Turbulent convection for different thermal boundary conditions at the plates. (25th November 2020)

• Record Type: Journal Article
• Authors: Foroozani, Najmeh; Krasnov, Dmitry; Schumacher, Jörg
• Is Part Of: Journal of fluid mechanics. Volume 907(2021)
• Publication Date: 2020-11-25
• Subjects: Bénard convection, -- boundary layer structure; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2020.830
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: Abstract : The influence of the different thermal boundary conditions at the bottom and top plates on the dynamics and statistics of a turbulent Rayleigh–Bénard convection flow is studied in three-dimensional direct numerical simulations. The flow evolves in a closed cylinder with an aspect ratio of $\varGamma =1/2$ in air for a Prandtl number $Pr=0.7$ and a Rayleigh number $Ra=10^7$ and in the liquid metal alloy GaInSn at $Pr=0.033$ and $Ra=10^7$, $10^8$ . We apply for each case three different thermal boundary conditions at the top and bottom of the fluid volume while leaving the solid sidewall thermally insulated: (i) fixed temperature, (ii) fixed heat flux and (iii) conjugate heat transfer which couples the temperature and heat flux in the working fluid to that of the finitely thick, solid plates enclosing the turbulent flow. The global heat transfer is enhanced by up to 19 % for the conjugate heat transfer case in comparison to that of isothermal plates. The differences decrease for the lower of the two Prandtl numbers; they remain generally smaller for the global turbulent momentum transfer. Mean temperature profiles and root mean square velocity fluctuations are surprisingly weakly affected. The largest difference appears for the distribution of local thermal boundary scales when the cases of fixed temperature and of conjugate heat transfer are compared. We also discuss our results in view to experimental uncertainties in liquid metal experiments.