Effect of Flapping Trajectory and Interfoil Distance on Propulsive Performance of a Tandem Flapping Foil

Abstract

In the present research, a 2D simulation of tandem flapping foil following an elliptical trajectory, i.e., altered from a simple flapping trajectory is performed. The purpose of the research is to evaluate the influence of the trajectory motion of the tandem flapping foil on hydrodynamics characteristics and propulsive efficiency. The study is carried out with tandem foil configurations as in such position, both the foils are subjected to the same flow, which allows the flapping foil to enhance the propulsive efficiencies with proper selection of foil position as well as the foil trajectory. The 2D simulation is carried out with NACA 0012 at Re = 1173 by varying Strouhal number (St) between 0.2 and 0.5. The results show that an elliptical motion trajectory pattern and interfoil spacing of 1cm–2cm (where cm is the mean chord length) between the foils would enhance the propulsive efficiency whereas an unfavorable spacing between the foils causes unfavorable wake interaction, which reduces propulsive efficiency as compared to solo flapping foil. When the results of the current numerical investigation of elliptical trajectory are compared to the results of simple trajectory tandem flapping, the current study shows a significant increase in propulsive efficiency. This study gives new insights in the development of biomimetic propulsors, as it strives to improve propulsive efficiency through the usage of wake vortex.