Isotherms in a horizontal differentially heated cavity at intermediate Rayleigh numbers

Rayleigh-Benard convection in a horizontal, differentially heated, high asp ect ratio fluid layer is considered. Experiments with three Rayleigh number s (13900, 34800 and 51800) corresponding to different Row regimes have been performed. The temperature field in the fluid has been recorded in the for m of interferometric projections, the fringe patterns representing isotherm s. For steady and quasi-steady flow, the three dimensional temperature fiel d has been obtained using an iterative algebraic reconstruction technique. Results show the formation of longitudinal rolls in the cavity at a Rayleig h number of 13900. The flow is unsteady at a Rayleigh number of 34800, but a strong indication of the formation of cubic rolls is seen. At a Rayleigh number of 51800, the flow field is completely unsteady with no discernible pattern. The local ray-averaged Nusselt numbers at each of the heated and c ooled walls have been determined at the two lower Rayleigh numbers. The sys tematic variation of Nusselt number over each of the solid surfaces confirm s the flow models proposed at these Rayleigh numbers. The average Nusselt n umber qualitatively matches the published correlations. (C) 1999 Elsevier S cience Ltd.