Power spectrum for the different kinetic energy components along the azimuthal direction in the disc midplane averaged over the radial direction. The black line shows the Kolmogorov spectrum decaying with | u(m) | ² ∝ m^{− 5 / 3}, where m denotes the azimuthal wave number. The top panel refers to the growth phase after 200 yr and the lower panel to the quasi-stationary phase after 1700 yr.