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How wide must Rayleigh–Bénard cells be to prevent finite aspect ratio effects in turbulent flow?

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Lohse,  Detlef
Max Planck Institute for Dynamics and Self-Organization, Max Planck Society;

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Citation

Stevens, R. J., Hartmann, R., Verzicco, R., & Lohse, D. (2024). How wide must Rayleigh–Bénard cells be to prevent finite aspect ratio effects in turbulent flow? Journal of Fluid Mechanics, 1000: A58. doi:10.1017/jfm.2024.996.


Cite as: https://hdl.handle.net/21.11116/0000-0010-4A00-B
Abstract
We employ direct numerical simulations to investigate the heat transfer and flow structures in turbulent Rayleigh-Benard convection in both cylindrical cells and laterally periodic domains, spanning an unprecedentedly wide range of aspect ratios 0.075 <=Gamma <= 32. We focus on Prandtl number Pr = 1 and Rayleigh numbers Ra = 2 x 10(7) and Ra = 10(8). In both cases, with increasing aspect ratio, the heat transfer first increases, then reaches a maximum (which is more pronounced for the cylindrical case due to confinement effects), and then slightly goes down again before it finally saturates at the large aspect ratio limit, which is achieved already at Gamma approximate to 4. Already for Gamma greater than or similar to 0.75, the heat transfers in both cylindrical and laterally periodic domains become identical. The large-Gamma limit for the volume-integrated Reynolds number and the boundary layer thicknesses are also reached at Gamma approximate to 4. However, while the integral flow properties converge at Gamma approximate to 4, the confinement of a cylindrical domain impacts the temperature and velocity variance distributions up to Gamma approximate to 16, as thermal superstructures cannot form close to the sidewall.