Numerical simulation of turbulence sharply arising in a free convection vertical-plate boundary layer behind a row of rectangular protuberances

The present paper covers results of direct numerical simulation of turbulence sharply arising in a vertical-plate free convection boundary layer of air behind a periodic row of 3D rectangular obstacles, which height is comparable with the thickness of the oncoming laminar layer. The obtained computational data are used first to estimate the length needed for adaptation of the artificially induced turbulence to its natural state corresponding to the quasi-equilibrium turbulent free convection boundary layer on an isothermally heated flat plate. Then, the characteristic flow profiles calculated for the quasi-equilibrium turbulent flow region are compared with the experimental data reported by Tsuji&Nagano [1]. A good agreement between the computer-generated and the measurement results has been established for both the first-order and the second-order statistics. Finally, predicted values of the local Nusselt number, Nux, versus the local Rayleigh number, Rax, are presented. Comparing to the natural transition case, a rather significant heat transfer augmentation is achieved within the Rax interval from 0.6·108 to about 0.3·109.