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Research Papers: Flows in Complex Systems

Looping Dynamic Characteristics of a Pump-Turbine in the S-shaped Region During Runaway

[+] Author and Article Information
Xiaoxi Zhang

State Key Laboratory of Water Resources and
Hydropower Engineering Science,
Wuhan University,
Wuhan 430072, China
e-mail: zhangxiaoxi@whu.edu.cn

Yongguang Cheng

State Key Laboratory of Water Resources and
Hydropower Engineering Science,
Wuhan University,
Wuhan 430072, China
e-mail: ygcheng@whu.edu.cn

Linsheng Xia

State Key Laboratory of Water Resources and
Hydropower Engineering Science,
Wuhan University,
Wuhan 430072, China
e-mail: xialinsheng@whu.edu.cn

Jiandong Yang

State Key Laboratory of Water Resources and
Hydropower Engineering Science,
Wuhan University,
Wuhan 430072, China
e-mail: jdyang@whu.edu.cn

Zhongdong Qian

State Key Laboratory of Water Resources and
Hydropower Engineering Science,
Wuhan University,
Wuhan 430072, China
e-mail: zdqian@whu.edu.cn

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received June 16, 2015; final manuscript received March 18, 2016; published online May 26, 2016. Assoc. Editor: Bart van Esch.

J. Fluids Eng 138(9), 091102 (May 26, 2016) (10 pages) Paper No: FE-15-1406; doi: 10.1115/1.4033297 History: Received June 16, 2015; Revised March 18, 2016

During transients, hydroturbines may demonstrate some dynamic characteristics that differ from the corresponding static characteristics in steady operating conditions. To study the dynamic characteristics of a pump-turbine, we simulated the runaway transients in a model pumped-storage plant by coupling one-dimensional (1D) water conveyance system and three-dimensional (3D) pump-turbine. The results show that the runaway dynamic trajectories form loops in the S-shaped region in the unit discharge and unit torque charts of the pump-turbine, not following the corresponding static characteristics. Theoretical analysis and flow patterns comparisons illustrate that the looping trajectories are mainly caused by the successive features of transient flow patterns, namely, the transient flows in the pump-turbine are influenced by their previous status. These features induce different performances between similar dynamic operating points in different moving directions. Furthermore, through comparing the transient parameters calculated by the dynamic and static characteristics separately, we found that both methods are available to capture the unstable behaviors of the pump-turbine, but the dynamic method displays more accurate results when simulating the critical transient parameters. Therefore, in practical engineering applications, we suggest to use the static characteristics method for stability analysis while dynamic characteristics method for transient parameters, which is important for optimizing the layout of water conveyance systems.

Copyright © 2016 by ASME
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Figures

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Fig. 8

Comparisons between the simulated transient parameters and the measured results

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Fig. 9

Comparison between the simulated and measured dynamic trajectories

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Fig. 7

Comparisons between the simulated static characteristics and the measured results

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Fig. 6

Mesh in the distributor and impeller channels

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Fig. 5

Calculated heads with different cells

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Fig. 3

Computational domain of the model pumped-storage system

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Fig. 2

Measured head difference between 2# and 3# pressure sensors

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Fig. 1

Schematic of the model pumped-storage system

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Fig. 14

Velocity streamlines in the middle horizontal section in vanes zone at characteristic operating points (a) DP1, (b) DP2, (c) DP3, (d) DP4, (e) DP5, (f) DP6, and (g) DP7

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Fig. 15

Velocity streamlines in impeller channels at characteristic operating points (The normalized velocity is defined as the ratio of the local velocity magnitude over the mean velocity magnitude at the impeller inlet.) (a) DP1, (b) DP2, (c) DP3, (d) DP4, (e) DP5, (f) DP6, and (g) DP7

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Fig. 10

Comparisons between the dynamic trajectories and the static operating points

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Fig. 11

Comparisons between the modified dynamic trajectories and the static operating points

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Fig. 12

Velocity triangle at the inlet of the impeller in turbine mode of a pump-turbine

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Fig. 13

Definition of the similar operating points

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Fig. 16

Comparisons among the results of dynamic, static numerical methods and model test (a) rotational speed, (b) discharge, (c) pressure head at spiral casing inlet, and (d) pressure head at draft tube inlet

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