Numerical and experimental analysis of instability phenomena in pump turbines

Gentner, Ch; Sallaberger, Manfred; Widmer, Ch; Braun, O; Staubli, Thomas

doi:10.1088/1755-1315/15/3/032042

Cited by 28 publications

(14 citation statements)

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“…The study conducted by Xia et al [6] shows that the flow losses at the runner entrance are also the leading cause of the S-shaped characteristics. To reduce or eliminate the Sshaped characteristics, many solutions have also been proposed, such as changing the shape of the leading edge of runner blades [7,8], broadening the meridional section of the runner [4], and adopting the misaligned guide vanes (MGV) scheme [9]. However, these solutions have not been proved to be fully effective without side effects.…”

Section: Introductionmentioning

confidence: 99%

Influence of rotational inertia on the runner radial forces of a model pump‐turbine running away through the S‐shaped characteristic region

Zhang

Cheng

Zheng

et al. 2020

IET Renewable Power Generation

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To enhance the power grid's stability and safety, pumped-storage power stations (PSPSs) have to keep themselves stable and safe strictly. However, instabilities happen frequently in some PSPSs due to the S-shaped characteristics of pumpturbines. When the operating point goes through the S-shaped region, intensive radial forces on the runner could cause shaft swing of the turbine-generator unit. In this study, the runaway transient scenarios of a pump-turbine in a model PSPS were simulated by using a one-dimensional and three-dimensional coupled computational fluid dynamics model, and the influence of the unit rotational inertia on the runner radial forces was investigated. The results show that when the pump-turbine runs in the S-shaped region, large rotational inertia is easier than a small one to induce abrupt increases in runner radial forces. The reason is that large rotational inertia gives slower changes in rotational speed and discharge, providing enough time to generate unstable and uneven flow patterns in the pump-turbine. This indicates that apart from the running away region in the characteristics plane, the running away duration is also essential for the transient instability of a pump-turbine. The finding is different from the traditional understandings and should be considered when selects the rotational inertia of a pump-turbine unit. ρ 0 initial density ρ density σ standard deviation of the relative discharges ω angular velocity at the current time-step ω p angular velocity at the previous time-step

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Section: Introductionmentioning

confidence: 99%

Influence of rotational inertia on the runner radial forces of a model pump‐turbine running away through the S‐shaped characteristic region

Zhang

Cheng

Zheng

et al. 2020

IET Renewable Power Generation

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“…The details about the pump instability and its influence factors are discussed in previous works. 76–78 When the operation of the unit is unstable, the machine or the pump characteristic is unacceptable and may lead to self-excited vibration of the hydraulic system. The pump instability can be reduced by avoiding high load pressures and high engine speed.…”

Section: Different Strategies Of Energy Savingsmentioning

confidence: 99%

Energy-saving strategies on power hydraulic system: An overview

Mahato

Ghoshal

2020

Proceedings of the Institution of Mechanical Engineers, Part I:

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Different strategies for improving the energy efficiency of a power hydraulic system have been reviewed in this article. The energy-saving scheme is classified into three categories: S ystem design, Improving components or product functions and Loss reduction. The sub-categories of energy-saving strategies are discussed briefly. Also, different energy-saving potentials of power hydraulic system are presented in tabular form for clear understanding on the chronological development toward energy-efficient fluid power system.

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“…As a widely-used, robust, and accurate method, CFD simulation is useful for predicting the turbomachinery flow cases. Currently, a lot of CFD based studies have been conducted in the pump-turbines for the flow regime [27,28], performance [29,30], cavitation [31], and stability problems [32,33]. These numerical results were compared with the tests and proved reliable and convenient.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the Guide Vane Jet-Vortex Flow and the Induced Noise in a Prototype Pump-Turbine

Tao

Wang

2019

Applied Sciences

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The start-up process of a pump-turbine in pump mode is found with obvious noise, especially at the small guide vane opening angle. The turbulent-flow-induced noise is an important part and must be reduced by flow control. Therefore, the computational fluid dynamics (CFD) method is used in this study to predict the internal flow in a high head prototype pump-turbine (the specific speed nq is 31.5) under an extremely off-design condition (Cφ = 0.015 and Cα = 0.096). The acoustic analogy method is also used to predict the near-field noise based on the turbulence field. Special undesirable flow structures including the flow ring between the runner trailing-edge and the guide vane, guide vane jet, twin-vortexes adjacent to guide vane jet, inter stay vane vortex, stay vane jet, and volute vortex-ring are found in a pump-turbine. These complex jet-vortex flow structures induce local high turbulence kinetic energy and an eddy dissipation rate, which is the reason why noise is generated at small guide vane opening angle. Three dominating frequencies are found on the turbulence kinetic energy pulsation. They are the runner blade frequency fb = 64.5 Hz, the dominate frequency in the guide vane and the stay vane fgsv = 9.6 Hz, and the dominate frequency in volute fvl = 3.2 Hz. The flow pulsation tracing topology gives a good visualization of frequency propagation. The dominating regions of the three specific frequencies are clearly visualized. Results show that different flow structures may induce different frequencies, and the induced specific frequencies will propagate to adjacent sites. This study helps us to understand the off-design flow regime in this prototype pump-turbine and provides guidance when encountering the noise and stability problems during pump mode’s start-up.

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Numerical and experimental analysis of instability phenomena in pump turbines

Cited by 28 publications

References 1 publication

Influence of rotational inertia on the runner radial forces of a model pump‐turbine running away through the S‐shaped characteristic region

Influence of rotational inertia on the runner radial forces of a model pump‐turbine running away through the S‐shaped characteristic region

Energy-saving strategies on power hydraulic system: An overview

Analysis of the Guide Vane Jet-Vortex Flow and the Induced Noise in a Prototype Pump-Turbine

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