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research-article

On the Efficiency Alteration Mechanisms due to Cavitation in Kaplan Turbines

[+] Author and Article Information
Sebastian Leguizamon

Laboratory for Hydraulic Machines (LMH) Department of Mechanical Engineering Swiss Federal Institute of Technology (EPFL) Avenue de Cour 33 Bis CH-1007 Lausanne
sebastian.legui@epfl.ch

Claire Ségoufin

Alstom Power Hydro 82 Avenue Léon Blum FR-38100 Grenoble
claire.segoufin@power.alstom.com

Hai-Trieu Phan

Alstom Power Hydro 82 Avenue Léon Blum FR-38100 Grenoble
hai-trieu.phan@power.alstom.com

François Avellan

Full Professor Laboratory for Hydraulic Machines (LMH) Department of Mechanical Engineering Swiss Federal Institute of Technology (EPFL) Avenue de Cour 33 Bis CH-1007 Lausanne
francois.avellan@epfl.ch

1Corresponding author.

ASME doi:10.1115/1.4035928 History: Received November 09, 2015; Revised December 03, 2016

Abstract

A transport-equation-based homogeneous cavitation model previously assessed and validated against experimental data is used to investigate and explain the efficiency alteration mechanisms in Kaplan turbines. On the one hand, it is shown that the efficiency increase is caused by a decrease in energy dissipation due to a decreased turbulence production driven by a drop in fluid density associated with the cavitation region. This region also entails an increase in torque, caused by the modification of the pressure distribution throughout the blade, which saturates on the suction side. On the other hand, the efficiency drop is shown to be driven by a sharp increase in turbulence production at the trailing edge. An analysis of the pressure coefficient distribution explains such behavior as being a direct consequence of the pressure-altering cavitation region reaching the trailing edge. Finally, even though the efficiency alteration behavior is very sensitive to the dominant cavitation type, it is demonstrated that the governing mechanisms are invariant to it.

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