An attempt is made to enhance the beneficial effects of the trapped vo
rtex by increasing its lingering period on the upper surface of a Jouk
owski airfoil in oscillating motions. Studies are made on the stabilit
y of a trapped free vortex when perturbed away from its equilibrium po
sition with a finite displacement, and on the lingering period of the
trapped free vortex in the upper vicinity of the airfoil. The computat
ional results show that a proper combination of oscillation and suctio
n might be an efficient method for trapping a free vortex to generate
high lift on an airfoil. It is found that the trailing-edge suction po
sition is more effective in capturing a free vortex for a longer linge
ring time and the lift increment directly dependent on the strength of
the trapped vortex. This result may provide an explanation of the hig
h lift generated by a dragonfly whose back wings are found to flap in
a flow containing vortices shed from the front wings.