Hydraulic efficiency improvement in a pump-turbine based on three-dimensional runner blade design: A comparative study

Pump-turbine runner design critically enhances the efficiency across the entire operating range of the pump and turbine modes. In this study, three sets of design parameters from different parts of the runner blade are selected for runner optimization: blade loading (BL) and blade high-/low-pressure side (BHS/BLS) control parameters. The optimization objectives are the efficiencies at the pump design, turbine rated, and turbine 40% load conditions. The optimization results indicate that, for efficiency under the pump design condition, the BHS optimization demonstrates the most significant improvement, followed by the BLS optimization, and then the BL optimization. For efficiency under the turbine rated condition, both the BHS and BLS optimizations yield comparable improvements, outperforming the BL optimization. For efficiency under the turbine 40% load condition, both the BL and BLS optimizations achieve notably better results than the BHS optimization. A main effect analysis reveals that all three optimization objectives are more sensitive to the BLS design parameters, followed by the BHS design parameters, and then the BL parameters. The entropy production rate (EPR) analysis shows that, for both the pump design and turbine rated conditions, the BHS and BLS optimizations substantially reduce the high-EPR area, whereas the BL optimization exhibits a weaker effect. For the turbine 40% load condition, both the BL and BLS optimizations significantly decrease the high-EPR area in the runner, whereas the BHS optimization shows no improvement. Overall, the BLS optimization method outperforms the other approaches, significantly enhancing the pump-turbine efficiencies across a wide load range.