Elusive transition to the ultimate regime of turbulent RBC: Dynamics of LSC in high-Ra cryogenic helium experiments
Abstract
Non Oberbeck-Boussinesq (NOB) effects may increase the heat transfer efficiency of turbulent Rayleigh-Bénard convection (RBC), when the top plate temperature approaches the saturation vapor curve (SVC) even far away from the critical point of the working fluid. Our recent experimental study using cryogenic 4He under conditions as close as possible to the Goettingen study using SF6 argues that the claim of having observed the transition to Kraichnan's ultimate Nu(Ra) scaling is likely due to NOB effects, and the important issue of transition to the ultimate state of RBC remains open. I will present here a detailed analysis of large-scale circulation (LSC) dynamics in the experiment. I will discuss dependences of the Reynolds numbers associated with LSC circulation and sloshing and of the LSC reversal frequency on the position in the p-T diagram of 4He, in particular on the boundary layer asymmetry due to NOB conditions near the SVC.
MEYS CR OPVVV CZ.02.2.69/0.0/0.0/18 070/0009944 (qCULTURA); Czech Science Foundation GACR 17-03572S.- Publication:
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APS Division of Fluid Dynamics Meeting Abstracts
- Pub Date:
- November 2019
- Bibcode:
- 2019APS..DFDH14001M