Trailing Edge Flexion Influences Leading Edge Vortices and Aerodynamic Forces in Flapping Wings

Abstract

Using force and flow measurements on flapping rigid and flexible airfoils, we show that control of the trailing edge flexion alters the leading edge vorticity and aerodynamic force generation in flapping flight. The degree of trailing edge flexion strongly correlates with the magnitude of vorticity at the leading edge which in turn correlates strongly with the aerodynamic force generation by these wings. As the trailing edge aligns with the ambient flow during forward flapping motion , it creates a negative camber that correspondingly decreases the strength of the leading edge vorticity as compared to the rigid wing. An opposite effect is observed when we use wings with a positive camber therevy causing a stronger leading edge vorticity than rigid wings. These results provide concrete evidence that leading edge vorticity is the primary determinant of aerodynamic forces during flapping flight, It also provides insight into the aerodynamic mechanisms underlying alterations in force generation by flexible wings during flapping flight.