THESIS
2021
1 online resource (xix, 129 pages) : illustrations (some color)
Abstract
Dragonflies are aerobatic insects with unique physiological features that help them to exploit
highly unsteady aerodynamic effects in the low Reynolds number regime. Such aerodynamic
effects include added mass effects, flow separation that results in the formation of wing attached
vortexes, as well as wake capture and forewing-hindwing interactions. The forewing and the
hindwing of a dragonfly have different geometry that could be an evolutionary specialization
for better aerodynamic performance via sophisticated wing pitch control. In this work the
complex dynamic wing morphology and kinematic control of dragonfly aerodynamics are
studied experimentally. First, the dragonfly wing surface is reconstructed, and the wing
deformation is measured in steady wind conditions with Fourier trans...[
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Dragonflies are aerobatic insects with unique physiological features that help them to exploit
highly unsteady aerodynamic effects in the low Reynolds number regime. Such aerodynamic
effects include added mass effects, flow separation that results in the formation of wing attached
vortexes, as well as wake capture and forewing-hindwing interactions. The forewing and the
hindwing of a dragonfly have different geometry that could be an evolutionary specialization
for better aerodynamic performance via sophisticated wing pitch control. In this work the
complex dynamic wing morphology and kinematic control of dragonfly aerodynamics are
studied experimentally. First, the dragonfly wing surface is reconstructed, and the wing
deformation is measured in steady wind conditions with Fourier transform profilometry (FTP).
It shows that a dragonfly wing has a complex surface and the wing deformation caused by the
wing flexibility has less effect on gliding flight. Second, the flow fields using time-resolved
particle image velocimetry (TR-PIV) and pitching angle variations are measured to study the
pitching effect and morphology of wings of a live dragonfly versus motor actuated wings.
Results show that pitching employed by the live dragonfly helps thrust generation, and the
different wing planforms of the hind and forewing affect local aerodynamic performance along
the span. Last, the wing kinematics and resulting flow fields of live dragonflies are studied in
two distinct flight modes, normal forward flight, and escape flight. It is found that a dragonfly
performs active pitch control, and to generate fluid momentum for an impulsive escape
maneuver, the dragonfly does not change its flapping frequency, but controls the angle of attack
of its wings via pitch and stroke angle adjustment, while the flapping phasing and stroke
amplitude of the wings decreases. The findings presented in this work can be considered for the
bio-inspired design of Micro Air Vehicles operating in the low Reynolds regime as natural
flyers.
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