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Research Papers: Flows in Complex Systems

Evolutions of Pressure Fluctuations and Runner Loads During Runaway Processes of a Pump-Turbine

[+] Author and Article Information
Linsheng Xia

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

Zhiyan Yang

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

Jianfeng You

State Key Laboratory of Water Resources
and Hydropower Engineering Science,
Wuhan University,
Wuhan 430072, China
e-mail: youjf@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 December 8, 2016; final manuscript received February 23, 2017; published online June 5, 2017. Assoc. Editor: Matevz Dular.

J. Fluids Eng 139(9), 091101 (Jun 05, 2017) (15 pages) Paper No: FE-16-1808; doi: 10.1115/1.4036248 History: Received December 08, 2016; Revised February 23, 2017

The pressure fluctuations and runner loads on a pump-turbine runner during runaway process are very violent and the corresponding flow evolution is complicated. To study these phenomena and their correlations in depth, the runaway processes of a model pump-turbine at four guide vane openings (GVOs) were simulated by three-dimensional computational fluid dynamics (3D-CFD). The results show that the flow structures around runner inlet have regular development and transition patterns—the reverse flow occurs when the trajectory moves to the turbine-brake region and the main reverse velocity shifts locations among the hub side, the shroud side and the midspan as the trajectory comes forward and backward in the S-shape region. The locally distributed reverse flow vortex structures (RFVS) enhance the local rotor–stator interaction (RSI) and make the pressure fluctuations in vaneless space at the corresponding section stronger than at the rest sections along the spanwise direction. The transitions of RFVS, turning from the hub side to midspan, facilitate the inception and development of rotating stall, which propagates at approximately 45–72% of the runner rotation frequency. The evolving rotating stall induces asymmetrical pressure distribution on the runner blade, resulting in intensive fluctuations of runner torque and radial force. During the runaway process, the changing characteristics of the reactive axial force are dominated by the change rate of flow discharge, and the amplitude of low frequency component of axial force is in proportion to the amplitude of discharge change rate.

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Figures

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Fig. 1

Computational domain and grid: (a) geometry and (b) gird

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Fig. 2

Grid dependence analysis and numerical reliability verification: (a) grid dependence analysis (b) comparisons between the results of model test and numerical simulation

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Fig. 3

Schematic diagram of monitoring points

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Fig. 4

Comparison between the dynamic trajectories and static characteristic curves: (a) n11 − Q11 and (b) n11 − T11

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Fig. 5

Distributions of velocity profiles at the runner inlet at static conditions

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Fig. 6

Variations of discharge, velocity fluctuations during runway processes at different GVOs: (a) 6 deg GVO, (b) 9 deg GVO, (c) 15 deg GVO, and (d) 24 deg GVO

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Fig. 7

Instantaneous flow patterns at four representative instant for 15 deg GVO: (a) sound flow, t = 0 s, (b) RFVS at hub side, t = 1.50 s, (c) RFVS at midspan, t = 2.16 s, and (d) RFVS at shroud side, t = 3.12 s

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Fig. 8

Time histories of pressure fluctuations in vaneless space under runaway process at different GVOs: (a) 6 deg GVO, (b) 9 deg GVO, (c) 15 deg GVO, and (d) 24 deg GVO

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Fig. 9

Spectrograms of pressure fluctuations in vaneless space for 6 deg GVO: (a) at shroud side (nd1), (b) at midspan (nz1), and (c) at hud side (ns1)

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Fig. 10

Spectrograms of pressure fluctuations in vaneless space for 9 deg GVO: (a) at shroud side (nd1), (b) at midspan (nz1), and (c) at hud side (ns1)

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Fig. 11

Spectrograms of pressure fluctuations in vaneless space for 9 deg GVO: (a) at shroud side (nd1), (b) at midspan (nz1), and (c) at hud side (ns1)

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Fig. 12

Spectrograms of pressure fluctuations in vaneless space for 9 deg GVO: (a) at shroud side (nd1), (b) at midspan (nz1), and (c) at hud side (ns1)

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Fig. 13

Variations of total discharge and standard deviation of interblade discharge among all runner channels during the runaway processes at different GVOs: (a) 6 deg GVO, (b) 9 deg GVO, (c) 15 deg GVO, and (d) 24 deg GVO

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Fig. 14

Instantaneous discharge within each runner channel at representative instants during the runaway process for 6 deg GVO

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Fig. 15

Instantaneous discharge within each runner channel at representative instants during the runaway process for 15 deg GVO

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Fig. 16

Instantaneous flow patterns on midspan section at representative instants for 15 deg GVO: (a) t = 6.54 s, (b) t = 6.60 s, (c) t = 6.66 s, (d) t = 6.72 s, (e) t = 6.78 s, (f) t = 6.84 s, (g) t = 6.90 s, and (h) t = 6.96 s

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Fig. 17

Instantaneous flow field, turbulence kinetic energy, and pressure distributions on the runner blades under rotating stall condition for 15 deg GVO (t = 6.84 s)

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Fig. 18

Runner blade torque fluctuations and their standard deviation during the runaway process for 15 deg GVO: (a) blade torque fluctuations of all runner blades and their standard deviations (low-pass-filtered signals with a cutoff frequency set to fn) and (b) partially enlarged view of the low-pass-filtered fluctuations of each blade torque under rotating stall condition

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Fig. 19

Evolution of the radial force vector during the runaway processes for the four GVOs, origin signals (left) and low-pass-filtered signals with a cutoff frequency set to fn (right): (a) 6 deg GVO, (b) 9 deg GVO, (c) 15 deg GVO, and (d) 24 deg GVO

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Fig. 20

Evolutions of the vortex rope in draft tube during runaway processes for 6 deg and 9 deg GVOs

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Fig. 21

Definition of the control volume and surface

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Fig. 22

Variations of axial force acting on the surfaces of runner channels and discharge change rate (red lines are the low-pass-filtered fluctuations using a cutoff frequency set to fn): (a) 6 deg GVO, (b) 9 deg GVO, (c) 15 deg GVO, and (d) 24 deg GVO

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Fig. 23

Amplitudes of the low frequency components of axial force fluctuations versus the amplitudes of discharge change rate

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Fig. 24

Oscillation amplitudes of the axial force at low frequency and the discharge change rate vary with the GVOs

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