Thermal boundary layer dynamics in low-Prandtl-number Rayleigh–Bénard convection

• Published in: Journal of fluid mechanics 2024-09, Vol.994, Article A4
• Main Authors: Kim, Nayoung, Schindler, Felix, Vogt, Tobias, Eckert, Sven
• Format: Article
• Language: English
• Subjects: Arrays; Aspect ratio; Boundary layer thickness; Boundary layers; Casting; Cold; Convection; Convection cells; Copper; Heat; Heated water; JFM Papers; Liquid metals; Prandtl number; Probability distribution; Rayleigh number; Rayleigh-Benard convection; Scaling; Sensors; Temperature; Thermal boundary layer; Thermal plumes
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2024.629

In this experimental study, we explore the dynamics of the thermal boundary layer in liquid metal Rayleigh–Bénard convection, covering the parameter ranges of $0.026 \leq$ Prandtl numbers $(Pr) \leq 0.033$ and Rayleigh numbers ($Ra$) up to $2.9\times 10^9$. Our research focuses on characterising the thermal boundary layer near the top plate of a cylindrical convection cell with an aspect ratio of 0.5, distinguishing between two distinct regions: the shear-dominated region around the centre of the top plate and a location near the side wall where the boundary layer is expected to be affected by the impact or ejection of thermal plumes. The dependencies of the boundary layer thickness on $Ra$ at these positions reveal deviating scaling exponents with the difference diminishing as $Ra$ increases. We find stronger fluctuations in the boundary layer and increasing deviation from the Prandtl–Blasius–Pohlhausen profile with increasing $Ra$, as well as in the measurements outside the centre region. Our data illustrate the complex interplay between flow dynamics and thermal transport in low-$Pr$ convection.