Aerodynamics

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Flapping Wing Aerodynamics


Cicada Forward Flight


The aerodynamics of insects’ flight has been extensively studied both experimentally and numerically, towards answering the central question of how lift is augmented by unsteady wing motion. Many aerodynamic mechanisms of force generation by flapping wings have been proposed based upon studies on rigid mechanical models, including wing–wake interactions and rotational circulation, delayed stall during the translation portion of the stroke, axial flow stabilized leading edge vortex (LEV), and rotational accelerations. However, one factor ignored in most studies of insects’ free flight is the insect body. The flight mechanism of insects with a wide body such as cicada may inspire the biomimetic design of flapping wing based micro air vehicles to carry large payloads. In this study, the aerodynamic performance is investigated using an in-house immersed-boundary-method-based computational fluid dynamics (CFD) solver. It’s found that two new vortices generated by the cicada’s wide body. One is the thorax-generated vortex, which helps the downwash flow, indicating a new phenomenon of lift enhancement. Another is the cicada posterior body vortex, which entangles with the vortex ring composed of wing tip, trailing edge and wing root vortices. In the cicada forward flight, approximately 79% of the total lift is generated during the downstroke. Cicada wings experience drag in the downstroke, and generate thrust during the upstroke.




animated

vortex formation

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Total force (wings + body) during a flapping cycle, the orange line indicates the weight.

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Force generated by right wing and body during a flapping cycle.


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