Volume 134, Number 3, May 2021
|Number of page(s)||7|
|Section||Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics|
|Published online||14 July 2021|
Effect of boundary conditions in turbulent thermal convection(a)
1 The Czech Academy of Sciences, Institute of Scientific Instruments - Královopolská 147, Brno, Czech Republic
2 Faculty of Mathematics and Physics, Charles University - Ke Karlovu 3, Prague, Czech Republic
Received: 6 May 2021
Accepted: 18 June 2021
We report an experimental study aiming to clarify the role of boundary conditions (BC) in high Rayleigh number turbulent thermal convection of cryogenic helium gas. We switch between BC closer to constant heat flux (CF) and constant temperature (CT) applied to the highly conducting bottom plate of the aspect-ratio-one cylindrical cell 30 cm in size, leading to dramatic changes in the temperature probability density function and in power spectral density of the temperature fluctuations measured at the bottom plate, while the dynamic thermal behaviour of the top plate and bulk convective flow remain unaffected. Within our experimental accuracy, we find no appreciable changes in Reynolds number Re(Ra) scaling, in the dimensionless heat transfer efficiency expressed via Nusselt number Nu(Ra) scaling, nor in the rate of direction reversals of large scale circulation.
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