Aerodynamic performance of a hovering hawkmoth with flexible wings: a computational approach

Abstract

Insect wings are deformable structures that change shape passively and dynamically owing to inertial and aerodynamic forces during flight. It is still unclear how the three-dimensional and passive change of wing kinematics owing to inherent wing flexibility contributes to unsteady aerodynamics and energetics in insect flapping flight. Here, we perform a systematic fluid-structure interaction based analysis on the aerodynamic performance of a hovering hawkmoth, Manduca, with an integrated computational model of a hovering insect with rigid and flexible wings. Aerodynamic performance of flapping wings with passive deformation or prescribed deformation is evaluated in terms of aerodynamic force, power and efficiency. Our results reveal that wing flexibility can increase downwash in wake and hence aerodynamic force: first, a dynamic wing bending is observed, which delays the breakdown of leading edge vortex near the wing tip, responsible for augmenting the aerodynamic force-production; second, a combination of the dynamic change of wing bending and twist favourably modifies the wing kinematics in the distal area, which leads to the aerodynamic force enhancement immediately before stroke reversal. Moreover, an increase in hovering efficiency of the flexible wing is achieved as a result of the wing twist. An extensive study of wing stiffness effect on aerodynamic performance is further conducted through a tuning of Young's modulus and thickness, indicating that insect wing structures may be optimized not only in terms of aerodynamic performance but also dependent on many factors, such as the wing strength, the circulation capability of wing veins and the control of wing movements.

Leading edge vortex in a slow-flying passerine

“…10 4 for the flycatcher's wing tip section (electronic supplementary material, table S2) we would expect the LEV to burst and separate from the hand wing before the end of the downstroke [13,14], as was found in a birdinspired flapper at similar l ds % p/(2k) ¼ 5.2, where k is reduced frequency [11]. The fact that this does not occur in the flycatcher could be owing to the relatively low a eff at the wingtip section (figure 2b), since in a computational model of a flapping insect wing, LEV bursting near the wing tip was delayed owing to flexible wing twisting [23]. Also, a mechanical insect wing model operating at comparable flow conditions did not suffer from LEV bursting when a eff was reduced below a critical value [14].…”

Scaling law and enhancement of lift generation of an insect-size hovering flexible wing

“…These small insect flyers have flexible wings that experience large deformations just like birds and bats [11,12]. It has been, for example, shown that wing deformations [13,14] can enhance the force generation and efficiency of a locust operating at Re % 4 Â 10 3 [13], or a hawkmoth at Re % 6.3 Â 10 3 [15]. Moreover, several studies have suggested that insect wing rotations may be passive [16,17], meaning that the resulting rotation is due to a dynamic balance between the wing inertial force, elastic restoring force and fluid dynamic force.…”

A fast Chebyshev method for simulating flexible-wing propulsion

“…Research on heterogeneous wings has appeared more recently [85,64,63,82,17,48,47,66]. The majority of these studies focus on insect flight and, more specifically, simulating the coupled aeroelastic dynamics of compositionally complex wings [64,63,82,66].…”