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The secrets of a bug's flight

How does an insect that’s stalled in mid flight recover from freefall?

Matthew Bross '12G, a mechanical engineering Ph.D. student at Lehigh University, along with Cem Ozem ‘11 Ph.D. and professor Donald Rockwell, are exploring the physics of the complex movement of an insect’s wings, comparing it to the fixed wings on a modern aircraft.

An insect such as a fruit fly hovers in the air by flapping its wings -- a complex motion akin to the freestyle stroke in swimming. The wing rotates in a single plane, and by varying the angle between the plane and its body, the insect can fly forward from a hovering position.

Bross simulated this process of flight by observing the way that water flowed around a rotating model of the insect’s wings. The wings rotated on axis that is similar to that of an airplane propeller. Researchers pumped water into the model perpendicular to the motion to simulate a stall midflight.

By viewing the model on a highly-detailed, three-dimensional computer visualizations of the flow around the wing, Bross was able to determine how the physics behind this phenomenon works.

"The results of this study highlight the effect rotation has on enhancing the performance of a bio-inspired air vehicle despite experiencing a stalled state prior to rotation," Bross explained. "This is in contrast to conventional fixed wing aircraft, where a stalled state often leads to a severe decrease in lift."

The team’s findings were published in the journal Physics of Fluids in the article “Flow structure on a rotating wing: effect of steady incident flow."

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