Shape of butterfly wing affects flow structures

The flight of butterfly has received a great deal of attention owing mainly to its larger-scale wingspan and lower wing-beat frequency than some insects as fruit fly and bee, especially the species of butterfly which has the migratory habit. The present work investigates the difference of the flow structures between the plate models of Papilio ulysses and Danaus plexippus, two of the migratory butterflies, through hydrogen bubble visualization as the attach angle increases. When flow passes over the two butterfly models under the same experimental condition, the leading-edge vortices, wing-tip vortices and other flow structures all appear on both model wings. Further more, the development tendencies of flow structures for the two butterfiles are similar to each other. Because of the difference between the shapes of the two model wings, some details of the flow field are not the same, such as the shape and the vortex strength of the leading-edge vortices, the wing-tip flow structure at the both side of the hindwings and so forth.