The influence of the wake of a flapping wing on the production of aerodynamic forces |
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Authors: | Wu Jianghao Sun Mao |
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Institution: | (1) Ministry-of-Education Key Laboratory of Fluid Mechanics, Institute of Fluid Mechanics, Beihang University, Beijing, 100083, China |
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Abstract: | The effect of the wake of previous strokes on the aerodynamic forces of a flapping model insect wing is studied using the
method of computational fluid dynamics. The wake effect is isolated by comparing the forces and flows of the starting stroke
(when the wake has not developed) with those of a later stroke (when the wake has developed). The following has been shown.
(1) The wake effect may increase or decrease the lift and drag at the beginning of a half-stroke (downstroke or upstroke),
depending on the wing kinematics at stroke reversal. The reason for this is that at the beginning of the half-stroke, the
wing ``impinges' on the spanwise vorticity generated by the wing during stroke reversal and the distribution of the vorticity
is sensitive to the wing kinematics at stroke reversal. (2) The wake effect decreases the lift and increases the drag in the
rest part of the half-stroke. This is because the wing moves in a downwash field induced by previous half-stroke's starting
vortex, tip vortices and attached leading edge vortex (these vortices form a downwash producing vortex ring). (3) The wake
effect decreases the mean lift by 6%–18% (depending on wing kinematics at stroke reversal) and slightly increases the mean
drag. Therefore, it is detrimental to the aerodynamic performance of the flapping wing.
The project supported by the National Natural Science Foundation of China (10232010) and the National Aeronautic Science Fund
of China(03A51049)
The English text was polished by Xing Zhang |
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Keywords: | Insect Flapping Unsteady aerodynamics Wing/wake interaction CFD analysis |
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