This study examines the S-characteristic, a key factor affecting the safe grid connection and operation of pumped-storage units, and its significant impact on the safety of pumped-storage power stations. We conducted numerical simulations and model experiments to investigate vortex motion characteristics in the vaneless space and runner passage of pump-turbines operating within the S-shaped region, along with an analysis of pressure pulsation characteristics. The accuracy of these simulations was validated through laser Doppler velocimetry experiments, and particle image velocimetry experiments were used to capture vortex motion in the vaneless space. We observed that vortices generated on the guide vane side follow the flow direction, blocking the guide vane passage, while those generated by runner blades move in the opposite direction. Employing an entropy production theory and the Liutex method, we investigated vortex distribution and hydraulic loss in the S-shaped region. The results show that reduced flow rates lead to significant vortices in the vaneless space and guide vane area, which become main contributors to energy loss in this region. These vortices, along with those in the runner passage, mainly arise from flow separation on blade and guide vane surfaces due to suboptimal inflow conditions. The study also identifies pressure fluctuations in the vaneless space, induced by a rotating stall, as the most significant pressure pulsation phenomenon, which significantly impacts the performance of the unit in both upstream and downstream directions.

Based on the solid–liquid two-phase flow model, SST k-ω model, and Lagrangian equation model of particle motion, numerical simulations of the sediment–water flow in the injector of a large Pelton turbine were conducted. The distribution rules of pressure, velocity, erosion rate, and erosion location of the injector were obtained by analyzing the sediment–water flow characteristics and sediment erosion distribution characteristics of the injector. The results revealed that the velocity distribution trend of the water inside the cylindrical jet exhibited a nonlinear distribution, and the phenomenon of “velocity deficit” occurred at the end of the needle guide and needle tip, resulting in a decrease in the jet quality of the injector. The sediment particle diameter affected the erosion rate of the needle and erosion location of the needle and nozzle port ring. This study provided guidance for sediment erosion analysis and the prediction of the utility of large Pelton turbines.

In order to investigate the impact of guide vane opening on channel vortex and pressure pulsation within the runner of a Francis turbine, this research examines the cavitation phenomenon, channel vortex phenomenon, and flow field characteristics of a power station's turbine in China. The investigation is conducted using computational fluid dynamics theory. Furthermore, the analysis focuses on the influence of changes in guide vane opening on the flow state within the turbine runner. The findings indicate that the occurrence of rotor cavitation is severe when the opening is small, and increasing the opening reduces the cavitation capacity of the rotor. The presence of a lobe vortex phenomenon is mainly observed within a small range of guide vane openings, and altering the opening modifies both the range of influence and flow characteristics of the lobe vortex. In the middle range of guide vane openings, vortex pressure pulsation dominates within the rotor, with the highest amplitude of pressure pulsation occurring at a 60% opening. In the large opening range, pressure pulsation mainly occurs in the lobe frequency pressure pulsation of the rotor within the lobe-less area. The amplitude of blade frequency is typically small, indicating good hydraulic stability of the unit. These study results elucidate the interval of stable operating conditions for the unit and offer valuable insights for maintaining its stable operation.

During the operation of a Pelton turbine, the centerline of the nozzle jet may deviate from the bucket pitch circle due to the low installation and maintenance accuracy, which will reduce the operating efficiency and the stability of the turbine and even cause severe vibrations and damages. Based on the VOF (Volume of Fluid) two-phase flow model and the SST k-ω turbulence model, the flow characteristics of a Pelton turbine were simulated with the nozzle jet deviating from the bucket pitch circle. The pressure pulsation inside the bucket and the force distribution of the runner were obtained, the turbine oscillation and efficiency were measured before and after the jet deviation, and the effects of the radial and axial deviations on the stability and efficiency of the Pelton turbine were analyzed. The results show that both the radial and axial deviations of the jet cause a significant increase in the axial force and the pressure pulsation amplitude of the turbine; the radial and tangential forces on the runner are slightly reduced; the maximum axial force on the runner is increased by 4 times and 2 times, respectively, after the axial and radial deviations within the maximum value allowed by the industry standard; and the efficiency of the turbine is reduced by 0.4% and 0.3%, respectively. The maximum relative amplitude of pressure pulsation in the radial offset case appears in the center of the bucket blade, while the axial offset case causes uneven pressure distribution on both sides of the diverter blade, uneven force on the bucket blade of the runner, and fatigue damage. By comparing the operation of the runner under the two offset cases, we can find that the axial offset of the jet has a greater impact on the stability of the runner than the radial offset, and the unit is more prone to vibration, increasing the risk of the unit lifting.

The Kizilsu River Basin in China is located in the desert Gobi area with high sediment content and high hardness. After 4798h operation, the maintenance of a high‐head Francis turbine in this basin found that the guide vane was seriously worn, and even most of the top and lower skirts of the front of the guide vane were worn off. In this study, the k‐ε turbulence model, ZGB cavitation model and sediment erosion prediction model were used to simulate the solid‐liquid two‐phase flow and cavitation of guide vane. The research results show that the guide vane of a high‐head Francis turbine in a sandy river has a high sediment velocity and serious surface erosion, with the maximum erosion rate of 1.0 × 10⁻⁶ kg/(m²·s), while the area near the skirt of the guide vane is a low‐pressure area lower than the saturated steam pressure, and cavitation is very easy to occur, with the maximum vapor volume fraction of 0.9. Serious cavitation erosion occurs near the skirt of the guide vane, and the combined effect of sand erosion and cavitation erosion on the surface of the skirt of the guide vane aggravates the damage of the skirt structure. The research results provide a technical basis for the antiabrasion design of the guide mechanism of the high‐head Francis turbine and the operation and maintenance of the hydropower station in the sandy river.

When a Pelton turbine operates in sand laden water, the abrasive wear of its overflow components by high-speed jets is serious. Based on the VOF (volume of fluid) multiphase flow model, the SST (shear stress transfer) k-ω turbulence model, the particle motion Lagrangian model, the generic wear model, and the SIMPLEC (Semi-Implicit Method for Pressure Linked Equations Consistent) algorithm, the liquid–air–solid three-phase flow in the key overflow components of a Pelton turbine were simulated, the abrasive wear was predicted, and the internal sand-water flow characteristics and the abrasive wear of the overflow components were analyzed. The results show that the trailing edge at the root of the runner bucket, the leading face of the bucket near the root, the notch, and the splitter are severely worn. The abrasive wear of the splitter and the notch is more severe than that of the leading face of the bucket. The wear rate from the splitter to the trailing edge increases first and then decreases. The wear pattern of the needle tip is mainly “dotted”, while that of the nozzle opening is “flaky”, and the abrasive wear of the nozzle opening is more severe than that of the needle. The predicted results are consistent with the actual conditions at the site of the power station. This study provides a technical method for the prediction of abrasive wear of the Pelton turbine and a technical basis for the operation and maintenance of the power station.