Mechanisms of Deflection Angle Change in the Near and Far Vortex Wakes behind a Heaving Airfoil

It has been reported that an asymmetric wake is formed downstream of a plunging airfoil at a moderate heaving amplitude and frequency. The behavior of vortex dipole in the wake is recognized as the key contributor that determines the deflection angle of the asymmetric wake. While previous literature deliberately discussed the vortex dipoles in the near wake region, this study shows that the deflection angle can change between the near wake and the far wake. The varying distance between the two consecutive vortices in the neighboring dipoles triggered by their unequal strength was found to be the primary mechanism that causes the deflection angle change from the near wake to the far wake behind the heaving airfoil. This switch of vortex pattern is also found to be the major reason that a heaving airfoil with an extremely high amplitude or frequency does not produce asymmetric wakes.