Physics – Fluid Dynamics
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aps..dfd.dn007b&link_type=abstract
American Physical Society, 53rd Annual Meeting of the Division of Fluid Dynamics November 19 - 21, 2000 Washington, DC Meeting I
Physics
Fluid Dynamics
Scientific paper
Understanding how millimeter-sized dust grants agglomerate to become kilometer-sized, self-gravitating "planetesimals" is a key problem in planet formation. One idea is that agglomeration is due to the grains settling into the mid-planes of accretion disks (around newly forming stars) until they reach a critical density and become gravitationally unstable and form planetesimals. However, turbulence within the disk is likely to stir up the dust grains and prevent them from reaching their critical density. We examine numerically and analytically the role of 3D vortices within a turbulent disk in aiding agglomeration of dust grains. We show that gas-drag between the fluid in the disk and the dust grains creates an attracting region within, or just outside, the vortices in which the grains accumulate. This basin of attraction has a nearly elliptical shape, and we show that its diameter depends on the ratio of the vortex turn-around time to the stopping-time of the grains due to the gas-drag. The flows within these vortices are more laminar than the turbulent flow that makes up most of the disk. The effect of the relaminarization on agglomeration of dust grains is also explored. Mergers between between dust-laden vortices can also enhance agglomeration. Vortices in statistical equilibria have their growth balanced by decay. They grow by merging with small vortices (and in doing so, capturing their dust). The vortices can decay by Rossby radiation which decreases their circulations, but does not allow grains to escape. We explore whether the net effect increases the grain density within vortices.
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