Influences of Rotational Speed Variations on the Flow-Induced Vibrational Performance of a Prototype Reversible Pump Turbine in Spin-No-Load Mode

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Xianghao Zheng ◽  
Yuning Zhang ◽  
Jinwei Li ◽  
Yuning Zhang
Keyword(s):  
Vibrational Level ◽  
Rotational Speed ◽  
Draft Tube ◽  
Dominant Frequency ◽  
Pump Turbine ◽  
Vortex Rope ◽  
Vibrational Levels ◽  
Load Mode ◽  
Swirling Vortex ◽  
Dominant Frequencies

Abstract During the spin-no-load mode, vibrational performance of the reversible pump turbine is an important criterion for the evaluation of the operational performances of the power station. In the present paper, the influences of rotational speed variations on the vibrational performances of the whole unit (including the top cover, the upper, and the lower brackets) are experimentally investigated with discussions of their sources and propagation characteristics. According to the whole vibrational levels and the dominant frequencies of the vibration signals obtained at the top cover, the investigated cases with different rotational speeds could be divided into three partitions with their main characteristics given as follows. In the first partition (with low rotational speeds), the vibrational level is quite limited, and its source is the pressure fluctuation generated by the swirling vortex rope in the draft tube. In the second partition (with medium rotational speeds), the vibrational level gradually increases and its source is the mechanical aspects of the impeller rotation. In the third partition (with high rotational speeds), the vibrational level is prominent with a prominent swirling vortex rope in the draft tube and intensive rotor–stator interactions in the vaneless space (VS). For the vibrations of the upper and the lower brackets, the vibrations mainly originate from the mechanical aspects of the impeller rotation and the amplitudes of the dominant frequency also increase with the increment of the rotational speed. Finally, differences between the vibrational performances of the spin-no-load mode and the generating mode are discussed.

Computational Study of Pump Turbine: Partial Load Operations

2020 ◽  
Author(s):  
Muhannad Altimemy ◽  
Justin Caspar ◽  
Alparslan Oztekin
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Computational Study ◽  
Pressure Fluctuations ◽  
System Stability ◽  
Pump Turbine ◽  
Vortex Rope ◽  
Signal Velocity ◽  
Partial Load ◽  
Les Model

Abstract The performance of a pump-turbine under partial flow rates, 85%, 75%, and 65%, is studied using the LES model. The power signal, velocity, vorticity, and pressure field is presented over the blades and throughout the draft tube. Pressure fluctuations are probed at various locations over the wall of the draft tube. Examining the flow field in the blade region can provide further insights into the system performance. Flow-induced pressure fluctuations can disrupt system stability. For this turbine, a strong swirling region is observed around the draft tube walls, causing pressure fluctuations. The size and intensity of this region decrease with the flow rate. A vortex rope is present in all cases. At the design point, the strength is constant throughout the draft tube. However, at partial load, the rope is weakened along the draft tube. Between the region dominated by the vortex rope and the wall, there is a swirling shear layer, which moves closer to the wall as the flow rate decreases. Both the magnitude of pressure fluctuations at the wall and the pressure difference over the blade decrease with the flow rate. The decreased pressure differences over the blade represent less power produced, and the decline in fluctuation magnitude at the wall represents more system stability. For this turbine, there appears to be a trade-off between power and strength of pressure fluctuations.

Energy Analysis in a Pump-Turbine During the Load Rejection Process

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Xiaolong Fu ◽  
Deyou Li ◽  
Hongjie Wang ◽  
Guanghui Zhang ◽  
Zhenggui Li ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Energy Conversion ◽  
Rotational Speed ◽  
Draft Tube ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Hydraulic Loss ◽  
Pump Turbine ◽  
Hydraulic Losses ◽  
Load Rejection Process

Complex energy conversion and energy dissipation occur in pump-turbines during the load rejection process. However, the underlying fluid mechanism is not clear. In order to solve these problems, in this study, a three-dimensional (3D) transient turbulent flow in a pump-turbine, with clearance during the load rejection process, was simulated using the method of coupling of the rigid rotor motion with flow and dynamic mesh technology. The simulated rotational speed shows good agreement with the experimental data. Most of the differences of rotational speed between simulations and experiments are very small and lower than 5%. Based on the numerical simulation, the energy conversion process, loss distribution, and flow mechanism in a pump-turbine were analyzed using the method of coupling of the entropy production analysis with the flow analysis. The results indicate that the load rejection process of a pump-turbine is an energy-dissipation process where the energy is converted among various energy forms. After load rejection, the hydraulic loss in the reverse pump process distributes primarily in the stay/guide vanes (GV), the vaneless space, and near draft tube inlet. While the hydraulic losses in the runaway process and the braking process are distributed mainly in the elbow section of the draft tube, the clearance of runner (RN), and the vaneless space, the hydraulic losses are mainly caused by viscous dissipation effects of the vortex flows, including the flow separation vortices, the shedding vortices of flow wake, the secondary flow, and the backflow.

scholarly journals Hydraulic Vibration and Possible Exciting Sources Analysis in a Hydropower System

2021 ◽  
Vol 11 (12) ◽  
pp. 5529
Author(s):  
Aili Shen ◽  
Yimin Chen ◽  
Jianxu Zhou ◽  
Fei Yang ◽  
Hongliang Sun ◽  
...  
Keyword(s):  
Vibration Mode ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Experimental Tests ◽  
Dominant Frequency ◽  
Rotational Frequency ◽  
Operating Conditions ◽  
Mode Shapes ◽  
Vortex Rope ◽  
Hydropower System

To understand the hydraulic vibration characteristics in a traditional hydropower system and identify possible exciting sources that may induce serious hydraulic vibrations in the flow passage, experimental tests and numerical calculations were conducted for different operating conditions. The experimental results show that the pressure fluctuations are mainly related to the vortex rope phenomena in the draft tube, and the dominant frequency of pressure fluctuation is 0.2~0.4 times the runner rotational frequency (fn). The numerical results show all the attenuating factors are negative, which indicates the system itself is stable on the condition that all the hydraulic elements have steady operating performance. The free vibration analyses confirm that the frequency range of the vortex rope in the draft tube partly overlaps the natural frequencies of the hydropower system. Apart from the vortex rope, the runner rotational frequency is another common frequency that is approximately equal to the frequency of the 10th vibration mode. From the vibration mode shapes, it is inferred that a small disturbance in its frequency close or equal to a specific natural frequency of the vibration mode could induce large pressure oscillations in the tail tunnel. In light of the system’s response to different forcing frequencies, the vortex rope formed under off-design conditions and runner rotational frequency is verified to be the potential exciting source of a traditional hydropower system, and the frequency 0.2 fn is much more dangerous than other disturbances to the system.

scholarly journals Effect of Air Injection on the Internal Flow Characteristics in the Draft Tube of a Francis Turbine Model

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1182
Author(s):  
Seung-Jun Kim ◽  
Yong Cho ◽  
Jin-Hyuk Kim
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Air Injection ◽  
Low Flow ◽  
Francis Turbine ◽  
Navier Stokes ◽  
Vortex Rope

Under low flow-rate conditions, a Francis turbine exhibits precession of a vortex rope with pressure fluctuations in the draft tube. These undesirable flow phenomena can lead to deterioration of the turbine performance as manifested by torque and power output fluctuations. In order to suppress the rope with precession and a swirl component in the tube, the use of anti-swirl fins was investigated in a previous study. However, vortex rope generation still occurred near the cone of the tube. In this study, unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted with a scale-adaptive simulation shear stress transport turbulence model. This model was used to observe the effects of the injection in the draft tube on the unsteady internal flow and pressure phenomena considering both active and passive suppression methods. The air injection affected the generation and suppression of the vortex rope and swirl component depending on the flow rate of the air. In addition, an injection level of 0.5%Q led to a reduction in the maximum unsteady pressure characteristics.

Measurement of Unsteady Flow in Pump-Turbine for Hydropower Using PIV Method

2009 ◽  
Author(s):  
Nobuhiko Fukuda ◽  
Satoshi Someya ◽  
Koji Okamoto
Keyword(s):  
Rotational Speed ◽  
Velocity Measurement ◽  
Numerical Procedure ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
High Time ◽  
Pump Turbine ◽  
Guide Vanes ◽  
Runner Blade ◽  
Wide Range

It is thought that the pressure fluctuation can occur due to the interaction between flow through guide vanes and flow into runner blades, resulting in a vibration of turbine and a blade cracking, in a hydraulic turbine operated in a wide range for flexible power demand. High accurate velocity measurement with high time/spatial resolution can help to clarify the mechanism of the interaction and to provide good experimental data for the validation of numerical procedure. So the aim of present study is to estimate the unstable velocity field quantitatively in the area between guide vanes and runner blades, using high time-resolved particle image velocimetry (PIV). Two types of velocity measurements were carried out, i.e., phase-locked measurement and high time sequential velocity measurement, in a pump-turbine model with 20 guide vanes and 6 runner blades. The characteristic of the flow field varied corresponding to the operating conditions such as flow rate and rotational speed. Opening angles of guide vanes were kept uniform. A clockwise vortex was generated at inside of the runner blade under smaller rotational speed. A counterclockwise vortex was separated at the backside of the runner blade under higher rotational speed. At any operating conditions, the velocity between guide vanes and runner blades oscillated periodically at the blade passing frequency.

scholarly journals Pressure Analysis in the Draft Tube of a Pump-Turbine under Steady and Transient Conditions

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4732
Author(s):  
Jing Yang ◽  
Yue Lv ◽  
Dianhai Liu ◽  
Zhengwei Wang
Keyword(s):  
Steady State ◽  
Pressure Pulsation ◽  
Transient Flow ◽  
Draft Tube ◽  
Simulation Method ◽  
Wall Pressure ◽  
Pump Turbine ◽  
Steady State Condition ◽  
Transient Conditions ◽  
Pumped Storage

Pumped-storage power stations play a regulatory role in the power grid through frequent transition processes. The pressure pulsation in the draft tube of the pump-turbine under transient processes is important for safe operation, which is more intense than that in the steady-state condition. However, there is no effective method to obtain the exact pressure in the draft tube in the transient flow field. In this paper, the pressure in the draft tube of a pump-turbine under steady-state and transient conditions are studied by means of CFD. The reliability of the simulation method is verified by comparing the real pressure pulsation data with the test results. Due to the distribution of the pressure pulsation in the draft tube being complex and uneven, the location of the pressure monitoring points directly affects the accurate judgement of cavitation. Eight monitoring surfaces were set in the straight cone of the draft tube and nine monitoring points were set on each monitoring surface to analyze the pressure differences on the wall and inside the center of the draft tube. The relationships between the pressure pulsation value inside the center of the draft tube and on the wall are studied. The “critical” wall pressure pulsation value when cavitation occurs is obtained. This study provides references for judging cavitation occurrences by using the wall pressure pulsation value in practical engineering.

scholarly journals Distribution of Pressure Fluctuations in a Prototype Pump Turbine at Pump Mode

2014 ◽  
Vol 6 ◽  
pp. 923937 ◽  
Author(s):  
Yuekun Sun ◽  
Zhigang Zuo ◽  
Shuhong Liu ◽  
Jintao Liu ◽  
Yulin Wu
Keyword(s):  
Mass Flow ◽  
Pressure Fluctuations ◽  
Dominant Frequency ◽  
Pump Mode ◽  
Pump Turbine ◽  
Guide Vanes ◽  
Path Direction ◽  
Mass Flow Rates ◽  
Operating Points ◽  
Spiral Casing

Pressure fluctuations are very important characteristics in pump turbine's operation. Many researches have focused on the characteristics (amplitude and frequencies) of pressure fluctuations at specific locations, but little researches mentioned the distribution of pressure fluctuations in a pump turbine. In this paper, 3D numerical simulations using SSTk − ω turbulence model were carried out to predict the pressure fluctuations distribution in a prototype pump turbine at pump mode. Three operating points with different mass flow rates and different guide vanes’ openings were simulated. The numerical results show how pressure fluctuations at blade passing frequency (BPF) and its harmonics vary along the whole flow path direction, as well as along the circumferential direction. BPF is the first dominant frequency in vaneless space. Pressure fluctuation component at this frequency rapidly decays towards upstream (to draft tube) and downstream (to spiral casing). In contrast, pressure fluctuations component at 3BPF spreads to upstream and downstream with almost constant amplitude. Amplitude and frequencies of pressure fluctuations also vary along different circumferential locations in vaneless space. When the mass flow and guide vanes’ opening are different, the distribution of pressure fluctuations along the two directions is different basically.

Hydraulic Instability Onset Detection in Kaplan Turbines by Monitoring Shaft Vibrations

2012 ◽  
Author(s):  
P. Pennacchi ◽  
P. Borghesani ◽  
S. Chatterton ◽  
A. Vania
Keyword(s):  
Experimental Test ◽  
Turbine Unit ◽  
Swirling Flow ◽  
Draft Tube ◽  
Operating Conditions ◽  
Low Flow ◽  
Operating Life ◽  
Vortex Rope ◽  
Power Load ◽  
Helical Vortex

Design of hydraulic turbines has often to deal with hydraulic instability. It is well-known that Francis and Kaplan types present hydraulic instability in their design power range. Even if modern CFD tools may help to define these dangerous operating conditions and optimize runner design, hydraulic instabilities may fortuitously arise during the turbine life and should be timely detected in order to assure a long-lasting operating life. In a previous paper, the authors have considered the phenomenon of helical vortex rope, which happens at low flow rates when a swirling flow, in the draft tube conical inlet, occupies a large portion of the inlet. In this condition, a strong helical vortex rope appears. The vortex rope causes mechanical effects on the runner, on the whole turbine and on the draft tube, which may eventually produce severe damages on the turbine unit and whose most evident symptoms are vibrations. The authors have already shown that vibration analysis is suitable for detecting vortex rope onset, thanks to an experimental test campaign performed during the commissioning of a 23 MW Kaplan hydraulic turbine unit. In this paper, the authors propose a sophisticated data driven approach to detect vortex rope onset at different power load, based on the analysis of the vibration signals in the order domain and introducing the so-called “residual order spectrogram”, i.e. an order-rotation representation of the vibration signal. Some experimental test runs are presented and the possibility to detect instability onset, especially in real-time, is discussed.

scholarly journals Vortex rope instabilities in a model of conical draft tube

2017 ◽  
Vol 159 ◽  
pp. 00048 ◽  
Author(s):  
Sergey Skripkin ◽  
Mikhail Tsoy ◽  
Pavel Kuibin ◽  
Sergey Shtork
Keyword(s):  
Draft Tube ◽  
Vortex Rope
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