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The flow in the draft tube of a Francis turbine is highly complex and unstable when the turbine operates far from its design point. To extend the Francis turbine operation range to meet the variable energy demand, a J-groove technology is introduced on the turbine draft tube wall to stabilize the unsteady flow in the draft tube. However, J-groove contributes to energy losses in the draft tube. In this study, the J-groove shape optimization process is proposed based on steady flow analysis using the response surface method. The energy loss and swirl intensity in the draft tube are selected as objectives for the optimization design. The flow characteristics in the draft tube without J-groove and with initial J-groove and optimized J-groove shape are compared. Results show that the swirl intensity in the draft tube with the optimized J-groove is suppressed effectively with the low energy loss in the draft tube. Moreover, the pressure fluctuation in the draft tube with the optimized J-groove is mitigated significantly to stabilize the Francis turbine operation under the off-design point condition. [ABSTRACT FROM AUTHOR]

The pressure fluctuations of the turbines are caused by the swirl component in the draft tube, which is an undesired phenomenon that needs to be improved when the turbine operates in the off-design condition. In order to avoid these kinds of unsteady flow phenomena, a technology of J-Groove on the draft tube wall is investigated by numerical method. The validation test of performance is conducted to compare the result of numerical and experimental methods. The steady and unsteady state analyses are conducted to investigate the internal flow of a Francis hydro turbine model draft tube with and without J-Groove. The swirl flow in the draft tube is significantly suppressed by the J-Groove installation. Moreover, according to the unsteady state analysis, the amplitude of pressure fluctuation in the draft tube is reduced effectively by the J-Groove. [ABSTRACT FROM AUTHOR]

Korea has a myriad of islands in the south western coast that extensively rely on diesel generators for power production, which increase cost and environment pollution. The small hydro pump-turbine system for ocean renewable energy storage system is a kind of hybrid system that can reduce the usage of diesel generators and help to contribute to the environment in a positive manner by helping to reduce carbon emissions. The study focuses on initial hydraulic design and numerical analysis of a 30 kW-class pump-turbine system for energy independent islands in South Korea. The purpose of the study is to propose an ocean renewable energy storage system using a small pump-turbine system working with seawater. A 30 kW-class pump-turbine does not require a large head; approximately 30 m is sufficient for the design and application. Several other renewable energy systems like wind turbines, tidal turbines, wave energy converters and solar energy could be used to make a hybrid system with pump-turbine. The initial design achieved more than 85 % efficiency in both pump and turbine modes. However, further optimizations of the impeller blade shape and number of guide vane and stay vanes could improve the overall efficiency of the system. [ABSTRACT FROM AUTHOR]

South Korea has huge renewable energy potential that has been to some extent and can be further extracted to reduce its heavy reliance on fossil fuels. This project focuses on ocean and coastal wind resources available in the south-western regions of Korea that are currently being monitored and found to have huge potential. The project will propose a new concept of wind, tidal current and wave energy converting systems combined together that can boost output power capacity at a single location also making it easier for grid connection. Wind turbines nowadays have been quite efficiently developed and implemented throughout the world both onshore and offshore. However, tidal current and wave energy have yet more room for improvement. The current study will combine the offshore wind turbine (HAWT) system with two tidal current turbines (HATCT) both in horizontal axis classification on a single tower. It will further discuss on adding a wave energy converter in between the wind and tidal current turbines. Optimization of the tower is also a minor part of this study. The structural analysis of the main tower, which is the main focus of the study, is investigated by dynamic response analysis to check its feasibility for combining the three types of renewable energy converters on one support. Actual extreme conditions of the wind, ocean currents and waves are simulated using ANSYS CFX fluid flow analysis. The results are used for conducting a one way FSI analysis assuming a rigid structure to verify the safety of the system. [ABSTRACT FROM AUTHOR]

As a core component of a hydropower station, hydro turbines play a vital role in the integration of a power station. Research on the technology of hydro turbine is continuously increasing with the development of water electricity. It is effective and successful to design a Francis turbine runner blade with good performance by one-dimensional hydraulic design method. For the one-dimensional hydraulic design, the runner blade angle at leading and trailing edges can be defined by calculation of Euler's head. Design of the runner blade profile at several cross sections is needed to design a runner shape. In this study, there are three different blade loadings conducted to compare the internal flow characteristics and performance. The result shows that the front loading achieves the best efficiency in comparison to other loadings, which is good at suppressing the loss at draft tube. [ABSTRACT FROM AUTHOR]