Abstract:

Previous studies on chordwise flexibility of flexible wings generally relied on simplified two-dimensional (2D) models. In the present study, we constructed a simplified three-dimensional (3D) model and identified the role of the chordwise flexibility in full flapping motion. This paper includes two parts, the first part discusses the aerodynamic effects of the chordwise flexibility in a typical hovering-flight case; the second part introduces a parametric study of four key parameters. The primary findings are as follows. Flexibility generally degrades the lift performance of the flexible wings. However, in two special cases, i.e. when stroke amplitude is low or pitch rotation is delayed, the flexible wings outperform their rigid counterparts in lift generation. Moreover, flexibility reduces the power consumption of the flexible wings. A wing with small flexibility generally achieves a marginally higher flapping efficiency than its rigid counterpart. Furthermore, reducing stroke amplitude can effectively improve the lift performance of the very flexible wings. Aerodynamic performances of the flexible wings are not as sensitive as the rigid wing to phase difference and mid-stroke angle of attack. The effects of Re are the same for the flexible and rigid wings.

Key words: flapping wing, chordwise flexibility, aerodynamic performances, parametric study