Effect of Structural Anisotropy and Geometric Nonlinearity on Forward Flapping Wing Flight

Abstract

Flapping flight is commonly used in nature at low Reynolds numbers. This work investigates the physical aspects of forward flight for flapping unmanned aerial systems. The kinematics discussed in this work is based on an anticlockwise eight-shaped flapping cycle. First the complex aerodynamic structures and their evolution (leading edge and trailing edge vortices) are presented. Then, the typical mechanisms for generating the lift and thrust are discussed with emphasis on the unsteadiness of the flow features during both the downstroke and upstroke phases.The inhomogeneity of the wing in terms of mass distribution is studied for the rigid case and it is shown that a higher density at the wing root is beneficial in respect to the mechanical power required to achieve the forward flight.The assumption of rigid wing is then removed and the elastic deformation and its effects are investigated. The relative importance of inertial/aerodynamic effects is assessed with the inclusion of structural geometric nonlinearities.