Turbulent convection in stars

Thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy at the University of the Witwatersrand, Johannesburg, 2017.This thesis investigates in detail the structure of models of turbulent convec tion with phenomenological closures for the eddy-viscosity. It explores the merits of replacing the canonical Mixing Length Theory of stellar convection with more realistic models of fluid turbulence that take into account the full spectrum of eddy sizes. The author provides a detailed exposition of the fun damental assumptions and the modus operandi of various approaches to the treatment of convective energy-transfer in stars. He focuses in particular on spectral descriptions of the convective process. The structure of several clo sure models developed by various authors are investigated, and he identifies and elucidates those aspects of these closures that lead to an improved descrip tion of convective turbulence in the stellar interior. The author also develops an implementation within the public-domain code, called Modules for Experi ments in Stellar Astrophysics, of two of these models and reports and discusses the results of his numerical experiments.XL201

The role of convection in stellar models

This thesis reviews the essential ingredients of local, time-independent mixing-length theory, the convective stability of uid elements in the stellar interior, the origins and in uence of convection zones in stars, and the numerical implementation of convection in some popular stellar evolution codes. The thesis concludes with a brief discussion of the future role of mixing-length theory in stellar modelling