Simulation of Flexible Flapping Wing of a Bird in Producing Thrust

Abstract

Bird wings in flapping can produces lift and thrust simultaneously. This gives an inspiration to engineers to create flapping wing based a machine. The thrust is generated due to interactions between fluid motion and flexible wing occurred periodically. In the interaction fluid flow generates aerodynamic forces and moments subjected to the wing causing the wing deformation. This deformation influences fluid flow around. The solution of fluid structure interaction is obtained computationally using two-way coupling interaction method. For simulation purpose, a rectangular wing with a flat plat cross section is used as a computational model. The wings are plugged vertically by applying clamp conditions at the leading edge. During down-stroke the wing pulls air flow down ward generating a rotational flow downstream until the lower position is reached.  After a while as up-stroking the wing which has flexible structure pushes back the flow to accelerate it. The acceleration gives flow jet effect so that maximum thrust is yielded. As a result, two peaks of thrust are generated in each cycle. Amount of thrust of the flexible wing is affected by frequency of the plunging motion