Change search
ReferencesLink to record
Permanent link

Direct link
Hydrodynamic simulations with a radiative surface
Stockholm University, Faculty of Science, Department of Astronomy.
2013 (English)Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
Abstract [en]

We solve the equations of radiation hydrodynamics to compute the time evolution toward one-dimensional equilibrium solutions using ageneralized Kramers opacity, κ=κ0 ρa Tb, with adjustable prefactor κ0 and exponents a and b on density ρ and temperature T, respectively. We choose our initial conditions to be isothermal and find that the early time evolution away from the isothermal state is fastest near the height where the optical depth is unity, and is slower both above and below it. In all cases where the quantity n=(3-b)/(1+a) is larger than -1, we find a nearly polytropic solution with ρTn in the lower part and a nearly isothermal solution in the upper part with a radiating surface in between, where the optical depth is unity. In the lower part, the radiative diffusivity is found to be approximately constant, while in the upper optically thin part it increases linearly. Interestingly, solutions with different parameter combinations and b that result in the same value of n are rather similar, but not identical. Increasing the prefactor increases the temperature contrast and lowers the value of the effective temperature. We find that the Péclet number based on sound speed and pressure scale height exceeds numerically manageable values of around 104 when the prefactor κ0 is chosen to be approximately six orders of magnitude below the physically correct value. In the special case where a=-1 and b=3, the value of n is undetermined and the radiative diffusivity is strictly constant everywhere. In that case we find a stratification that is approximately adiabatic. Finally, exploratory two-dimensional calculations are presented where we include turbulent values of viscosity and diffusivity and find that onset of convection occurs when these values are around 31013 cms-1. The addition of an imposed horizontal magnetic field suppresses small-scale convection, but has not led to instability in the cases investigated so far.

Place, publisher, year, edition, pages
2013. , 67 p.
Keyword [en]
The Sun, Magnetohydrodynamics, radiative transfer
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-90307OAI: diva2:624567
2013-05-29, FB52, AlbaNova University Center, 106 91, Stockholm, 18:41 (English)
Available from: 2013-06-10 Created: 2013-06-01 Last updated: 2013-06-10Bibliographically approved

Open Access in DiVA

fulltext(1702 kB)238 downloads
File information
File name FULLTEXT01.pdfFile size 1702 kBChecksum SHA-512
Type fulltextMimetype application/pdf

By organisation
Department of Astronomy
Astronomy, Astrophysics and Cosmology

Search outside of DiVA

GoogleGoogle Scholar
Total: 238 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 212 hits
ReferencesLink to record
Permanent link

Direct link