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Logarithmic Mean Temperature Profiles and Their Connection to Plume Emissions in Turbulent Rayleigh-Bénard Convection.

Research paper by Erwin P EP van der Poel, Rodolfo R Ostilla-Mónico, Roberto R Verzicco, Siegfried S Grossmann, Detlef D Lohse

Indexed on: 10 Nov '15Published on: 10 Nov '15Published in: Physical review letters



Abstract

Two-dimensional simulations of Rayleigh-Bénard convection at Ra=5×10^{10} show that vertical logarithmic mean temperature profiles can be observed in regions of the boundary layer where thermal plumes are emitted. The profile is logarithmic only in these regions and not in the rest of the boundary layer where it is sheared by the large-scale wind and impacted by plumes. In addition, the logarithmic behavior is not visible in the horizontal average. The findings reveal that the temperature profiles are strongly connected to thermal plume emission, and they support a perception that parts of the boundary layer can be turbulent while others are not. The transition to the ultimate regime, in which the boundary layers are considered to be fully turbulent, can therefore be understood as a gradual increase in the fraction of the plume-emitting ("turbulent") regions of the boundary layer.