Resonance investigation of pump-turbine during startup process

He, Liang; Wang, Z W; Kurosawa, Shunsuke; Nakahara, Yü̅suke

doi:10.1088/1755-1315/22/3/032024

Cited by 30 publications

(25 citation statements)

References 3 publications

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“…The mean strain value was correctly captured while the strain fluctuations were underestimated by a factor of two. A pump-turbine model was numerically investigated during the start-up [27]. Pressure fluctuations at the guide vane outlet were in a good agreement with the experimental results.…”

Section: Introductionsupporting

confidence: 59%

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Experimental Investigation of a 10 MW Prototype Kaplan Turbine during Start-Up Operation

et al. 2019

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An increase in the start/stop cycles of hydraulic turbines due to the penetration of intermittent renewable energy sources is important. Hydraulic instabilities that occur in hydraulic turbines during start/stops may cause structural issues in the turbine components. High-stress fluctuations on the runner blades are expected during start-ups due to the unsteady pressure loading on the runner blades. This paper presents experiments performed on a 10 MW prototype Kaplan turbine at the Porjus Hydropower Center during a start-up cycle. Synchronized unsteady pressure and strain measurements on a runner blade and axial, bending (in two directions) and torsion strain measurements on the shaft were performed. In addition, the general parameters of the turbine (e.g., rotational speed, guide vane opening and runner blade angle) were acquired. Low-frequency fluctuations (0-15 Hz) were observed in the pressure data on the runner blade after opening the guide vanes from the completely closed position. A higher strain value was observed on the strain gauges installed on the runner blade near the hub (200-500 µm/m ) compared to the ones near the shroud at the leading and trailing edge. The strain fluctuation level on the shaft decreased after loading the generator by further opening the guide vanes. Higher fluctuations were observed in the torsion strain compared to axial and bending strain. In addition, the torsion strain peak-to-peak value reached 12 times its corresponding value at 61% guide vane opening.Energies 2019, 12, 4582 2 of 20 slow cycle fatigue [5]. In addition, high amplitude vibrations can occur due to the resonance between the low frequencies developed during the start-up operation and the natural frequencies of the runner. The runner blades experience random and periodic stress that is induced by stochastic and periodic flow during the start-up cycle [5][6][7]. The damage to the runner blade caused by one start-up cycle to a runner blade was observed to be equivalent to thirty years of turbine operation under a partial load operating condition, approximately 60% of the best efficiency point where the pressure pulsations in the draft tube are maximum [8]. In addition, no clear correlation between pressure pulsations in the draft tube and strain values on the runner blade was observed.Guide vane opening limit and opening rate are two parameters that can influence pressure fluctuations in the turbine during the start-up operation. A start-up operation creates a complex flow and stochastic pressure loads in the turbine due to the change in the runner speed and transient pressure variation. The startup and shutdown scheme are defined during the turbine commissioning and can be changed during the refurbishment in power plants. An optimized start-up and shutdown scheme can reduce the damage and increase the life expectancy [9]. Nevertheless, this operation should be performed on a case-by-case basis because each turbine exhibits a unique behavior during a start-up cycle, and general methods have not yet been proposed ...

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Section: Introductionsupporting

confidence: 59%

“…Compared with prototype turbines, the numerical simulations of model turbines, including flow simulations and fluid-structure coupled simulations, are affordable during the start-up operation [24][25][26][27]. Numerical simulations showed an overestimation of the synchronous speed by 5% for a bulb turbine model during speed-no-load [26].…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of a 10 MW Prototype Kaplan Turbine during Start-Up Operation

et al. 2019

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“…The boundary conditions of the unit are shown in Figure 3. If the upper and lower boundary nodes of the runner are numbered as 1 and 2, then according to formula (5) and (6), the water head balance equation of the runner boundary can be obtained as follows:…”

Section: Pump-turbinementioning

confidence: 99%

“…He et al analyzed the transient characteristics of the pump turbine in the start-up process by using the three-dimensional full flow channel numerical simulation method and discussed the relationship among pressure pulsation, mechanical vibration, and the dynamic stress of the runner. Hydraulic excitation has a significant effect on the dynamic stress and pressure pulsation of the runner [5]. Zhao et al established a full flow channel model for a certain type of pump turbine, simulated the flow characteristics in the flow channel of the turbine using CFD technology, analyzed the pressure pulsation in the flow channel of the turbine, and discussed the source and mechanism of the pressure pulsation [6].…”

Section: Introductionmentioning

confidence: 99%

Transient Simulation for a Pumped Storage Power Plant Considering Pressure Pulsation Based on Field Test

Zhang

et al. 2019

Energies

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In this study, fast Fourier transform and inverse transform are adopted for noise reduction filtering the data of load rejection pressure of a single unit in a one-tube, four-unit pumped storage power station. Five-spot triple smoothing method is used to extract the time-average and pulsation value of the water hammer pressure of the spiral case and draft tube inlet. The reasonable correction formula is put forward, and the pulsating pressure rise rate of the spiral case (4.44%) and the draft tube inlet (−1.22%) are obtained. A mathematical model is also established for the transition process of the water conveyance and power generation system of the pumped storage power station, and the field single-unit load rejection condition is simulated. The simulation results are consistent with the measurements, and the accuracy of the calculation model in predicting the time-average pressure of water hammer is verified. Thus, the extreme successive load rejection conditions can be simulated based on the proposed model. Combining with the pulsating pressure rise rate of unit, the actual extreme value of extreme working condition is reasonably calculated. The conclusion shows that the pressure of spiral case and draft tube inlet after considering pressure pulsation can meet the control requirements, avoid the damage caused by extreme working condition test to unit, and ensure the operation safety of unit.

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“…Nevertheless, most of these effects have not been yet determined in real turbines. A review of actual research works shows that for turbine runners in still water, natural frequencies and mode shapes obtained with finite element simulations have a good agreement with experimental ones [13][14][15][16][17]. The simulation of real turbine runners has been also performed by means of two way FSI, combining CFD (Computational Fluid Dynamics) and FEM (Finite Element Model), which requires much more time but it can predict not only the natural frequencies but also the damping ratios [18][19][20].…”

mentioning

confidence: 95%

Cavitation Effects on the Structural Resonance of Hydraulic Turbines: Failure Analysis in a Real Francis Turbine Runner

et al. 2018

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When discussing potential resonances in hydraulic turbine runners, cavitation effects are usually neglected. Nevertheless, recent studies have experimentally proved, that large cavitation volumes in the proximity of flexible simple structures, such as hydrofoils, greatly modify their natural frequencies.In this paper, we analyze a resonance case in a Francis runner that leads to multiple fractures on the trailing edge of the blades, after just one day of operation at deep part load. If simple acoustic Fluid-Structure-Interaction (FSI) simulations are used, where the runner's surrounding fluid is considered as a homogenous acoustic medium (water), the risk of structural resonances seems to be limited as the predicted natural frequencies are far enough from the excited frequencies by the flow. It is shown that the only hydraulic phenomenon which could have produced such fractures in the present case is the Rotor Stator Interaction (RSI). In order to analyze possible cavitation effects on the natural frequencies of the turbine runner, CFD simulations of the deep part load conditions have been performed, which predict large inter-blade vortex cavities. These cavities have been then introduced in the acoustical FSI model showing that under such conditions, natural frequencies of the runner increase approaching to some of the RSI excited frequencies. In particular, a possible resonance of the four-nodal diameter (4ND) mode has been found which would explain the fast behavior of the crack propagation. Furthermore, the shape and the position of the real fracture found agree with the local maximum stress spots at the junction between the trailing edges and the crown.Energies 2018, 11, 2320 2 of 16 almost one century ago. More recently, the researches of Amabili et al. [4,5] and Kwak [6] revise and improve the analytical work performed by Lamb. Furthermore, many studies performed in the last decade show that acoustical FSI simulations are perfectly capable to predict natural frequencies of submerged structures [7][8][9]. In all the aforementioned studies simple thin plates have been considered.In the particular case of reaction hydraulic Turbines, which are completely submerged, added mass effects play an important role and have to be considered for the calculation of the natural frequencies as well. In this case the added mass phenomenon is even more complicated, as the gaps turbine-casing (usually considered as rigid boundaries) are extremely small (less than 1% of the turbine diameter), the turbine is rotating, and the water couples the turbine with the casing. Some effects such as rotation [10], influence of non-rigid surfaces [11] and acoustic modes [12] have been recently discussed using numerical FSI simulations and contrasting experimental results. Nevertheless, most of these effects have not been yet determined in real turbines. A review of actual research works shows that for turbine runners in still water, natural frequencies and mode shapes obtained with finite element simulations have a good agreement with exp...

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Resonance investigation of pump-turbine during startup process

Cited by 30 publications

References 3 publications

Experimental Investigation of a 10 MW Prototype Kaplan Turbine during Start-Up Operation

Experimental Investigation of a 10 MW Prototype Kaplan Turbine during Start-Up Operation

Transient Simulation for a Pumped Storage Power Plant Considering Pressure Pulsation Based on Field Test

Cavitation Effects on the Structural Resonance of Hydraulic Turbines: Failure Analysis in a Real Francis Turbine Runner

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