The Investigation of Buoyant Flows in Differentially Heated Cavities

This combined experimental and numerical investigation focusses on the effects of angle of inclination on buoyancy-driven flows inside tall, rectangular, differentially-heated cavities. It considers a rectangular cavity with an aspect ratio of 28.6, with its two long sides maintained at different temperatures and the two short, end-walls, thermally insulated. The Rayleigh number, based on the temperature difference and spacing on the long sides is 0.86 x 106 and the working fluid is air (Prandtl number 0.71). Experimental data, for the flow and thermal fields from a 2.18m ×0.52m×0.0762m cavity, are presented for a cavity inclined at 60o to the horizontal, with the hot surfacebeing the upper surface, and also for a 15o inclination angle, with the hot surface the lower one. Twodimensional RANS computations are provided for a 60o and a 5o angle of inclination, with the hot surface being the upper one for both angles. A number of strategies are employed for the modelling of near-wall turbulence, including the analytical wall function (AWF) and also for the modelling of the turbulent stresses and heat fluxes. The experiments show that in the 60o stable case, the main differences from the vertical case are in the reduced levels of fluctuations of the velocity and temperature fields, while in the 15o unstable case, four longitudinal vortices are formed across the cavity which make the flow 3-dimensional and enhance mixing. Computations show that the AWF approach results in reliable flow and thermal predictions, while the prediction of temperature fluctuations improves with the introduction of 2nd-moment closures.