The research to be carried out here centers on the transportation of mass and angular momentum in protoplanetary disks surrounding young stars. "Turbulence" or "eddy viscosities" have been invoked to solve a variety of problems, including the transport of angular momentum outward from a disk to allow mass to accrete onto a central protostar, the accumulation of dust to produce planetesimals, and their ability to act as an enhanced viscosity which allows planetesimals or planets to migrate radially in the disk away from the regions in which they formed. However, computing the transport of angular momentum, dust, planetesimals, and planets within a disk using transport rates from "eddy viscosities" may well be incorrect. Here, the sustainability of another process, magnetohydrodynamic turbulence (which is highly dissipative) and its ability to transport angular momentum, will be studied as a function of the disk's ionization. In addition, the investigator's previous work has shown that vortices are efficient at transporting angular momentum. His 3D modeling further indicates that grains can be trapped in these vortices and concentrated. Using two new codes, one a hybrid particle/gas code and the other a two-phase flow code in which one phase is the gas and the other is the dust, the accumulation of dust in the disk's mid-plane, in the vortices that form within a disk, and in the inter-eddy regions of the turbulence will be examined. All of these locations have been suggested to be regions where dust concentrates and then undergoes agglomeration or instability to produce planetesimals. A proposed scenario by which protoplanetary disks fills with vortices will also be investigated. In this model a small, initial perturbation produces weak internal gravity waves. Those waves, in a rotating, shearing stratified flow, create vortices. The vortices are not steady, but oscillate, creating new gravity waves, and the disk fills with waves and vortices. The tools employed here are applicable to other problems as well, including the circulation of Jupiter's atmosphere, modeling wake-vortices produced by wide body aircraft, and the role of particulates in climate pollution. The results of this work will be disseminated to the public through public lectures and popular articles. A graduate student will be supported and trained in numerical modeling of fluid flows.
