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Experiments in Fluids

, 57:168 | Cite as

LDV survey of cavitation and resonance effect on the precessing vortex rope dynamics in the draft tube of Francis turbines

  • A. FavrelEmail author
  • A. Müller
  • C. Landry
  • K. Yamamoto
  • F. Avellan
Research Article

Abstract

The large-scale penetration of the electrical grid by intermittent renewable energy sources requires a continuous operating range extension of hydropower plants. This causes the formation of unfavourable flow patterns in the draft tube of turbines and pump-turbines. At partial load operation, a precessing cavitation vortex rope is formed at the Francis turbine runner outlet, acting as an excitation source for the hydraulic system. In case of resonance, the resulting high-amplitude pressure pulsations can put at risk the stability of the machine and of the electrical grid to which it is connected. It is therefore crucial to understand and accurately simulate the underlying physical mechanisms in such conditions. However, the exact impact of cavitation and hydro-acoustic resonance on the flow velocity fluctuations in the draft tube remains to be established. The flow discharge pulsations expected to occur in the draft tube in resonance conditions have for instance never been verified experimentally. In this study, two-component Laser Doppler Velocimetry is used to investigate the axial and tangential velocity fluctuations at the runner outlet of a reduced scale physical model of a Francis turbine. The investigation is performed for a discharge equal to 64 % of the nominal value and three different pressure levels in the draft tube, including resonance and cavitation-free conditions. Based on the convective pressure fluctuations induced by the vortex precession, the periodical velocity fluctuations over one typical precession period are recovered by phase averaging. The impact of cavitation and hydro-acoustic resonance on both axial and tangential velocity fluctuations in terms of amplitude and phase shift is highlighted for the first time. It is shown that the occurrence of resonance does not have significant effects on the draft tube velocity fields, suggesting that the synchronous axial velocity fluctuations are surprisingly negligible compared to the velocity fluctuations induced by the vortex precession.

Keywords

Cavitation Draft Tube Laser Doppler Velocimetry Precession Frequency Precess Vortex Core 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

The research leading to the results published in this paper is part of the HYPERBOLE research project, granted by the European Commission (ERC/FP7- ENERGY-2013-1-Grant 608532). The authors would also like to thank BC Hydro for making available the reduced scale model, in particular Danny Burggraeve and Jacob Iosfin. Moreover, the authors would like to acknowledge the commitment of the Laboratory for Hydraulic Machines’ technical staff, especially Georges Crittin, Maxime Raton, Victor Rivas, Alain Renaud and Vincent Berruex.

References

  1. Adrian R, Yao C (1987) Power spectra of fluid velocities measured by laser Doppler velocimetry. Exp Fluids 5(1):17–28Google Scholar
  2. Alligné S, Nicolet C, Tsujimoto Y, Avellan F (2014) Cavitation surge modelling in Francis turbine draft tube. J Hydraul Res 52(3):1–13CrossRefGoogle Scholar
  3. Arpe J, Nicolet C, Avellan F (2009) Experimental evidence of hydroacoustic pressure waves in a Francis turbine elbow draft tube for low discharge conditions. J Fluids Eng 131(8):081102CrossRefGoogle Scholar
  4. Bendat JS, Piersol AG (2010) Random data: analysis and measurement procedures, 4th edn. Wiley, New YorkCrossRefzbMATHGoogle Scholar
  5. Brennen C, Acosta A (1976) Dynamic transfer function for a cavitating inducer. J Fluids Eng 1(2):182–191CrossRefGoogle Scholar
  6. Couston M, Philibert R (1998) Partial load modelling of gaseous Francis turbine rope. Int J Hydropower Dams 1:146–158Google Scholar
  7. Dörfler P (1982) System dynamics of the Francis turbine half load surge. In: Proceedings of the 11th IAHR symposium on operating problem of pump stations and powerplants, Amsterdam, NetherlandsGoogle Scholar
  8. Dörfler P, Ruchonnet N (2012) A statistical method for draft tube pressure pulsation analysis. In: IOP conference series: earth and environmental science 15 (26th IAHR symposium on hydraulic machinery and systems, Beijing, China)Google Scholar
  9. Dreyer M (2015) Mind The gap: tip leakage vortex dynamics and cavitation in axial turbines. PhD thesis, EPFL, Lausanne, SwitzerlandGoogle Scholar
  10. Duparchy A, Guillozet J, De Colombel T, Bornard L (2014) Spatial harmonic decomposition as a tool for unsteady flow phenomena analysis. In: IOP conference series: earth and environmental science 22 (27th IAHR symposium on hydraulic machinery and systems, Montreal, Canada)Google Scholar
  11. Escudier M (1987) Confined vortices in flow machinery. Annu Rev Fluid Mech 19:27–52CrossRefGoogle Scholar
  12. Fanelli M (1989) Vortex rope in the draft tube of Francis turbines operating at partial load. a proposal for a mathematical model. J Hydraul Res 27(6):769–807CrossRefGoogle Scholar
  13. Favrel A, Landry C, Müller A, Yamamoto K, Avellan F (2014) Hydro-acoustic resonance behavior in presence of a precessing vortex rope: observation of a lock-in phenomenon at part load Francis turbine operation. In: IOP conference series: earth and environmental science 22 (27th IAHR symposium on hydraulic machinery and systems, Montreal, Canada)Google Scholar
  14. Favrel A, Müller A, Landry C, Yamamoto K, Avellan F (2015) Study of the vortex-induced pressure excitation source in a Francis turbine draft tube by particle image velocimetry. Exp Fluids 56(12):1–15CrossRefGoogle Scholar
  15. Fernandes E, Heitor M, Shtork S (2006) An analysis of unsteady highly turbulent swirling flow in a model vortex combustor. Exp Fluids 40(2):177–187CrossRefGoogle Scholar
  16. Glas W, Forstner M, Kuhn K, Jaberg H (2000) Smoothing and statistical evaluation of laser Doppler velocimetry data of turbulent flows in rotating and reciprocating machinery. Exp Fluids 29(5):411–417CrossRefGoogle Scholar
  17. Griffiths A, Yazdabadi P, Syred N (1998) Alternate eddy shedding set up by the nonaxisymmetric recirculation zone at the exhaust of a cyclone dust separator. J Fluids Eng 120(1):193–199CrossRefGoogle Scholar
  18. Heitor M, Whitelaw J (1986) Velocity, temperature, and species characteristics of the flow in a gas-turbine combustor. Combust Flame 64(1):1–32CrossRefGoogle Scholar
  19. IEC Standards (1999) 60193: hydraulic turbines, storage pumps and pump-turbines—model acceptance tests, 2nd edn. International Commission, GenevaGoogle Scholar
  20. Iliescu M, Ciocan G, Avellan F (2008) Analysis of the cavitating draft tube vortex in a Francis turbine using particle image velocimetry measurements in two-phase flow. J Fluids Eng 130(2):021105CrossRefGoogle Scholar
  21. Iliescu M, Houde S, Lemay S, Fraser R, Deschênes C (2011) Investigation of the cavitational behavior of an axial hydraulic turbine operating at partial discharge by 3D-PIV. In: Proceedings of the 9th international symposium on particle image velocimetry, Kobe, Japan, JulyGoogle Scholar
  22. Landry C, Favrel A, Müller A, Nicolet C, Avellan F (2016) Local wave speed and bulk flow viscosity in Francis turbines at part load operation. J Hydraul Res 54(2):185–196CrossRefGoogle Scholar
  23. Lucca-Negro O, O’Doherty T (2001) Vortex breakdown: a review. Prog Energy Combust Sci 27(4):431–481CrossRefGoogle Scholar
  24. Martinelli F, Cozzi F, Coghe A (2012) Phase-locked analysis of velocity fluctuations in a turbulent free swirling jet after vortex breakdown. Exp Fluids 53(2):437–449CrossRefGoogle Scholar
  25. Müller A, Dreyer M, Andreini N, Avellan F (2013) Draft tube discharge fluctuation during self-sustained pressure surge: fluorescent particle image velocimetry in two-phase flow. Exp Fluids 54(4):1–11CrossRefGoogle Scholar
  26. Müller A, Favrel A, Landry C, Yamamoto K, Avellan F (2014) On the physical mechanisms governing self-excited pressure surge in Francis turbines. In: IOP conference series: earth and environmental science 22 (27th IAHR symposium on hydraulic machinery and systems, Montreal, Canada)Google Scholar
  27. Müller A, Yamamoto K, Alligné S, Yonezawa K, Tsujimoto Y, Avellan F (2016) Measurement of the self-oscillating vortex rope dynamics for hydroacoustic stability analysis. ASME J Fluids Eng 138(2):021206CrossRefGoogle Scholar
  28. Nishi M, Liu S (2013) An outlook on the draft-tube-surge study. Int J Fluid Mach Syst 6(1):33–48CrossRefGoogle Scholar
  29. Reynolds WC, Hussain A (1972) The mechanics of an organized wave in turbulent shear flow. Part 3. Theoretical models and comparisons with experiments. J Fluid Mech 54:263–288CrossRefGoogle Scholar
  30. Rheingans W (1940) Power swings in hydroelectric power plants. Trans ASME 62:171–184Google Scholar
  31. Ruchonnet N, Alligné S, Nicolet C, Avellan F (2012) Cavitation influence on hydroacoustic resonance in pipe. J Fluids Struct 28:180–193CrossRefGoogle Scholar
  32. Syred N (2006) A review of oscillation mechanisms and the role of the precessing vortex core (PVC) in swirl combustion systems. Prog Energy Combust Sci 32(2):93–161CrossRefGoogle Scholar
  33. Yamamoto K, Müller A, Ashida T, Yonezawa K, Avellan F, Tsujimoto Y (2015) Experimental method for the evaluation of the dynamic transfer matrix using pressure transducers. J Hydraul Res 53(4):466–477CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • A. Favrel
    • 1
    Email author
  • A. Müller
    • 1
  • C. Landry
    • 1
  • K. Yamamoto
    • 1
  • F. Avellan
    • 1
  1. 1.Laboratory for Hydraulic MachinesEcole Polytechnique Fédérale de LausanneLausanneSwitzerland

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