Impact of radial truncation on global 2D hydrodynamic simulations for a Sun-like model

TL;DR

This study uses 2D global hydrodynamic simulations to examine how radial truncation affects convection, overshooting, and internal gravity waves in a Sun-like star, revealing boundary effects are significant at the outer edge.

Contribution

It demonstrates that the outer boundary location significantly influences stellar convection and wave dynamics, while the inner boundary has minimal impact, clarifying boundary effects in stellar simulations.

Findings

Outer boundary extension increases convection zone perturbations.

Inner boundary location has negligible effect on convection dynamics.

Boundary conditions at the outer edge significantly affect wave and overshoot properties.

Abstract

Stellar convection is a non-local process responsible for the transport of heat and chemical species. It can lead to enhanced mixing through convective overshooting and excitation of internal gravity waves (IGWs) at convective boundaries. The relationship between these processes is still not well understood and requires global hydrodynamic simulations to capture the important large-scale dynamics. The steep stratification in stellar interiors suggests that the radial extent of such simulations can affect the convection dynamics, the IGWs in the stably stratified radiative zone, and the depth of the overshooting layer. We investigate these effects using two-dimensional global simulations performed with the fully compressible stellar hydrodynamics code MUSIC. We compare eight different radial truncations of the same solar-like stellar model evolved over approximately 400 convective turnover times. We find that the location of the inner boundary has an insignificant effect on the convection dynamics, the convective overshooting and the travelling IGWs. We relate this to the background conditions at the lower convective boundary which are unaffected by the truncation, as long as a significantly deep radiative layer is included in the simulation domain. However, we find that extending the outer boundary by only a few percent of the stellar radius significantly increases the velocity and temperature perturbations in the convection zone, the overshooting depth, the power and the spectral slope of the IGWs. The effect is related to the background conditions at the outer boundary, which are determined in essence by the hydrostatic stratification and the given luminosity.