With the background of offshore wind energy projects, this paper studies aerodynamic performance and geometric characteristics of large capacity wind turbine rotors （1 to 10 MW）, and the main ...characteristic parameters such as the rated wind speed, blade tip speed, and rotor solidity. We show that the essential criterion of a high- performance wind turbine is a highest possible annual usable energy pattern factor and a smallest possible dimension, capturing the maximum wind energy and producing the maximum annual power. The influence of the above-mentioned three parameters on the pattern factor and rotor geometry of wind turbine operated in China＇s offshore meteoro- logical environment is investigated. The variation patterns of aerodynamic and geometric parameters are obtained, analyzed, and compared with each other. The present method for aerodynamic analysis and its results can form a basis for evaluating aerodynamic performance of large-scale offshore wind turbine rotors.
This paper describes the performance of a micro vertical-axis wind turbine with variable-pitch straight blades. The proposed variable-pitch angle mechanism has an eccentric point that is different ...from the main rotational point. A feature of the mechanism is to be able to vary the pitch angle of blades according to the azimuth angle of the main-links, without actuators. The performance of wind turbines was measured by using an open circuit type wind tunnel. The performance of the vertical axis wind turbines with this mechanism was better than that those with fixed pitch blades. The wind turbine with variable-pitch straight blades has directivity for the wind. It was found that the performance of the wind turbine is dependent on the offset of blade pitch angle, the amplitude of the pitch angle, the size of the turbine, the number of blades and the airfoil profiles.
The performance of the vertical-axis wind turbine with straight blades in a shear flow was investigated by the experiment in an open circuit-type wind tunnel, and two and three-dimensional ...computational fluid dynamics. The diameter (D) and height of wind turbine were 800mm, respectively. The number of straight blades with a NACA0018 airfoil section was three. Two-dimensional shear flow was generated by using the porous flat plate. The effect of the location of shear flow to the rotor on the performances of the vertical-axis wind turbine were found. The power coefficient of VAWT in a shear flow has become more than that in the uniform flow. The optimum position of the porous plate was at Ψ (Yp/D) = 0.125, where Yp is the position of tip of porous plate. Good agreement was found between the experiments and numerical simulations when the large-eddy simulation was employed. The relation between the increment of torque and the three-dimensional flow structure around a blade has been clarified by the computational fluid dynamics.
A feasibility study on the tidal current power generation by making use of a bridge pier in the narrow strait is introduced. Current velocity increases near the pier, therefore the tidal power ...generation becomes more efficient because the power is proportional to the cubic of the current velocity. Furthermore, the pier is convenient for the maintenance of the hydraulic turbine and the power unit. The project is now underway at the Ikitsuki Bridge in Tatsuno-Seto Strait of Nagasaki Prefecture. A Darrieus turbine is adopted for tidal current power generation because it is simple in structure with straight wings rotating around a vertical axis, so that it has no directionality against the motion of tidal flow which changes its direction twice a day. However, there is one defect in the Darrieus turbine; its small starting torque. Once it stops, a Darrieus turbine is hard to re-start until a fairly fast current is exerted on it. To improve the starting torque of the Darrieus turbine, a hybrid turbine, composed of a Darrieus turbine and a Savonius rotor is proposed. A combined Darrieus and Savonius turbine was tested in the circulating water channel. Finally, power generation experiments using a 48 pole electric generator were conducted in a towing tank and the power coefficients were compared with the results of experiments obtained in the circulating water channel.
Based on a harmonic analysis of the feed voltages of controlled rectifiers with transformers with rotating magnetic fields under different types of loads, the relationships between the coefficients ...of feed voltage harmonic and the number of power-key pairs of rectifiers’ commutators with transformers of rotating magnetic fields were clarified.
Wells turbine is a self-rectifying air turbine capable of converting pneumatic power of the periodically reversing air stream in Oscillating Water Column (OWC) into mechanical energy. The Wells ...turbine has inherent disadvantages; lower efficiency, poorer starting characteristics, higher axial force and lower tangential force in comparison with conventional turbines. Guide vanes before and after the rotor suggest a means to improve the tangential force, hence its efficiency. In the present computational investigations, the performance of the Wells turbine is predicted for constant chord (CONC) rotor, variable chord (VARC) rotor and variable chord rotor using guide vanes on upstream and downstream side of rotor. The predicted values of pressure drop with flow coefficient shows almost a linear variation and are in agreement with the experimental results. Power coefficient obtained from the VARC rotor with and without guide vanes is more than the CONC rotor at all flow coefficients. Due to recovery of rotor exit kinetic energy by the downstream guide vanes, the pressure drop across the turbine has increased, resulting in higher energy transfer and consequently higher turbine efficiency in VARC rotor.
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