DOI: 10.1017/jfm.2022.224

Abstract:

The vortex dynamics of leading-edge vortices on plunging high-aspect-ratio (AR = 10)
wings and airfoils were investigated by means of volumetric velocity measurements,
numerical simulations and stability analysis to understand the deformation of the
leading-edge vortex filament and spanwise instabilities. The vortex filaments on both
the wing and airfoil exhibit spanwise waves, but with different origins. The presence of
a wing-tip causes the leg of the vortex to remain attached to the wing upper surface,
while the initial deformation of the filament near the wing tip resembles a helical
vortex. The essential features can be modelled as the deformation of an initially L-shaped
semi-infinite vortex column. In contrast, the instability of the vortices is well captured by
the instability of counter-rotating vortex pairs, which are formed either by the trailing-edge
vortices or the secondary vortices rolled-up from the wing surface. The wavelengths
observed in the experiments and simulations are in agreement with the stability analysis
of counter-rotating vortex pairs of unequal strength.