Investigation of ground effect on aerodynamic forces and three-dimensional flow structures for a flapping wing

The aim of the present work is to provide an insight into the aerodynamic performances of the beetle during take-off which had been estimated in previous investigations. We employed a scaled-up electromechanical model flapping wing to measure the aerodynamic forces and the three-dimensional flow structures on the flapping wing. The ground effect on the unsteady forces and the flow structures was also characterized. The present dynamically-scaled wing model could replicate the general stroke pattern of the beetle's hind wing kinematics during take-off flight. The instantaneous aerodynamic forces for four strokes during beetle's take-off were measured by the force sensor attached at the wing base. Flow visualization provided the general picture of the evolution of the three-dimensional leading edge vortex (LEV) on the beetle hind wing model. The LEV is stable during each stroke and increases radically with the distance from the root to the tip, forming a leading-edge spiral vortex. The force measurement results show that the vertical force generated by hind wing is large enough to lift the beetle up. For the beetle hind wing kinematics, the total vertical force production increases 18.4% and 8.6 % for the first and the second stroke, respectively, due to the ground effect.