Computation of 3D Hydrodynamic, Hydromagnetic and Dust-Laden Flows in Protoplanetary Disks and Their Roles in Planetesimal and Star Formation

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ABSTRACTThe research to be carried out here centers on the transportation of mass and angularmomentum in protoplanetary disks surrounding young stars. "Turbulence" or "eddyviscosities" have been invoked to solve a variety of problems, including the transport ofangular 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 enhancedviscosity which allows planetesimals or planets to migrate radially in the disk away fromthe regions in which they formed. However, computing the transport of angularmomentum, 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 transportangular momentum, will be studied as a function of the disk's ionization. In addition, theinvestigator's previous work has shown that vortices are efficient at transporting angularmomentum. His 3D modeling further indicates that grains can be trapped in these vorticesand concentrated. Using two new codes, one a hybrid particle/gas code and the other atwo-phase flow code in which one phase is the gas and the other is the dust, theaccumulation of dust in the disk's mid-plane, in the vortices that form within a disk, andin the inter-eddy regions of the turbulence will be examined. All of these locations havebeen suggested to be regions where dust concentrates and then undergoes agglomerationor instability to produce planetesimals. A proposed scenario by which protoplanetarydisks fills with vortices will also be investigated. In this model a small, initialperturbation produces weak internal gravity waves. Those waves, in a rotating, shearingstratified flow, create vortices. The vortices are not steady, but oscillate, creating newgravity waves, and the disk fills with waves and vortices.The tools employed here are applicable to other problems as well, including thecirculation of Jupiter's atmosphere, modeling wake-vortices produced by wide bodyaircraft, and the role of particulates in climate pollution. The results of this work will bedisseminated to the public through public lectures and popular articles. A graduatestudent will be supported and trained in numerical modeling of fluid flows.