0
Research Papers: Flows in Complex Systems

Analysis of the Unstable Behavior of a Pump-Turbine in Turbine Mode: Fluid-Dynamical and Spectral Characterization of the S-shape Characteristic

[+] Author and Article Information
Giovanna Cavazzini

Department of Industrial Engineering,
University of Padova,
Via Venezia 1,
Padova 35131, Italy
e-mail: giovanna.cavazzini@unipd.it

Alberto Covi

Department of Industrial Engineering,
University of Padova,
Via Venezia 1,
Padova 35131, Italy
e-mail: alberto.covi@unipd.it

Giorgio Pavesi

Department of Industrial Engineering,
University of Padova,
Via Venezia 1,
Padova 35131, Italy
e-mail: giorgio.pavesi@unipd.it

Guido Ardizzon

Department of Industrial Engineering,
University of Padova,
Via Venezia 1,
Padova 35131, Italy
e-mail: guido.ardizzon@unipd.it

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received February 2, 2015; final manuscript received August 14, 2015; published online September 10, 2015. Assoc. Editor: Frank C. Visser.

J. Fluids Eng 138(2), 021105 (Sep 10, 2015) (12 pages) Paper No: FE-15-1085; doi: 10.1115/1.4031368 History: Received February 02, 2015; Revised August 14, 2015

The most common mechanical equipment adopted in the new generation of pumped-hydro power plants is represented by reversible pump-turbines (RPT), required to rapidly switch between pumping and generating modes in order to balance the frequent changes in electricity production and consumption caused by unpredictable renewable energy sources. As a consequence, pump-turbines are required to extend their operation under off-design conditions in unstable operating areas. The paper presents a numerical analysis of the unstable behavior of a pump-turbine operating in turbine mode near the no-load condition. To study in depth the unsteady phenomena which lead to the S-shape of the turbine characteristic, a load rejection scenario at constant and large guide vane opening (GVO) was numerically analyzed by running through the flow-speed characteristic up to the turbine brake region. The flow field analysis led to the onset and development of unsteady phenomena progressively evolving in an organized rotating stall (RS) (65.1% of the runner rotation frequency) during the turbine brake operation. These phenomena were characterized by frequency and time–frequency analyses of several numerical signals (static pressure, blade torque, mass flow rate in blade passages). The influence of the development of these unsteady phenomena on the pump-turbine performance in a turbine operation was also analyzed, and the potential causes that generated the S-shaped characteristic curve were also investigated.

Copyright © 2016 by ASME
Your Session has timed out. Please sign back in to continue.

References

Ardizzon, G. , Cavazzini, G. , and Pavesi, G. , 2014, “ A New Generation of Small Hydro and Pumped-Hydro Power Plants: Advances and Future Challenges,” Renewable Sustainable Energy Rev., 31, pp. 746–776. [CrossRef]
Fisher, R. , Koutnik, J. , Meier, L. , Loose, V. , Engels, K. , and Beyer, T. , 2012, “ A Comparison of Advanced Pumped Storage Equipment Drivers in the U.S. and Europe,” HydroVision 2012, Louisville, KY.
Zhou, J. X. , Karney, B. W. , and Xu, J. C. , 2011, “ Analytical Study on Possible Self-Excited Oscillation in S-Shaped Regions of Pump Turbines,” Proc. Inst. Mech. Eng. A, 225(8), pp. 1132–1142. [CrossRef]
Gentner, C. , Sallaberger, M. , Widmer, C. , Braun, O. , and Staubli, T. , 2012, “ Analysis of Unstable Operation of Pump Turbines and How to Avoid It,” Hydro 2012 Innovative Approaches to Global Challenges, Bilbao, Spain, Oct. 29–31, pp. 1–8.
Pejovic, S. , Zhang, Q. F. , Karney, B. , and Gajic, A. , 2011, “ Analysis of Pump-Turbine S Instability and Reverse Waterhammer Incidents in Hydropower Systems,” 4th International Meeting on Cavitation and Dynamic Problems in Hydraulic Machinery Systems, Belgrade, Serbia.
Olimstad, G. , Nielsen, T. , and Børresen, B. , 2012, “ Dependency on Runner Geometry for Reversible Pump Turbine Characteristic in Turbine Mode of Operation,” ASME J. Fluids Eng., 134(12), p. 121102. [CrossRef]
Olimstad, G. , Nielsen, T. , and Børresen, B. , 2012, “ Stability Limits of Reversible Pump Turbines in Turbine Mode of Operation and Measurements of Unstable Characteristic,” ASME J. Fluids Eng., 134(11), p. 111202. [CrossRef]
Seidel, U. , Koutnik, J. , and Martin, G. , 2012, “ S-Curve Characteristic of Pump-Turbines,” Hydro 2012 Innovative Approaches to Global Challenges, Bilbao, Spain, Oct. 29–31, pp. 1–9.
Wang, L. Q. , Yin, J. L. , Jiao, L. , Wu, D. , and Qin, D. , 2011, “ Numerical Investigation on the “S” Characteristic of a Reduced Pump Turbine Model,” Sci. China Ser. E, 54(5), pp. 1259–1266. [CrossRef]
Sun, H. , Xiao, R. , Liu, W. , and Wang, F. , 2013, “ Analysis of the S Characteristic and Pressure Pulsation in a Pump Turbine With Misaligned Guide Vanes,” ASME J. Fluids Eng., 135(5), p. 051101. [CrossRef]
Brennen, C. E. , 1994, Hydrodynamics of Pumps, Oxford University Press, Oxford, UK.
Hasmatuchi, V. , Farhat, M. , Roth, S. , Botero, F. , and Avellan, F. , 2011, “ Experimental Evidence of Rotating Stall in a Pump Turbine at Off Design Conditions in Generating Mode,” ASME J. Fluids Eng., 133(5), p. 051104. [CrossRef]
Hasmatuchi, V. , Farhat, M. , Roth, S. , Botero, F. , and Avellan, F. , 2011, “ Hydrodynamics of a Pump Turbine at Off Design Conditions in Generating Mode: Experimental Investigation,” SHF Conference on Cavitation and Hydraulic Machines, Lausanne, Switzerland, May 26–27, pp. 1–4.
Widmer, C. , Staubli, T. , and Ledergerber, N. , “ Unstable Characteristics and Rotating Stall in Turbine Brake Operation of Pump-Turbines,” ASME J. Fluids Eng., 133(4), p. 041101. [CrossRef]
Botero, F. , Hasmatuchi, V. , Roth, S. , and Farhat, M. , 2014, “ Non-Intrusive Detection of Rotating Stall in Pump-Turbines,” Mech. Syst. Signal Process., 48(1–2), pp. 162–173. [CrossRef]
Houdeline, J.-B. , Liu, J. , Lavigne, S. , Laurant, Y. , and Balarac, L. , 2011, “ Start-Up Improvement in Turbine Mode for High Head PSP Machine,” IOP Conf. Ser.: Earth Environ. Sci., 15(4), pp. 1–10.
Yin, J. , Wang, D. , Wei, X. , and Wang, L. , 2013, “ Hydraulic Improvement to Eliminate S-Shaped Curve in Pump Turbine,” ASME J. Fluids Eng., 135(7), p. 0711105. [CrossRef]
Yang, J. , Pavesi, G. , Yuan, S. , Cavazzini, G. , and Ardizzon, G. , 2015, “ Experimental Characterization of a Pump–Turbine in Pump Mode at Hump Instability Region,” ASME J. Fluids Eng., 137(5), p. 051109. [CrossRef]
Pavesi, G. , Cavazzini, G. , and Ardizzon, G. , 2008, “ Time–Frequency Characterization of the Unsteady Phenomena in a Centrifugal Pump,” Int. J. Heat Fluid Flow, 29(5), pp. 1527–1540. [CrossRef]
Krause, N. , Zähringer, K. , and Pap, E. , 2005, “ Time-Resolved Particle Image Velocimetry for the Investigation of Rotating Stall in a Radial Pump,” Exp. Fluids, 39(2), pp. 192–201. [CrossRef]
Lucius, A. , and Brennen, G. , 2011, “ Numerical Simulation and Evaluation of Velocity Fluctuations During Rotating Stall of a Centrifugal Pump,” ASME J. Fluids Eng., 133(8), p. 081102. [CrossRef]
Farge, M. , 1992, “ Wavelet Transforms and Their Application to Turbulence,” Annu. Rev. Fluid Mech., 24, pp. 395–457. [CrossRef]
Shao, W. Y. , 2009, “ Improving Stability by Misaligned Guide Vanes in Pumped Storage Plant,” Asia-Pacific Power and Energy Engineering Conference, Wuhan, China, Mar. 28–31, pp. 1–5.

Figures

Grahic Jump Location
Fig. 1

S-shaped characteristic curve of a pump-turbine in generating mode: discharge–speed curve at a constant GVO

Grahic Jump Location
Fig. 2

Scheme of the tested configuration

Grahic Jump Location
Fig. 3

Sketch of the runner and distributor with references of the main diameters

Grahic Jump Location
Fig. 4

Guide vanes reference position (λ = 0 deg)

Grahic Jump Location
Fig. 5

Meridional view of the numerical model. Regions filled in gray refer to the blades; region filled in black refers to the leakage system.

Grahic Jump Location
Fig. 6

Detail of the coarse mesh of the numerical model: inlet duct, return channel, guide vanes, runner, draft tube, and part of the meshed leakage system

Grahic Jump Location
Fig. 7

Scheme of the experimental setup

Grahic Jump Location
Fig. 8

Comparison between numerical and experimental performance curves

Grahic Jump Location
Fig. 9

Percentage errors in performance between experimental and numerical results

Grahic Jump Location
Fig. 10

Starting and ending points of the numerical simulation of the turbine brake (at constant GVO and constant speed)

Grahic Jump Location
Fig. 11

Flow pattern in the unstable branch of the characteristic (Q = 21.8%Qbep) inside the runner (relative streamlines) and inside the guide vanes (absolute streamlines)

Grahic Jump Location
Fig. 12

Instantaneous velocity flow field inside runner and guide vanes at midspan at three different instants: (a) t1 − Q = 45.1%Qbep; (b) t2 − Q = 37.8%Qbep; and (c) t3 − Q = 21.8%Qbep

Grahic Jump Location
Fig. 13

Evolution of the instantaneous flow rate passing through each channel of the runner (a) and of the guide vanes (b) during the turbine brake. εi=−1 means blocked channel; εi<−1 means back flow in the channel

Grahic Jump Location
Fig. 14

Pressure profiles on a runner blade (blade 2) at midspan at four different instants: (a) Q = 45.1%Qbep; (b) Q = 37.8%Qbep; and (c) Q = 21.8%Qbep

Grahic Jump Location
Fig. 15

Evolution of the blade torque during the turbine brake: (a) runner (blades 2, 4, and 6) and (b) guide vanes (blades 1, 7, 13, and 19)

Grahic Jump Location
Fig. 16

Flow field inside runner and guide vanes for Q = 20.3%Qbep: (a) flow pattern by means of absolute (guide vanes) and relative (runner) streamlines; (b) instantaneous velocity flow field at midspan

Grahic Jump Location
Fig. 17

Scheme of the positions of the acquired numerical signals

Grahic Jump Location
Fig. 18

Power-spectra of the mass flow rates through runner channels (a) and of the torques acting on the runner blades (b)

Grahic Jump Location
Fig. 19

Power-spectra of the mass flow rates through the distributor channels (a) and of the torques (b) acting on seven guide vanes blades

Grahic Jump Location
Fig. 20

Power-spectra of the static pressure signals acquired at the guide vanes inlet (a) and outlet (b)

Grahic Jump Location
Fig. 21

Cross-spectra of the mass flow rates (a) and torque signals (b) between different runner blades

Grahic Jump Location
Fig. 22

Cross-spectra of the mass flow rates (a) and torque signals (b) between different guide vanes

Grahic Jump Location
Fig. 23

Cross-spectra of the static pressure at (a) guide vanes outlet and (b) guide vanes inlet

Grahic Jump Location
Fig. 24

Wavelets of (a) the mass flow rate in runner channel 2 and (b) of the torque acting on runner blade 2

Grahic Jump Location
Fig. 25

Wavelets of (a) the mass flow rate in guide vanes channel 1 and (b) of the torque acting on guide vanes blade 1

Grahic Jump Location
Fig. 26

Wavelets of static pressure data series at (a) p3,1 and (b) p4,1

Grahic Jump Location
Fig. 27

Performance curve of the pump-turbine: (a) head and (b) mechanical power

Grahic Jump Location
Fig. 28

Contributions in head of the runner and guide vanes

Grahic Jump Location
Fig. 29

Numerical dimensionless discharge–speed curve

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In