AbstractsEngineering

A critical review of the progress of research on the effects of aerodynamics/kinematics and aeroelasticity on flapping-wing propulsion reveals the complexity of the subject. As there are multiple intertwined factors that influence the propulsion and aerodynamic performance of a wing/insect, it is necessary to study a variety of insects. Bumblebees and hoverflies are chosen as two insects for further study in this thesis due to their desirable characteristics for MAV applications; the former can carry heavy loads while the latter are capable of stable hovering in mid-air. Firstly, the bumblebee wings and body are modeled as rigid bodies and three computational models created. Two models comprise only the wing-pair and one with both the wings and body. It is found that wing-body interactions have a very small influence (approximately 2%) on the time-averaged lift and input power. In addition, the unusual stiffness distribution of bumblebee wings is analyzed for the first time, with two flexible-wing models and one rigid-wing model tested. It is found that the rigid wing produces drag while both flexible models produce thrust. In forward flight, such as in our simulations, the positive thrust clearly highlights the importance of flexibility for bumblebee propulsion. Hoverfly models, both rigid and flexible, are analyzed to investigate the effects of flexibility on hoverfly propulsion and the functions of the alula which is a flap-like structure near the hoverfly's wing root. There are several important findings obtained from this analysis: firstly, the alula is unlikely to function as a high-lift device or increase lift production; secondly, deflecting the alula affects the magnitude and direction of thrust and side-force; thirdly, pitching and yawing moments are more sensitive than rolling moments to a change in the alula’s position; fourthly, symmetrical flipping of the alula significantly alters the linear and angular accelerations of the body; and, fifthly, having and operating the alula cost the hoverfly less than 2% extra consumption of power. This indicates the possibility of the alula functioning as an active flow control device to maintain the hoverfly's position during hovering flight or shift it to another position.