Three-equation turbulent convection models in classical variables

¹ ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, Szombathely Szent Imre h. u. 112. H-9700, Hungary
² HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly Observatory, MTA Centre of Excellence Konkoly Thege Miklós út 15-17. H-1121 Budapest, Hungary
³ Eötvös Loránd University, Institute of Physics and Astronomy Pázmány Péter sétány 1/a H-1117 Budapest, Hungary
⁴ MTA–HUN-REN CSFK Lendület “Momentum” Stellar Pulsation Research Group Konkoly Thege Miklós út 15-17. H-1121 Budapest, Hungary

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 27 August 2025
Accepted: 17 December 2025

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.