Monday, January 07, 20133:00 PM - 4:00 PMCNLS Conference Room (TA-3, Bldg 1690)|
Turbulent convection at very high Rayleigh and Taylor numbers
Joe NiemelaICTP Trieste
Turbulence is widespread, indeed almost the rule in the flow of fluids. Of these turbulent convection is perhaps the most prominent, playing a major role in the energy transport within stars in addition to atmospheric and oceanic circulations, the generation of the earth's magnetic field and countless engineering processes in which heat transport is important. The talk will cover the motivation and recent observations for controlled laboratory experiments of a simplified, well-characterized system, namely Rayleigh-Benard convection, at extreme values of the principal control parameters. These parameters-- the Rayleigh number and the Taylor number (with rotation)-- are made large by using helium near its critical point at 5.2K. It turns out that properties of metals at low temperatures play a very important role here, producing near-ideal boundary conditions on the heated surfaces necessary for sustaining the time-dependent production of plumes at the highest Rayleigh numbers, as well as allowing for novel experiments otherwise difficult or impossible at room temperature. One example is the generation and detection of high frequency heat waves propagated into the bulk, which has been used to directly measure an effective diffusivity of the turbulence, and where comparison to standard, static measurements of the heat transfer has revealed a number of interesting surprises.
Host: Bob Ecke, CNLS