  Planets are born in protostellar disks, which are now observed with enough
resolution to address questions about internal gas flows. Candidates for
driving the flows include magnetic forces, but ionization state estimates
suggest much of the gas mass decouples from magnetic fields. Thus,
hydrodynamical instabilities could play a major role. We investigate disk
dynamics under conditions typical for a T Tauri system, using global 3D
radiation hydrodynamics simulations with embedded particles and a resolution of
70 cells per scale height. Stellar irradiation heating is included with
realistic dust opacities. The disk starts in joint radiative balance and
hydrostatic equilibrium. The vertical shear instability (VSI) develops into
turbulence that persists up to at least 1600 inner orbits (143 outer orbits).
Turbulent speeds are a few percent of the local sound speed at the midplane,
increasing to 20%, or 100 m/s, in the corona. These are consistent with recent
upper limits on turbulent speeds from optically thin and thick molecular line
observations of TW Hya and HD 163296. The predominantly vertical motions
induced by the VSI efficiently lift particles upwards. Grains 0.1 and 1 mm in
size achieve scale heights greater than expected in isotropic turbulence. We
conclude that while kinematic constraints from molecular line emission do not
directly discriminate between magnetic and nonmagnetic disk models, the small
dust scale heights measured in HL Tau and HD 163296 favor turbulent magnetic
models, which reach lower ratios of the vertical kinetic energy density to the
accretion stress.
