Wall-sheared thermal convection: heat transfer enhancement and turbulence relaminarization

Abstract

We studied the flow organization and heat transfer properties in two-dimensional and three-dimensional Rayleigh-Bénard cells that are imposed with different types of wall shear. The external wall shear is added with the motivation of manipulating flow mode to control heat transfer efficiency. We imposed three types of wall shear that may facilitate the single-roll, the horizontally stacked double-roll, and the vertically stacked double-roll flow modes, respectively. Direct numerical simulations are performed for fixed Rayleigh number $Ra=10^8$ and fixed Prandtl number $Pr=5.3$, while the wall-shear Reynolds number ($R{e}_w$) is in the range $60\le R{e}_w\le 6000$. Generally, we found enhanced heat transfer efficiency and global flow strength with the increase of $R{e}_w$. However, even with the same magnitude of global flow strength, the heat transfer efficiency varies significantly when the cells are under different types of wall shear. An interesting finding is that by increasing the wall-shear strength, the thermal turbulence is relaminarized, and more surprisingly, the heat transfer efficiency in the laminar state is higher than that in the turbulent state. We found that the enhanced heat transfer efficiency at the laminar regime is due to the formation of more stable and stronger convection channels. We propose that the origin of thermal turbulence laminarization is the reduced amount of thermal plumes. Because plumes are mainly responsible for turbulent kinetic energy production, when the detached plumes are swept away by the wall shear, the reduced number of plumes leads to weaker turbulent kinetic energy production. We also quantify the efficiency of facilitating heat transport via external shearing, and find that for larger $R{e}_w$, the enhanced heat transfer efficiency comes at a price of a larger expenditure of mechanical energy.

27 pages, 16 figures

References in corpus (9)

• Flow states in two-dimensional Rayleigh-Bénard convection as a function of aspect-ratio and Rayleigh number
• Controlling heat transport and flow structures in thermal turbulence using ratchet surfaces
• Heat transport in boiling turbulent Rayleigh-Bénard convection
• Multi-GPU thermal lattice Boltzmann simulations using OpenACC and MPI
• Correlation of internal flow structure with heat transfer efficiency in turbulent Rayleigh-Bénard convection
• The effect of Prandtl number on turbulent sheared thermal convection
• Tristable flow states and reversal of the large-scale circulation in two-dimensional circular convection cells
• What rotation rate maximizes heat transport in rotating Rayleigh-Bénard convection with Prandtl number larger than one?
• Heat transfer enhancement in Rayleigh-Bénard convection using a single passive barrier

Cited by in corpus (3)

• Particle-resolved thermal lattice Boltzmann simulation using OpenACC on multi-GPUs
• Optimization study of a Z-type airflow cooling system of a lithium-ion battery pack
• Particle transport and deposition in wall-sheared thermal turbulence