Three dimensional unsteady flow and active morphing effect in flapping wings
Abstract
Bumble bee cannot fly, if we ignore the significant differences between flapping wings and fixed wings, and falsely apply the conventional fixed wing aerodynamic principles to the bumble bee flight. The classic fixed wing aerodynamics originated from the two-dimensional attached flow analysis, where the three-dimensional and unsteady effects can be ignored without introducing too much error. Insects and hummingbirds, however, flap their low aspect ratio and highly deformable wings reciprocally, creating very complex flow structures, which are highly three-dimensional and unsteady. In the meanwhile, the flexibility and complex textures of the wings introduce even more complexities to the problem from the aspect of aero-elasticity. Therefore, to see the entire picture of flapping wing aerodynamics, the three factors: unsteadiness, three-dimensional effect and wing morphing have to be taken into account and this thesis aims to provide some understanding about those issues and the couplings related to them. The state of art V3V system was used to study the coupling between unsteadiness and three-dimensional effect of the flow on a mechanical flapper with rigid wings, revealing a linked vortex ring structure in the near field with two layers of strong vortical flow in the far field. On the other hand, the coupling of unsteadiness and wing morphing was studied on a quasi-2-dimensional translating wing with an active trailing edge flap, suggesting both the flow and force characteristics were greatly affected by the flap deflection timing. Finally, to study the coupling of all the three factors: unsteadiness, three-dimensional effect and wing morphing, a new method of flow visualization was successfully developed and applied to freely flying hawkmoth. For the first time, the entirety of the highly three-dimensional and unsteady vortex structure was observed and reported experimentally on a freely flying insect.
Degree
Ph.D.
Advisors
Deng, Purdue University.
Subject Area
Mechanical engineering|Biomechanics
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