A k-omega model for stellar turbulent convection

Abstract

Both observations and numerical simulations show that stellar convective motions are composed of semi-regular flows of convective rolling cells and the fully developed turbulence. Although the convective rolling cells are crucial for the properties of the stellar convection that transports heat and mixes materials in the stellar interior, their contributions have not been included in turbulent convection models proposed up to now. We simplify the structure of the convective rolling cells as a cellular pattern moving circle by circle with different angular velocities around the center, estimating their typical size by solving approximately for the temperature difference over the stationary temperature background and their average shear of velocity by evaluating approximately their kinetic energy transformed by themselves working as thermal engines from the heat involved in the convective rolling cells. We obtain a steady state solution in the fully local equilibrium which is similar to what is obtained in the standard mixing-length theory, by applying such model assumptions to the standard $k$-$\varepsilon$ model and properly choosing the model parameter $c_{\varepsilon 3}$. Accordingly, we propose a $k$-$ω$ model to include the transport effect of turbulence in stars. Preliminary results of their applications to the sun and other stars with different masses and in different evolutionary stages show good agreements with results of the standard mixing-length theory and results of numerical simulations for the stellar convection.