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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Experimental and Numerical Investigation of the Flow Behind a Sphere Moving Vertically in a Stratified Fluid

Get access (open in a dialog) DOI: 10.1615/IHTC15.ipj.009047
pages 4595-4606

Résumé

The flow behind a sphere moving vertically downward at constant speeds in stratified fluids is investigated by both experiments and numerical simulations. In previous experiments using shadowgraph methods and dye visualizations, it has been found that a strong vertical ‘jet’ is generated downstream/upward of a descending sphere. In experiments, we measure the more details of density distributions in density boundary layers on the sphere and those in the jet, applying a laser-induced fluorescence (LIF) method to a salt-stratified fluid. Patterns of the jets and wakes in this phenomenon are determined by the Froude number Fr and the Reynolds number Re . Our results show that the width of the jet and the density boundary layer become thinner under stronger stratification. In general, the fluid dragged down by the sphere would finally return to its original height, and under strong stratification, the return would occur sooner since the buoyancy force is stronger. Therefore, the fluid volume dragged by the sphere becomes smaller. Thinner boundary layer explains also the thinner jet, since the latter is a continuation of the boundary layer across the rear/upper stagnation point of sphere. In numerical simulations, we have found that the radius of the jets is scaled by the square root of Fr/Re . Though the jet width observed by the experiment is narrower than that of the simulation, the experimental result also shows a linearity to the square root of the Froude number.