Correlating Sediment Erosion in Rotary–Stationary Gaps of Francis Turbines with Complex Flow Patterns

Nirmal Acharya (), Saroj Gautam, Sailesh Chitrakar, Igor Iliev and Ole Gunnar Dahlhaug
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Nirmal Acharya: Waterpower Laboratory, Department of Energy & Process Engineering, Norwegian University of Science and Technology, 7034 Trondheim, Norway
Saroj Gautam: Turbine Testing Lab, Kathmandu University, Dhulikhel 45200, Nepal
Sailesh Chitrakar: Turbine Testing Lab, Kathmandu University, Dhulikhel 45200, Nepal
Igor Iliev: Aker Solutions Hydropower AS, 1325 Lysaker, Norway
Ole Gunnar Dahlhaug: Waterpower Laboratory, Department of Energy & Process Engineering, Norwegian University of Science and Technology, 7034 Trondheim, Norway

Energies, 2024, vol. 17, issue 23, 1-24

Abstract: Secondary flows in Francis turbines are induced by the presence of a gap between guide vanes and top–bottom covers and rotating–stationary geometries. The secondary flow developed in the clearance gap of guide vanes induces a leakage vortex that travels toward the turbine downstream, affecting the runner. Likewise, secondary flows from the gap between rotor–stator components enter the upper and lower labyrinth regions. When Francis turbines are operated with sediment-laden water, sediment-containing flows affect these gaps, increasing the size of the gap and increasing the leakage flow. This work examines the secondary flows developing at these locations in a Francis turbine and the consequent sediment erosion effects. A reference Francis turbine at Bhilangana III Hydropower Plant (HPP), India, with a specific speed (Ns = 85.4) severely affected by a sediment erosion problem, was selected for this study. All the components of the turbine were modeled, and a reference numerical model was developed. This numerical model was validated with numerical uncertainty measurement and experimental results. Different locations in the turbine with complex secondary flows and the consequent sediment erosion effects were examined separately. The erosion effects at the guide vanes were due to the development of leakage flow inside the guide vane clearance gaps. At the runner inlet, erosion was mainly due to a leakage vortex from the clearance gap and leakage flow from rotor–stator gaps. Toward the upper and bottom labyrinth regions, erosion was mainly due to the formation of secondary vortical rolls. The simultaneous effects of secondary flows and sediment erosion at all these locations were found to affect the overall performance of the turbine.

Keywords: Francis turbine; guide vane clearance gaps; leakage vortex; labyrinth; secondary flow; sediment erosion (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: 2024
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