Agile Maneuvering: Damselfly Backward Flight and Its Aerodynamic Mechanism

Researchers have often looked to insects and small birds for inspiration to design highly maneuverable flapping-winged aerial vehicles. While considerable progress has been made in understanding the forward and turning flights of these animals, their remarkable ability to use backward flight to transition between flight modes has been largely overlooked. This study examines the body kinematics and aerodynamics of damselflies performing backward maneuvering flight. High-speed videos were captured to record damselflies in backward flight before transitioning to forward flight. A point-based reconstruction method was employed to accurately model the kinematics and deformation of the damselfly's body and wings. Using an in-house immersed-boundary-method-based (IBM) incompressible flow solver combined with the local refinement method, we accurately simulated the flow around the damselfly and its force production throughout the maneuver. Strong leading-edge vortices (LEVs) were generated on all four wings, with the LEV-induced leading-edge suction enabling effective and efficient lift and thrust production. The phase difference between the forewings and hindwings facilitated strong vortex interactions between the wings. This study provides a detailed analysis of vortex formation, wing kinematics, and their relation to the force production of the damselfly during backward maneuvers.