Velocity power spectra for the two simulations. Top panel: 2D power spectrum of the three velocity components 10 Myr after the activation of level 20. The curves are compensated by k³. Curves from to the F65 run are plotted in bold, and the thin lines show the F10 run. The F10 power spectra are shifted down by 3 dex for the sake of clarity. Bottom panel: evolution of the power-law index of the fit of the velocity power spectra. Curves related to the F65 run are shown in bold.