Convectons in unbalanced natural doubly diffusive convection

TL;DR

This paper investigates how localized convection patterns, called convectons, form and persist in natural doubly diffusive convection when the ideal balanced conditions are not met, revealing new behaviors in thermally dominated regimes.

Contribution

It extends understanding of convecton formation by analyzing the effects of unbalanced buoyancy forces and the emergence of anticonvectons in natural doubly diffusive convection.

Findings

Convectons bifurcate differently without a conduction state.

Anticonvectons are linked to localized convection rolls at the end-walls.

Localized states are robust against changes in buoyancy ratio.

Abstract

Fluids subject to both thermal and compositional variations can undergo doubly diffusive convection when these properties both affect the fluid density and diffuse at different rates. In natural doubly diffusive convection, the gradients of temperature and salinity are aligned with each other and orthogonal to gravity. The resulting buoyancy-driven flows are known to lead to the formation of a variety of patterns, including spatially localized states of convection surrounded by quiescent fluid, which are known as convectons. Localized pattern formation in natural doubly diffusive convection has been studied under a specific balance where the effects of temperature and salinity changes are opposite but of equal intensity on the fluid density. In this case, a steady conduction state exists and convectons bifurcate from it. The aforementioned buoyancy balance underpins our knowledge of this pattern formation but it is an ideal case that can hardly be met experimentally or in nature. This article addresses how localized pattern formation in natural doubly diffusive convection is affected by departures from the balanced case. In particular, the absence of a conduction state leads to the unfolding of the bifurcations to convectons. In thermally dominated regimes, the background flow promotes localized states with convection rolls attached to the end-walls, known as anticonvectons, and the existence of these states is found to be related to the emergence of convectons. The results presented here shed light on the convecton robustness against changes in the buoyancy ratio and extend the scope of our understanding of localized pattern formation in fluid systems.