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Fig. 6. Lift coefficients are plotted as functions of time for one stroke cycle.
The arrows along the axis show the times at which streamline plots in Figs
9,
10 were drawn. The angles of
attack were chosen to produce a symmetric stroke. In all cases, the angle of
attack was 45°. Reynolds number (Re) was varied by changing the
translational velocity of the wing from 0.00375 to 0.06 m s-1. Lift
coefficients fall into two patterns. For Re
64, lift peaks during
the initial acceleration of the wing and oscillate during pure translation for
the downstroke. Large lift coefficients are generated during wing rotation.
During the upstroke, lift coefficients show strong oscillations during pure
translation. For Re
32, lift coefficients peak during acceleration
and drop to a constant value during pure translation. Lift coefficients peak
again during the acceleration and rotation of the wing. The lift coefficients
then drop again to relatively constant values during pure translation.
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