Summary: Plume Fragmentation by Bulk Interactions in Turbulent Rayleigh-BeŽnard Convection
and Guenter Ahlers1
Department of Physics, University of California, Santa Barbara, California 93106, USA
Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Gošttingen, 37073, Germany
(Received 21 October 2011; published 1 February 2012)
Using compressed gases with Prandtl numbers near 0.7, we obtained flow visualizations of turbulent
Rayleigh-BeŽnard convection in a cylindrical sample with an aspect ratio À D=L ffi 10 (D is the
diameter and L the height) by the shadowgraph method. Focusing on the plumes under the top plate,
we found that their length had a log-normal distribution, suggesting a fragmentation process.
Fragmentation events could be visually identified in the images and involved plume interactions with
bulk fluctuations or upwelling domain walls. We found the mean spacing between plumes to vary with the
Rayleigh number in proportion to the volume-averaged Kolmogorov length of the turbulent bulk
fluctuations, providing further evidence for plume-bulk interactions.
DOI: 10.1103/PhysRevLett.108.054501 PACS numbers: 47.27.te, 47.20.Bp, 47.20.Ib, 47.27.De
Turbulent flows generally are characterized by the time
and length scales of their spatial structures. Here we exam-