Flow Field of Flapping Monarch and Swallowtail Butterfly-like Wings

Abstract

This paper presents a part of our ongoing development of a butterfly-like ornithopter (flapping wing) micro-aerial vehicle (MAV). Two kinds of butterfly were selected for studies: Monarch butterfly (Danaus plexippus) and Swallowtail butterfly (Papilio troilus)). The Monarch butterfly is well-known for its ability for long distance migratory flight. The Monarch butterfly is well-known for its high agility. It is also selected as baseline for comparison. The Swallowtail butterfly has unique tails (streamers) at the trailing edge of its hind wings. For both types of butterfly, the flow physics show that during free flights, they use a variety of unconventional aerodynamic mechanisms to generate force: wake capture, two different types of leading-edge vortex, active and inactive upstrokes. Free-flying butterflies often used different aerodynamic mechanisms in successive strokes. For Swallowtail butterflies, the streamer appears to help their flight more stable, by aligning the wake vortices behind its hind wings. The subsequent horse-shoes vortices also help create more vortex lift. For flexible wing, the result from fluid-structure interaction shows that the swallowtail butterfly deflect more than Monarch butterfly.