Archiviertes Physik-Kolloquium:

09. Jun. 2011, 16:15 Uhr, Gebäude NW1, Raum H3

Search for the "Ultimate State" in turbulent Rayleigh-Bénard convection

Prof. Dr. Guenter Ahlers , Deptartment of Physics, University of California at Santa Barbara

Many geophysical and astrophysical phenomena involve turbulent Rayleigh- Benard convection (RBC) at Rayleigh nymbers (dimensionless temperature differences) Ra > 1020. Laboratory studies of RBC for the most part have been limited to Ra < 10^12. It is expected theoretically that the basic physical processes involved in this phenomenon will change fundamentally for Ra near 10^14. Thus extrapolation from laboratory results to the parameter values characterizing many phenomena in nature at best is highly uncertain. This talk will report on efforts to extend the experimentally explored Ra range to Ra ~ 10^15. The experiments were carried out in a new facility for the study of RBC at the Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany. Measurements of the heat transport, in the dimensionless form of the Nusselt number Nu, over the Rayleigh-number range 10^11 < Ra < 10^15 using gaseous N2 and SF6 as the fluid have been obtained. They were made at pressures up to 19 bars for a cylindr