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Research Papers: Flows in Complex Systems

Analysis of S Characteristics and Pressure Pulsations in a Pump-Turbine With Misaligned Guide Vanes

[+] Author and Article Information
Hui Sun

e-mail: sh0929@163.com

Ruofu Xiao

e-mail: xrf@cau.edu.cn
College of Water Resources
and Civil Engineering,
China Agricultural University,
Beijing 100083, China

Weichao Liu

Dongfang Electric Machinery Co., Ltd.,
Deyang, Sichuan Province, 618000, China
e-mail: hustlwc@163.com

Fujun Wang

College of Water Resources
and Civil Engineering,
China Agricultural University,
Beijing 100083, China
e-mail: wangfj@cau.edu.cn

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received March 12, 2012; final manuscript received January 8, 2013; published online March 29, 2013. Assoc. Editor: Chunill Hah.

J. Fluids Eng 135(5), 051101 (Mar 29, 2013) (6 pages) Paper No: FE-12-1122; doi: 10.1115/1.4023647 History: Received March 12, 2012; Revised January 08, 2013

Growing environmental concerns and the need for better power balancing and frequency control have increased attention in renewable energy sources such as the reversible pump-turbine which can provide both power generation and energy storage. Pump-turbine operation along the S-shaped curve can lead to difficulties in loading the rejection process with unusual increases in water pressure, which lead to machine vibrations. Pressure fluctuations are the primary reason for unstable operation of pump-turbines. Misaligned guide vanes (MGVs) are widely used to control the stability in the S region. There have been experimental investigations and computational fluid dynamics (CFD) simulations of scale models with aligned guide vanes and MGVs with spectral analyses of the S curve characteristics and the pressure pulsations in the frequency and time-frequency domains at runaway conditions. The course of the S characteristic is related to the centrifugal force and the large incident angle at low flow conditions with large vortices forming between the guide vanes and the blade inlets and strong flow recirculation inside the vaneless space as the main factors that lead to the S-shaped characteristics. Preopening some of the guide vanes enables the pump-turbine to avoid the influence of the S characteristic. However, the increase of the flow during runaway destroys the flow symmetry in the runner leading to all asymmetry forces on the runner that leads to hydraulic system oscillations. The MGV technique also increases the pressure fluctuations in the draft tube and has a negative impact on stable operation of the unit.

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Figures

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Fig. 1

Characteristic pump-turbine operating curves

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Fig. 2

Pump-turbine components and part of the computational grid for the flow field

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Fig. 3

Comparison of predicted and measured performance curves

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Fig. 4

CFD performance curves

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Fig. 5

Schematic diagram of the MGVs

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Fig. 6

Comparisons of the CFD results with experimental data for MGVs

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Fig. 7

Streamlines on the runner

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Fig. 8

Streamlines on the runner for aligned guide vanes and MGVs

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Fig. 9

Simulation conditions in the draft tube

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Fig. 10

Forces and amplitude spectra on the runner

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Fig. 11

Streamlines in runner for various MGVs

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Fig. 12

Pressure fluctuations and amplitudes in the draft tube at monitoring point 3

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