TY - JOUR
T1 - Physical Mechanism of Interblade Vortex Development at Deep Part Load Operation of a Francis Turbine
AU - Yamamoto, Keita
AU - Müller, Andres
AU - Favrel, Arthur
AU - Avellan, François
N1 - Funding Information:
The research leading to the results published in this paper is part of the HYPERBOLE research project. The authors would also like to thank BC Hydro for making available the reduced scale model, in particular Danny Burggraeve and Jacob Iosfin. Moreover, the authors would like to acknowledge the commitment of the Laboratory for Hydraulic Machines technical staff, especially Georges Crittin, Alain Renaud, and Vincent Berruex. European Commission (ERC/FP7- ENERGY-2013-1-Grant 608532; Funder ID: 10.13039/501100000780).
Publisher Copyright:
© 2019 by ASME.
PY - 2019/11/1
Y1 - 2019/11/1
N2 - For seamless integration of growing electricity production from intermittent renewable energy sources, Francis turbines are under increasing demand to extend their operating range. This requires Francis turbines to operate under off-design conditions, where various types of cavitation are induced. At deep part load condition, an interblade cavitation vortex observed in a runner blade channel is a typical cavitation phenomenon causing pressure fluctuations and erosion, which prevent a reliable operation of Francis turbines at deep part load. The underlying mechanisms of its development are, however, yet to be understood. In an objective of revealing its developing mechanisms, the present study is aimed at investigating flow structures inside runner blade channels by comparison of three different operating conditions at deep part load using numerical simulation results. After demonstrating interblade vortex structures are successfully simulated by performed computations, it is shown that flow inside the runner at deep part load operation is characterized by a remarkable development of recirculating flow on the hub near the runner outlet. This recirculating flow is concluded to be closely associated with interblade vortex development. The skin-friction analyses applied to the hub identify the flow separation caused by a nonuniform distribution of flow, which describes the underlying physical mechanism of interblade vortex development. Investigations are further extended to include a quantitative evaluation of the specific energy loss induced by interblade vortex development. The integration of energy flux defined by rothalpy evidences the energy loss due to the presence of strong interblade vortex structures.
AB - For seamless integration of growing electricity production from intermittent renewable energy sources, Francis turbines are under increasing demand to extend their operating range. This requires Francis turbines to operate under off-design conditions, where various types of cavitation are induced. At deep part load condition, an interblade cavitation vortex observed in a runner blade channel is a typical cavitation phenomenon causing pressure fluctuations and erosion, which prevent a reliable operation of Francis turbines at deep part load. The underlying mechanisms of its development are, however, yet to be understood. In an objective of revealing its developing mechanisms, the present study is aimed at investigating flow structures inside runner blade channels by comparison of three different operating conditions at deep part load using numerical simulation results. After demonstrating interblade vortex structures are successfully simulated by performed computations, it is shown that flow inside the runner at deep part load operation is characterized by a remarkable development of recirculating flow on the hub near the runner outlet. This recirculating flow is concluded to be closely associated with interblade vortex development. The skin-friction analyses applied to the hub identify the flow separation caused by a nonuniform distribution of flow, which describes the underlying physical mechanism of interblade vortex development. Investigations are further extended to include a quantitative evaluation of the specific energy loss induced by interblade vortex development. The integration of energy flux defined by rothalpy evidences the energy loss due to the presence of strong interblade vortex structures.
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U2 - 10.1115/1.4043989
DO - 10.1115/1.4043989
M3 - Article
AN - SCOPUS:85068933159
SN - 0098-2202
VL - 141
JO - Journal of Fluids Engineering, Transactions of the ASME
JF - Journal of Fluids Engineering, Transactions of the ASME
IS - 11
M1 - 111113
ER -