Vortex merging and spectral cascade in two-dimensional flows

The merging of two identical vortices is studied numerically using a spectral code. It is noted that the enstrophy cascade is most active on the distorted vortex boundaries, with a Kolmogorov-like spectrum E(k)≊k−α, α≤4, developed at high wave numbers. The inverse energy cascade is completed when the vortices merge into one of larger size.