Spectral analysis of boundary layers in Rayleigh-Benard convection

Abstract

A combined experimental and numerical study of the boundary layer in a 4:1 aspect-ratio Rayleigh-Bénard cell over a four-decade range of Rayleigh numbers has been undertaken aimed at gaining a better insight into the character of the boundary layers. The experiments involved the simultaneous Laser Doppler Anemometry (LDA) measurements of fluid velocity at two locations, i.e. in the boundary layer and far away from it in the bulk, for Rayleigh numbers varying between $1.6\times 10^7$ and $2.4\times 10^9$. In parallel, direct numerical simulations (DNS) have been performed for the same configuration for Rayleigh numbers between $7.0\times 10^4$ and $7.7\times 10^7$. The temperature and velocity probability density functions and the power spectra of the horizontal velocity fluctuations measured in the boundary layer and in the bulk flow are found to be practically identical. Except for the smallest Rayleigh numbers, the spectra in the boundary layer and in the bulk central region are continuous and have a wide range of active scales. This indicates that both the bulk and the boundary layers are turbulent in the $\text{Ra}$ number range considered. However, molecular effects can still be observed and the boundary layer does not behave like a classical shear-driven turbulent boundary layer.

arXiv comment10 pages, 6 figures, Accepted for publication in Phys. Rev. E

References in corpus (3)

• Scaling in thermal convection: A unifying theory
• Thermal convection for large Prandtl numbers
• Probability density function of turbulent velocity fluctuation

Cited by in corpus (5)

• Boundary layer structure in turbulent thermal convection and its consequences for the required numerical resolution
• Wind and boundary layers in Rayleigh-Benard convection. I: analysis and modeling
• Anomalous diffusion as a stochastic component in the dynamics of complex processes
• Anomalous diffusion in the dynamics of complex processes
• Wind and boundary layers in Rayleigh-Benard convection. Part 2: boundary layer character and scaling