scholarly journals Internal Mechanism and Improvement Criteria for the Runaway Oscillation Stability of a Pump-Turbine

2018 ◽  
Vol 8 (11) ◽  
pp. 2193 ◽  
Author(s):  
Qin Zhou ◽  
Linsheng Xia ◽  
Chunze Zhang
Keyword(s):  
Energy Dissipation ◽  
Guide Vane ◽  
Flow Characteristics ◽  
Energy Dissipation Rate ◽  
Sharp Change ◽  
Pump Turbine ◽  
Oscillation Process ◽  
Internal Mechanism ◽  
Pumped Storage ◽  
Runaway Process

The runaway oscillation process of the pump-turbine in a high head pumped-storage power plant is usually unstable. The root cause of its instability is still unclear. In this paper, its internal mechanism and the improvement method were studied in depth. First, the flow characteristics in a model pump-turbine during the runaway process at four guide-vane openings (GVOs) were investigated by 3D transient numerical simulations. Then, the energy dissipation characteristics of different types of backflow vortex structures (BFVSs) occurring at the runner inlet and their impacts on the runaway stability were investigated by the entropy production theory. The results show that the location change of BFVSs between the hub side and the mid-span of the runner inlet around the no-load point leads to the sharp change in the energy dissipation rate, which makes the slope of dynamic trajectory positive and the runaway oscillation self-excited. If the occurrence of BFVSs at the hub side is suspended, the runaway process will be damped. Finally, the pump-turbine runner was improved to obtain a wider stable operating range.

Domain Partitioned Transformation of Pump-Turbine Characteristic Curves in 3-D Space

2014 ◽  
Author(s):  
Wei Zeng ◽  
Jiandong Yang ◽  
Yongguang Cheng
Keyword(s):  
Guide Vane ◽  
Theoretical Method ◽  
Transformation Method ◽  
Measured Data ◽  
Pump Turbine ◽  
Characteristic Curves ◽  
Hydraulic Transient ◽  
Transient Simulations ◽  
Pumped Storage ◽  
Conventional Representation

Pump-turbine characteristic curves are the most important boundary condition in the hydraulic transient simulation of a pumped-storage hydropower station. Conventional representation of them, however, has serious defects, For instance, the “S” and “hump” shapes, composed of multiple values and steep twists, lead to the difficulty in interpolation between known guide-vane opening curves, which is necessary in hydraulic transient simulations. Here, a new transformation method was figured out to settle this problem thoroughly and to improve the accuracy of interpolation between the constant opening curves. Prior to the transformation, the characteristic curves are partitioned into eight domains. Curves of each domain were transformed through different formulae that fit the curves well. Eight characteristic surfaces in the 3-D space can be obtained by adding the guide vane opening as the coordinate axis. The theoretical method has been validated by the excellent agreements achieved by comparing the curves interpolated on the characteristic surfaces with the measured data.

scholarly journals Analysis of Internal Flow Characteristics of a Startup Pump Turbine at the Lowest Head under No-Load Conditions

2021 ◽  
Vol 9 (12) ◽  
pp. 1360
Author(s):  
Wei Wang ◽  
Xi Wang ◽  
Zhengwei Wang ◽  
Mabing Ni ◽  
Chunan Yang
Keyword(s):  
High Speed ◽  
Pressure Pulsation ◽  
Working Condition ◽  
Guide Vane ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Operating Conditions ◽  
Small Range ◽  
Pressure Balance ◽  
Pump Turbine

The instability of the no-load working condition of the pump turbine directly affects the grid connection of the unit, and will cause vibration and damage to the components of the unit in severe cases. In this paper, a three-dimensional full flow numerical model including the runner gap and the pressure-balance pipe was established. The method SST k-ω model was used to predict the internal flow characteristics of the pump turbine. The pressure pulsation of the runner under different operating conditions during the no-load process was compared. Because the rotation speed, flow rate, and guide vane opening of the unit change in a small range during the no-load process, the pressure pulsation characteristics of the runner are basically the same. Therefore, a working condition was selected to analyze the transient characteristics of the flow field, and it was found that there was a high-speed ring in the vaneless zone, and a stable channel vortex was generated in the runner flow passage. Analyzing the axial water thrust of each part of the runner, it was found that the axial water thrust of the runner gap was much larger than the axial water thrust of the runner blades, and it changed with time periodically. It was affected by rotor stator interaction. The main frequency was expressed as a multiple of the number of guide vanes, that is, vanes passing frequency, 22fn. During the entire no-load process, the axial water thrust of the runner changed slowly with time and fluctuated slightly.

Flow Analysis of the Guide Vanes Region of Pump Turbine at the Slight Opening in the Pumping Startup Process

2016 ◽  
Author(s):  
Honggang Fan ◽  
Qingfeng Ji ◽  
Weili Liao ◽  
Haixia Yang
Keyword(s):  
Guide Vane ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Main Flow ◽  
Three Dimensional Model ◽  
Pump Turbine ◽  
Guide Vanes ◽  
Abrupt Changes ◽  
Dimensional Simulation ◽  
Pumped Storage

The unit of a Pumped Storage Power Station experienced abnormal noise and vibration in the guide vanes at the slight opening when the pump turbine was in the process of startup in the pumping mode. Based on this phenomena, the three dimensional model of the pump turbine was established, RNG k-epsilon two equations turbulence model was selected for the flow numerical simulation in the pump turbine because this model can simulate both the flow separation and vortex dynamics, and it is more accurate in the near wall areas. The governing equations were discretized with the finite volume method. The computation was carried out with three steps, 1.steady calculation, 2.unsteady calculation with constant guide vane opening, 3.unsteady calculations with the increase of the opening of guide vanes, by using the results of the last step as the initial condition. According to the three dimensional simulation results, the main flow between the guide vanes was deflected from attaching to the one vane to the other vane with the opening of the guide vanes. The calculation of complete 3D flow indicated that the deflections of the flows between the different adjacent guide vanes were basically the same, however, the deflections starting times had a few differences. The variation of the torque on the guide vane was also investigated, and the results shown the abrupt changes occurred during the deflection process of the main flow. When the torque produced by the servomotor cannot adapt quickly enough to the abrupt changes, the vibration and loud scrape noise might occur.

scholarly journals Optimization of Pump Turbine Closing Operation to Minimize Water Hammer and Pulsating Pressures During Load Rejection

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 1000 ◽  
Author(s):  
Jiawei Ye ◽  
Wei Zeng ◽  
Zhigao Zhao ◽  
Jiebin Yang ◽  
Jiandong Yang
Keyword(s):  
Guide Vane ◽  
Water Hammer ◽  
Nsga Ii ◽  
Pump Turbine ◽  
Guide Vanes ◽  
Multi Objective ◽  
Spiral Case ◽  
Transitional Processes ◽  
Pumped Storage ◽  
Load Rejection Process

In load rejection transitional processes in pumped-storage plants (PSPs), the process of closing pump turbines, including guide vane (GVCS) and ball valve closing schemes (BVCS), is crucial for controlling pulsating pressures and water hammer. Extreme pressures generated during the load rejection process may result in fatigue damage to turbines, and cracks or even bursts in the penstocks. In this study, the closing schemes for pump turbine guide vanes and ball valves are optimized to minimize water hammer and pulsating pressures. A model is first developed to simulate water hammer pressures and to estimate pulsating pressures at the spiral case and draft tube of a pump turbine. This is combined with genetic algorithms (GA) or non-dominated sorting genetic algorithm II (NSGA-II) to realize single- or multi-objective optimizations. To increase the applicability of the optimized result to different scenarios, the optimization model is further extended by considering two different load-rejection scenarios: full load-rejection of one pump versus two pump turbines, simultaneously. The fuzzy membership degree method provides the best compromise solution for the attained Pareto solutions set in the multi-objective optimization. Employing these optimization models, robust closing schemes can be developed for guide vanes and ball valves under various design requirements.

scholarly journals Experimental and numerical investigation of flow over a spillway bend with different combinations of permeable spur dikes

2021 ◽  
Author(s):  
Jinmeng Yang ◽  
Zhenzhong Shen ◽  
Jing Zhang ◽  
Xiaomin Teng ◽  
Wenbing Zhang ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Dissipation Rate ◽  
Water Surface ◽  
Longitudinal Velocity ◽  
Flow Characteristics ◽  
Energy Dissipation Rate ◽  
Bottom Plate ◽  
Dye Tracing ◽  
Spur Dike ◽  
Spur Dikes

Abstract In this paper, the effects of different combinations of permeable spur dikes installed in the bend section of spillway on flow characteristics and energy dissipation rate were experimentally and numerically investigated. The results indicate that The permeable spur dikes installed in the spillway bend appreciably contributes to the improvement on the water surface uniformity, and the water surface uniformity can reach 90.13% with three permeable spur dikes installed in the bend. The permeable spur dike can lead to different degrees of decrease in the time-averaged longitudinal velocity in each zone of spillway bend. Different from previous study, no circulation zone is formed upstream and downstream of permeable spur dike due to the presence of permeable holes, and the flow upstream of permeable spur dikes could be divided into three distinctly different flow modes according to dye tracing. The presence of permeable spur dikes causes the concentration of TKE zone at concave bank of the spillway bend, except for TKE zone immediately next to the bottom plate. The TKE first increases and then decreases with the increase in the vertical distance from the bottom plate of the spillway bend, exhibiting a typical parabolic distribution. The energy dissipation rate in the spillway bend with permeable spur dike was calculated using a modified integral method, and the dissipation rate can reach as high as 21.08% with three spur dikes installed in the bend.

Mechanism and influence factors of hydraulic fluctuations in a pump-turbine

2021 ◽  
pp. 095765092110285
Author(s):  
Xiaolong Fu ◽  
Deyou Li ◽  
Hongjie Wang ◽  
Guanghui Zhang ◽  
Xianzhu Wei
Keyword(s):  
Guide Vane ◽  
Three Dimensional ◽  
Influence Factors ◽  
Simulation Method ◽  
Power Station ◽  
Pump Turbine ◽  
Available Energy ◽  
Exciting Forces ◽  
Pump Storage Power ◽  
Pumped Storage

Pumped-storage power technology is currently the only available energy storage technology in the grid net, and its reliability is receiving attention increasingly. However, when a pump-turbine unit undergoes runaway transitions, hydraulic fluctuations intensively affect the reliable operation of a pumped-storage power station. To reduce hydraulic fluctuations, this study investigated the formation mechanism of hydraulic fluctuations and explored its influence factors. In this study, a developed one-dimensional and three-dimensional (1 D-3D) coupling simulation method was adopted. Transient runaway transitions of a pump-turbine with three different inertias (0.5 J, 1 J, and 2.0 J) at three different guide vane openings (21°, 15°, and 12°, respectively) were simulated and compared. The results suggest that, at smaller guide vane openings (15° and 12°), water hammer owing to the increase in rotational speed is the primary unstable issue compared to the pulsation of radial hydraulic exciting forces on the runner. However, at a larger guide vane opening (21°), the latter owing to the back-flow near the runner inlet is the primary unstable issue. Moreover, it is found that a sufficiently large inertia improves the hydraulic fluctuations of the pump-storage power station, particularly in reducing the pulsation of radial hydraulic exciting loads on the runner. The findings of this study provide a valuable reference for determining suitable rotor inertia.

scholarly journals Hydraulic Characteristics and Numerical Simulation of the Entrance Section of Ladder-Shaped Spillway

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
X. B. Gu ◽  
Q. H. Wu ◽  
Y. Wang ◽  
H. X. Zhao
Keyword(s):  
Numerical Simulation ◽  
Energy Dissipation ◽  
Dissipation Rate ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Energy Dissipation Rate ◽  
Numerical Results ◽  
Experimental Results ◽  
Flow State ◽  
Hydraulic Characteristics

The ladder-shaped spillway in a certain reservoir junction is set as the engineering background in the paper. The hydraulic similarly model experiment and three-dimensional numerical simulation of hydraulic characteristics of water flow are performed. The outflow capacity, flow state analysis, velocity distribution, water surface line, pressure, and the energy dissipation rate are analyzed, and experimental results are compared with the numerical results. The conclusions demonstrate that the numerical results of the flow characteristics are very proximate to actual experimental results, the changeable law is the same, and their energy dissipation rate is basically consistent; it shows the feasibility of three-dimensional numerical simulation; the conclusions can provide the basis for the optimization about the flow state of the ladder-shaped spillway in the future.

Effect of Interface Condition on the Hydraulic Performance of a Pump-Turbine at Various Guide Vane Opening Conditions in Pumping Mode

2019 ◽  
Author(s):  
Jun-Won Suh ◽  
Seung-Jun Kim ◽  
Young-Seok Choi ◽  
Jin-Hyuk Kim ◽  
Won-Gu Joo ◽  
...  
Keyword(s):  
Stokes Equations ◽  
Guide Vane ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Rotating Stall ◽  
Interface Condition ◽  
Navier Stokes ◽  
Pump Mode ◽  
Pump Turbine ◽  
High Flexibility

Abstract Nowadays, pumped-storage power stations require high flexibility and reliability in operation under off-design conditions, especially in the pump mode. When a pump-turbine operates under various part load conditions in pump mode, highly dynamic phenomenon such as stationary vortex and rotating stall occur. Therefore, the performance characteristics in pump mode are vital for the safe and effective operation. A number of studies have been conducted to investigate the flow characteristics in turbine or pump mode under different GVOs through numerical simulations. However, the studies about influence of the position of interface and interface condition on the pump characteristics of pump-turbines are not completely clear. In this paper, the three-dimensional steady and unsteady Reynolds-averaged Navier–Stokes equations were solved for a detailed analysis of the influence of interface conditions with various guide vane opening conditions in pump mode. To ensure the reliability of the numerical analysis, the numerical results were validated in comparison with the experimental data.

Effect of the Speed Factor On the Amplitude of the Blade Passing Frequency in the Vaneless Space of a Pump Turbine in Turbine Mode

2021 ◽  
Author(s):  
Jinhong Hu ◽  
Jiebin Yang ◽  
Wei Zeng ◽  
Jiandong Yang
Keyword(s):  
Strouhal Number ◽  
Goodness Of Fit ◽  
Guide Vane ◽  
Mathematical Relationship ◽  
Pump Turbine ◽  
Speed Factor ◽  
Blade Passing Frequency ◽  
Rotor Stator Interaction ◽  
Pumped Storage ◽  
Turbine Mode

Abstract An exponential expression describing the relationship between the amplitude of the blade passing frequency in the vaneless space of a pump turbine operating in the turbine mode and the speed factor is proposed based on statistical analysis. This mathematical relationship was discovered through signal processing of the data recorded during the emergency load rejection process of a prototype pump turbine. Subsequently, based on the pumped-storage test rig at Wuhan University, an experimental investigation was conducted to verify this mathematical relationship. The results indicated that, under the optimal guide vane opening of the model pump turbine, the goodness of fit of this mathematical relationship was quite high. As for the Francis pump turbine, the speed factor corresponds to the Strouhal number. Therefore, for this correlation, the underlying physical mechanism is the influence of the Strouhal number. This relation could inform the design and operation of pump turbines to control the intensity of pressure pulsations in the vaneless space. In addition, based on this mathematical relationship, the intensity of the rotor-stator interaction for different pump turbines can be compared quantitively.

Study of flow characteristics in the S-shaped region of a pump-turbine at Baoquan pumped storage power station

2015 ◽  
Vol 10 (2) ◽  
pp. 242-249
Author(s):  
Jun Li ◽  
Yongmei Cao ◽  
Lei Wang ◽  
Xiaochong Chen
Keyword(s):  
Cfd Simulation ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Modern Society ◽  
Stable Operation ◽  
Power Station ◽  
Pump Turbine ◽  
Research Findings ◽  
Computational Fluid Dynamics Cfd ◽  
Pumped Storage

Pumped storage power plays increasingly important roles in modern society but requires some complex equipment. The characteristics of the S-shaped region of a reversible pump-turbine caused significant difficulties in the stable operation of the unit. In this paper, the 1# pump-turbine at Baoquan storage power station is studied. The basic variations of the internal flow were understood using Computational Fluid Dynamics (CFD) simulation, and the relationship between head variation and the ‘S’ characteristic was analyzed. It was found that the basis of the ‘S’ characteristics was channel congestion caused by vortices. Methods that might be used to eliminate the effects of the ‘S’ characteristic are also given. The authors believe that the research findings in this paper could provide the technical support needed for stable operation of such units, as well as further studies of the ‘S’ characteristic.

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