A Priori Validation of Subgrid-scale Models for Astrophysical Turbulence
Journal
The Astrophysical Journal
Journal Volume
900
Journal Issue
1
Start Page
29
ISSN
0004-637X
1538-4357
Date Issued
2020-08-27
Author(s)
Chi-Ting 庭 Chiang 蔣季
Abstract
We perform a priori validation tests of subgrid-scale (SGS) models for the turbulent transport of momentum, energy, and passive scalars. To this end, we conduct two sets of high-resolution hydrodynamical simulations with a Lagrangian code: an isothermal turbulent box with rms Mach numbers of 0.3, 2, and 8, and the classical wind tunnel where a cold cloud traveling through a hot medium gradually dissolves due to fluid instabilities. Two SGS models are examined: the eddy diffusivity (ED) model widely adopted in astrophysical simulations and the "gradient model"due to Clark et al. We find that both models predict the magnitude of the SGS terms equally well (correlation coefficient >0.8). However, the gradient model provides excellent predictions for the orientation and shape of the SGS terms while the ED model predicts both poorly, indicating that isotropic diffusion is a poor approximation to the instantaneous turbulent transport. The best-fit coefficient of the gradient model is in the range of [0.16, 0.21] for the momentum transport, and the turbulent Schmidt number and Prandtl number are both close to unity, in the range of [0.92, 1.15].
Publisher
American Astronomical Society
Type
journal article