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Energies 2016, 9(3), 149; doi:10.3390/en9030149

Investigation of a High Head Francis Turbine at Runaway Operating Conditions

1
Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim NO-7491, Norway
2
Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå 97187, Sweden
3
Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee 247667, India
*
Author to whom correspondence should be addressed.
Academic Editor: Juan Ignacio Pérez-Díaz
Received: 22 December 2015 / Revised: 5 February 2016 / Accepted: 19 February 2016 / Published: 2 March 2016
(This article belongs to the Special Issue Hydropower)

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-ε, k-ω 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. View Full-Text
Keywords: CFD; Francis turbine; pressure pulsation; runaway; runner; transient CFD; Francis turbine; pressure pulsation; runaway; runner; transient
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Trivedi, C.; Cervantes, M.J.; Gandhi, B.K. Investigation of a High Head Francis Turbine at Runaway Operating Conditions. Energies 2016, 9, 149.

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