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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]

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]

In recent times, optimization began to be popular in the turbomachinery field. The development of computational fluid dynamics (CFD) analysis and optimization technology provides the opportunity to maximize the performance of hydro turbines. The optimization techniques are focused mainly on the rotating components (runner and guide vane) of the hydro turbines. Meanwhile, fixed flow passages (stay vane, casing, and draft tube) are essential parts for the proper flow uniformity in the hydro turbines. The suppression of flow instabilities in the fixed flow passages is an inevitable process to ensure the power plant safety by the reduction of vortex-induced vibration and pressure pulsation in the hydro turbines. In this study, a CFD-based shape design optimization process is proposed with response surface methodology (RSM) to improve the flow uniformity in the fixed flow passages of a Francis hydro turbine model. The internal flow behaviors were compared between the initial and optimal shapes of the stay vane, casing, and the draft tube with J-Groove. The optimal shape design process for the fixed flow passages proved its remarkable effects on the improvement of flow uniformity in the Francis hydro turbine. [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]