Effects of pitch angle and blade camber on flow characteristics and performance of small-size Darrieus VAWT
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R E G UL A R P A P E R
Chein-Chang Chen • Cheng-Hsiung Kuo
Effects of pitch angle and blade camber on flow characteristics and performance of small-size Darrieus VAWT Received: 14 February 2012 / Revised: 22 June 2012 / Accepted: 2 September 2012 / Published online: 12 October 2012 Ó The Visualization Society of Japan 2012
Abstract This study builds up a simulation model, via Ansys/Fluent, to investigate the effects of pitch angle and blade camber on the flow characteristics and performance of small-size Darrieus vertical axis wind turbine (VAWT). The VAWT system is driven by a uniform wind speed (10 m/s). The blade profiles with three different cambers are NACA0012, 2412 and 4412, respectively; and the pitch angles vary between 10° and -10°. The user-defined function is employed to calculate the instantaneous moments produced by all the blades and rotate the VAWT system from rest. The flow structures, the vorticity fields and the performance on the blades will be addressed; also, the self-starting ability and the moment coefficient of the VAWT system are discussed. For the blade profiles studied, the initial acceleration is the largest at h = -10° and decreases monotonously as the pitch angle increases from h = -10° to h = 10°. Further, at the same pitch angle, the larger the camber of the blade (NACA4412), the better is the self-starting ability of the VAWT system. The maximum root mean square moments have the maximum values at h = 5° for all the blade profiles studied herein. The root mean square moments for NACA2412 are much higher than those of NACA0012 and 4412 at all pitch angles. However, the root mean square moments for NACA4412 are relatively insensitive to the variations in pitch angles. Keywords VAWT CFD Pitch-angle variation Self-start Moment coefficient
1 Introduction In the past, humans have used a large amount of fossil fuels for industrial development. Due to excess and frequent use of fossil fuels, we produce a lot of pollutants such as carbon dioxide, nitrogen oxide and sulfur dioxide. Worldwide, acid rain and the greenhouse effect have resulted from these pollutants. According to a report (American Wind Energy Association 1997), the average annual temperature has increased year after year since 1980. So far, this has caused serious environmental pollution, the rising of sea level and global climatic change, leading to unexpected weather situations. Therefore, the development and use of renewable energy is urgent to reduce the use of fossil fuel and to mitigate the global climate change. Among the renewable energy, wind energy is the cleanest choice. The wind energy is extracted by wind turbines which can be divided into two kinds by the direction of the rotational axis: the horizontal axis wind turbine (HAWT) and the vertical axis wind turbine (VAWT). Because the HAWT system has high efficiency at large tip speed ratio (TSR), the tower of
C.-C. Chen (&) C.-H. Kuo Department of Mechanical Engineering, National Chung Hsing University, Taichung 402, Taiwan E-mail: [email protected] C
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