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Vortex Rope Formation in a High Head Model Francis Turbine
Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee.
Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee.
Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee.
Number of Authors: 3
2017 (English)In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 139, no 4, 041102Article in journal (Refereed) Published
Abstract [en]

Francis turbine working at off-design operating condition experiences high swirling flow at the runner outlet. In the present study, a high head model Francis turbine was experimentally investigated during load rejection, i.e., best efficiency point (BEP) to part load (PL), to detect the physical mechanism that lies in the formation of vortex rope. For that, a complete measurement system of dynamic pressure, head, flow, guide vanes (GVs) angular position, and runner shaft torque was setup with corresponding sensors at selected locations of the turbine. The measurements were synchronized with the twodimensional (2D) particle image velocimetry (PIV) measurements of the draft tube. The study comprised an efficiency measurement and maximum hydraulic efficiency of 92.4±0.15% was observed at BEP condition of turbine. The severe pressure fluctuations corresponding to rotor-stator interaction (RSI), standing waves, and rotating vortex rope (RVR) have been observed in the draft tube and vaneless space of the turbine. Moreover, RVR in the draft tube has been decomposed into two different modes; rotating and plunging modes. The time of occurrence of both modes was investigated in pressure and velocity data and results showed that the plunging mode appears 0.8 s before the rotating mode. In the vaneless space, the plunging mode was captured before it appears in the draft tube. The physical mechanism behind the vortex rope formation was analyzed from the instantaneous PIV velocity vector field. The development of stagnation region at the draft tube center and high axial velocity gradients along the draft tube centerline could possibly cause the formation of vortex rope

Place, publisher, year, edition, pages
2017. Vol. 139, no 4, 041102
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-62111DOI: 10.1115/1.4035224ScopusID: 2-s2.0-85013453549OAI: oai:DiVA.org:ltu-62111DiVA: diva2:1076083
Note

Validerad; 2017; Nivå 2; 2017-03-03 (andbra)

Available from: 2017-02-22 Created: 2017-02-22 Last updated: 2017-03-03Bibliographically approved

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