Aerodynamic characteristics of two-bladed H-Darrieus at various solidities and rotating speeds Sungjun Joo a, 1 , Heungsoap Choi b, 2 , Juhee Lee c, * a Department of CO-OP, Hoseo University, Chungnam 336-795, Republic of Korea b Department of Mechanical & Design Engineering, Hongik University, Sejong 339-701, Republic of Korea c Department of Mechatronics Engineering, Hoseo University, Chungnam 336-795, Republic of Korea article info Article history: Received 9 October 2014 Received in revised form 15 May 2015 Accepted 7 July 2015 Available online xxx Keywords: H-Darrieus wind turbine CFD (computational fluid dynamics) TSR (tip speed ratio) Solidity Blockage abstract Three-dimensional unsteady numerical analysis has been performed in order to analyze the aerodynamic characteristics of an H-Darrieus vertical axis wind turbine with two straight blades. The reliability of the numerical models has been demonstrated through good agreement between the calculated and measured efficiency of an H-Darrieus. Flow characteristics are closely investigated according to tip speed ratios and solidities. A comparison of aerodynamic characteristics at various operational conditions, including the maximum power point is performed. The direction of the free stream approaching the blade is considerably bent following the interaction between blade-to-blade and blade-to-free stream. Even though, the peak value of a torque increases as solidity increases, the blockage and interaction also increase, and thus, increasing the solidity alone does not improve the performance of the H-Darrieus. On the other hand, decreasing the solidity can reduce the effect of blockage and interaction, but the self- starting features via the negative torque at the low tip speed ratio becomes lost. Therefore, a theoret- ical model such as the DMST (double multiple stream tube) is not suitable for predicting the performance of H-Darrieus with a high solidity. The blockage by blades in the upwind revolution and the interaction between blades significantly change the magnitude of an incidence velocity, and the angle of attack. Thus, the tip speed ratio of the operation point (i.e. the highest power coefficient point) is found to be lower than it is expected. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction With the ever-growing concern over the effects of fossil fuels on global warming, there is presently a resurgence of interest in the use of wind turbines as a clean, sustainable and renewable source of energy. This interest is reflected in a corresponding increase in research activity among academic institutions and a proliferation of designs based on several aerodynamic models. Wind turbines are categorized into two types based on the orientation of the rota- tional axis: the HAWT(horizontal axis wind turbine) and the VAWT(vertical axis wind turbine). Although the HAWT is more common in the wind turbine industry worldwide and its technol- ogy better developed, the VAWT, (e.g. the Savonius, Troposkein Darrieus and H-Darrieus types) has been gaining increasing attention for a number of its advantages, the primary being a simplicity of design which allows for energy conversion at any wind angle. Moreover, low starting torque makes it an ideal candidate for use in urban areas where wind speeds are relatively low and changes rapidly [1,2]. The modern Darrieus VAWT was invented by French engineer George Jeans Mary Darrieus, with his U.S. patent submitted in 1931 [3] for both the “eggbeater (curve-bladed)” and “straight-bladed” types. In addition to the general advantages of VAWTs over HAWTs, the straight-bladed H-Darrieus type, consisting of two or three straight blades (airfoils), has the following further advantages: 1. low noise owing to the low rotating speed; 2. self-starting and low maintenance costs; 3 ease of design and construction owing to the use of simple straight airfoils. * Corresponding author. Tel.: þ82 41 540 9669; fax: þ82 41 540 5808. E-mail addresses: yesdrjoo@hoseo.edu (S. Joo), scheung@hongik.ac.kr (H. Choi), juheelee@hoseo.edu (J. Lee). 1 Tel.: þ82 41 540 9966. 2 Tel.: þ82 44 860 2864. Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2015.07.051 0360-5442/© 2015 Elsevier Ltd. All rights reserved. Energy xxx (2015) 1e13 Please cite this article in press as: Joo S, et al., Aerodynamic characteristics of two-bladed H-Darrieus at various solidities and rotating speeds, Energy (2015), http://dx.doi.org/10.1016/j.energy.2015.07.051