Limiting regimes of turbulent horizontal convection. Part I: Intermediate and low Prandtl numbers

TL;DR

This paper identifies two new turbulent regimes in horizontal convection at intermediate and low Prandtl numbers, revealing how turbulence affects heat and momentum transport and linking theoretical models to extend the regime diagram.

Contribution

It introduces two new turbulent regimes in horizontal convection at low Prandtl numbers and integrates existing theories to extend the regime diagram at high Rayleigh numbers.

Findings

Discovery of two new turbulent regimes in horizontal convection.

HC and Rayleigh-Bénard share similar turbulence characteristics at low Prandtl numbers.

Fully turbulent HC enhances heat and momentum transport.

Abstract

We report the existence of two new limiting turbulent regimes in horizontal convection (HC) using direct numerical simulations at intermediate to low Prandtl numbers. The flow driven by a horizontal gradient along a horizontal surface, perpendicular to the acceleration of gravity is shown to transition to turbulence in the plume and the core, modifying the rate of heat and momentum transport. These transitions set a sequence of scaling laws blending the theoretical arguments from both the Shishkina, Grossmann & Lohse (SGL) theory with the Hughes, Griffiths & Mullarney (HGM) regime. These results embed the HGM model in the SGL theory, agree, and extend the known regime diagram of horizontal convection at high Rayleigh numbers. In particular, we show that HC and Rayleigh-B\'enard share similar turbulent characteristics at low-Prandtl numbers, where HC is shown for the first time to be ruled by its core dynamics and turbulent boundary layers. This new scenario confirms that fully turbulent HC enhances the transport of heat and momentum with respect to previously reported regimes at high Rayleigh numbers. This work provides new insights on the applicability of horizontal convection for geophysical flows such as overturning circulations found in the atmosphere, the oceans, and flows near the earth's inner core.