This study conducts numerical simulations and experimental tests of a model pump turbine to explore the improvement and influence of an optimized runner blade profile on the flows in a reversible pump turbine working in the hump region. A simulation analysis on its performance is made for the optimized C-type profile. Based on the vortex identification method

we discuss the flow and vortex distributions in each section of its flow passage in the hump region before and after runner modification

and reveal the influence of the new profile on the flows in the hump region. We find that after optimization

the hump range and hump margin of the pump turbine are smaller

and the trend of its head variations with flow rate is milder. And

the vortex zones become smaller in its draft tube

guide vane section

and runner section under a large flow rate. Compared with the model before optimization

the backflow is significantly reduced

and only a small amount of backflow comes from the rotating runner at the draft tube outlet under the hump region conditions. The zones of flow separation in the guide vane and runner sections are reduced

and the vortices in the vaneless region are significantly reduced

indicating the runner blade profile optimization helps improve the hump characteristics and internal flow characteristics of the pump.