An experimental study on the upper part-load elliptical vortex instability in a Francis turbine

Ali Amini*, Elena Vagnoni, Arthur Favrel, Kazuhiko Yamaishi, Andres Müller, François Avellan

*この研究の対応する著者

研究成果: Conference article査読

抄録

This paper presents preliminary results of an experimental study on the occurrence and development of the upper part-load instability in a reduced-scale Francis turbine. The study includes draft tube pressure measurements, high-speed flow visualization, and particle image velocimetry. Our results reveal that for an operating point within the range of the upper part-load instability (70 to 85 % of the nominal discharge), the vortex rope has a circular cross section in non-cavitating conditions, which is preserved even after the appearance of cavitation within the vortex core. It is only below a certain cavitation number that the vortex cross section turns into an ellipse, which is associated with an abrupt increase in the pressure fluctuations with a distinct peak in the frequency domain. A further decrease in the cavitation number results in a constant decrease in the activated frequency while the amplitude of these oscillations experience a rise followed by a quick drop. Phase-averaged velocity fields show that the occurrence and development of cavitation within the vortex rope result in a more diffused distribution of the angular momentum. The instantaneous velocity fields, on the other hand, reveal that the elliptical vortex has various states with either diffused or concentrated velocity distributions, which makes the use of the averaged velocity field for this point less relevant.

本文言語English
論文番号012002
ジャーナルIOP Conference Series: Earth and Environmental Science
774
1
DOI
出版ステータスPublished - 2021 6 15
イベント30th IAHR Symposium on Hydraulic Machinery and Systems, IAHR 2020 - Lausanne, Virtual, Switzerland
継続期間: 2021 3 212021 3 26

ASJC Scopus subject areas

  • 環境科学(全般)
  • 地球惑星科学(全般)

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