Unsteady flow mechanisms revisited in insect flapping flight

The unsteady flow mechanisms of insect flapping flight arerevisited with the theoretical modeling approach proposed. Accordingto analysis of the flapping motion in insect hovering flight, it is revealedthat, limitations of the aerodynamic lift at low Reynolds numbers may bereleased by the highly unsteady condition in insect wing flapping, in whichcase the controlling parameter is the Strouhal number (St \gg 1/Re).Furthermore,in the present theoretical modeling study, three factors have been found inlift generation and regulation: (1) the remarkable instantaneous addedinertial effect is excited by the high unsteadiness of wing flapping; (2)keeping the leading edge vortex on the upper wing surface can avoid liftdecreasing; (3) enhancing the strength of the trailing edge vortex andaccelerating its shedding can produce high lift.