Performance improvement of a flapping foil energy harvester using a trailing edge rotating cylinder

Abstract

A novel method is proposed to enhance the oscillating airfoil energy extraction from wind or ocean current by utilizing a cylinder in lieu of the rear section of the airfoil. A CFD method is utilized to investigate how variations in both geometric configuration and motion parameters of a rotating cylinder located at the trailing edge affect the energy conversion efficiency of a flapping foil system. Findings indicate that at lower reduced frequencies, the primary contribution to energy output arises from the heaving motion of the foil. As the trailing edge cylinder's rotational speed ratio rises, the efficiency of energy extraction initially improves before subsequently declining, with peak performance occurring at an optimal speed ratio of 5. Conversely, at higher reduced frequencies, the pitching moment becomes the principal contributor to energy generation. The energy harvesting efficiency improves with the increase of the rotation speed ratio of the rotating cylinder. The optimal rotation speed ratio i_max is 10. Moreover, positioning the rotating cylinder at the rear section of the airfoil allows it to attain higher energy harvesting efficiency with a smaller rotation speed than when placed at the leading edge, suggesting greater potential for practical applications.