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

K. Yamamoto, A. Müller, Arthur Tristan Favrel, F. Avellan

Research output: Contribution to journalArticle

8 Citations (Scopus)

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.

Original languageEnglish
Article number142
JournalExperiments in Fluids
Volume58
Issue number10
DOIs
Publication statusPublished - 2017 Oct 1
Externally publishedYes

Fingerprint

Francis turbines
turbines
cavitation flow
blades
Cavitation
Turbomachine blades
Vortex flow
vortices
hubs
suction
Visualization
Binary images
Flow separation
guide vanes
Computer simulation
Pressure measurement
wall pressure
flow separation
renewable energy
energy sources

ASJC Scopus subject areas

  • Computational Mechanics
  • Mechanics of Materials
  • Physics and Astronomy(all)
  • Fluid Flow and Transfer Processes

Cite this

Experimental evidence of inter-blade cavitation vortex development in Francis turbines at deep part load condition. / Yamamoto, K.; Müller, A.; Favrel, Arthur Tristan; Avellan, F.

In: Experiments in Fluids, Vol. 58, No. 10, 142, 01.10.2017.

Research output: Contribution to journalArticle

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