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Research Papers: Flows in Complex Systems

Numerical Analysis of the Effect of Misaligned Guide Vanes on Improving S-Shaped Characteristics for a Pump-Turbine

[+] Author and Article Information
Xiao Yexiang

State Key Laboratory of Hydroscience
and Engineering,
Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: xiaoyex@mail.tsinghua.edu.cn

Zhu Wei

State Key Laboratory of Hydroscience
and Engineering,
Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: ctrlzcj@126.com

Wang Zhengwei

State Key Laboratory of Hydroscience
and Engineering,
Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: wzw@mail.tsinghua.edu.cn

Zhang Jin

State Key Laboratory of Hydroscience
and Engineering,
Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: Zhangjin119@mail.tsinghua.edu.cn

Ahn Soo-Hwang

State Key Laboratory of Hydroscience
and Engineering,
Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: ansh13@mails.tsinghua.edu.cn

Zeng Chongji

State Key Laboratory of Hydroscience
and Engineering,
Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: cengcj12@mails.tsinghua.edu.cn

Luo Yongyao

State Key Laboratory of Hydroscience
and Engineering,
Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: luoyy@mail.tsinghua.edu.cn

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 24, 2016; final manuscript received September 12, 2017; published online October 24, 2017. Assoc. Editor: Bart van Esch.

J. Fluids Eng 140(3), 031102 (Oct 24, 2017) (10 pages) Paper No: FE-16-1545; doi: 10.1115/1.4038077 History: Received August 24, 2016; Revised September 12, 2017

The S-shaped characteristic curves in pump-turbines complicate synchronization with the electrical grid and affect system safety. Misaligned guide vanes (MGVs) are one of the most effective solutions to avoid S-shaped characteristics. The internal flow mechanism with the MGV for improving S-shaped characteristics was studied by numerical analysis. Six operating conditions were modeled in the S-shaped region. Four guide vanes were arranged as the MGVs to qualitatively and quantitatively analyze the flow behavior. The internal flow was quite complex at the four operating points without the MGV; here, the attack angle and the flow behavior had no obvious difference at each vane. For the similar conditions with MGVs, attack angles and internal flow fields varied clearly at each vane, especially in the vaneless region and in the runner blade passages. For the same discharge rates, total openings, and rotating speeds, the internal flows were quite different between with and without the MGVs. The MGVs disrupt the high-speed circumferential water ring (appreciably faster compared to the main flow) in the vaneless region and maintain operation with higher unit speeds. Consequently, the unit speed is larger at the same unit discharge in the S-shaped region. Therefore, the MGV method can reduce S-shaped characteristics.

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Figures

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Fig. 1

Computational flow domain in the model pump-turbine

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Fig. 2

Sketch map of the MGV arrangement

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Fig. 3

Pump-turbines performance runaway and inflection curves: (a) test performance curve for ns of 126, (b) test performance curve for ns of 157 [9], and (c) test performance curve for ns of 44 [15]

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Fig. 4

Measured and predicted performance curves: (a) n11Q11 performance curve and (b) n11M11 performance curve

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Fig. 5

Distribution of the four operating conditions for the unsteady simulations

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Fig. 6

Meshes in the spiral case, runner, and draft tube: (a) spiral case mesh, (b) runner mesh, and (c) draft tube mesh

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Fig. 7

Local meshes for the three different guide vane openings: (a) GV7.07 deg, (b) MGV30.72 deg, and (c) GV11.65 deg

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Fig. 8

Streamline on the vane midspan surface for inflection conditions (steady)

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Fig. 9

Streamline on the vane midspan surface for inflection conditions (unsteady)

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Fig. 10

Streamline on the vane midspan surface for small discharge conditions (steady)

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Fig. 11

Attack angles for each guide vane: (a) inflection points and (b) small discharge points

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Fig. 12

Attack angles for each runner blade inlet: (a) inflection points and (b) small discharge points

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Fig. 13

Flow behavior in the S-shaped region with and without the MGV

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