Flow of a Non-Newtonian Liquid Around a Sphere

When a sphere is pulled through a liquid with a yield stress, a fluidized region near the sphere is formed. Based on computer simulations, this region can be described as spindle torus shape. To determine the size of the fluidized region, we pulled steel spheres through tubes of different diameters filled with a non-Newtonian fluid. By measuring the drag force on the sphere as a function of container size we determined the extent of the fluidized region surrounding the sphere. Also, we found that the drag force is not proportional to the velocity, as it is for Newtonian fluids. To study the shape of the fluidized region around the sphere, poppy seeds were scattered throughout the non-Newtonian liquid. Using particle tracking techniques we tracked the position of the poppy seeds and visualized the fluidized region as a steel sphere moved through the liquid.