Velocity measurements in the free convection flow above a heated horizontal cylinder

The fluid dynamics of the free convection water flow above a heated horizontal cylinder were investigated using particle image velocimetry. Velocity measurements were obtained in three orthogonal planes, with each plane acquired independently in time. The experiment was performed for a Rayleigh number of 1.33 × 106 and for water heights above the cylinder surface of H/D = 1, 2, 4, 6, 8, and 12. The top water surface was open to room air, and the height of the free surface introduced different effects of vertical confinement. For all water heights studied, the plume above the cylinder and its interaction with the free surface were observed. For water heights of H/D = 4 and 6, the appearance of a swaying motion was captured in the plane perpendicular to the cylinder axis, and a meandering motion was detected in the other two orthogonal planes. A vortex was observed to form alongside of the plume and rise to the free surface, where it detached from the plume structure and moved along the free surface. Vortex dynamics and the physical characteristics of the swaying and meandering motions appeared to be interdependent, providing a possible relation between vortex formation, swaying, and meandering. Comparisons with previous analytical and experimental results highlight the complicated three-dimensional flow structure that governs heat transfer from the cylinder.