An experiment combining flow visualization and temperature measurement is conducted in the present study to explore the inertia- and buoyancy-driven vortex flow resulting from a round air jet impinging onto a large confined heated horizontal circular disk. Particular attention is paid to examining the effects of Rej and Ra on the appearance of new vortex flow patterns. In this experiment the jet-disk separation distance is varied from 12.5 and 25.0 mm, the jet Reynolds number from 20 to 676, and the Rayleigh number from 0 to 7,340. The major results obtained in the present study can be briefly summarized in the following:
1. The results from the flow visualization for H=25.0 mm indicate that the vortex flow is characterized by the primary and/or secondary inertia-driven circular rolls along with several buoyancy-driven rolls. The number of the buoyancy induced rolls increases with the buoyancy-to-inertia ratio, which can vary from 1 to 5. Besides, at a low Gr/Rej2
slightly deformed circular buoyancy rolls prevail in the test section. For slightly higher Gr/Rej2 the flow is dominated by the highly deformed curved rolls. The roll pattern becomes somewhat irregular for a further increase in Gr/Rej2 . For all cases examined here the vortex flow is unsteady at long time after the initial transients have died out and is irregular to a certain degree since the buoyancy effect is rather strong for the large impinging plate tested here.
In addition to the roll deformation, the mutual pushing, merging and splitting of the buoyancy rolls occur nonperiodically in time. This unsteady and irregular vortex flow is also reflected in the data for the air
temperature variations with time. Some quantitative buoyancy-driven vortex flow characteristics such as the size and location of the buoyancy rolls are summarized and correlated empirically. Moreover, a flow regime map is provided to delineate various induced vortex flow patterns and the boundaries separating various vortex flow patterns are also correlated empirically.
2. When the jet-disk separation distance is reduced to 12.5 mm, circular waves traveling in the radial direction and radial vortex rolls appear in the confined impinging jet flow. These waves are somewhat deformed and are not axisymmetric. The radial rolls originate in the stagnation region of the impinging jet and grow in size in the radial direction. The size of the radial rolls is also nonuniform in the circumferential direction. Besides, the moving waves and radial rolls can coexist in the flow. Moreover, the ranges of the jet Reynolds number and Rayleigh numbers leading to the new vortex flow patterns are determined.
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