Influence mechanism of splitter blades on unstable flow and energy loss in the hump region of a pump-turbine

As the core equipment in pumped storage power station, the stability of the pump-turbine significantly impacts the safe and steady operation of the station, however, the frequent occurrence of the hump region under pump mode leads to a sharp deterioration in unit stability, severely affecting the normal operation of the power station. To address this, this study combines reverse design with numerical simulation to systematically investigate the influence of three splitter blade configurations (6 + 6, 7 + 7, and 8 + 8) on the flow characteristics within the hump region. The research indicates that while the efficiency of pump-turbines with splitter blades decreases slightly due to the increased blade count, the head enhancement is significant, with the 8 + 8 runner performing the best; at the runner inlet, flow uniformity near the hub is less affected by blade configuration, whereas in the mid-span and near-shroud regions, the standard deviation of flow angles for the modified runners are significantly lower than that of the original runner, indicating superior flow stability; at the runner outlet, the 8 + 8 runner exhibits a more regular flow angle distribution and lower peak dispersion, effectively suppressing flow separation, whereas the prototype and 6 + 6 runners show higher flow non-uniformity, which tends to induce energy loss; pressure pulsation analysis further validates these findings, as the 8 + 8 runner significantly reduces the dominant frequency amplitudes and the root mean square (RMS) values within the critical low-frequency band of flow instability in both the frequency and time domains, with better control over the crest factor and effective suppression of flow separation. Overall, through the optimization of splitter blade design, the 8 + 8 runner demonstrates comprehensive leadership in head performance, flow stability, and pressure pulsation control, and these research findings provide an important reference for the high-efficiency and stable design of pump-turbines.