Influence of Prandtl number on heat transfer over a permeable wall

Abstract

The work considers a fully turbulent flow with heat transfer in a channel half-filled with an array of cubes based on the work of Breugem and Boersma (2005) and Chandesris et al. (2013), at ${\mathrm{Re}}_{\mathrm{bulk}}=5485$ and three different Prandtl numbers, $\mathrm{Pr}=\mathrm{0.71,0.1,0.05}$. The temperature is modelled as a passive scalar and two different boundary condition configurations are simulated. The influence of the Prandtl number on the mean temperature, its variance and the terms of the temperature budget is highlighted, including the analysis of the distribution and relative importance of the turbulent heat transfer, molecular diffusion, tortuosity and Brinkman terms near the porous-fluid interface. The latter two have been found to be insignificant for the highest $\mathrm{Pr}$. A set of terms, typically neglected during the upscaling procedure (related to the Taylor expansion of the filtered variables), is analysed for the first time for turbulent heat transfer at the porous-fluid interface, and these terms are found to be significant at low $\mathrm{Pr}$. The upscaled fields are evaluated with three different cellular-average kernels: linear (i.e., tent), quadratic and cubic, and the influence of the chosen filter is additionally studied.