1. The intensity of turbulent convection in a fluid heated from below is characterized by a dimensionless parameter known as the Rayleigh number Ra. This number is proportional to a combination of fluid properties, to the cube of the sample height L, to the applied temperature difference, and to the gravitational acceleration. Many natural and industrial processes involve very large Ra, up to Ra ~ 10 22 or so. Most laboratory investigations have been for Ra <10 12. In an attempt to reach large Ra, investigators have used fluid helium at low temperatures which has favorable properties. Unfortunately two separate investigations, one in Grenoble, France and the other in Eugene, Oregon, led to contradictory results for Ra > 10 11. The Grenoble results showed a transition in the heat transport near Ra = 10 11 ; there was no transition in the Oregon data. In collaboration with the Max Planck Institute for Dynamics and Self- Organization in Goettingen, Germany, and with support from this NSF grant, we built a very large convection cell, with height L = 2.2 m, that could be inserted in a very large pressure vessel known as the “Uboot of Goettingen” (see figure). We made measurements of the heat transport using sulfur hexafluoride at pressures up to 19 bars. The properties of this fluid and the large height both favor large Ra, and we reached Ra = 2x10 15. Our results are inconsistent with the Grenoble data and fall somewhat below the Oregon data. They reveal an unanticipated new transition near Ra = 6x10 13 which remains to be understood. Note that at Ra = 2x10 15 the heat transport is a factor of 4000 larger than that of the quiescent fluid! However, we are still a long way from the astrophysically relevant values of Ra up to 10 22 or so (see next slide). "Search for the "ultimate state" in turbulent Rayleigh-Benard convection", D. Funfschilling, E. Bodenschatz, and G. Ahlers, Phys. Rev. Lett. 103, 014503 (2009). “Turbulent Convection”, G. Ahlers, Physics, in print (Sept. 2009) Turbulent Convection Guenter Ahlers, University of California-Santa Barbara, DMR 0702111 Left: The High-Pressure Convection Facility, weighing approximately 2000 kg, is being inserted into the turret of the Uboot. Below: The turbulent heat transport (ratio of the effective conductivity to the diffusive conduc- tivity) as a function of the Rayleigh number Ra. Green stars: Grenoble data Purple stars: Oregon data. Black circles” This work.

2. Turbulent Convection Guenter Ahlers, University of California-Santa Barbara, DMR 0702111 Granules and a Sunspot in the Sun's photosphere, observed on August 8, 2003 by Göran Scharmer and Kai Langhans with the Swedish 1-m Solar Telescope operated by the Royal Swedish Academy of Sciences. Turbulent convection plays a major role in numerous natural and industrial processes. It occurs in Earth's outer core, atmosphere, and oceans, and is found in the outer layer of the sun and in giant planets. A beautiful example is seen in the photosphere of the Sun (see the Figure), where a dominant feature is an irregular polygonal pattern of bright areas surrounded by darker boundaries. These granules are convection cells with a width of typically 1000 km; they fluctuate constantly and have a lifetime of only about 10 to 20 minutes. Convection occurs as well in the Earth’s Mantle where it causes continental drift which in turn leads to earth quakes and vulcanism. Turbulent convection is of great importance in the cooling of nuclear reactors as well as in many other industrial processes. Pu'u O'o is an active vent on Kilauea volcano in Hawaii. From http://www.fema.gov/ Reactors and cooling towers at the SusquehannaSusquehanna Steam Electric Station south of Shickshinny, Pennsylvania.Shickshinny, Pennsylvania From Wikipedia.