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DY: Fachverband Dynamik und Statistische Physik

DY 29: Focus Session: Rayleigh Benard System and Convective Turbulence

DY 29.3: Hauptvortrag

Donnerstag, 14. März 2013, 16:00–16:30, H44

Temperature statistics near the ultimate state of turbulent Rayleigh-Bénard convection * — •Xiaozhou He1, Dennis van Gils1, Eberhard Bodenschatz1, and Guenter Ahlers1,21MPI-DS, Goettingen, Germany — 2UCSB, USA

We report on the study of temperature statistics in turbulent Rayleigh-Bénard convection (RBC) for Ra up to 1015 and for Pr ≃ 0.8. The experiment had been conducted in a pressure vessel known as the “Uboot" of Göttingen with compressed sulfur hexafluoride (SF6) at a pressure up to 19 bars. We used two upright cylindrical RBC samples with the same diameter D=112 cm but different heights L=112 and 224 cm, corresponding to aspect-ratios Γ ≡ D/L=1.00 and 0.50 respectively.

Using the elliptical approximation, we derived local velocities from temperature space-time cross-correlation functions CT(r,τ) and found a Gaussian distribution for velocity fluctuations. We also determined an effective Reynolds number in both samples and observed a transition from the classical state to the ultimate state of turbulent RBC1 near Ra ≃ 1014, which agrees with the prediction by GL 2. Finally, we observed the Kolmogorov −5/3 scaling in temperature energy spectra E(k), E(k) ∼ k−5/3, above Ra ≃ 1014 in both samples.

1 X. He, D. Funfschilling, H. Nobach, E. Bodenschatz and G. Ahlers, Phys. Rev. Lett. 108, 024502 (2012)

2 S. Grossmann and D. Lohse, Phys. Rev. E 66, 016305 (2002)

* Supported by the Max Planck Society, the Volkswagen Stiftung, the DFG SFB963, and NSF grant DMR11-58514.

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DPG-Physik > DPG-Verhandlungen > 2013 > Regensburg