Energy extraction characteristic of the flapping wing type vertical axis turbine

Flapping wings are known to be used not only for propulsion, but also for energy extraction from the surrounding fluid environment. In this work, the authors propose a vertical axis turbine based on flapping wings. Numerical experiments have been conducted. Results show (i) In a certain range of frequency, the vertical axis turbine equipped with flapping wings of circular or reversed-D motion trajectory demonstrates better energy extraction performance when compared to the traditional vertical axis wind turbine. (ii) For the reversed-D motion trajectory, as two airfoils begin to move apart from each other, the downstream flapping-wing takes advantage of the trailing edge vortex of the upstream flapping-wing to enhance its own energy extraction ability. However, for the circular motion trajectory, the two airfoils are usually located far away from each other. This leads to the result that the mutual influence between the two airfoils is very weak. Generally speaking, the application of flapping wings in the vertical axis turbine can improve the energy extraction efficiency in a certain range, which can provide another method for the design of a new type of vertical axis turbine in the research and industry.