An IS80-50-315 centrifugal pump reverse-acting turbine was selected as the research object. On the basis of the concept of long, medium, and short blades, 6 medium blades and 12 short blades are added to the original 6-blade impeller to construct two composite impeller models, Z = 6 + 6 and Z = 6 + 6 + 12. The effect of composite impellers on the external characteristics, blade loads, and force characteristics of a pump as a turbine under different operating conditions was investigated through experiments and numerical simulations. The results indicate that composite impellers can improve head and efficiency and improve internal flow uniformity at low flow rates, but channel blockage at high flow rates can reduce efficiency. Both the Z = 6 + 6 and Z = 6 + 6 + 12 models can significantly reduce tongue pulsation, optimize the blade load distribution at low flow rates, and effectively reduce radial and axial forces, enhancing operational stability. At low flow rates, the radial force of the Z = 6 + 6 + 12 model decreases by 54.63% compared to the Z = 6 + 6 model and decreases by 37.09% compared with that of the original model; its axial force is reduced by 0.071%, which is better than 0.064% for Z = 6 + 6. Therefore, Z = 6 + 6 + 12 is the optimal model, which can guide the optimization of the pump as the impeller of turbine and ensure stable operation of the unit.
Zong et al. (Sun,) studied this question.