FLOW PAST A SPHERE ROTATING BETWEEN PARALLEL PLANES IN A BINGHAMPLASTIC FLUID

The torque on a sphere rotating inside a non-Newtonian, Bingham fluid has been calculated numerically. The sphere is placed between two parallel infinite planes, and the rotation axis is either perpendicular or parallel to planes. The Bingham number varied between 0 and 10 x 10(2); the Reynolds number varied between 1 and 2 x 10(2); and the gap between the planes from 1.1 to 2. In the region 0 <= Bn <= 1, the torque is sensitive to Reynolds number, a gap between the planes, and rotation axis. However, at high Bingham numbers (5.0 <= Bn) a thin ring of flowing fluid is formed around the sphere and the torque is independent of the Reynolds number, independent of the gap between the planes, and independent of rotation axis (vertical or horizontal).