# Confined Rayleigh-B\'enard, Rotating Rayleigh-B\'enard, and Double Diffusive Convection: A unifying view on turbulent transport enhancement through coherent structure manipulation

## TL;DR

This paper demonstrates that in various Rayleigh-Bénard convection systems, moderate stabilizing forces can unexpectedly enhance turbulent transport by reorganizing flow structures, despite weakening overall flow motion.

## Contribution

It provides a unifying analysis of how different stabilizing forces can enhance turbulent flux in Rayleigh-Bénard convection through flow structure manipulation.

## Key findings

- Flux enhancement occurs at moderate stabilizing forces.
- Flow structures become more organized in the bulk.
- Transition in boundary layer thicknesses near optimal transport.

## Abstract

Many natural and engineering systems are simultaneously subjected to a driving force and a stabilizing force. The interplay between the two forces, especially for highly nonlinear systems such as fluid flow, often results in surprising features. Here we reveal such features in three different types of Rayleigh-B\'enard (RB) convection, i.e. buoyancy-driven flow with the fluid density being affected by a scalar field. In the three cases different {\it stabilizing forces} are considered, namely (i) horizontal confinement, (ii) rotation around a vertical axis, and (iii) a second stabilizing scalar field. Despite the very different nature of the stabilizing forces and the corresponding equations of motion, at moderate strength we counterintuitively but consistently observe an {\it enhancement} in the flux, even though the flow motion is weaker than the original RB flow. The flux enhancement occurs in an intermediate regime in which the stabilizing force is strong enough to alter the flow structures in the bulk to a more organised morphology, yet not too strong to severely suppress the flow motions. Near the optimal transport enhancements all three systems exhibit a transition from a state in which the thermal boundary layer (BL) is nested inside the momentum BL to the one with the thermal BL being thicker than the momentum BL.