Aerodynamics of a Dragonfly

Abstract

Nature has been optimizing for millions of years the aerodynamics of dragonflies. The main goal of
the present thesis is to understand these mechanisms so that they can be further applied in future
bio-inspired designs.

To start with, the experimental and numerical methodology is described (chapter 3). Next, a
single flapping wing is studied under different conditions (chapter 4). Reynolds number, angle of
attack, wing shape and corrugation effects are characterized. It is shown that dragonflies leading
edge vortex is responsible for a great amount of lift production. Leading edge vortex circulation
increases with Reynolds number, and so does lift. However, drag is also found to be a crucial
contributor to the force balance that sustains dragonflies hovering. Additionally, corrugation effects
improve aerodynamic efficiency in the studied flow regime.

Finally, wing-wing interaction effects are studied numerically in a whole dragonfly (chapter 5). It
is illustrated that phase changes between hindwings and forewings can maximize force production or
be tuned to achieve a more stable and efficient hovering. However, not all phases are appropriate for
maximum efficiency. Phase has to be tuned to maximize wake-capturing mechanisms and therefore
flying efficiency. Finally, vorticity removal mechanisms are depicted to maintain a clean and uniform
background flow that optimizes hovering efficiency.