Wake Structure and Vortex Development in Flight of Fruit Flies Using High-Speed Particle Image Velocimetry

Understanding the dynamics of force and energy control in flying insects requires the exploration of how oscillating wings interact with the surrounding fluid. In two-winged insects, such as flies, the fluid acceleration fields produced by each wing strongly interact during wing stroke reversals, when the wings reverse their flapping direction. The main finding of this study is that this wing-wake interaction potentially budgets the elevated energy expenditures required for wing flapping by actively lowering the kinetic energy in the wake. This is demonstrated by quantitative flow measurements in flying fruit flies using high-speed particle image velocimetry and measurements in robotic, model wings. Vorticity estimates suggest that, compared to rigid robotic wings, elastic fly wings recycle energy from detached leading edge vortices by a novel mechanism termed vortex trapping. This finding is of great interest in the field of biomimetic aircraft design because it may help to improve the endurance of the next generation of man-made wing-flapping aerial devices such as micro air vehicles.