Experimental investigation on the flow structure over a simplified Papilio Ulysses model

The aerodynamic characteristics of butterflies, especially those which can migrate overseas, have received a great deal of attention because they have larger-scale wingspans and lower flapping frequencies than other insects such as drosophilae and bees. The objective of this work is to investigate the flow structures over a simplified model of Papilio Ulysses, one kind of migratory butterflies, through hydrogen bubble visualizations, and leading-edge vortices, wing-tip vortices, separation bubbles and horseshoe vortex wake are observed. Moreover, the variations of these structures with the angle of attack are discussed in detail. A new type of leading-edge vortices which resembles the inversed Chinese character is observed in the experiment.