Direct numerical simulations of dragonfly-inspired corrugated tandem airfoils at low Reynolds number.

Abstract

A corrugated wing is known to significantly enhance aerodynamic efficiency in the low Reynolds number regime. Although the result may be relatable directly to two-winged insects, larger insects flying at similar Reynolds numbers, like dragonflies, have four wings, and the role of the gap between the fore and hind wings in flight has rarely been analyzed. In particular, we perform direct numerical simulations of the flow past a tandem corrugated airfoil configuration at a chord Reynolds number of 10⁴that is of relevance to the micro-unmanned aerial vehicle (MAV) community. We assessed the tandem wing configuration for different horizontal and vertical offsets. In general, the aerodynamic efficiency for tandem configurations is quite high (∼ 10). Furthermore, we find that vertical offsets have a greater impact on aerodynamic forces than horizontal offsets. Positioning the hindwing below the forewing improves aerodynamic efficiency compared to placing the hindwing above because of the generation of a favorable pressure gradient on the forewing. The vortex shedding and correlations evaluate the hindwing/forewing interaction and the fluctuation of the forces. The horizontal offset results demonstrate improved aerodynamic efficiency and reduced flow unsteadiness as the gap between the two wings is minimized, primarily because the interaction between the forewing's wake and the hindwing is suppressed. A study with NACA 0008 is done to corroborate the range of optimal configurations and assess performance benefits of corrugated profile. In addition, the study reveals that the tandem wing configuration maintains efficiency comparable to that of a single wing, allowing us to utilize its advantages for MAV applications.