摘要：Context. Among the candidates for generating turbulence in accretion
discs in situations with low intrinsic ionization, the vertical shear instability (VSI)
has become an interesting candidate, since it relies purely on a vertical gradient in the
angular velocity. Existing numerical simulations have shown that α-values a few times
10-4 can be
generated.
Aims. The particle growth in the early planet formation phase is
determined by the dynamics of embedded dust particles. Here, we address, in particular,
the efficiency of VSI-turbulence in concentrating particles to generate overdensities and
low collision velocities.
Methods. We perform three-dimensional (3D) numerical hydrodynamical
simulations of accretion discs around young stars that include radiative transport and
irradiation from the central star. The motion of embedded particles within a size range of
a fraction of mm up to several m is followed using standard drag formula.
Results. We confirm that, under realistic conditions, the VSI is able to
generate turbulence in full 3D protoplanetary discs. The irradiated disc shows turbulence
within 10 to 60 au. The mean radial motion of the gas is such that it is directed inward
near the midplane and outward in the surface layers. We find that large particles drift
inward with the expected speed, while small particles can experience phases of outward
drift. Additionally, the particles show bunching behaviour with overdensities reaching
five times the average value, which is strongest for dimensionless stopping times around
unity.
Conclusions. Particles in a VSI-turbulent discs are concentrated in
large-scale turbulent eddies and show low relative speeds that allow for growing
collisions. The reached overdensities will also enable the onset of streaming
instabilities, further enhancing particle growth. The outward drift for small particles at
higher disk elevations enable the transport of processed high temperature material in the
solar system to greater distances.
关键词：instabilities;hydrodynamics;accretion, accretion disks;radiative transfer
