Global and local statistics in turbulent convection at low Prandtl numbers

Abstract

Statistical properties of turbulent Rayleigh-Benard convection at low Prandtl numbers (Pr), which are typical for liquid metals such as mercury, gallium or liquid sodium, are investigated in high-resolution three-dimensional spectral element simulations in a closed cylindrical cell with an aspect ratio of one and are compared to previous turbulent convection simulations in air. We compare the scaling of global momentum and heat transfer. The scaling exponents are found to be in agreement with experiments. Mean profiles of the root-mean-square velocity as well as the thermal and kinetic energy dissipation rates have growing amplitudes with decreasing Prandtl number which underlies a more vigorous bulk turbulence in the low-Pr regime. The skin-friction coefficient displays a Reynolds-number dependence that is close to that of an isothermal, intermittently turbulent velocity boundary layer. The thermal boundary layer thicknesses are larger as Pr decreases and conversely the velocity boundary layer thicknesses become smaller. We investigate the scaling exponents and find a slight decrease in exponent magnitude for the thermal boundary layer thickness as Pr decreases, but find the opposite case for the velocity boundary layer thickness scaling. A growing area fraction of turbulent patches close to the heating and cooling plates can be detected by exceeding a locally defined shear Reynolds number threshold. This area fraction is larger for lower Pr at the same Ra. Our analysis of the kurtosis of the locally defined shear Reynolds number demonstrates that the intermittency in the boundary layer is significantly increased for the lower Prandtl number and for sufficiently high Rayleigh number compared to convection in air. This complements our previous findings of enhanced bulk intermittency in low-Prandtl-number convection.

References in corpus (4)

• A Comparison of Turbulent Thermal Convection Between Conditions of Constant Temperature and Constant Flux
• Comparison between two and three dimensional Rayleigh-Bénard convection
• Local boundary layer scales in turbulent Rayleigh-Benard convection
• Dissipation Layers in Rayleigh-Bénard Convection: A Unifying View

Cited by in corpus (6)

• Thermal Rayleigh-Marangoni convection in a three-layer liquid-metal-battery model
• Transitional boundary layers in low-Prandtl-number convection
• Mean Temperature Profiles in Turbulent Thermal Convection
• Heat and momentum transfer for magnetoconvection in a vertical external magnetic field
• Predicting transition ranges to turbulent viscous boundary layers in low Prandtl number convection flows
• The transition to the ultimate regime of thermal convection from a stochastic one-dimensional turbulence perspective