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Research Papers: Flows in Complex Systems

Analysis of the Cavitating Draft Tube Vortex in a Francis Turbine Using Particle Image Velocimetry Measurements in Two-Phase Flow

[+] Author and Article Information
Monica Sanda Iliescu

Laboratory for Hydraulic Machines, Ecole Polytechnique Fédérale de Lausanne (EPFL), Avenue de Cour 33bis, CH-1007 Lausanne, Switzerlandmsiliescu@yahoo.fr

Gabriel Dan Ciocan

Laboratory for Hydraulic Machines, Ecole Polytechnique Fédérale de Lausanne (EPFL), Avenue de Cour 33bis, CH-1007 Lausanne, Switzerlandgabrieldan.ciocan@orange.fr

François Avellan

Laboratory for Hydraulic Machines, Ecole Polytechnique Fédérale de Lausanne (EPFL), Avenue de Cour 33bis, CH-1007 Lausanne, Switzerlandfrancois.avellan@epfl.ch

J. Fluids Eng 130(2), 021105 (Jan 25, 2008) (10 pages) doi:10.1115/1.2813052 History: Received June 29, 2006; Revised July 01, 2007; Published January 25, 2008

Partial flow rate operation of hydroturbines with constant pitch blades causes complex unstable cavitating flow in the diffuser cone. A particle image velocimetry (PIV) system allows investigating the flow velocity field in the case of a developing cavitation vortex, the so-called vortex rope, at the outlet of a Francis turbine runner. The synchronization of the PIV flow survey with the rope precession allows applying the ensemble averaging by phase technique to extract both the periodic velocity components and the rope shape. The influence of the turbine setting level on the volume of the cavity rope and its centerline is investigated, providing a physical knowledge about the hydrodynamic complex phenomena involved in the development of the cavitation rope in Francis turbine operating regimes.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Development of the vapor core rope for σ=0.380

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Figure 2

Francis turbine scale model

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Figure 3

Two-phase PIV setup for measuring in the diffuser cone of the Francis turbine scale model

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Figure 4

Waterfall diagram of the power spectra of the wall pressure fluctuations in the diffuser cone

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Figure 5

Image-processing flowchart

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Figure 6

Extraction of the rope diameter by image processing from each instantaneous image

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Figure 7

Streamlines on instantaneous velocity fields for the same corresponding phase τ∕T∼=0.61 and different σ values

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Figure 8

Phase averaged vectors field for σ=0.380

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Figure 9

Vortex center detection for noncavitating conditions

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Figure 10

Vortex centerlines for σ=0.380 and σ=1.180

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Figure 11

Reconstruction of the rope volume

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Figure 12

Standard deviation of the rope position and rope volume

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Figure 13

Rope diameter variations versus the σ value

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Figure 14

Rope diameter variations versus the vortex phase τ

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Figure 15

Rope center variations versus the σ value

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Figure 16

Vortex position variations for σ1.180 and 0.380 values versus the vortex phase τ

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