Analytical and numerical studies have shown that multipolar vortices can
emerge in two-dimensional flow due to azimuthal normal mode perturbations of
shielded vortices. It has been found that mode 2 and 3 perturbations can
lead to the formation of stable tripoles and quadrapoles, respectively,
while higher order modes result in more complex unstable compound vortices.
We have used the lattice Boltzmann method to simulate the effect of azimuthal
perturbations on shielded vortices at moderate Reynolds numbers. We have found that
azimuthal normal mode perturbations result in the formation of multipoles, which
decay due to viscous dissipation. We could also observe that the outcome of such simulations
is very sensitive to the displacement of perturbations above wavenumber-3 excitations,
in spite of the significant viscosity we used.