 
Summary: Under consideration for publication in J. Fluid Mech. 1
Heat transport by turbulent rotating
RayleighB´enard convection
Stephan Weiss and Guenter Ahlers
Department of Physics, University of California, Santa Barbara, CA 93106, USA
(Received 15 March 2011)
We report on the influence of rotation about a vertical axis on heat transport by turbulent
RayleighB´enard convection in a cylindrical vessel with aspect ratio D/L = 0.50 (D
is the diameter and L the height of the sample) and compare the results with those
for larger . The working fluid was water at Tm = 40 where the Prandtl number
Pr is 4.38. For rotation rates < 1 rad s1
, corresponding to inverse Rossby numbers
1/Ro between zero and twenty, we measured the Nusselt number Nu for six Rayleigh
numbers Ra in the range 2.2 × 109 < Ra < 7.2 × 1010
. For small rotation rates and at
constant Ra, the reduced Nusselt number Nured Nu(1/Ro)/Nu(0) initially increased
slightly with increasing 1/Ro, but at 1/Ro = 1/Ro0 0.5 it suddenly became constant or
decreased slightly depending on Ra. At 1/Roc 0.85 a second sharp transition occurred
in Nured to a state where Nured increased with increasing 1/Ro. We know from direct
numerical simulation that the transition at 1/Roc corresponds to the onset of Ekman
