Three-equation turbulent convection models in classical variables

TL;DR

This paper develops a three-equation turbulent convection model tailored for radial stellar pulsation, incorporating nonlocal effects and anisotropy to better approximate multidimensional results in a computationally efficient manner.

Contribution

It introduces five novel extensions to Kuhfuss's model, including enhanced dissipation, anisotropy modeling, and turbulence damping, advancing 1D stellar pulsation simulations.

Findings

Enhanced dissipation correction improves model accuracy.

Local anisotropy model replaces eddy viscosity.

Second-order correction for turbulent ion transport.

Abstract

Context. Turbulent convection models in nonlinear radial stellar pulsation models rely on an extra equation for turbulent kinetic energy and fail to adequately explain mode-selection problems. Since multidimensional calculations are computationally expensive, it is reasonable to search for generalizations of physically grounded 1D models that approximate multidimensional results with sufficient accuracy, at least in a given parameter range. A natural way of progressing from one-equation models is to use additional nonlocal equations. While these types of models also exist in the literature, they have not been adopted for this type of object. Aims. We aim to adapt the three-equation turbulent convection model from Kuhfuss to radial stellar pulsation modeling. Methods. We use a Reynolds-stress one-point closure approach to derive our extensions alongside the model, while using additional models from the literature to close the anisotropy and dissipation terms. Results. We provide five extensions to the original model. These include an enhanced dissipation correction to the mixing length, a local anisotropy model replacing eddy viscosity, a second-order correction for turbulent ion transport in the atmosphere (alongside opacity effects), and turbulent damping of entropy fluctuations and convective flux.