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Experiments in Fluids

, 58:142 | Cite as

Experimental evidence of inter-blade cavitation vortex development in Francis turbines at deep part load condition

  • K. YamamotoEmail author
  • A. Müller
  • A. Favrel
  • F. Avellan
Research Article

Abstract

Francis turbines are subject to various types of cavitation flow depending on the operating condition. To enable a smooth integration of the renewable energy sources, hydraulic machines are now increasingly required to extend their operating range, especially down to extremely low discharge conditions called deep part load operation. The inter-blade cavitation vortex is a typical cavitation phenomenon observed at deep part load operation. However, its dynamic characteristics are insufficiently understood today. In an objective of revealing its characteristics, the present study introduces a novel visualization technique with instrumented guide vanes embedding the visualization devices, providing unprecedented views on the inter-blade cavitation vortex. The binary image processing technique enables the successful evaluation of the inter-blade cavitation vortex in the images. As a result, it is shown that the probability of the inter-blade cavitation development is significantly high close to the runner hub. Furthermore, the mean vortex line is calculated and the vortex region is estimated in the three-dimensional domain for the comparison with numerical simulation results. In addition, the on-board pressure measurements on a runner blade is conducted, and the influence of the inter-blade vortex on the pressure field is investigated. The analysis suggests that the presence of the inter-blade vortex can magnify the amplitude of pressure fluctuations especially on the blade suction side. Furthermore, the wall pressure difference between pressure and suction sides of the blade features partially low or negative values near the hub at the discharge region where the inter-blade vortex develops. This negative pressure difference on the blade wall suggests the development of a backflow region caused by the flow separation near the hub, which is closely related to the development of the inter-blade vortex. The development of the backflow region is confirmed by the numerical simulation, and the physical mechanisms of the inter-blade vortex development is, furthermore, discussed.

Notes

Acknowledgements

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, Alain Renaud and Vincent Berruex.

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Copyright information

© Springer-Verlag GmbH Germany 2017

Authors and Affiliations

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

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