Wind tunnel tests for a flapping wing model with a changeable camber using macro-fibercomposite actuators

Abstract

In the present study, a biomimetic flexible flapping wing was developed on areal ornithopter scale by using macro-fiber composite (MFC) actuators. Withthe actuators, the maximum camber of the wing can be linearly changed from−2.6% to+4.4% of the maximum chord length. Aerodynamic tests were carried out in a low-speed windtunnel to investigate the aerodynamic characteristics, particularly the camber effect, thechordwise flexibility effect and the unsteady effect. Although the chordwise wing flexibilityreduces the effective angle of attack, the maximum lift coefficient can be increased by theMFC actuators up to 24.4% in a static condition. Note also that the mean values of theperpendicular force coefficient rise to a value of considerably more than 3 in an unsteadyaerodynamic flow region. Additionally, particle image velocimetry (PIV) tests wereperformed in static and dynamic test conditions to validate the flexibility and unsteadyeffects. The static PIV results confirm that the effective angle of attack is reduced by thecoupling of the chordwise flexibility and the aerodynamic force, resulting in adelay in the stall phenomena. In contrast to the quasi-steady flow condition of arelatively high advance ratio, the unsteady aerodynamic effect due to a leading edgevortex can be found along the wing span in a low advance ratio region. The overallresults show that the chordwise wing flexibility can produce a positive effect onflapping aerodynamic characteristics in quasi-steady and unsteady flow regions; thus,wing flexibility should be considered in the design of efficient flapping wings.