Leakage Vortex Progression through a Guide Vane’s Clearance Gap and the Resulting Pressure Fluctuation in a Francis Turbine

Nirmal Acharya, Saroj Gautam, Sailesh Chitrakar, Chirag Trivedi and Ole Gunnar Dahlhaug
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Nirmal Acharya: Waterpower Laboratory, Department of Energy & Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
Saroj Gautam: Turbine Testing Lab, Kathmandu University, Dhulikhel 45210, Nepal
Sailesh Chitrakar: Turbine Testing Lab, Kathmandu University, Dhulikhel 45210, Nepal
Chirag Trivedi: Waterpower Laboratory, Department of Energy & Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
Ole Gunnar Dahlhaug: Waterpower Laboratory, Department of Energy & Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway

Energies, 2021, vol. 14, issue 14, 1-19

Abstract: A clearance gap (CG) between guide vanes (GVs) and facing plates exists at both ends of a Francis turbine and allows the opening angle to be adjusted for varying operating conditions. Leakage flow is induced through this gap due to the pressure difference between the two sides of the guide vanes. While some research works have used qualitative approaches to visualize and predict the strength of a leakage vortex (LV), this paper presents a method for quantifying vortices along a trajectory. In this paper, a prototype high-head Francis runner with specific speed of 85.4 is considered as a reference case. A systematic investigation across both space and time is carried out, i.e., analysis of the spatial temporal progression of LV for three operating conditions. While travelling from the CG to runner leading edge, LV evolution and trajectory data are observed and the values of vorticity and turbulent kinetic energy are calculated for the LV trajectory. Frequency spectrum analyses of pressure oscillations in the vaneless space, runner blade, and draft tube are also performed to observe the peak pressure pulsation and its harmonics. Unsteady fluctuations of the runner output torque are finally studied to identify the patterns and magnitudes of torque oscillations.

Keywords: clearance gap; leakage vortex; rotor stator interaction; pressure pulsation (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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