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Investigation of local turbulent heat transport in Rayleigh-Benard convection by means of DNS and LES

DOI: 10.1615/ICHMT.2006.TurbulHeatMassTransf.1040
pages 503-506

Olga Shishkina
DLR - Institute for Aerodynamics and Flow Technology, Bunsenstrasse 10, 37073 Göttingen, Germany

Claus Wagner
German Aerospace Center (DLR), Institute for Aerodynamics and Flow Technology, Bunsenstrasse 10, 37073 Göttingen, Germany; Ilmenau University of Technology, Institute of Thermodynamics and Fluid Mechanics, Germany

Abstract

Vertical heat flux Ω in turbulent Rayleigh-Benard convection [1],[2] is studied based on data obtained in Direct Numerical Simulations (DNS) for Rayleigh numbers Ra = 106 and 107 and Large-Eddy Simulation (LES) for Ra = 108. The well resolved LES uses the tensor-diffusivity model [3] together with the top-hat filter. In all simulations the Prandlt number and the aspect ratio of the cylindrical container are Pr = 0.7 and Γ = 5, respectively.
An analysis of the spatial distribution of the vertical heat flux shows that the volume of the fluid with negative Ω-values increases with the Rayleigh number and fills out one third of the total volume for Ra = 108. With growing Ra the zones with high values of the mean local heat flux (averaged in time and in azimuthal direction) nestle closer to the corners, where the horizontal and vertical walls intersect. For the considered Rayleigh numbers and Γ = 5 it is shown that the portion of the whole domain, in which the thermal dissipation rate is relatively small, increases with Ra. Earlier a similar result was obtained for Γ = 10 [4]. These observations support the conjecture by Grossmann and Lohse [2] that the background part of the thermal dissipation rate increases with the Rayleigh number.

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