Unidirectional Forward Flight of a Flapping Wing

Wednesday, June 28, 2006 - 2:00pm - 3:00pm
Lind 409
Jun Zhang (New York University)
The locomotion of most fish and birds is realized by flapping wings or
fins transverse to the direction of travel. Here, we study experimentally
the dynamics of a wing that is flapped up and down but is free to move in
the horizontal direction. In this table-top prototype experiment, we show
that flapping flight occurs abruptly at a critical flapping frequency as a
symmetry-breaking bifurcation. We then investigate the separate effects of
the flapping frequency, the flapping amplitude, the wing geometry and the
influence from the solid boundaries nearby. Through dimensional analysis,
we found that there are two dimensionless parameters well describe this
intriguing problem that deals with this fluid-solid interaction. The
first one is the dynamical aspect ratio that combines four length scales,
including the wing geometry and the flapping amplitude. The second
parameter, the Strouhal number, relates the vertical flapping speed and
its resultant forward flight speed. Overall, we emphasize the robustness
of the thrust-generating mechanisms determining the forward flight speed
of a flapping wing, as observed in our experiments.
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