On DNS and LES of natural convection of wall-confined flows: Rayleigh-Bénard convection

Turbulent natural convection of a fluid inside an enclosure heated from below (Rayleigh-Bénard convection), has been object of many theoretical and experimental investigations (Grötzbach,

1983

; Niemela et al.,

2000

). Over the past decades numerical simulations have become a powerful tool for providing extensive data in turbulence structures and flow dynamics, but flow statistics for DNS at relative high Ra numbers are still limited by insufficient time integration (Amati et al.,

2005

). In this sense, LES can be an attractive alternative for the resolution of natural convection problems at high Ra numbers. As LES models the smallest scales of the fluid their results are not only dependent on the grid resolution and the spatial and temporal discretization but also on the choice of the appropriate subgrid scale stress (SGS) model for describing the flow behavior. There are scarce long-term first and second order statistics results in literature for comparing LES results. Furthermore, time integration for most of the statistical data available does not guarantee their independence with the LSC reversals. Thus, the objective of this work is twofold: i) to provide useful long-term accurate statistical data by means of DNS of a cylindrical enclosure of aspect ratio (Γ=

D

/

H

) 0.5 at

Ra

=2×10

9

and

Pr

=0.7 and, ii) to assess the behavior of different LES models by direct comparison with our DNS results.