Wing Kinematics, Deformations, and Aerodynamics of Dragonflies in Free Flight

Title of dissertation: WING KINEMATICS, DEFORMATIONS, AND AERODYNAMICS OF DRAGONFLIES IN FREE FLIGHT Nathan Shumway Doctor of Philosophy, 2019 Dissertation directed by: Assistant Professor Stuart Laurence Department of Aerospace Engineering The development of Micro Aerial Vehicles (MAVs) has led researchers to study insects in order to better understand aerodynamic mechanisms and wing kinematics that achieve high performance flight at small scales. Dragonflies in particular are a good candidate for study, as their size is comparable to the target size of MAVs and they are able remain stable while flying in highly variable conditions. To better understand undisturbed steady flight and gust response of dragonflies, experiments were conducted to measure detailed wing kinematics and deformations in free flight both through a quiescent environment and when encountering a lateral gust. A custom testing environment was developed in which dragonflies would fly through an enclosed area with high-speed cameras capturing both their body motion and that of markers placed on their wings. Due to the nature of the setup and how the dragonflies were released, they would frequently fly while inverted rather than upright and a comparison between upright and inverted flight is included in this work. During inverted flight the tested specimens flew in such a way that their wings had a similar orientation in the global reference frame to that of the wings in the upright flights. The two primary kinematic variables that were changed to produce this result were the wing pitch angle and the body elevation angle. In addition, the dragonflies modulated the amount of time spent in the downstroke versus the upstroke so that in either case their wings spent more time moving down in the global frame. When dragonflies encountered a lateral gust, they increased the pitching of their windward wings, using left-right asymmetric kinematics to maintain a straight flight path through the disturbance. From these experimental data, models were developed for both the wing kinematics and the wing deformations, and these were incorporated into flapping wing simulations using the OVERTURNS computational fluid dynamics (CFD) code. Two sets of such CFD simulations were run: one of rigid wings and the other of deforming wings. For both rigid and deforming wings, the interaction between the foreand hindwing increased the force production on both wings when compared to foreand hindwings in isolation. The largest differences between isolated and tandem wings were seen for the hindwing as it passed through the wake of the forewing. The wing deformations slightly decreased the total force production, compared to the rigid wings, by reducing the amount of flow separation on the bottom of the wing during the upstroke. The impact of the camber deformation, during the bodyrelative downstroke, was dependent on the specific wing kinematics. Though the total force produced decreased, the wing deformations substantially increased the efficiency for both wings. WING KINEMATICS, DEFORMATIONS, AND AERODYNAMICS OF DRAGONFLIES IN FREE FLIGHT