RECENT FINDINGS RELATED TO SEDIMENT EROSION IN FRANCIS TURBINES

Sailesh Chitrakar,Hari Prasad NEOPANE,Gunnar Dahlhaug 한국신재생에너지학회 2017 AFORE Vol.2017 No.11

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.

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.

TURBINE TESTING LAB, NEPAL – ACHIEVEMENTS, CHALLENGES AND OPPORTUNITIES

Sailesh Chitrakar,Hari Prasad NEOPANE,Young Ho LEE 한국신재생에너지학회 2017 AFORE Vol.2017 No.11

Computational Design of Bifurcation

Ravi Koirala,Sailesh Chitrakar,Hari Prasad Neopane,Balendra Chhetri,Bhola Thapa 한국유체기계학회 2017 International journal of fluid machinery and syste Vol.10 No.1

Bifurcation refers to wye division of penstock to divide the flow symmetrically or unsymmetrically into two units of turbine for maintaining economical, technical and geological substrates. Particularly, water shows irrelevant behavior when there is a sudden change in flow direction, which results into the transition of the static and dynamic behavior of the flow. Hence, special care and design considerations are required both hydraulically and structurally. The transition induced losses and extra stresses are major features to be examined. The research on design and analysis of bifurcation is one of the oldest topics related to R&D of hydro-mechanical components for hydropower plants. As far as the earlier approaches are concerned, the hydraulic designs were performed based on graphical data sheet, head loss considerations and the mechanical analysis through simplified beam approach. In this paper, the multi prospect approach for design of Bifurcation, incorporating the modern day’s tools and technology is identified. The hydraulic design of bifurcation is a major function of dynamic characteristics of the flow, which is performed with CFD analysis for minimum losses and better hydraulic performances. Additionally, for the mechanical design, a simplified conventional design method as pre-estimation and Finite Element Method for a relevant result projections were used.

Selection of Optimal Number of Francis Runner Blades for a Sediment Laden Micro Hydropower Plant in Nepal

Binaya Baidar,Sailesh Chitrakar,Ravi Koirala,Hari Prasad Neopane 한국유체기계학회 2015 International journal of fluid machinery and syste Vol.8 No.4

The present study is conducted to identify a better design and optimal number of Francis runner blades for sediment laden high head micro hydropower site, Tara Khola in the Baglung district of Nepal. The runner is designed with in-house code and Computational Fluid Dynamics (CFD) analysis is performed to evaluate the performance with three configurations; 11, 13 and 17 numbers of runner blades. The three sets of runners were also investigated for the sediment erosion tendency. The runner with 13 blades shows better performance at design as well as in variable discharge conditions. 96.2% efficiency is obtained from the runner with 13 blades at the design point, and the runners with 17 and 11 blades have 88.25% and 76.63% efficiencies respectively. Further, the runner with 13 blades has better manufacturability than the runner with 17 blades as it has long and highly curved blade with small gaps between the blades, but it comes with 65% more erosion tendency than in the runner with 17 blades.

Selection of Optimal Number of Francis Runner Blades for a Sediment Laden Micro Hydropower Plant in Nepal

Baidar, Binaya,Chitrakar, Sailesh,Koirala, Ravi,Neopane, Hari Prasad Korean Society for Fluid machinery 2015 International journal of fluid machinery and syste Vol.8 No.4

The present study is conducted to identify a better design and optimal number of Francis runner blades for sediment laden high head micro hydropower site, Tara Khola in the Baglung district of Nepal. The runner is designed with in-house code and Computational Fluid Dynamics (CFD) analysis is performed to evaluate the performance with three configurations; 11, 13 and 17 numbers of runner blades. The three sets of runners were also investigated for the sediment erosion tendency. The runner with 13 blades shows better performance at design as well as in variable discharge conditions. 96.2% efficiency is obtained from the runner with 13 blades at the design point, and the runners with 17 and 11 blades have 88.25% and 76.63% efficiencies respectively. Further, the runner with 13 blades has better manufacturability than the runner with 17 blades as it has long and highly curved blade with small gaps between the blades, but it comes with 65% more erosion tendency than in the runner with 17 blades.

Computational Design of Bifurcation: A Case Study of Darundi Khola Hydropower Project

Koirala, Ravi,Chitrakar, Sailesh,Neopane, Hari Prasad,Chhetri, Balendra,Thapa, Bhola Korean Society for Fluid machinery 2017 International journal of fluid machinery and syste Vol.10 No.1

Bifurcation refers to wye division of penstock to divide the flow symmetrically or unsymmetrically into two units of turbine for maintaining economical, technical and geological substrates. Particularly, water shows irrelevant behavior when there is a sudden change in flow direction, which results into the transition of the static and dynamic behavior of the flow. Hence, special care and design considerations are required both hydraulically and structurally. The transition induced losses and extra stresses are major features to be examined. The research on design and analysis of bifurcation is one of the oldest topics related to R&D of hydro-mechanical components for hydropower plants. As far as the earlier approaches are concerned, the hydraulic designs were performed based on graphical data sheet, head loss considerations and the mechanical analysis through simplified beam approach. In this paper, the multi prospect approach for design of Bifurcation, incorporating the modern day's tools and technology is identified. The hydraulic design of bifurcation is a major function of dynamic characteristics of the flow, which is performed with CFD analysis for minimum losses and better hydraulic performances. Additionally, for the mechanical design, a simplified conventional design method as pre-estimation and Finite Element Method for a relevant result projections were used.

A Case Study of Wear in a High Head Francis Turbine Due to Suspended Sediment and Secondary Flow in a Hydropower Plant of Nepal

Shekhar Aryal,Sailesh Chitrakar,Rajendra Shrestha,Ajay Kumar Jha 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.4

The hydropower plants under Himalayan basins are mostly characterized by heavy sediment load due to geographical and metamorphic constraints. Run-off-river projects with limited size of the desilting basins allow suspended sediments to get carried into the turbine components causing wear due to sediment erosion. In the case of high head power plants consisting of Francis turbines, a large portion of the hydraulic energy is transformed into kinetic energy within the guide vanes. This causes various instabilities in the flow due to high acceleration and velocity. Some recent studies have shown that due to the combined effect of the secondary flow around the guide vanes and sediment carrying flow, the size of the clearance gap increases, which further aggravates the performance of the turbine. This study takes a reference of one of the power plants in Nepal containing high head Francis turbines. An in-depth analysis of the effect of the sediment in this power plant and sediment erosion in the turbine components has been performed. A CFD analysis of the guide vanes and runner blades corresponding to the same turbine has been conducted and the results are used to analyze the erosion pattern on the actual turbine. The detailed erosion analysis is made possible with a 3D scanner, such that the eroded regions can be captured and classified based on the flow behavior at those regions. Guide vanes and runner blades are found to be the predominant components affected by erosion. It has been seen that most of the erosion affected regions are originated from increasing clearance gaps between guide vane and facing plates caused due to continuous leakage flow within the two sides of the guide vanes.