Tip leakage vortex has an important influence on the performance of semi-open centrifugal pumps. Simulations based on the three-dimensional Reynolds-Averaged Navier–Stokes were conducted to study the structural characteristics of tip leakage vortex and its effects on the internal flow field, and the Shear Stress Transport k-ω turbulence model was used to simulate the whole flow passage of centrifugal pumps with tip clearances of 0 mm and 1 mm. Then, the tip leakage vortex was analyzed using the relative vorticity transport equation. The numerical data and experimental results agreed well. The leakage vortex formed in the tip clearance led to 18.7% and 14.4% decrease in head and efficiency under design condition, respectively, and the bigger the flow rate, the fast the performance decreased. Tip leakage vortex formed at the leading edge of the blade moved along the suction surface. Whereas the tip leakage vortex formed near the middle of the blade extended to the pressure surface of the adjacent blade. This phenomenon deteriorated the flow field and induced passage vortex, thereby reducing the static pressure and blade load and changing the static pressure distribution law. The formation and development of leakage vortex could be attributed to the relative vortex stretching the term. The Coriolis force term could reflect the change of vorticity caused by leakage flow, and the viscous diffusion term served as the vorticity source.

The flow pattern of the forebay of the pumping station has a considerable effect on the operating efficiency and stability of the pump unit. A good forebay flow pattern can enable the pump unit to improve efficiency and operating conditions. This study takes a large pumping station as the research object and considers two rectification schemes, namely, a single bottom sill and a “bottom sill + diversion pier”. Without rectification facilities under different start-up schemes, the forebay flow pattern after the addition of rectification facilities is calculated, and the influence of single and combined rectification facilities is analyzed. Results show large-scale undesirable flow structures such as backflow and vortex in the forebay of the original design that without rectification facilities and uneven flow distribution occurs in the operating unit. The addition of a bottom sill in the forebay can control the central water beam from the water diversion pipe. The flow is divided to spread to both sides of the forebay and can be rectified twice after installing the diversion piers. The combined rectifier facility of “bottom sill + diversion pier” is beneficial to disperse incoming flow and make the flow distribution of each unit more uniform. The backflow and vortex inside the forepond are basically eliminated, and the flow state of the forepond is significantly improved.

The units of pumped-storage power station always have a serious instability when the pump turbine working at transition process of turbine mode. Both the steady and unsteady numerical simulation were carried out to simulate the inner flow in pump-turbine. When considering and not considering the weak compressibility of water respectively, the internal flow field of two kinds of turbine operating mode and pressure fluctuation of a small opening condition of turbine operating mode are analyzed. The results show that the ''water seals'', a plurality of annular flow area which appeared in vaneless zone, under the small opening during turbine mode and those water seals blocked infiow from the guide vane domain. A pressure pulsation, which dominant frequency is 7fn, has emerged in the vaneless space under the small opening condition during the turbine mode. The amplitude of the pressure pulsation of the case which considered the compressibility is slightly larger than the others. Additionally, a pressure pulsation, dominant frequency is rotating frequency, has occurred in draft tube. And this pressure fluctuation is related to the structure of spiral vortex. Furthermore, when the compressibility is considered, there is a pressure pulsation occurred at the main frequency of 10fn in the draft tube. Meanwhile, the spiral vortex zone becomes heavier.

The operation of semi-spiral case Kaplan turbines at large flow rate conditions is restricted by factors such as severe cavitation and severe vibration, which limit the maximum output of the unit. In order to explore the main hydraulic factors that cause the poor operating stability of the unit at large flow rate conditions, and provide a reference for the operation and design of the turbine, the numerical simulation method is adopted to conduct the performance study of an semi-spiral case Kaplan turbine at different operating conditions, by comparing and analysing the results at the optimal conditions and large flow rate conditions, the unstable hydraulic factors at large flow rate conditions is obtained. The research results show that: at large flow rate conditions, the uneven flow distribution in the semi-spiral case cause vortices between the guide vanes, lead to the large fluctuations of blade torque, and generate unstable back-flow and vortices in the draft tube. These phenomena combined with the various gap flows in the runner, make the internal flow of the Kaplan turbine at large flow rate conditions deteriorate, cavitation increase, efficiency decrease, and cause severe vibration, thereby limiting the stable operation of Kaplan turbine at large flow rate conditions.

The maximum and minimum water head difference of bulb turbine is only a few meters to ten meters, and the performance is highly sensitive to the change of water head, especially in low head operation, the bulb turbine performance deteriorates and vibration intensifies, this seriously affect the normal operation of the power station. Therefore, considering the free surface and water gravity, a numerical method is adopted to study the performance of prototype bulb turbines at different water head, by analysing the distribution of flow parameters with water head in hydraulic turbine, it is revealed that the stress of blade is uneven and the cause of cavitation and vibration at low head operation. The results show that: with the decrease of water head, the cavitation performance of the runner becomes worse, the low pressure area moves from the suction side to the pressure side of blade; the water torque of the guide vanes and the runner blades in different positions is different, which could cause the guide vane and blade angle asynchronism during adjustment; with the decrease of water head, the torque difference generated by the blades at different positions on the rotating shaft of the hydraulic turbine increase, the blades experience dynamic stresses, It threatens the strength of the blade and the stable operation of the unit.