Counter-gradient heat transport in two-dimensional turbulent Rayleigh-Bénard convection

Abstract

We present high-resolution numerical investigations of heat transport by two-dimensional (2D) turbulent Rayleigh-Bénard (RB) convection over the Rayleigh number range $10^8⩽Ra⩽10^{10}$ and the Prandtl number range $0.7⩽Pr⩽10$. We find that there exist strong counter-gradient local heat flux with magnitude much larger than the global Nusselt number $Nu$ of the system. Two mechanisms for generating counter-gradient heat transport are identified: one is due to the bulk dynamics and the other is due to the competitions between the corner-flow rolls and the large-scale circulation (LSC). While the magnitude of the former is found to increase with increasing Prandtl number, that of the latter maximizes at medium $Pr$. We further reveal that the corner-LSC competitions lead to the anomalous $Nu$-$Pr$ relation in 2D RB convection, i.e. $Nu(Pr)$ minimizes, rather than maximizes as in three-dimensional cylindrical case, at $Pr\approx 2\sim 3$ for moderate $Ra$.

11 pages, 6 figures, Accepted by J. Fluid Mech. as a Rapids paper

References in corpus (11)

• Boundary layer structure in turbulent thermal convection and its consequences for the required numerical resolution
• Flow reversals in thermally driven turbulence
• A Comparison of Turbulent Thermal Convection Between Conditions of Constant Temperature and Constant Flux
• Flow reversals in turbulent convection via vortex reconnections
• Connecting flow structures and heat flux in turbulent Rayleigh-Bénard convection
• Rayleigh and Prandtl number scaling in the bulk of Rayleigh-Benard turbulence
• Flow states in two-dimensional Rayleigh-Bénard convection as a function of aspect-ratio and Rayleigh number
• Heat transport in boiling turbulent Rayleigh-Bénard convection
• Aspect ratio dependence of heat transport by turbulent Rayleigh-Bénard convection in rectangular cells
• Temporal evolution and scaling of mixing in two-dimensional Rayleigh-Taylor turbulence
• Horizontal Structures of Velocity and Temperature Boundary Layers in 2D Numerical Turbulent Rayleigh-Bénard Convection

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