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Numerical and experimental study of the leakage flow in guide vanes with different hydrofoils
Sailesh Chitrakar,Biraj Singh Thapa,Ole Gunnar Dahlhaug,Hari Prasad Neopane 한국CDE학회 2017 Journal of computational design and engineering Vol.4 No.3
Clearance gaps between guide vanes and cover plates of Francis turbines tend to increase in size due to simultaneous effect of secondary flow and erosion in sediment affected hydropower plants. The pressure difference between the two sides of the guide vane induces leakage flow through the gap. This flow enters into the suction side with high acceleration, disturbing the primary flow and causing more erosion and losses in downstream turbine components. A cascade rig containing a single guide vane passage has been built to study the effect of the clearance gap using pressure sensors and PIV (Particle Image Velocimetry) technique. This study focuses on developing a numerical model of the test rig, validating the results with experiments and investigating the behavior of leakage flow numerically. It was observed from both CFD and experiment that the leakage flow forms a passage vortex, which shifts away from the wall while travelling downstream. The streamlines contributing to the formation of this vortex have been discussed. Furthermore, the reference guide vane with symmetrical hydrofoil has been compared with four cambered profiles, in terms of the guide vane loading and the consequent effect on the leakage flow. A dimensionless term called Leakage Flow Factor (Lff) has been introduced to compare the performances of hydrofoils. It is shown that the leakage flow and its effect on increasing losses and erosion can be minimized by changing the pressure distribution over the guide vane.
Fully coupled FSI analysis of Francis turbines exposed to sediment erosion
Sailesh Chitrakar,Michel Cervantes,Biraj Singh Thapa 한국유체기계학회 2014 International journal of fluid machinery and syste Vol.7 No.3
Sediment erosion is one of the key challenges in hydraulic turbines from a design and maintenance perspective in Himalayas. The present study focuses on choosing the best design in terms of blade angle distribution of a Francis turbine runner which has least erosion effect without influencing the efficiency and the structural integrity. A fully coupled Fluid-Structure-Interaction (FSI) analysis was performed through a multi-field solver, which showed that the maximum stress induced in the optimized design for better sediment handling, is less than that induced in the reference design. Some numerical validation techniques have been shown for both CFD and FSI analysis.
Fully coupled FSI analysis of Francis turbines exposed to sediment erosion
Chitrakar, Sailesh,Cervantes, Michel,Thapa, Biraj Singh Korean Society for Fluid machinery 2014 International journal of fluid machinery and syste Vol.7 No.3
Sediment erosion is one of the key challenges in hydraulic turbines from a design and maintenance perspective in Himalayas. The present study focuses on choosing the best design in terms of blade angle distribution of a Francis turbine runner which has least erosion effect without influencing the efficiency and the structural integrity. A fully coupled Fluid-Structure-Interaction (FSI) analysis was performed through a multi-field solver, which showed that the maximum stress induced in the optimized design for better sediment handling, is less than that induced in the reference design. Some numerical validation techniques have been shown for both CFD and FSI analysis.