Abstract:
Flying with low wing beats, erratic trajectory, and broad wings, the flight motion of butterfly is unique and very different from that of other insect. The dancing-liked flight motion of the butterfly can be contributed to two reasons; unsteady flight speed and significant rotation of body. These two phenomena, however, were often neglected and scarcely examined in previous studies. In this talk, we are going to reveal the flight features of butterflies and damselflies, which are regarded as two of the better models for MAVs.
We first recorded the flight motion of butterflies (Kallima inachus) in forward flight freely. A three-dimensional numerical model of a butterfly is then created to study the butterflies in transient flight based on the experimental data. The fluid domain is solved with the commercial software (FLUENT), a finite volume base solver. To achieve the butterfly in transient flight, two-way fluid structure interaction is applied. The aerodynamic force acting on the butterfly is integrated around the butterfly surface, by which the flight speed and the center mass of butterfly are updated in each tine step. The butterfly in this model is allowed translating freely in both vertical and horizontal directions, which is similar to the butterfly in free flight.
We investigate how the body posture affects the butterfly flight. Body motion in a simulation is prescribed and tested with varied initial body angle and rotational amplitude. From the flight trajectories, butterflies tend to fly vertically with vertical body and high rotation amplitude, and tend to fly horizontally with low body angle and rotation amplitude. The analysis reveals that the rotation of body motion helps the butterflies to control the direction of the vortex rings generated, and further affects their flight modes. In engineering perspective, to create the flight vehicle with lower wing beat as butterflies is easier and more achievable. The inspiration of flight controlled with body motion from the flight of a butterfly might yield an alternative way to control future micro flight vehicles.
Brief Bio:
Professor Yang received his Ph.D. degree in 1983 from the Energy Division of the Mechanical Engineering Department of the University of Wisconsin at Madison and became a professor of the Department of Mechanical Engineering at National Taiwan University in August, 2008. He had been the faculty of the Department of Power Mechanical Engineering at National Tsing Hua University during 1983-2008. The core of his multidisciplinary research is fluid mechanics. Current research topics contain energy and green engineering, microfluidics and lab-on-a-chip, biomimetic engineering and biophysics, jet propulsion, and laser diagnostics.