Effect of boundary conditions in turbulent thermal convection

We report an experimental study aiming to clarify the role of boundary conditions (BC) in high Rayleigh number 10(8) < Ra < 3 x 10(12) 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. Copyright (C) 2021 The author(s)

Automated summary

This experimental study focused on the role of boundary conditions in turbulent thermal convection of cryogenic helium gas at high Rayleigh numbers. Switching between constant heat flux and constant temperature boundary conditions resulted in significant changes in temperature fluctuations at the bottom plate, while top plate dynamics and bulk convective flow remained unaffected. There were no observable changes in Reynolds number scaling, Nusselt number scaling, or rate of direction reversals of large scale circulation within the experimental accuracy.