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Evolution and characteristics of forced shear flows in polytropic atmospheres: Large and small Péclet number regimes

Witzke, V., Silvers, L. J. ORCID: 0000-0003-0619-6756 and Favier, B. (2019). Evolution and characteristics of forced shear flows in polytropic atmospheres: Large and small Péclet number regimes. Monthly Notices of the Royal Astronomical Society, 482(1), pp. 1338-1351. doi: 10.1093/mnras/sty2698

Abstract

Complex mixing and magnetic field generation occurs within stellar interiors particularly where there is a strong shear flow. To obtain a comprehensive understanding of these processes, it is necessary to study the complex dynamics of shear regions. Due to current observational limitations, it is necessary to investigate the inevitable small-scale dynamics via numerical calculations. Here, we examine direct numerical calculations of a local model of unstable shear flows in a compressible polytropic fluid primarily in a two-dimensional domain, where we focus on determining how key parameters affect the global properties and characteristics of the resulting saturated turbulent phase. We consider the effect of varying both the viscosity and the thermal diffusivity on the non-linear evolution. Moreover, our main focus is to understand the global properties of the saturated phase, in particular estimating for the first time the spread of the shear region from an initially hyperbolic tangent velocity profile. We find that the vertical extent of the mixing region in the saturated regime is generally determined by the initial Richardson number of the system. Further, the characteristic quantities of the turbulence, i.e. typical length-scale and the root-mean-square velocity are found to depend on both the Richardson number, and the thermal diffusivity. Finally, we present our findings of our investigation into saturated flows of a ‘secular’ shear instability in the low Péclet number regime with large Richardson numbers.

Publication Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record, Witzke, V., Silvers, L. J. and Favier, B. (2018). Evolution and characteristics of forced shear flows in polytropic atmospheres: Large and small Péclet number regimes. Monthly Notices of the Royal Astronomical Society, is available online at: https://doi.org/10.1093/mnras/sty2698
Publisher Keywords: methods: numerical, stars: interiors, hydrodynamics, instabilities, turbulence
Subjects: Q Science > QA Mathematics
Q Science > QB Astronomy
Departments: School of Mathematics, Computer Science & Engineering > Mathematics
URI: http://openaccess.city.ac.uk/id/eprint/20701
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