Numerical and experimental study of the dragonfly corrugated airfoil aerodynamics at very low Reynolds numbers

The interest in effective very low Reynolds numbers aerodynamics is of current technological interest and a fundamental scientific challenge. The Reynolds number range of interest in this work is 2,000<Re<12,000. At these Reynolds numbers the natural insect flight could provide inspiration for technology development. The insect wings are commonly characterized by corrugated airfoils. Particularly, the dragonfly which is able to glide can be used for two-dimensional aerodynamic study of rigid and fixed wings. In this study, a simplified dragonfly airfoil is numerically analyzed, in steady free-stream flow conditions. Its aerodynamic performance (such as mean and fluctuating lift and drag), are first compared with a "traditional" low Reynolds number airfoil: the Eppler 61. The numerical results emphasize the superior range and endurance performance of the corrugated airfoil. In order to validate the numerical results, a series of experimental measurements were performed on the corrugated airfoil in a low-speed wind-tunnel, showing quantitative agreement with the mean drag and shedding frequencies while demonstrating 2D flow. A flow physics numerical study is performed in order to understand the underlying flow mechanism of such corrugated airfoils at very low Reynolds numbers and preliminary conclusions are proposed.