Hydrodynamic and Magnetohydrodynamic Convection in Accretion Disks
type: CreativeWork
description: The prevalence and consequences of convection perpendicular to the plane of accretion disks have been discussed for several decades. Recent simulations combining convection and the magnetorotational instability have given fresh impetus to the debate, as the interplay of the two processes can enhance angular momentum transport, at least in the optically thick outburst stage of dwarf novae. In this thesis we seek to isolate and understand the most generic features of disk convection, and so undertake its study in both hydrodynamical and magnetohydrodynamical models. In the first part of this thesis we investigate hydrodynamic convection in disks. First, we investigate the linear phase of the instability, obtaining estimates of the growth rates both semi-analytically, using one-dimensional spectral computations, as well as analytically, using WKBJ methods. Next we perform three-dimensional, vertically stratified, shearing box simulations with the conservative, finite-volume code PLUTO, both with and without explicit diffusion coefficients. We find that hydrodynamic convection can, in general, drive outward angular momentum transport, a result that we confirm with ATHENA, an alternative finite-volume code. Moreover, we establish that the sign of the angular momentum flux is sensitive to the diffusivity of the numerical scheme. Finally, in sustained convection, whereby the system is continuously forced to an unstable state, we observe the formation of various coherent structures, including large-scale and oscillatory convective cells, zonal flows, and small vortices. In the second part of this thesis we investigate magnetohydrodynamic convection in disks. First, we perform inviscid, three-dimensional, vertically stratified zero-net-flux MHD shearing box simulations with the conservative, finite-volume code PLUTO without explicit cooling. We find that MRI heating and weak cooling facilitated through advection of material across the vertical boundaries alone results in a c…
abstract: The prevalence and consequences of convection perpendicular to the plane of accretion disks have been discussed for several decades. Recent simulations combining convection and the magnetorotational instability have given fresh impetus to the debate, as the interplay of the two processes can enhance angular momentum transport, at least in the optically thick outburst stage of dwarf novae. In this thesis we seek to isolate and understand the most generic features of disk convection, and so undertake its study in both hydrodynamical and magnetohydrodynamical models. In the first part of this thesis we investigate hydrodynamic convection in disks. First, we investigate the linear phase of the instability, obtaining estimates of the growth rates both semi-analytically, using one-dimensional spectral computations, as well as analytically, using WKBJ methods. Next we perform three-dimensional, vertically stratified, shearing box simulations with the conservative, finite-volume code PLUTO, both with and without explicit diffusion coefficients. We find that hydrodynamic convection can, in general, drive outward angular momentum transport, a result that we confirm with ATHENA, an alternative finite-volume code. Moreover, we establish that the sign of the angular momentum flux is sensitive to the diffusivity of the numerical scheme. Finally, in sustained convection, whereby the system is continuously forced to an unstable state, we observe the formation of various coherent structures, including large-scale and oscillatory convective cells, zonal flows, and small vortices. In the second part of this thesis we investigate magnetohydrodynamic convection in disks. First, we perform inviscid, three-dimensional, vertically stratified zero-net-flux MHD shearing box simulations with the conservative, finite-volume code PLUTO without explicit cooling. We find that MRI heating and weak cooling facilitated through advection of material across the vertical boundaries alone results in a c…
author: Held, Loren Everett
language: eng
keywords: Astrophysics, Convection, Hydrodynamics, Magnetohydrodynamics, Accretion Discs
license: https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/b9ad3c1b-f642-4fa9-a7df-1667d159bed3/download
license: https://www.rioxx.net/licenses/all-rights-reserved/
date published: 2020-06-15
date modified: 2026-07-22T22:24:28Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.58446