  The transition of the vortex pattern and the lift generated by a heaving wing
in a uniform flow was investigated numerically. Motivated by insects' flight
maneuverability, we studied the relationship between a temporal change in the
heaving wing motion and the change in the global vortex pattern. At a Strouhal
number that generates an asymmetric vortex pattern, we found that temporal
angular frequency reduction causes inversion of both the global vortex pattern
and the lift sign. The inversion is initiated by the transfer of the
leading-edge vortex, which interferes with the vortex pattern generated at the
trailing edge. Successful inversion is conditioned on the starting phase and
the time interval of the frequency reduction. The details of the process during
the transition are discussed.
