Crossover of the relative heat transport contributions of plume ejecting and impacting zones in turbulent Rayleigh-B\'enard convection

TL;DR

This study uses 2D numerical simulations to identify a crossover in heat transport mechanisms in turbulent Rayleigh-Bénard convection, from impacting to ejecting plume zones, driven by the development of a turbulent mixing zone.

Contribution

It reveals a specific Rayleigh number where the dominant heat transfer mechanism shifts, linking this crossover to the growth of a turbulent mixing zone in 2D convection.

Findings

Crossover in heat transport at Ra ≈ 3×10^11.

Development of a turbulent mixing zone causes the shift.

Results consistent with lower Ra 3D convection trends.

Abstract

Turbulent thermal convection is characterized by the formation of large-scale structures and strong spatial inhomogeneity. This work addresses the relative heat transport contributions of the large-scale plume ejecting versus plume impacting zones in turbulent Rayleigh-B\'enard convection. Based on direct numerical simulations of the two dimensional (2-D) problem, we show the existence of a crossover in the wall heat transport from initially impacting dominated to ultimately ejecting dominated at a Rayleigh number of $Ra\approx 3 \times 10^{11}$. This is consistent with the trends observed in 3-D convection at lower Ra, and we therefore expect a similar crossover to also occur there. We identify the development of a turbulent mixing zone, connected to thermal plume emission, as the primary mechanism for the crossover. The mixing zone gradually extends vertically and horizontally, therefore becoming more and more dominant for the overall heat transfer.