Measurements of Velocity Fields Around Objects Moving in Non-Newtonian Liquids
Gas bubbles and solid objects moving under the influence of gravity in a non-Newtonian liquid are known to exhibit several interesting phenomena. For example Astarita and Apuzzo found that the terminal rise velocity vs. volume curve for single isolated air bubbles may exhibit a discontinuity at a certain “critical” volume, a phenomenon observed later by others2-4. Also Riddle, Narvaez and Bird have investigated the interaction between two identical spheres falling along their line of centers in a non-Newtonian liquid. They found that for small initial separations the two spheres eventually converge, while for large initial separations the two spheres eventually diverge. In the present study we have measured the axial component on the axis of gas bubbles and solid spheres moving in a non-Newtonian liquid. The most striking feature of the observed flow fields is the occurrence of a region in the wake behind the objects where the liquid velocity (referred to an observer at rest with respect to the liquid far from the objects) is in the direction opposite to that in which the object is moving. We have called this phenomenon “negative wake”.
KeywordsTest Section Liquid Velocity Axial Component Solid Sphere Test Fluid
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