Root mean square of as a functionof time t. The root mean square is computed using the mass-weighted average over the vertical domain size and over 1 au extending from r = 50  to 51 au. In the domain with a vertical dimension of four gas scale heights (blue and orange lines), the Mach number saturates at . This value is consistent with the one which Flock et al. (2017) find in their numerical study of the vertical shear instability. The turbulent strength is similar in the simulation with the fiducial resolution (iso_Lr=90au_Lz=4Hg; blue line) and the one with the doubled resolution (iso_Lr=90au_Lz=4Hg_dou_res; orange line); however, it remains lower until the simulations end in the domain with a vertical size of two gas scale heights (simulation iso_Lr=90au; green line).