Modeling and analysis of insect-like flexible wings at low Reynolds number

• Aerodynamic performance of a whole range of insect-type wings with graduated flexibility was studied.
• Realistic, insect-like wing deformation is obtained with combined span- and chord-wise flexible wings.
• Flexible wings have superior aerodynamic performance over equivalent rigid wings.
• Wing flexibility prolongs leading edge vortex attachment.
• The role of elastic energy storage in high aerodynamic performance is explained.

Much of the aerodynamic research conducted on insects to date has assumed that their wings are predominantly flat and rigid. In this paper, we investigate the effects of wing flexibility on the aerodynamic performance of a simple wing modeled after that of the Fruitfly, at the Reynolds number of 150. Analyses were first carried out to understand how distribution of stiffness property influences its deformation/deflection under simple static, inertial and inertial-cum-aerodynamic loadings. A class of leading-edge reinforced (LER) wings with stiffness that is sharply reduced towards the wing tip and trailing edge was found to exhibit deformations that resemble well those observed for insect wings in flight. The LER-type wings are shown to be aerodynamically superior to rigid wing and wings of uniform stiffness in terms of their improved cycle-mean lift-to-drag and lift-to-power ratios. The positive roles played by wing deformation in the aerodynamics and the beneficial energetics of elastic wing storage are discussed.