0
Research Papers: Flows in Complex Systems

Detection of Draft Tube Surge and Erosive Blade Cavitation in a Full-Scale Francis Turbine

[+] Author and Article Information
Xavier Escaler

Universitat Politècnica de Catalunya,
Av. Diagonal 647, Barcelona ES-08028, Spain
e-mail: escaler@mf.upc.edu

Jarle V. Ekanger

Norwegian University of Science
and Technology,
Kolbjørn Hejes v 1B,
Trondheim NO-7491, Norway
e-mail: jarle.ekanger@fdb.no

Håkon H. Francke

Flow Design Bureau AS,
C/o Ipark, Stavanger NO-4068, Norway
e-mail: hakon.francke@fdb.no

Morten Kjeldsen

Flow Design Bureau AS,
C/o Ipark, Stavanger NO-4068, Norway
e-mail: morten.kjeldsen@fdb.no

Torbjørn K. Nielsen

Norwegian University of Science
and Technology,
Kolbjørn Hejes v 1B,
Trondheim NO-7491, Norway
e-mail: torbjorn.nielsen@ntnu.no

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received November 18, 2013; final manuscript received April 25, 2014; published online September 10, 2014. Assoc. Editor: Frank C. Visser.

J. Fluids Eng 137(1), 011103 (Sep 10, 2014) (9 pages) Paper No: FE-13-1676; doi: 10.1115/1.4027541 History: Received November 18, 2013; Revised April 25, 2014

A full-scale Francis turbine has been experimentally investigated over its full range of operation to detect draft tube swirling flows and cavitation. The unit is of interest due to the presence of severe pressure fluctuations at part load and of advanced blade suction-side cavitation erosion. Moreover, the turbine has a particular combination of guide vanes (20) to runner blades (15) that makes it prone to significant rotor-stator interaction (RSI). For that, a complete measurement system of dynamic pressures, temperatures, vibrations, and acoustic emissions has been setup with the corresponding transducers mounted at selected sensitive locations. The experiments have comprised an efficiency measurement, a signal transmissibility evaluation, and the recording of the raw signals at high sampling rates. Signal processing methods for demodulation, peak power estimation, and cross correlation have also been applied. As a result, draft tube pressure fluctuations have been detected around the Rheingans frequency for low loads and at 4% of the rotating frequency for high loads. Moreover, maximum turbine guide bearing acoustic emissions have been measured at full load with amplitude modulations at both the guide vane passing frequency and the draft tube surge frequency.

Copyright © 2015 by ASME
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Fig. 1

Photograph showing the advanced cavitation erosion on the runner blade suction side near the trailing edge

Grahic Jump Location
Fig. 2

Schematic of the Francis turbine with the measuring positions

Grahic Jump Location
Fig. 3

Measured efficiency curve of the hydropower unit

Grahic Jump Location
Fig. 4

Averaged power spectra of draft tube absolute pressure

Grahic Jump Location
Fig. 5

Force applied with the hammer on the blade (top), total acoustic emission measured on the turbine guide bearing pedestal (middle), and acoustic emission filtered in the frequency band from 40 to 45 kHz (bottom).

Grahic Jump Location
Fig. 6

Gain and coherence functions between the hammer excitations on the blade and both the vibration acceleration and the acoustic emission responses on the turbine guide bearing pedestal with the turbine still and empty of water.

Grahic Jump Location
Fig. 7

Averaged power spectra of acoustic emission signals measured on the turbine guide bearing pedestal for different operating conditions.

Grahic Jump Location
Fig. 8

Averaged power spectra of vibration acceleration signals measured on the turbine guide bearing pedestal (top left and bottom left), on the guide vane (top right), and on the draft tube (bottom right) for different operating conditions

Grahic Jump Location
Fig. 9

Vibration acceleration rms levels of the frequency band from 15 to 20 kHz and acoustic emission rms levels of the frequency band from 40 to 45 kHz

Grahic Jump Location
Fig. 10

Envelopes of the acoustic emission signal filtered in the band from 40 to 45 kHz for minimum and maximum loads (top) and corresponding averaged amplitude modulation power spectra (bottom).

Grahic Jump Location
Fig. 11

Zoomed view of the averaged amplitude modulation power spectra from 186 to 214 Hz for all the operating loads for acoustic emission signals in the band from 40 to 45 kHz (top) and vibration accelerations on the turbine guide bearing 90 deg apart from 15 to 20 kHz (bottom).

Grahic Jump Location
Fig. 12

Zoomed view of the averaged amplitude modulation power spectra from 0 to 9 Hz for all the operating loads for acoustic emission signals in the band from 40 to 45 kHz

Grahic Jump Location
Fig. 13

Estimated power around 200 and 195 Hz of demodulated acoustic emission signals from 40 to 45 kHz as well as difference between both estimates for all the turbine loads (top); estimated power difference between 200 and 195 Hz (bottom) of demodulated vibration acceleration signals from 15 to 20 kHz on turbine guide bearing, guide vane, and draft tube for all the turbine loads.

Grahic Jump Location
Fig. 14

Estimated power around 0.4 and 1.4 Hz of demodulated acoustic emission signals from 40 to 45 kHz as well as difference between both estimates for all the turbine loads

Grahic Jump Location
Fig. 15

Coherence levels (top) and cross power spectrum phases (bottom) at 200 Hz between couples of vibration acceleration envelopes for all the turbine loads

Grahic Jump Location
Fig. 16

Comparison of averaged power spectra of turbine guide bearing accelerations obtained in analogous measurements elapsed 1 year

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In