Experimental investigation of buoyant flows in inclined differentially heated cavities

This experimental 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, using Laser Doppler anemomentry, and thermal fields, using thermocouple traverses, from a 2.18m 0.52m 0.0762m cavity are presented for a cavity inclined at 60o to the horizontal, with the hot surface being the upper surface and also for a 15o inclination angle, with the hot surface the lower one. For the latter case additional data are presented for a Rayleigh number of 1.54 x106. For moderate angles of inclination, under stable temperature stratification, the flow is two-dimensional and the effects of inclination are primarily confined to the fluctuating fields. For large angles of inclination with unstable temperature stratification, a set of four longitudinal vortices are formed over the entire length of the cavity, which make the dynamic field three-dimensional. The enhanced mixing at 15o leads to uniform temperature in the cavity core and thus only minor deviations from two-dimensionality in the thermal field. A modest rise in Rayleigh number does not affect the mean motion, but causes an increase in the normalised turbulence intensities, which in turn leads to a more uniform temperature within the cavity core and a practically two-dimensional thermal field.