High-fidelity simulations of a perturbed vortex pair in ground effect*

The influence of a planar wall on the temporal development of the long-wavelength instability of a counter- rotating trailing vortex pair is studied computationally. The unsteady flow field is computed using high-fidelity implicit large-eddy simulations, where viscous and inviscid wall conditions are considered to further elucidate the effect of the wall on the vortex pair. The principal effect of the wall is to suppress the long-wavelength Crow instability growth rate as the vortex pair splits and moves along the planar boundary. The evolution of the perturbed vortex pair system is compared to an inviscid theoretical model for the perturbation development, which corroborates the temporary suppression of perturbation growth and shift of the maximum perturbation amplitude to a higher wavenumber. Inviscid simulations reveal that the perturbation inhibition process can be attributed to the rotation of the instability plane angle and to the diverging vortex center positions of the vortex pair, which are consistent with theoretical predictions and with the behavior of the vortex pair in a viscous fluid.