Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

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 Ahlers^1,2 — ¹MPI-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 C_T(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.