This animation shows a dynamically adaptive numerical simulation of the 2D incompressible Navier-Stokes equations at Reynolds-number 2×10⁴ for 10 turn-over times as: left, physical-space vorticity field (from negative to positive); and right, Fourier-space kinetic-energy spectrum vs radial wavenumber (curves colored by time up to the present). Initially the spectrum decays very quickly because the vorticity is merely a sum of 3 Gaussians, but over time there appear wavenumber ranges exhibiting near-power-law behavior (associated with vortex filaments), as indicated by the straight lines with slopes −6,…−1. This provides both an application of a new exact Fourier transform on spectral elements (Fournier 2006), as well as a comparison of GASpAR simulation (Rosenberg et al. 2006) using a varying scale (5 octaves) and number of elements (of 2D polynomial degree 7×7) against a challenging test problem in the literature (Charton & Perrier 1996, Kevlahan & Farge 1997, Schneider et al. 1997).