Abstract
We propose a ballistic coalescence model (punctuated-Hamiltonian approach) mimicking the fusion of vortices in freely decaying two-dimensional turbulence. A temporal scaling behaviour is reached where the vortex density evolves like t−ξ. A mean-field analytical argument yielding the approximation ξ = 4/5 is shown to slightly overestimate the decay exponent ξ whereas Molecular Dynamics simulations give ξ = 0.71 ± 0.01, in agreement with recent laboratory experiments and simulations of Navier-Stokes equation.