Insights into the Physics of Flapping Flight: Extending Axioms on Force Generation, Flow Features and Body Deformation in Insect Flight

In nature, only three organisms have been able to successfully achieve sustained flight; birds, bats and insects. Among these, insects are by far the most proficient and evolved flight over 300 million years ago. With advances in visualization techniques, high speed camera systems, experimental methods as well as computational fluid dynamics (CFD) simulations, Engineers have unraveled some of the mechanisms of flapping flight which govern aerodynamic force generation due to wing motions and body deformation.
The current consensus is that during flight, the downstroke flapping phase generates most of the aerodynamic forces with unsteady mechanisms, primarily, a leading edge vortex (LEV) aiding the forewings but this LEV is absent on the hindwings in the case of four-wing fliers. The upstroke is also mostly inactive and subsequently generates minimal aerodynamic forces during flight compared to the downstroke. However, these conclusions are based on well-studied flight modes such as forward flight, maneuvers and hovering and a considerable amount of the works were based on tethered flight. The coordination of wing and body motions and the role of unsteady aerodynamic mechanisms in other free flight modes such as flight initiation and reverse flight is not well known.
Auxiliary flight mechanisms such as body deformation may also influence flight mechanics. Most previous works on auxiliary flight mechanics have been based on observations in tethered flight where abdominal deflection may be exaggerated. Body deformation has been proposed as a mechanism for fine-tuning moments, ensuring pitch stability, modifying effective stability derivatives, and as an aerodynamic rudder during flight. However, it is not known whether there are energy savings benefits due to body deformation in free flight.
In this thesis, insight is provided on aerodynamic force generation, flow physics and body deformation during free flight from unique perspectives and methods. The roles of the wings in aerodynamic force generation in previously unstudied flight modes of four-winged fliers are investigated. Emphasis is placed on high-lift mechanisms employed during flight, the roles of the downstroke and more importantly the upstroke in generating flight forces, and the coordination of wing and body motion in flight. To this end, CFD simulations were employed to study novel flight modes which include non-jumping takeoffs in damselflies and backward flight in dragonflies. Additionally, an auxiliary flight mechanism such as body deformation was studied. The main question sought to be answered is whether there could be energy savings benefits from body deformation during free flight maneuvers. An optimization algorithm was employed to study body deformation in free flight maneuvers of Dragonflies.
The findings from this work advance knowledge on the physics of flapping flight by clarifying which mechanisms could benefit flight in different modes with relevant applications in the design of next generation robust MAVs.