DOI: 10.1615/ICHMT.2012.ProcSevIntSympTurbHeatTransfPal
ISBN Print: 978-1-56700-302-4
ISSN: 2377-2816
Measurements of Reynolds number near the transition to the ultimate-state of turbulent Rayleigh−Bénard convection
ABSTRACT
A Reynolds number Reeff was measured in turbulent Rayleigh-Bénard convection (RBC) of a cylindrical sample over the Rayleigh-number range 1012 ≤ Ra ≤ 1015 and for Prandtl numbers Pr near 0.8 (He et al., 2012). The aspect ratio Γ ≡ D / L of the cylindrical sample was 0.50 (D = 1.12 m was the diameter and L = 2.24 m was the height). The measurements of Reeff were conducted at a distance L/4 above the bottom plate and 1.0 cm away from the sidewall inside the sample. For Ra ≤ 1013 the results showed Reeff α Raζeff with ζeff ≈ 0.43, consistent with classical turbulent RBC. After a transition region for 1013 ≤ Ra ≤ 5×1014, where multi-stability occurred, we found an exponent ζ ≈ 0.50, in agreement with the predictions of Grossmann and Lohse (2011) for the large-Ra asymptotic state. We believe that our measurements revealed the transition of RBC to the ultimate state predicted by Kraichnan (1962).