Search Results (13)

Pumped storage power is considered an ideal regulated power source for new energy. However, the traditional one-dimensional characteristic line method cannot predict the pulsating pressure caused by the reverse “S” characteristic of a pump–turbine. In this paper, a variable-step Euler algorithm is presented to calculate the hydraulic transient process of pumped storage units, the interval times of start-up and load regulation between two pump–turbine units are investigated by using the method of peak staggering and valley filling, and the closure law of guide vanes in the transient process of load rejection is optimized. The results show that the presented method is valid, and that pulsating pressure is accurately captured during the transient process of load rejection. The water level fluctuation amplitude in the surge chamber is greatly reduced by the sequential start-up mode. The rotational speed fluctuation amplitude of the sequential load reduction is also reduced. After the load of two pump–turbine units is rejected at the same time, the duration of pulsating pressure in the spiral case is shortened by 45% by using the quick-then-slow closure law compared with the straight-line closure law. Moreover, the pulsating pressure amplitude and the second peak value of rotational speed are also reduced accordingly, and the transient characteristics of the pump–turbine units are greatly improved. Full article

To address the escalating demand for power grid load regulation, pumped storage power stations must frequently switch between operational modes. As a key component of such stations, the pump turbine has seen extensive research on its steady-state flow behavior. However, the intricate dynamics of its transient flow have not yet been thoroughly examined. Notably, the no-load condition represents a quintessential transient state, the instability of which poses challenges for grid integration. Under certain extreme conditions, this could result in the impairment of the unit’s elements, interruption of its functioning, and endangerment of the security of the power station’s output as well as the stability of the power network’s operations. Thus, investigating the flow characteristics of pump turbines under no-load conditions is of significant practical importance. This paper focuses on the transient flow characteristics of a Weifang hydro-generator unit under no-load conditions, exploring the internal unsteady flow features and their underlying mechanisms. The study reveals that under no-load conditions, the runner channel is obstructed by a multitude of vortices, disrupting the normal pressure gradient within the runner and resulting in substantial hydraulic losses. Within the draft tube, a substantial reverse flow zone is present, predominantly along the walls. This irregular flow pattern within the tube generates a potent, stochastic pressure fluctuation. In addition to the interference frequencies of dynamic and static origins, the pressure pulsation frequency at each measurement point also encompasses a substantial portion of low-frequency, high-amplitude components. Full article

During the operation of a reversible pump-turbine, a hump area can easily appear under the pump condition, which will greatly affect the performance of a storage unit, with pressure pulsation being the key factor for the stable operation of a pump-turbine. Therefore, in order to explore the pressure pulsation characteristics of each flow component in the hump area, this paper first compared the full characteristics of the model test under different working conditions, and then it analyzed the pressure pulsation characteristics. By analyzing the pressure pulsation characteristics in the unit’s flow component under different flow rates in the hump area, the pulsation rule of a pump-turbine running in the hump area was revealed. It was found that the peak-to-peak value of the draft tube in the hump area was the smallest under the optimal flow condition, and the peak-to-peak value increased along the flow direction, with the rotor and stator interaction (RSI) effects being continuously enhanced. When away from the runner basin, the influence of RSI gradually weakened after leaving the runner. No low frequency was found in the optimal traffic. The peak-to-peak value of the low flow condition increased compared with the optimal flow condition, and the distribution was not uniform. The main frequency of the whole basin was relatively complex, indicating that the flow of water was unstable in the condition of partial load, resulting in the hump area during the unit operation. The research results can provide a theoretical reference for improving the stability of pump-turbines. Full article

Pump–turbine units with high heads are subjected to strong pressure pulsations from the unsteady transient flow in fluid channels, which can produce severe vibrations and high stresses on the pump–turbine structural components. Therefore, reducing transient flow-induced stresses on prototype reversible pump–turbine units is an important measure for ensuring their safe and efficient operation. A high-head prototype reversible pump–turbine with a rated head of 440 m was used to investigate the transient flow characteristics and the flow-induced-stresses in this study. First, the flow passages of the pump–turbine unit and the structure of the reversible pump–turbine runner were constructed with CAD tools. Next, CFD simulations at the full load were performed to investigate the pressure pulsation characteristics of the pump turbine in both the time domain and the frequency domain. After this, the pressure files calculated by the CFD were exported and applied to a finite element model of the pump–turbine runner to calculate the transient flow-induced dynamic stresses. The results show that the pressure pulsations in the flow passage are closely related to the rotational speed, the guide vane number, and the runner blade number of the pump–turbine unit. The maximum flow-induced stresses on the pump–turbine runner at the full load were below 2 MPa and lower than the allowable value, which reveals that the designs of the pump–turbine runner and the flow passage are acceptable. The conclusions can be used as a reference to evaluate the design of high-head pump–turbines units. The approaches used to carry out the transient flow-induced stress calculations can be applied not only to pump–turbines units but also to other types of fluid turbomachinery such as pumps, turbines, fans, compressors, turbochargers, etc. Full article

The focus of this paper is to investigate how various numbers of blades impact the performance of a two-way contra-rotating axial-flow pump-turbine when operating in pump mode. In order to meet the two-way operation of the pump-turbine, the front and rear impellers are mirror-symmetric with the same hydraulic model, which ensures the consistent performance of the forward and reverse working conditions. However, when the two-stage impellers have the same number of blades, the dynamic–dynamic interference can be severe, which can threaten the stability of the unit. The present study explores the use of two-stage impellers with varying numbers of blades as a means of enhancing the performance of tidal energy units. By conducting numerical simulations on the front and rear impellers under different flow rates in pump mode, the impact of increasing the number of blades in each stage on the external characteristics of the pump-turbine is revealed. The internal flow characteristics of different models are analyzed, and the impact of the number of blades on the vortex is studied. Different blade numbers will have a certain impact on the internal flow of the two-way contra-rotating axial-flow pump–turbine. Increasing the number of blades will affect the development of tip-leakage vortices and promote their intersection with the wake. In addition, changes in the number of blades will have an impact on the location of the leading edge (LE) water impact on the rear impeller, which in turn affects the contours of vorticity of the rear impeller near the LE and the location of the suction surface (SS) flow separation. The findings of this study offer valuable insights for future research on the operation of contra-rotating axial-flow pump-turbines. Full article

An axial-flow pump as a turbine (PAT), as compared to the conventional Francis turbine, has the advantages of not being restricted by the terrain and having lower cost to reverse the pump as a turbine for power generation. When an axial-flow pump is reversed as a turbine, the internal flow pattern is more complicated than when in the pump mode, which can cause instability in the whole system and result in degradation of the hydraulic performance and structural vibration. The impeller and guide vane are the core of the axial-flow PAT unit. This research compares the experimental and numerical simulation results in order to verify the energy performance and pressure pulsation signal of the axial-flow PAT. The unsteady flow regime, fluid force, and pressure pulsation characteristics of the impeller-guide vane hydraulic coupling zone are analyzed in detail. The findings demonstrate that both the dominant frequency of the fluid force pulsation signal and the flow field pressure pulsation signal appear at 3 times of the rotation frequency. The blade passing frequency (BPF) of the impeller is the dominant frequency, and other frequency components are also dominated by the harmonic frequency of the BPF. The impeller and guide vane are primarily subject to radial fluid force. Under partial working conditions, the pressure pulsation intensity in the flow field greatly increases, and the pressure pulsation amplitude at the guide vane outlet and impeller outlet appears to be more sensitive to the flow rate change. Full article

A major issue in the renewable energy supply of buildings is to establish a simultaneity of the fluctuating renewable energy generation and the energy consumption in buildings. This work provides a new case for a better understanding of how to establish this simultaneity. Future solutions are being explored in practice on the campus of the FH Westküste University of Applied Sciences in the Lecturing and Exhibition Building (LEB). The motivation was to design and operate a case building for research in energy science for teaching the bachelor’s program Green Building Systems as well as for demonstration purposes for the general public. With a floor space of 207 m, the LEB is supplied with renewable energy from the adjacent energy park consisting of a 10 kW wind turbine and photovoltaic modules with 10 kWp. The heat and cold generation system consists of two reversible heat pumps: one is an air–water heat pump with approx. 7 kW heating and 6 kW cooling power, and the second is a brine–water heat pump with approx. 8 kW heating power and a depth of the two boreholes of 80 m. To match the energy generation and the energy consumption, different kinds of storage units, i.e., batteries with 3 × 8 kWh and storage tanks with 1000 L heat storage and 600 L cold storage, were installed as well as a smart automation system with a database. This paper evaluates measurement data from 2021. It is demonstrated that a fully renewable energy supply of the building is possible for most of the time from spring to autumn. In winter, an additional long-term energy storage, e.g., hydrogen, is necessary for certain days. Full article

The internal flow problem of a reversible pump turbine restricts its safe and stable operation. Among them, the influence of the guide vane on the internal flow field is very crucial. The flow–head relationship is of great significance in the performance stability of the unit. In this study, the performance and flow field characteristics under different flow rates were analyzed for different guide vane opening angles. By comparing the results of the model test and computational fluid dynamics simulation, it was found that the simulation can well predict the energy characteristics and flow field distribution. There is an optimal efficiency range under each guide vane opening angle. The increase or decrease in flow will reduce the efficiency. For the head, it will decrease significantly with a decrease in the flow rate, especially when it deviates seriously from the optimal efficiency region. From the contour of the flow energy loss and the vector of velocity, it can be seen that the head drop is closely related to the flow blockage caused by the difference between the runner incoming flow direction and the installation direction of the guide vane. This study deeply revealed the valley and peak of head variation under different guide vane opening conditions. It can provide technical support for improving the wide range operation stability of a pump turbine. Full article

During the load rejection transient process of the prototype pump turbine units, the pressure fluctuations of the entire flow passage change drastically due to the rapid closing of guide vanes. The extremely unsteady pressure distribution in the flow domains including the crown chamber and the band chamber may cause a strong vibration on the stationary structures of the unit and result in large dynamic stress on the head cover, stay ring and bottom ring. In this paper, the numerical fluid dynamic analysis of the entire flow passage of a reversible prototype pump turbine during load rejection was performed. The flow characteristics in the runner passage, crown chamber, band chamber, seal labyrinths and balance tubes are analysed. The corresponding unsteady flow-induced dynamic behaviour of the head cover, stay vanes and bottom ring was investigated in detail. The analysed results show that the total deformation of the inner edge of the head cover closed to the main shaft is larger than that of other stationary structures of the unit during the load rejection. The maximum stress of the stay ring is larger than that of the head cover and the bottom ring and the maximum equivalent stress is located at the fillet of the stay vane trailing edge. The fluid–structure coupling calculation method and the analysed results can provide guidance for the design of stationary components of hydraulic machinery such as pump turbines, Francis turbines and centrifugal pumps with different heads. Full article

When the Francis-type reversible pump-turbine runs under partial load, the pressure pulsation amplitude and frequency in vaneless space are high, posing a serious threat to the stability of unit operation. Water presents weak compressibility in a high-head pump-turbine, thereby affecting the amplitude–frequency characteristics of pressure pulsation. This study used numerical simulations in a model and prototype pump-turbine and particle image velocimetry (PIV) in a model pump-turbine to examine the internal flow field and pressure pulsation characteristics and determine the effect of the flow in the vaneless space on the amplitude–frequency characteristics of the pressure pulsation. The pressure pulsation amplitude–frequency characteristics were verified through prototype tests. The effects of the weak compressibility of the water on the propagation law of pressure pulsation throughout the flow passage of the prototype and model pump-turbine were roughly similar but exhibited certain differences. Considering the weak compressibility of water, the pressure pulsation fluctuations in each flow passage of the prototype and model pump-turbine exhibit varying degrees of improvement, which is more obvious at the prototype scale. Therefore, the pressure wave disturbance caused by the weak compressibility of the water has different effects on the prototype scale and model scale of the high-head Francis pump-turbine. Full article

Hydraulic pumped storage is a special power generation and electricity shortage technology, which is usually operated with thermal power and nuclear power units, and plays a key role in ultra-high voltage and smart grid. Pressure fluctuations are the main reasons for the instability of the S-shaped region of pump–turbines, which seriously affects their lifespan and operation stability. To reveal the mechanism and propagation law of pressure fluctuations in the S-shaped region as well as numerical simulations at the turbine, the braking and the reverse pump operating conditions of a pump–turbine were carried out. Numerical results were validated using the performance experiments, and the generation mechanism and propagation law of pressure fluctuation were analyzed in detail. The analyses show that high-amplitude pressure fluctuations mainly occur in the braking and reverse pump operating conditions. Under the braking condition, a 0.49-f_n low-frequency pressure fluctuation was captured, which is caused by the rotation of the backflow in the vanes. Under the reverse pump condition, a 0.19-f_n low-frequency pressure fluctuation was confirmed, which is caused by the periodic rotation of the vortex between the vaneless space. This study has important guiding significance for practical engineering application. Full article

The transient characteristic of the power-off process is investigated due to its close relation to hydraulic facilities’ safety in a pumped storage hydropower (PSH). In this paper, power-off transient characteristics of a PSH station in pump mode was studied using a three-dimensional (3D) unsteady numerical method based on a single-phase and volume of fluid (SP-VOF) coupled model. The computational domain covered the entire flow system, including reservoirs, diversion tunnel, surge tank, pump-turbine unit, and tailrace tunnel. The fast changing flow fields and dynamic characteristic parameters, such as unit flow rate, runner rotate speed, pumping lift, and static pressure at measuring points were simulated, and agreed well with experimental results. During the power-off transient process, the PSH station underwent pump mode, braking mode, and turbine mode, with the dynamic characteristics and inner flow configurations changing significantly. Intense pressure fluctuation occurred in the region between the runner and guide vanes, and its frequency and amplitude were closely related to the runner’s rotation speed and pressure gradient, respectively. While the reversed flow rate of the PSH unit reached maximum, some parameters, such as static pressure, torque, and pumping lift would suddenly jump significantly, due to the water hammer effect. The moment these marked jumps occurred was commonly considered as the most dangerous moment during the power-off transient process, due to the blade passages being clogged by vortexes, and chaos pressure distribution on the blade surfaces. The results of this study confirm that 3D SP-VOF hybrid simulation is an effective method to reveal the hydraulic mechanism of the PSH transient process. Full article

Due to the increasing share of new renewable energies like wind and solar in the generation of electricity the need for power regulation and energy storage is becoming of paramount importance. One of the systems to store huge amounts of energy is pumped storage using reversible hydropower units. The machines used in these power plants are pump-turbines, which can operate as a pump and as a turbine. The surplus of electrical energy during low consumption hours can be converted into potential hydraulic energy by pumping water to a higher level. The stored energy can be converted into electricity again by operating the runner as a turbine. Due to new regulation requirements machines have to extend the operating range in order to match energy generation with consumption for the grid stability. In this paper the consequences of extending the operating range in existing pump-turbines have been studied. For that purpose, the data obtained after two years of condition monitoring were analyzed. Vibrations and pressure fluctuations of two pump-turbines of 85 MW each have been studied during pump and turbine operation. For turbine operation the effects of extending the operating range from the standard range of 45–85 MW to and increased range of 20–85 MW were analyzed. The change in vibration levels and signatures at very low load are presented with the identification of the phenomena that occur under these conditions. The influence of head in the vibration behavior is also presented. The appearance of fluid instabilities generated at part load that may produce power swing is also presented. Finally, the effect of head on the vibration levels for pump operation is shown and analyzed. Full article