Problems of Astrophysical Turbulent Convection: Thermal convection in a layer without boundaries

TL;DR

This paper investigates turbulent thermal convection in a fluid layer without fixed boundaries, revealing how convection can occur in an unstably stratified region separated from boundaries, differing from traditional boundary-driven convection.

Contribution

It introduces a model of convection driven by internal heat sources in a boundary-free environment, highlighting the role of internal stratification in turbulent convection.

Findings

Convection initiates in an unstably stratified inner region.

Boundary absence does not hinder convection due to stratification separation.

Reversal of the temperature gradient occurs at lower amplitudes, disappearing at higher amplitudes.

Abstract

Thermal convection in fluid layers heated from below are usually realized experimentally as well as treated theoretically with fixed boundaries on which conditions for the temperature and the velocity field are prescribed. The thermal and velocity boundary layers attached to the upper and lower boundaries determine to a large extent the properties of turbulent convection at high Rayleigh numbers. Fixed boundaries are often absent in natural realizations of thermal convection. This paper studies the properties of convection driven by a planar heat source below a cooling source of equal size immersed in an otherwise stably stratified fluid layer are studied in this paper. Unavoidable boundaries do not influence the convection flow since they are separated from the active convection layer by nearly motionless stably stratified regions. The onset of convection occurs in an inner unstably stratified region where the mean temperature gradient is reversed. But the region of a reversed horizontally averaged temperature gradient disappears at higher amplitudes of convection such that the vertical derivative of the mean temperature no longer changes its sign.