Evolutions of flow patterns and pressure fluctuations in a prototype pump-turbine during the runaway transient process after pump-trip

Zheng, Yang; Cheng, Yongguang; Xia, Linsheng; Meng, Wanwan; Liu, Ke; Zhang, Xiaoxi

doi:10.1016/j.renene.2020.01.079

Cited by 53 publications

(13 citation statements)

References 25 publications

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“…Under the influence of the water level difference between the upstream and the downstream, the rotation speed of the impeller continues to speed up until the maximum value, called runaway speed. Under the runaway condition, the centrifugal force in the impeller and the vortex rope in the inlet pipe are produced inevitably [3], which will cause harm to the rotation device and constraint components [4]. In addition, the unstable flow pattern will generate severe pressure pulsation, which may damage the pump device [5].…”

Section: Introductionmentioning

confidence: 99%

Experiment on Pressure Pulsation of Axial Flow Pump System with Different Runaway Head

Liu

Huang²,

et al. 2021

Processes

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The runaway condition is a damage condition for pumps and turbines which can induce the wake vortex, reverse flow, and severe pressure pulsation. This study aimed to research the characteristics of pressure pulsation of axial flow pumps under different runaway conditions, and the runaway model test was performed with different blade angles and heads. Moreover, four pressure sensors were uniformly arranged at the impeller inlet section to eliminate the random error. The time domain and frequency domain analysis were the main methods to obtain the change regulations. Results showed that the pressure pulsation under the runaway condition are mainly influenced by the rotation frequency, blade passing frequency, and wake vortex frequency. The dimensionless pressure pulsation coefficient of rotation frequency and wake vortex frequency increased obviously with the runaway head increasing, but changed little with different blade angles. In addition, the dimensionless pressure coefficient of wake vortex frequency of the sensors around the impeller inlet section differed a lot, which means that the wake vortex core is not in center of the rotation axis. The average dimensionless pressure pulsation coefficient of wake vortex frequency is higher than that of rotation frequency with the same runaway head, owing to the severer wake vortex.

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Section: Introductionmentioning

confidence: 99%

Experiment on Pressure Pulsation of Axial Flow Pump System with Different Runaway Head

Liu

Huang²,

et al. 2021

Processes

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“…The SAS modifications to the standard k-ω SST turbulence model allow for a decrease in the turbulent viscosity where the turbulence may be partially or fully resolved [25]. This turbulence model has recently been successfully used in a number of studies concerning transient operations in a hydropower context [14,15,26]. The simulations were carried out on the full 3D computational domain shown in Figure 1b.…”

Section: Governing Equations and Numerical Schemesmentioning

confidence: 99%

“…Recent studies of Francis-like pump-turbines have shown that it is possible to numerically predict the flow characteristics during transient sequences such as load-rejection and mode-switching [14][15][16][17]. The current study investigated the shutdown and startup sequences for a model-scale CRPT, in both pump and turbine modes.…”

Section: Introductionmentioning

confidence: 99%

Flow Characteristics of Preliminary Shutdown and Startup Sequences for a Model Counter-Rotating Pump-Turbine

2021

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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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“…A time-frequency analysis of the transient pressure pulsations at the monitoring points was performed by using the Short Time Fourier Transform (STFT) method [30][31][32]. From Figures 9-12, at the beginning of the runaway process, the characteristics of pressure pulsations are mainly influenced by the runner.…”

Section: Pressure Fluctuations In Time-frequency Domain At the Runner Inletsmentioning

confidence: 99%

Differences of Flow Patterns and Pressure Pulsations in Four Prototype Pump-Turbines during Runaway Transient Processes

et al. 2020

Self Cite

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Frequent working condition conversions in pumped-storage power stations often induce stability problems, especially when the operating point enters the S-shaped region, during which flow transitions and pressure fluctuations are serious. The pump-turbines with different specific speed values show different characteristics, but their differences in stability features are still not clear. In this study, four different pump-turbines were selected to simulate the runaway processes from turbine modes. The similarities and differences of flow patterns and pressure fluctuations were analyzed. For the similarities, pressure pulsations increase gradually and fluctuate suddenly once the backflows occur at the runner inlets. For the differences, the evolutions of backflows and pressure pulsations are related to specific speeds and runner shapes. Firstly, it is easier for the lower specific speed turbines to enter the reverse pump mode. Secondly, the blade lean angle influences the position where backflows occur, because it determines the pressure gradient at the runner inlets. Thirdly, the runner inlet height influences pressure pulsations in the vaneless space, because the relative range of backflow transitions will be enlarged with the decrease of specific speed. Overall, investigating the mechanisms of flow pattern transitions and pressure variations is important for runner design and transient process control.

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Evolutions of flow patterns and pressure fluctuations in a prototype pump-turbine during the runaway transient process after pump-trip

Cited by 53 publications

References 25 publications

Experiment on Pressure Pulsation of Axial Flow Pump System with Different Runaway Head

Experiment on Pressure Pulsation of Axial Flow Pump System with Different Runaway Head

Flow Characteristics of Preliminary Shutdown and Startup Sequences for a Model Counter-Rotating Pump-Turbine

Differences of Flow Patterns and Pressure Pulsations in Four Prototype Pump-Turbines during Runaway Transient Processes

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