Temperature Structure Functions in Turbulent Convection at Low Prandtl Number

1995 ◽  
Vol 32 (5) ◽  
pp. 413-418 ◽  
Author(s):  
S Cioni ◽  
S Ciliberto ◽  
J Sommeria
Keyword(s):  
Prandtl Number ◽  
Structure Functions ◽  
Turbulent Convection ◽  
Temperature Structure

scholarly journals Stellar Convection as a Low Prandtl Number Flow

1991 ◽  
Vol 130 ◽  
pp. 57-61
Author(s):  
Josep M. Massaguer
Keyword(s):  
Nusselt Number ◽  
Prandtl Number ◽  
Heat Transport ◽  
Large Scale ◽  
Shear Layers ◽  
Turbulent Convection ◽  
The Sun ◽  
Stellar Convection ◽  
Cool Stars ◽  
Number Flow

AbstractThermal convection in the Sun and cool stars is often modeled with the assumption of an effective Prandtl number σ ≃ 1. Such a parameterization results in masking of the presence of internal shear layers which, for small σ, might control the large scale dynamics. In this paper we discuss the relevance of such layers in turbulent convection. Implications for heat transport – i.e. for the Nusselt number power law – are also discussed.

scholarly journals Enhanced enstrophy generation for turbulent convection in low-Prandtl-number fluids

2015 ◽  
Vol 112 (31) ◽  
pp. 9530-9535 ◽  
Author(s):  
Jörg Schumacher ◽  
Paul Götzfried ◽  
Janet D. Scheel
Keyword(s):  
Kinetic Energy ◽  
Prandtl Number ◽  
Kinematic Viscosity ◽  
Isotropic Turbulence ◽  
Turbulent Convection ◽  
Principal Strain ◽  
Small Scale ◽  
Strain Rates ◽  
Mean Values ◽  
Liquid Mercury

Turbulent convection is often present in liquids with a kinematic viscosity much smaller than the diffusivity of the temperature. Here we reveal why these convection flows obey a much stronger level of fluid turbulence than those in which kinematic viscosity and thermal diffusivity are the same; i.e., the Prandtl number Pr is unity. We compare turbulent convection in air at Pr=0.7 and in liquid mercury at Pr=0.021. In this comparison the Prandtl number at constant Grashof number Gr is varied, rather than at constant Rayleigh number Ra as usually done. Our simulations demonstrate that the turbulent Kolmogorov-like cascade is extended both at the large- and small-scale ends with decreasing Pr. The kinetic energy injection into the flow takes place over the whole cascade range. In contrast to convection in air, the kinetic energy injection rate is particularly enhanced for liquid mercury for all scales larger than the characteristic width of thermal plumes. As a consequence, mean values and fluctuations of the local strain rates are increased, which in turn results in significantly enhanced enstrophy production by vortex stretching. The normalized distributions of enstrophy production in the bulk and the ratio of the principal strain rates are found to agree for both Prs. Despite the different energy injection mechanisms, the principal strain rates also agree with those in homogeneous isotropic turbulence conducted at the same Reynolds numbers as for the convection flows. Our results have thus interesting implications for small-scale turbulence modeling of liquid metal convection in astrophysical and technological applications.

Structure functions of temperature fluctuations in turbulent shear flows

1978 ◽  
Vol 84 (3) ◽  
pp. 561-580 ◽  
Author(s):  
R. A. Antonia ◽  
C. W. Van Atta
Keyword(s):  
Temperature Fluctuations ◽  
Structure Functions ◽  
Inertial Subrange ◽  
Turbulent Shear ◽  
Temperature Structure ◽  
Odd Order ◽  
Even Order ◽  
Inner Region ◽  
Heated Jet ◽  
Reynolds Number Dependence

Structure functions of turbulent temperature and velocity fluctuations are measured both for the atmosphere, in the surface layer over land, and for the laboratory, in the inner region of a thermal boundary layer and on the axis of a heated jet. Even-order temperature structure functions, up to order eight, generally compare favourably with the analysis of Antonia & Van Atta over the inertial subrange. The Reynolds number dependence of these structure functions, as predicted by the analysis, is in qualitative agreement with the measured data. Odd-order temperature structure functions depart significantly from the isotropic value of zero, particularly at large time delays. This departure is reasonably well predicted, over the inertial subrange, by postulating a simple ramp model for the temperature fluctuations. Assumptions involved in this model are directly tested by measurements in the heated jet. The ramp structure does not seriously affect either the even-order temperature structure functions or the mixed velocity-temperature functions, which include even-order moments of the temperature difference.

Effects of Prandtl number in two-dimensional turbulent convection

2021 ◽  
Author(s):  
Jian-Chao He ◽  
Ming-Wei Fang ◽  
Zhen-Yuan Gao ◽  
Shi-Di Huang ◽  
Yun Bao
Keyword(s):  
Prandtl Number ◽  
Turbulent Convection ◽  
Two Dimensional
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