Johannes Bosbach, DLR Göttingen

Plume Fragmentation by Bulk Interactions in Turbulent Rayleigh-Bénard Convection

Using compressed gases with Prandtl numbers near 0.7, flow visualizations of turbulent Rayleigh-Bénard convection were obtained in a cylindrical sample with an aspect ratio Γ≡D/L≅10 (D is the diameter and L the height) by the shadowgraph method. Focusing on the plumes under the top plate, it was 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. The mean spacing between plumes was found 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.