Horizontal axis wind turbines (HAWTs) are the more common form of wind energy production, but attention is increasingly given to vertical axis wind turbines (VAWTs), which have their main rotor shaft positioned transverse the wind. VAWTs can accept wind coming from any direction and operate in harsher wind conditions. However, VAWT usage grows slower than that of HAWTs, especially in large scale, because they also have shortcomings, like trouble self-starting and lower power efficiency. To increase power efficiency, researchers from universities in China and Denmark proposed and evaluated a new blade design for H-type VAWTs. They report their findings in the Journal of Renewable and Sustainable Energy.
H-type VAWTs, which have two blades, are more efficient if they have variable-pitch (VP) technology, in which blade pitch can change. There are two main strategies of active VP technology: cyclic and cycloidal. In both, the blades experience low-efficiency regions with every rotation, decreasing a VAWT’s overall productivity. To address this problem, the researchers designed a new VP strategy with a bigger change of angle of attack in the low-efficiency region of blade. They then evaluated the performance of the new design using a double-disk multiple streamtube model, a momentum model that calculates the streamwise aerodynamic force exerted by wind flow on blades, to simulate a small scale VAWT with 2-meter height and 2-meter rotational diameter.
Coauthor Zhenzhou Zhao says their analysis indicated that the new design significantly narrows regions of low efficiency, generating an 18.9 percent growth in overall power efficiency. The researchers will further optimize their new technology using computational fluid dynamics to visually simulate wind flow, and plan to test a real-life VAWT in a wind tunnel.
Source: “Study on variable pitch strategy in H-type wind turbine considering effect of small angle of attack,” by Zhenzhou Zhao, Siyuan Qian, Wen Zhong Shen, Tongguang Wang, Bofeng Xu, Yuan Zheng, and Ruixin Wang, Journal of Renewable and Sustainable Energy (2017). The article can be accessed at https://doi.org/10.1063/1.4989795.
