change gently, and the smooth iso velocity lines can be clearly observed in both X-sections.