This article presents preliminary results of an experimental study of the upper-part load instability and the associated elliptical form of the cavitation vortex rope in a Francis turbine draft tube. The influence of the operating parameters on the onset and the development of the instability is first briefly studied by pressure measurements in the draft tube. Visualizations of the cavitation vortex rope and its associated elliptical form are performed by using two synchronized high-speed cameras spaced by an angle of 90°. This allows to reconstruct the instantaneous position of the vortex center along the draft tube. It is confirmed that using a single camera leads to biased estimations of the cavitation volume fluctuations. The breathing behaviour of the vortex rope, responsible for the pressure pulsations according to several authors, cannot be definitely demonstrated without a proper reconstruction of the vortex shape based on high-speed videos from several positions. Finally, unique intermittent collapses of cavitation in the vortex center, giving rise to two distinct cavities connecting on both sides the vortex rope, are highlighted.
|Journal||IOP Conference Series: Earth and Environmental Science|
|Publication status||Published - 2019 Dec 20|
|Event||8th IAHR International Workshop on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems, IAHR 2019 - Stuttgart, Germany|
Duration: 2019 Oct 9 → 2019 Oct 11
ASJC Scopus subject areas
- Environmental Science(all)
- Earth and Planetary Sciences(all)