The Computation of Buoyant Flows in Differentially Heated Cavities

atural convection flows are often encountered both in nature and also in engineering applications. Turbulent natural convection flows, even in geometrically simple systems, can be physically very complex. The buoyant force, depending on the orientation of the temperature gradients, can either enhance or suppress turbulence. Earlier numerical studies of such flows, based on RANS1, found it necessary to use low-Reynolds-number models of turbulence, which need fine near-wall grids. This study explores the potential of a recently developed wall-function strategy for the economical and reliable prediction of natural convection flows. This strategy, AWF2, involves the use of large near-wall control volumes and the analytical solution of boundary-layer forms of the momentum and enthalpy equations, to provide wall boundary conditions for momentum, temperature and the turbulence parameters. The conventional wall-function strategy, based on the log-law, is also used for base-line comparisons The turbulent stresses are approximated through high-Reynolds- number turbulence models, which include the k- and 2nd-moment closures. In 2nd-moment closures, elaborate, approximations are employed for the modeling of the turbulent heat fluxes. extending to solution of equations for the temperature fluctuation and its dissipation rate. The proposed paper will include comparisons between RANS predictions that result from the use ofthese models and experimental data, for several cavities. One case is that of a square cavity3 with differentially heated vertical walls, Fig. 1. Nusselt number comparisons, such as those of Fig. 2, suggest that as theAWF provides a cost-effective alrernative to low-Reynolds number models. b1 Ince N Z and Launder B E, Int. Journal of Heat and Fluid Flow, 10, Np 2, pp 110-117, 1989 2 Craft T. J., Gerasimov A V, Iacovides H. and Launder B.E., International Journal of Heat and Fluid Flow, 23, 148-16,2002 3Ampofo, F. and Karayiannis, T.G., Int. J. of Heat and Mass Transfer 46, pp. 35513572, 2003.