Ultimate heat transfer in turbulent permeable-channel flow

Genta Kawahara
Osaka University
Graduate School of Engineering Science

Direct numerical simulations have been performed for turbulent heat and momentum transfer in permeable-channel flow, on which consistent thermal and mechanical conditions are imposed. On the permeable wall surface the transpiration velocity is assumed to be proportional to the local pressure fluctuations (Jimenez et al. 2001 J. Fluid Mech. 442, 89-117). Turbulent heat and momentum transfer has been found to be substantially enhanced by the appearance of large-scale spanwise rolls from the Kelvin-Helmholtz instability of a shear layer on the permeable wall. At high Reynolds numbers we have achieved the ultimate heat transfer represented by a wall heat flux being independent of thermal conductivity, although the heat transfer on the wall is dominated by thermal conduction. The key to the ultimate heat transfer is interpreted in terms of significant heat transfer enhancement by large-scale intense turbulence of comparable length and velocity scales to the channel height and the bulk-mean velocity, respectively, without flow separation on the permeable wall.

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