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Journal ArticleDOI: 10.1080/00221686.2020.1780488

Mechanism of low frequency high amplitude pressure fluctuation in a pump-turbine during the load rejection process

04 Mar 2021-Journal of Hydraulic Research (Taylor & Francis)-Vol. 59, Iss: 2, pp 280-297
Abstract: Owing to the complexity of the load rejection process, the accompanied complex low frequency pressure fluctuations and their sources have not been determined. Herein, the load rejection transient p...

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Topics: Load rejection (67%), Transient (oscillation) (52%)
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12 results found


Journal ArticleDOI: 10.1007/S11431-021-1867-2
Deyou Li1, Liang Yu1, XuYu Yan1, Hongjie Wang1  +2 moreInstitutions (1)
Abstract: Pressure fluctuations induced by a vortex rope are the major causes of hydraulic turbine vibration in partial load operating conditions. Hence, an effective control strategy should be adopted to improve rotating characteristics of the vortex rope and reduce the corresponding pressure fluctuation. In this study, two new types of runner cones (i.e., abnormally shaped and long straight cones) were proposed to optimize the pressure distribution in the draft tube, and unsteady numerical simulations were performed to determine their mechanism of action. Numerical results were validated using flow observation and pressure fluctuation experiments. Detailed analyses were conducted to understand the effects of the helical vortex rope operating conditions. The results indicated that pressure fluctuations in the draft tube at partial load operation result primarily from low frequency fluctuations induced by the rotation of the helical vortex rope, whose amplitudes are related to the rotating radius of the helical vortex rope. Both runner cone types could effectively reduce the pressure-fluctuation amplitude. The long straight type could reduce the amplitude of low-frequency fluctuation induced by vortex rope to a maximum of 74.08% and the abnormal-shape type to 38.31%. Thus, the effective optimization of the runner cone can potentially reduce pressure-fluctuation amplitudes. Our research findings were applied to a real hydraulic plant in China.

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Topics: Draft tube (53%)

2 Citations


Open accessJournal ArticleDOI: 10.1063/5.0065660
Deyou Li1, Xiaolong Fu1, Hongjie Wang1, Rundong Zhao1  +1 moreInstitutions (1)
01 Oct 2021-Physics of Fluids
Topics: Turbine (56%)

2 Citations


Open accessJournal ArticleDOI: 10.3390/EN14123593
16 Jun 2021-Energies
Abstract: Pumped Hydropower Storage (PHS) is the maturest and most economically viable technology for storing energy and regulating the electrical grid on a large scale. Due to the growing amount of intermittent renewable energy sources, the necessity of maintaining grid stability increases. Most PHS facilities today require a geographical topology with large differences in elevation. The ALPHEUS H2020 EU project has the aim to develop PHS for flat geographical topologies. The present study was concerned with the initial design of a low-head model counter-rotating pump-turbine. The machine was numerically analysed during the shutdown and startup sequences using computational fluid dynamics. The rotational speed of the individual runners was decreased from the design point to stand-still and increased back to the design point, in both pump and turbine modes. As the rotational speeds were close to zero, the flow field was chaotic, and a large flow separation occurred by the blades of the runners. Rapid load variations on the runner blades and reverse flow were encountered in pump mode as the machine lost the ability to produce head. The loads were less severe in the turbine mode sequence. Frequency analyses revealed that the blade passing frequencies and their linear combinations yielded the strongest pulsations in the system.

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2 Citations


Journal ArticleDOI: 10.1016/J.JCLEPRO.2021.128228
Xiaolong Fu1, Deyou Li1, Hongjie Wang1, Zhenggui Li2  +2 moreInstitutions (2)
Abstract: This study developed a one-dimensional and three-dimensional (1D–3D) coupling transient flow simulation method to investigate the effect of nonlinear fluctuations of pressures and hydraulic thrusts on the impeller and reveal their underlying flow mechanism during a combined operation mode, comprising two parallel pump-turbines, in a complex water conveyance pipeline system at an actual pumped-storage power station. Experimental verification suggested that the 1D–3D coupling method could accurately simulate the pressure fluctuations and rotational speed of the impeller. Additionally, three combined operation modes consisting of two parallel pump-turbines in a complex hydraulic pipeline system at an actual pumped-storage power station were simulated to test the performances of the developed 1D–3D coupling method. Test results suggested that the proposed method can successfully capture the nonlinear fluctuations of pressures and hydraulic thrusts on the impeller and water hammer phenomena. Additionally, it can reproduce the local and global backflow in the impeller, which induce fluctuations in the pressures and hydraulic thrusts. This study demonstrated that the 1D–3D coupling flow simulation method can provide more transient flow in a pumped-storage power station, possessing a complex long-distance hydraulic pipeline system, using lower computational cost than the conventional pure 1D and full 3D simulation method.

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Topics: Impeller (56%), Water hammer (55%), Backflow (52%)

1 Citations


Open accessJournal ArticleDOI: 10.3390/PR9050886
18 May 2021-
Abstract: The turbulence dissipation will cause the increment of energy loss in the multiphase pump and deteriorate the pump performance. In order to research the turbulence dissipation rate distribution characteristics in the pressurized unit of the multiphase pump, the spiral axial flow type multiphase pump is researched numerically in the present study. This research is focused on the turbulence dissipation rate distribution characteristics in the directions of inlet to outlet, hub to rim, and in the circumferential direction of the rotating impeller blades. Numerical simulation based on the RANS (Reynolds averaged Navier–Stokes equations) and the k-ω SST (Shear Stress Transport) turbulence model has been carried out. The numerical method is verified by comparing the numerical results with the experimental data. Results show that the regions of the large turbulence dissipation rate are mainly at the inlet and outlet of the rotating impeller and static impeller, while it is almost zero from the inlet to the middle of outlet in the suction surface and pressure surface of the first-stage rotating impeller blades. The turbulence dissipation rate is increased gradually from the hub to the rim of the inlet section of the first-stage rotating impeller, while it is decreased firstly and then increased on the middle and outlet sections. The turbulence dissipation rate distributes unevenly in the circumferential direction on the outlet section. The maximum value of the turbulence dissipation rate occurs at 0.9 times of the rated flow rate, while the minimum value at 1.5 times of the rated flow rate. Four turning points in the turbulence dissipation rate distribution that are the same as the number of impeller blades occur at 0.5 times the blade height at 0.9 times the rated flow rate condition. The turbulence dissipation rate distribution characteristics in the pressurized unit of the multiphase pump have been studied carefully in this paper, and the research results have an important significance for improving the performance of the multiphase pump theoretically.

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Topics: Impeller (59%), Turbulence (58%), Reynolds-averaged Navier–Stokes equations (54%) ... read more

1 Citations


References
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37 results found


Journal ArticleDOI: 10.1016/J.IJMULTIPHASEFLOW.2017.12.002
Xinping Long1, Huaiyu Cheng1, Bin Ji1, Roger E. A. Arndt2  +1 moreInstitutions (2)
Abstract: In the present paper, large eddy simulations combined with the Zwart cavitation model are conducted to simulate the transient cavitating turbulent flow around a Delft Twisted hydrofoil. Numerical results show a reasonable agreement with the available experimental data. A three dimensional Lagrangian technology is developed to provide an alternative method for the analyses in cavitating flow, which is based on Lagrangian viewpoint. With this technology, the track lines of re-entrant and side-entrant jets are straightforwardly displayed and clearly indicate that collisions of the mainstream, the re-entrant jet and the side-entrant jet play an important role in the primary and secondary shedding. The evolution of U-type structures and the interactions between cavitation and vortices are well captured and discussed in detail from the Eulerian viewpoint. The numerical results show that during the stage of attached cavity, the topology of the cavity leaves an important influence on the vortex structure. Once the cavity is cut off, the vortex structure evolution will affect significantly the local cavitating flow. Further analysis demonstrates that the lift acting on U-type structures, which is induced by velocity circulation around U-type structures, significantly affects the formation and the development of U-type structures. Lagrangian Coherent Structures (LCSs) obtained with the three dimensional Lagrangian technology are used to reveal the influence of U-type structures on local flow patterns and it shows that there is a close relationship between the local flow separation and vortex structures. Our work provides an insight into the interactions of cavitation-vortex in the cavitating flow around a twisted hydrofoil and demonstrates the potential of 3D LCSs in the analyses of cavitating flow.

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Topics: Vortex (55%), Flow separation (55%), Turbulence (53%) ... read more

98 Citations


Journal ArticleDOI: 10.1016/J.RSER.2014.09.011
Zhigang Zuo1, Shuhong Liu1, Yuekun Sun1, Yulin Wu1Institutions (1)
Abstract: In high-head pump-turbines, observations in the engineering field show that the most detrimental hydraulic instabilities are pressure fluctuations in the vaneless space. For example, these pressure fluctuations can cause vibrations and fatigue failures in hydraulic components. It has been recognized that pressure fluctuations in vaneless space are induced primarily by the interactions between runner blades and guide vanes, i.e., rotor–stator interactions (RSI). The present paper presents and discusses studies in this field, which are carried out by various investigators. Studies include mechanism research on RSI, experimental and numerical investigations on RSI characteristics, discussions on the relationship between vibrations and pressure fluctuations, studies on the geometric and operating parameters of the unit that influence the pressure fluctuations in vaneless space, and precautions and countermeasures to reduce these pressure fluctuations.

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90 Citations


Journal ArticleDOI: 10.1016/S1001-6058(16)60715-1
Bin Ji1, Bin Ji2, Yun Long1, Xinping Long1  +2 moreInstitutions (2)
Abstract: In this paper, the turbulent attached cavitating flow around a Clark-Y hydrofoil is investigated by the large eddy simulation (LES) method coupled with a homogeneous cavitation model. The predicted lift coefficient and the cavity volume show a distinctly quasi-periodic process with cavitation shedding and the results agree fairly well with the available experimental data. The present simulation accurately captures the main features of the unsteady cavitation transient behavior including the attached cavity growth, the sheet/cloud cavitation transition and the cloud cavitation collapse. The vortex shedding structure from a hydrofoil cavitating wake is identified by the criterion, which implies that the large scale structures might slide and roll down along the suction side of the hydrofoil while being further developed at the downstream. Further analysis demonstrates that the turbulence level of the flow is clearly related to the cavitation and the turbulence velocity fluctuation is much influenced by the cavity shedding.

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Topics: Large eddy simulation (55%), Cavitation (54%), Vortex shedding (54%) ... read more

78 Citations


Journal ArticleDOI: 10.1115/1.4027794
Abstract: The penetration of intermittent wind and solar power to the grid network above manageable limits disrupts electrical power grids. Consequently, hydraulic turbines synchronized to the grid experience total load rejection and are forced to shut down immediately. The turbine runner accelerates to runaway speeds in a few seconds, inducing high-amplitude, unsteady pressure loading on the blades. This sometimes results in a failure of the turbine components. Moreover, the unsteady pressure loading significantly affects the operating life of the turbine runner. Transient measurements were carried out on a scale model of a Francis turbine prototype (specific speed = 0.27) during an emergency shutdown with a transition into total load rejection. A detailed analysis of variables such as the head, discharge, pressure at different locations including the runner blades, shaft torque, and the guide vane angular movements are performed. The maximum amplitudes of the unsteady pressure fluctuations in the turbine were observed under a runaway condition. The amplitudes were 2.1 and 2.6 times that of the pressure loading at the best efficiency point in the vaneless space and runner, respectively. Such high-amplitude, unsteady pressure pulsations can affect the operating life of the turbine.

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Topics: Francis turbine (62%), Turbine (62%), Draft tube (59%) ... read more

75 Citations


Journal ArticleDOI: 10.1016/S1001-6058(16)60774-6
Yun Long1, Yun Long2, Xinping Long2, Bin Ji2  +3 moreInstitutions (2)
Abstract: In this paper, we investigate the verification and validation (V&V) procedures for the URANS simulations of the turbulent cavitating flow around a Clark-Y hydrofoil. The main focus is on the feasibility of various Richardson extrapolation-based uncertainty estimators in the cavitating flow simulation. The unsteady cavitating flow is simulated by a density corrected model (DCM) coupled with the Zwart cavitation model. The estimated uncertainty is used to evaluate the applicability of various uncertainty estimation methods for the cavitating flow simulation. It is shown that the preferred uncertainty estimators include the modified Factor of Safety (FS1), the Factor of Safety (FS) and the Grid Convergence Index (GCI). The distribution of the area without achieving the validation at the Vv level shows a strong relationship with the cavitation. Further analysis indicates that the predicted velocity distributions, the transient cavitation patterns and the effects of the vortex stretching are highly influenced by the mesh resolution.

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Topics: Turbulence (51%)

65 Citations


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