An experimental investigation of the rotating stall in reduced scale model of a low specific speed radial pump-turbine at runaway and turbine brake conditions in generating mode is achieved. Measurements of wall pressure in the stator are performed along with high-speed flow visualizations in the vaneless gap with the help of air bubbles injection. When starting from the best efficiency point (BEP) and increasing the impeller speed, a significant increase of the pressure fluctuations is observed mainly in the wicket gates channels. The spectral analysis shows a rise of a low frequency component (about 70% of the impeller rotational frequency) at runaway, which further increases as the zero discharge condition is approached. Analysis of the instantaneous pressure peripheral distribution in the vaneless gap reveals one stall cell rotating with the impeller at sub-synchronous speed. High-speed movies reveal a quite uniform flow pattern in the guide vanes channels at the normal operating range, whereas at runaway the flow is highly disturbed by the rotating stall passage. The situation is even more critical at very low positive discharge, where backflow and vortices in the guide vanes channels develop during the stall cell passage. A specific image processing technique is applied to reconstruct the rotating stall evolution in the entire guide vanes circumference for a low positive discharge operating point. The findings of this study suggest that one stall cell rotates with the impeller at sub-synchronous velocity in the vaneless gap between the impeller and the guide vanes. It is the result of rotating flow separations developed in several consecutive impeller channels which lead to their blockage.
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e-mail: vlad.hasmatuchi@epfl.ch
e-mail: mohamed.farhat@epfl.ch
e-mail: steven.roth@epfl.ch
e-mail: francisco.botero@epfl.ch
e-mail: francois.avellan@epfl.ch
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Experimental Evidence of Rotating Stall in a Pump-Turbine at Off-Design Conditions in Generating Mode
Vlad Hasmatuchi,
e-mail: vlad.hasmatuchi@epfl.ch
Vlad Hasmatuchi
Doctoral Assistant
École Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Hydraulic Machines
, Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland
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Mohamed Farhat,
e-mail: mohamed.farhat@epfl.ch
Mohamed Farhat
Senior Scientist
École Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Hydraulic Machines
, Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland
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Steven Roth,
e-mail: steven.roth@epfl.ch
Steven Roth
Doctoral Assistant
École Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Hydraulic Machines
, Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland
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Francisco Botero,
e-mail: francisco.botero@epfl.ch
Francisco Botero
Doctoral Student
École Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Hydraulic Machines
, Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland
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François Avellan
e-mail: francois.avellan@epfl.ch
François Avellan
Professor
École Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Hydraulic Machines
, Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland
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Vlad Hasmatuchi
Doctoral Assistant
École Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Hydraulic Machines
, Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland
e-mail: vlad.hasmatuchi@epfl.ch
Mohamed Farhat
Senior Scientist
École Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Hydraulic Machines
, Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland
e-mail: mohamed.farhat@epfl.ch
Steven Roth
Doctoral Assistant
École Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Hydraulic Machines
, Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland
e-mail: steven.roth@epfl.ch
Francisco Botero
Doctoral Student
École Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Hydraulic Machines
, Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland
e-mail: francisco.botero@epfl.ch
François Avellan
Professor
École Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Hydraulic Machines
, Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland
e-mail: francois.avellan@epfl.ch
J. Fluids Eng. May 2011, 133(5): 051104 (8 pages)
Published Online: June 7, 2011
Article history
Received:
December 10, 2010
Revised:
April 20, 2011
Online:
June 7, 2011
Published:
June 7, 2011
Citation
Hasmatuchi, V., Farhat, M., Roth, S., Botero, F., and Avellan, F. (June 7, 2011). "Experimental Evidence of Rotating Stall in a Pump-Turbine at Off-Design Conditions in Generating Mode." ASME. J. Fluids Eng. May 2011; 133(5): 051104. https://doi.org/10.1115/1.4004088
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