Particle-Trapping Eddies in Protoplanetary Accretion Disks
H. H. Klahr, T. Henning;
Icar, 1997, 128, 213
ABSTRACT:In this paper, we present a new mechanism for number density enhancement and size segregation of particles in a nonlaminar accretion disk,
e.g., the solar nebula.
It can be shown that, if there is a vortical flow with a
rotational frequency smaller than the local orbital frequency of the disk and a
rotational axis parallel to the midplane of the nebula, particles will be trapped
and concentrated in the gas flow.
Due to the centrifugal force, a particle
can be driven out of an eddy.
It will be shown that this process is inhibited
by the gravitational force induced by the protostar.
Candidates for
such slowly circulating flows are turbulent flow features in a size range
close to the integral size of the turbulence as well as huge convection
cells.
The efficiency of the particle concentration depends on the coupling of
the particle to the gas, i.e., the friction time.
On account of the mass
dependence of the friction time, a given eddy becomes a trap for particles of a
characteristic size and causes a local change in the dust density.
We calculate the
maximal dust inhomogeneity due to this process.
The strongest effect was
observed for millimeter-sized particles, which can be concentrated by a factor
of 100 within only 100 years.
Our general estimates do not depend on
special turbulence or convection models.
In addition, we compare the
analytical estimates with the results of numerical simulations of the dust
motion.
The effect will have an impact on the dust coagulation process and may be a
link to the size distribution of chondrules.
PERSOKEY:dust, size distribution, ,
CODE: klahr97