Bhola Thapa

Velocity and pressure measurements in guide vane clearance gap of a low specific speed Francis turbine

In Francis turbine, a small clearance gap between the guide vanes and the cover plates is usually required to pivot guide vanes as a part of governing system. Deflection of cover plates and erosion of mating surfaces causes this gap to increase from its design value. The clearance gap induces the secondary flow in the distributor system. This effects the main flow at the runner inlet, which causes losses in efficiency and instability. A guide vane cascade of a low specific speed Francis turbine has been developed for experimental investigations. The test setup is able to produce similar velocity distributions at the runner inlet as that of a reference prototype turbine. The setup is designed for particle image velocimetry (PIV) measurements from the position of stay vane outlet to the position of runner inlet. In this study, velocity and pressure measurements are conducted with 2 mm clearance gap on one side of guide vane. Leakage flow is observed and measured together with pressure measurements. It is concluded that the leakage flow behaves as a jet and mixes with the main flow in cross-wise direction and forms a vortex filament. This causes non-uniform inlet flow conditions at runner blades.

Computational and experimental study of effects of sediment shape on erosion of hydraulic turbines

Hard particles as Quartz and Feldspar are present in large amount in most of the rivers across the Himalayan basins. In run-off-river hydro power plants these particles find way to turbine and cause its components to erode. Loss of turbine material due to the erosion and subsequent change in flow pattern induce several operational and maintenance problems in the power plants. Reduction in overall efficiency, vibrations and reduced life of turbine components are the major effects of sediment erosion of hydraulic turbines. Sediment erosion of hydraulic turbines is a complex phenomenon and depends upon several factors. One of the most influencing parameter is the characteristics of sediment particles. Quantity of sediment particles, which are harder than the turbine material, is one of the bases to indicate erosion potential of a particular site. Research findings have indicated that shape and size of the hard particles together with velocity of impact play a major role to decide the mode and rate of erosion in turbine components. It is not a common practice in Himalayan basins to conduct a detail study of sediment characteristics as a part of feasibility study for hydropower projects. Lack of scientifically verified procedures and guidelines to conduct the sediment analysis to estimate its erosion potential is one of the reasons to overlook this important part of feasibility study. Present study has been conducted by implementing computational tools to characterize the sediment particles with respect to their shape and size. Experimental studies have also been done to analyze the effects of different combinations of shape and size of hard particles on turbine material. Efforts have also been given to develop standard procedures to conduct similar study to compare erosion potential between different hydropower sites. Digital image processing software and sieve analyzer have been utilized to extract shape and size of sediment particles from the erosion sensitive power plants. The experimental studies of impact of different shapes and sizes of sediment particles on hydraulic turbine material have been conducted on two different test rigs method at Kathmandu University, High velocity test rig method and Rotating Disc apparatus (RDA) at Kathmandu University. Twenty one different sediment shape samples and four different sand size range were studied to correlate the effects of sediment shape and size with the erosion of turbine material. It was observed that the shape of sediment particles have considerable effect on erosion of turbine material. In general Irregular shapes have more erosion potential than regular shapes. It was also observed that the particles with the irregular shape of smaller size induce higher erosion rates than that of the larger size with the same shape. These findings will help to select the proper site of a power plant in erosion prone basins and would also help to design suitable settling basins to trap sediment particles having higher erosion potentials.

Performance Comparison of Optimized Designs of Francis Turbines Exposed to Sediment Erosion in various Operating Conditions

Erosion on hydro turbine mostly depends on impingement velocity, angle of impact, concentration, shape, size and distribution of erodent particle and substrate material. In the case of Francis turbines, the sediment particles tend to erode more in the off-designed conditions than at the best efficiency point. Previous studies focused on the optimized runner blade design to reduce erosion at the designed flow. However, the effect of the change in the design on other operating conditions was not studied. This paper demonstrates the performance of optimized Francis turbine exposed to sediment erosion in various operating conditions. Comparative study has been carryout among the five different shapes of runner, different set of guide vane and stay vane angles. The effect of erosion is studied in terms of average erosion density rate on optimized design Francis runner with Lagrangian particle tracking method in CFD analysis. The numerical sensitivity of the results are investigated by comparing two turbulence models. Numerical results are validated from the velocity measurements carried out in the actual turbine. Results show that runner blades are susceptible to more erosion at part load conditions compared to BEP, whereas for the case of guide vanes, more erosion occurs at full load conditions. Out of the five shapes compared, Shape 5 provides an optimum combination of efficiency and erosion on the studied operating conditions.

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

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.

Strategic rehabilitation of the earthquake affected microhydropower plants in Nepal

Most people in the rural areas of Nepal rely on Micro-hydro Power Plants (MHPs) for their energy sources. With around four decade experiences in design and development of MHPs, Nepalese techno-entr ...

University cooperation as a development tool in poor countries

This paper describes the development of Kathmandu University (KU) and how the vision of three Nepali university entrepreneurs have been realized in an academic institution that has the development of the social and economic conditions in the country as its foremost goal. KUs development strategy has been to seek cooperative partners from developed countries, and to utilize the considerable number of development agencies and donors that have sought partners in Nepal to its advantage. Another important part of KUs strategy has been to motivate its young Nepalese staff to train for advanced degrees at internationally renowned universities as an opening for full professorship at the institution. Through an NGO, a link to the Norwegian University of Science and Technology, NTNU, was established and a mutual cooperation between KU and NTNU was developed, as well as cooperation with a number of other universities. The paper describes this cooperation between a university in an industrialized country and a start-up university in a poor country and highlights it as the most effective means for north-south cooperation, motivated by the attitude that wealthy countries have a moral obligation to support poor countries in their struggle to improve the social and economic well-being of their citizen. An aim of balance and symmetry in the cooperation is regarded as ethically important.

Analysis of the flow condition in a cross flow turbine

Energy insufficiency in developing countries arise when the locally available resources are discarded. Nepal having a huge potential in rural electrification will intensify through the development of Micro Hydro turbines. Cross flow type of hydro turbines are extensively used in micro hydropower in rural areas of Nepal. An experiment for efficiency measurement and flow analysis has been performed in cross flow turbine which was installed in The Waterpower Laboratory at the Norwegian University of Science and Technology, NTNU. Efficiency was measured for various head, nozzle opening and speed to find the best efficiency point. The flow condition in the cross flow turbine at different performance was recorded. A high speed camera FASTCAM SA5 was used to get the better flow visualization at the best efficiency point which was 77.7 % in 5m head with 80% nozzle opening at rotational speed of 350rpm. Various discussion is made on turbine performance for varying head, speed and nozzle opening. This paper is based on the flow pattern of cross-flow turbine between two stages visualized through high speed camera and compare them with theoretical velocity vectors.