Regensburg 2019 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 5: Convection

DY 5.1: Invited Talk

Monday, April 1, 2019, 10:00–10:30, H3

Direct numerical simulations towards ultimate turbulence — •Richard Stevens¹, Roberto Verzicco², and Detlef Lohse^1,3 — ¹Physics of Fluids, University of Twente, Enshede, The Netherlands — ²University of Rome Tor Vergata, Roma, Italy — ³Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany

Both in experiments and simulations of Rayleigh-Bénard (RB) convection it is a major challenge to reach the ultimate regime in which the boundary layers transition from laminar to turbulent. In the ultimate regime the scaling exponent γ in the relation Nu ∼ Ra^γ, where Nusselt Nu is the dimensionless heat transport and Rayleigh Ra is the dimensionless temperature difference between the plates, increases. The critical Rayleigh number (Ra^*) for the transition to the ultimate regime has been observed in the Göttingen experiments around Ra^* ≈ 2 × 10¹⁴. So far, the highest Ra obtained in direct numerical simulations (DNS) is Ra=2 × 10¹² for aspect ratio Γ=0.5 (Stevens, Lohse, Verzicco, JFM 688, 31 (2011)). Here we present a comparison between the Göttingen experiments and DNS up to Ra=10¹³. We find perfect agreement between experiments and simulations, both for the heat transfer and for the mean and temperature variance profiles close to the sidewall. In addition, we discuss simulations for Γ=0.23 up to Ra=10¹⁴, which agree well with measurements by Roche et al., NJP 12, 085014 (2010). In addition, we discuss the influence of the aspect ratio on the heat transfer and flow structures in high Rayleigh number convection.