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Investigation and validation of a Francis turbine at runaway operating conditions

Trivedi, Chirag; Cervantes, Michel; Gandhi, BK
Journal article, Peer reviewed
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URI
http://hdl.handle.net/11250/2384258
Date
2016
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  • Institutt for energi og prosessteknikk [3297]
  • Publikasjoner fra CRIStin - NTNU [26591]
Original version
Energies 2016, 9(3)   10.3390/en9030149
Abstract
Hydraulic turbines exhibit total load rejection during operation because of high fluctuations

in the grid parameters. The generator reaches no-load instantly. Consequently, the turbine runner

accelerates to high speed, runaway speed, in seconds. Under common conditions, stable runaway is

only reached if after a load rejection, the control and protection mechanisms both fail and the guide

vanes cannot be closed. The runner life is affected by the high amplitude pressure loading at the

runaway speed. A model Francis turbine was used to investigate the consequences at the runaway

condition. Measurements and simulations were performed at three operating points. The numerical

simulations were performed using standard k-", k-! shear stress transport (SST) and scale-adaptive

simulation (SAS) models. A total of 12.8 million hexahedral mesh elements were created in the

complete turbine, from the spiral casing inlet to the draft tube outlet. The experimental and numerical

analysis showed that the runner was subjected to an unsteady pressure loading up to three-times the

pressure loading observed at the best efficiency point. Investigates of unsteady pressure pulsations at

the vaneless space, runner and draft tube are discussed in the paper. Further, unsteady swirling flow

in the blade passages was observed that was rotating at a frequency of 4.8-times the runaway runner

angular speed. Apart from the unsteady pressure loading, the development pattern of the swirling

flow in the runner is discussed in the paper.
Publisher
MDPI
Journal
Energies

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