The measurement of the flow around a sphere settling in a rectangular box using 3-dimensional particle image velocimetry

A novel three-dimensional particle image velocimetry technique is used to m easure the planar three-dimensional flow field about the centreline of a sp here sedimenting in a rectangular shaped box. Measurements are made in the center of the container and also one diameter from a plane wall. Results ar e presented for a sphere failing in both a constant viscosity elastic (Boge r) fluid and a shear-thinning elastic liquid. In the center of the box, the flow field is essentially two-dimensional as expected. Near the wall, ther e is substantial out-of-plane motion in the shear-thinning solution due to the presence of the wall. Surprisingly, there is little out-of-plane motion for a sphere sedimenting near the wall in the Boger fluid. There are signi ficant qualitative differences in the flow field for the sphere sedimenting in the shear-thinning and constant viscosity elastic liquids. The results are compared with previously published work for a sphere settling in a non- Newtonian fluid and also with results obtained in an identical geometry for a Newtonian fluid. Reasons for the differences in the velocity maps are di scussed. The drag coefficient for each geometry and fluid is calculated.