# 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 Leading-Edge Guiding Characteristics of the Blade
As shown in Figure 12, the main difference in the pressure distribution before and after the runner blade is the flatness of the isoline of the runner working face, and the isoline inflection point of the runner pressure distribution after cutting is close to 120\({}^{\circ}\). On the suction surface of the blade, the area where the negative pressure of the suction surface of the blade with a cutting angle of 12\({}^{\circ}\) is less than \(-80\) kPa is slightly larger than that of the other two schemes. The hydraulic loss of the impeller with a cutting angle of 12\({}^{\circ}\) decreases, the hydraulic loss of the guide vane increases, and the overall working efficiency obviously decreases. The work capacity of the blade with a cutting angle of 12\({}^{\circ}\) becomes stronger, which reduces the hydraulic loss of the impeller, but because the structure of the guide vane remains unchanged, the hydraulic loss of the guide vane region increases, and the overall working efficiency still decreases. The purpose of blade cutting is to reduce the probability of the fish hitting the leading edge of the blade and to make the fish move towards one side of the hub and reduce its linear speed. In terms of the operation efficiency of the axial flow pump and the flow pattern of the outlet channel, the scheme of a cutting angle Ang = 12\({}^{\circ}\) has a slight advantage. But in contrast, the negative pressure level of the suction chamber and the velocity gradient at the back end of the runner in the Ang = 18\({}^{\circ}\) scheme are better, and the runner efficiency is better. Although the efficiency of the whole machine is slightly lower than the former, it is more in line with the design value of this paper to sacrifice a small part of the efficiency for the viability of fish. Therefore, the Ang = 18\({}^{\circ}\) scheme was chosen in this section. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Blade Cutting** & **Discharge** & **Head** & \multicolumn{2}{c}{**Average Pressure at Inlet and**} & \multicolumn{2}{c}{**Shaft**} & \multicolumn{2}{c}{**Runner**} & \multicolumn{1}{c}{**Machine**} \\
**Angles** & **Discharge** & & \multicolumn{2}{c}{**Outlet of Runner**} & \multicolumn{2}{c}{**Power**} & \multicolumn{1}{c}{**Efficiency**} & \multicolumn{1}{c}{**Efficiency**} \\ \hline
**Ang (\({}^{\circ}\))** & **Q (m\({}^{3}\)-s\({}^{-1}\))** & **H (m)** & **P1 (kPa)** & **P0 (kPa)** & **\(\Delta\)P (kPa)** & **N (kw)** & \(\eta\) (\%)** & \(\eta\) (\%) \\ \hline
6 & 8.02 & 5.91 & \(-45.9\) & 11.9 & 57.9 & 518.8 & 89.38 & 74.50 \\
12 & 8.01 & 5.95 & \(-46.0\) & 12.2 & 58.3 & 529.6 & 88.20 & 72.62 \\
18 & 8.02 & 5.90 & \(-44.8\) & 12.8 & 57.6 & 523.0 & 88.33 & 71.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Operating parameters of axial flow pump with different blade cutting angles. Figure 11: Cross-section velocity and pressure distribution of axial flow pump at different cutting angles. Figure 12: Pressure distribution on the front and back of blades at different cutting angles.