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Analysis and correlation of fluid motions in natural thermal convection in a cylindrical vessel

A natural thermal convection system is set up in a cylindrical vessel with aspect ratio of 2 having a temperature gradient in the vertical direction, and the fluid motions due to convection are investigated. The 2-dimensional velocity field along the plane passing through the diameter of the vessel is obtained using particle image velocimetry. The results indicate that the convection is in the transition stage and the mean velocity fields show two pairs of counter-rotating circulations. The mean motions are predominant in the vertical direction under the influence of the temperature gradient, while the fluctuations in the x and y directions have the same order of magnitude. Probability density functions of fluctuation velocities at seven characteristic points show different behaviors. The space-time correlations in the regions where the circulations interact exhibit the iso-correlation lines predicted by the elliptical approximation hypothesis. The space-time correlations of the stream wise and vertical fluctuations show distinct movements which imply the existence of anisotropy around the interaction region.
PAPER REVISED: 2018-09-10
PAPER ACCEPTED: 2018-11-10
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