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Jet pumps are special-purpose pumps without moving and rotating parts. The annular jet pump (AJP) is preferred for goods transportation over the central jet pump. However, cavitation is an inevitable phenomenon in the AJP, which damages transported goods. Cavitation suppression in the AJP can ensure the safe transportation and the high value of goods. Considering the simple design of AJP, J-groove is suitable for suppressing cavitation in the AJP. J-groove is a rectangular groove installed on the wall of the AJP and effectively suppresses cavitation. In this study, the optimal J-groove passage shape is achieved via multi-objective optimization. This shape is suitable for improving suction performance without depleting the efficiency of the AJP. The J-groove corner shape was modified into edge, round, and chamfer to design a proper corner shape. The AJP with edge J-groove corner shape is suitable for the safe and efficient transportation of sensitive objects. [ABSTRACT FROM AUTHOR]

Flow instability and pressure fluctuation are common problems in hydro turbines, especially in partial flow conditions. When Francis hydro turbine operates at partial flow rate, swirl flow occurs at the runner outlet, which is the cause of pressure pulsations, vortex core, noise and vibration in the draft tube. Among various methods, J-groove was selected and mounted in the draft tube to suppress the swirl flow. The study focuses on the J-groove incorporation in a draft tube from the design process to optimization. The optimization focused on the suppression of swirl flow with minimum efficiency drop. The turbine efficiency and swirl number were selected for the optimization, which encounters global and local effects of J-groove installation on the Francis hydro turbine. J-groove shape optimization was performed by response surface methodology (RSM) and multi-objective genetic algorithm (MOGA). The flow behavior in the draft tube was compared without and with the initial and optimal J-groove shapes. The optimal J-groove shape is more effective in swirl flow suppression than the initial J-groove shape. Additionally, the installation of the J-groove did not hinder turbine performance. Therefore, the optimal J-groove shape improved flow behavior in the draft tube at the partial flow rate. [ABSTRACT FROM AUTHOR]

The effect of design variables on the performance measures in the entire design space can be evaluated by global sensitivity analysis (GSA). Therefore, a high-dimensional engineering problem can be transformed to a reduced-dimensional problem by ascertaining important design variables according to GSA. Subsequently, the reduction of design variables helps save computational cost and the duration of design optimization. In this study, GSA was applied to determine the most influential design variable in the design of two reaction hydro turbine components - stay vane and casing. The global sensitivity index technique is selected among GSA methods because it can evaluate both the individual and interaction effects of design variables. Genetic aggregation surrogate models are used to reduce the number of computational fluid dynamics (CFD) analyses for GSA and design optimization. The responses from surrogate models are evaluated to obtain global sensitivity indices for performance measures. The important design variables are selected according to the indices. Using a multiobjective genetic algorithm (MOGA), design optimizations with the selected design variables are performed and the results are compared to the optimum designs with all design variables. The optimum designs using the selected design variables show comparable performances to those of the full-dimensional optimum designs. [ABSTRACT FROM AUTHOR]

The oscillating flow is a problem occurring in the stay vane passage of hydro turbines. The improper shape of the stay vane causes wake formation and sheds large eddies in the trailing edge of the stay vane. The wake at the trailing edge of the stay vane produces pressure fluctuation in the stay vane passage, which leads to noise and vibration during the turbine operation. Therefore, the improper shape of the stay vane may cause flow oscillation in the stay vane passage. Thus, a proper shape design of the stay vane considering the oscillating flow is necessary to mitigate the flow instability. Consequently, experiment and CFD analyses showed that the initial stay vane (ISV) shape causes recirculation and pressure fluctuation. An optimum design methodology is adopted to improve the flow behavior around the stay vane. Optimization of the stay vane is also conducted by using two objective functions (turbine efficiency and flow uniformity) and 12 design variables. The optimal stay vane (OSV) shape is attained by a multi-objective genetic algorithm. Finally, the flow behavior in the stay vane passage with ISV and OSV is compared by experiment and CFD analyses. Thus, the flow instabilities are mitigated with OSV. The installation of OSV improved the flow angle distribution, secondary flow, and pressure fluctuation in the Francis hydro turbine. [ABSTRACT FROM AUTHOR]

A spiral casing is an important component of Francis hydro turbine for the even distribution of kinetic energy along the stay and guide vanes. The fluid flow around the runner is dependent on the flow condition of a spiral casing. The shape of the casing plays an important role in proper flow distribution. In this study, the optimization of the shape of a spiral casing is based on a steady-state flow analysis. Numerical optimization is performed using response surface methodology (RSM) and multiobjective genetic algorithm (MOGA). The flow uniformity and head loss in the spiral casing are selected as objectives for the optimal design of the spiral casing. The optimal design is selected from the solution acquired by RSM and MOGA. Moreover, the flow characteristics in the initial and optimal designs of the spiral casing are compared. The flow conditions in the optimal design improve significantly with the optimal design of the spiral casing. Thus, the inlet conditions for the stay vane are improved with the optimal design of the spiral casing. [ABSTRACT FROM AUTHOR]

Abstract: The study concentrates on the shape design and numerical analysis of a 1 MW horizontal axis tidal current turbine (HATCT), which can be applied near the southwest regions of Korea. On the basis of actual tidal current conditions of south-western region of Korea, configuration design of 1 MW class turbine rotor blade is carried out by blade element momentum theory (BEMT). The hydrodynamic performance including the lift and drag forces, is conducted with the variation of the angle of attack using an open source code of X-Foil. The optimized blade geometry is used for Computational Fluid Dynamics (CFD) analysis with hexahedral numerical grids. This study focuses on developing a new hydrofoil and designing a blade with relatively shorter chord length in contrast to a typical TCT blade. Therefore, after a thorough study of two common hydrofoils, (S814 and DU-91-W2-250, which show good performance for rough conditions), a new hydrofoil, MNU26, is developed. The new hydrofoil has a 26% thickness that can be applied throughout the blade length, giving good structural strength. Power coefficient, pressure and velocity distributions are investigated according to Tip Speed Ratio by CFD analysis. As cavitation analysis is also an important part of the study, it is investigated for all the three hydrofoils. Due to the shorter chord length of the new turbine blade in contrast to a typical TCT blade design, a Fluid Structure Interaction (FSI) analysis is also done. Concrete conclusions have been made after comparing the three hydrofoils, considering their performance, efficiency, occurrence of cavitation and structural feasibility. [Copyright &y& Elsevier]

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]

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 tidal currents in the region of South-Western sea of Korea can be utilized for the development of tidal current power, benefiting many fishing nurseries and nearby islands. Furthermore, it can contribute to promoting energy independent islands. This study focuses on floating-bridge type small tidal current turbine, which can be installed between the small islands limited space unlike large tidal current turbines. The aim is to develop a floating-bridge type 15 kW-class small horizontal axis tidal current turbine. As part of the research for the reduced model experiment of hydrofoils, a 50 W-class horizontal axis tidal current turbine model was investigated. Therefore, for this study, blade design was carried out using two different hydrofoils (MNU26 and NACA63421). Performance and hydrodynamic characteristics are investigated by using computational fluid dynamics and experimental methods. Among the two blades, NACA63421 blade showed the best power coefficient at low Reynolds number, whereas MNU26 blade performed better for higher Reynolds number. The MNU26 hydrofoil was applied to the blade design from the previous study. The MNU26 hydrofoil has a 26% thickness in contrast to the NACA63421, which has a 21% thickness. This indicates that the MNU26 can be applied throughout the blade length for the 15 kW-class turbine whilst providing good structural strength. [ABSTRACT FROM AUTHOR]