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Turbulent radiative diffusion and turbulent Newtonian cooling
Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Stockholm University, Faculty of Science, Department of Astronomy. Carnegie Mellon University, USA; Ilia State University, Georgia.ORCID iD: 0000-0002-7304-021X
Stockholm University, Nordic Institute for Theoretical Physics (Nordita).ORCID iD: 0000-0003-2302-2280
Number of Authors: 22021 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 33, no 9, article id 095125Article in journal (Refereed) Published
Abstract [en]

Radiation transport plays an important role in stellar atmospheres, but the effects of turbulence are being obscured by other effects such as stratification. Using radiative hydrodynamic simulations of forced turbulence, we determine the decay rates of sinusoidal large-scale temperature perturbations of different wavenumbers in the optically thick and thin regimes. Increasing the wavenumber increases the rate of decay in both regimes, but this effect is much weaker than for the usual turbulent diffusion of passive scalars, where the increase is quadratic for small wavenumbers. The turbulent decay is well described by an enhanced Newtonian cooling process in the optically thin limit, which is found to show a weak increase proportional to the square root of the wavenumber. In the optically thick limit, the increase in turbulent decay is somewhat steeper for wavenumbers below the energy-carrying wavenumber of the turbulence, but levels off toward larger wavenumbers. In the presence of turbulence, the typical cooling time is comparable to the turbulent turnover time. We observe that the temperature takes a long time to reach equilibrium in both the optically thin and thick cases, but in the former, the temperature retains smaller scale structures for longer.

Place, publisher, year, edition, pages
2021. Vol. 33, no 9, article id 095125
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-199878DOI: 10.1063/5.0065485ISI: 000717659200010OAI: oai:DiVA.org:su-199878DiVA, id: diva2:1625855
Available from: 2022-01-10 Created: 2022-01-10 Last updated: 2022-01-10Bibliographically approved

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Brandenburg, AxelDas, Upasana

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