Investigating the Role of Radially Varying Diffusivities in Stellar Convection Modeling

Convection is ubiquitous in stellar and planetary interiors and is integral to the generation of their respective dynamos. These interiors remain hidden to direct observation. As a result, our understanding of interior convective phenomena largely comes from computational and theoretical models. In these models, radially varying forms of the viscous (𝛎) and thermal (𝞳) diffusivity are routinely utilized as an ad-hoc representation of the effects of subgrid scale motion. However, the values of even these diffusivities are constrained to unphysically high values due to computational limitations. Moreover, the different choices for the different functional forms of these diffusion coefficients can lead to very different behaviors in the fluid. To date, no systematic studies exist that compare the radially varying diffusivities and their effect on the dynamics within global convection zone simulations. We present results for a series of non-rotating solar-like convection models with varying radial functions for the diffusivities and differing boundary conditions. We show that alternative formulations for the diffusivity lead to different distributions of turbulence within the shell and that the kinetic energy scales similarly regardless of diffusivity. In contrast, the heat transfer is dependent on the functional form of the diffusivity and changes proportionately with the boundary conditions.