Rotation of a sphere in a viscoelastic fluid under flow

The rotation speed of spherical particles in a shear flow is studied experimentally in rheologically different fluids. The fluids, selected to highlight specific constitutive features, include a Newtonian fiuid, a Boger fluid, a wormhke micellar surfactant solution, and a shear thinning elastic polymer solution. It is shown experimentally that particle rotation slows down, when compared to the Newtonian case, as elasticity increases. This is in qualitative agreement with TFEM simulation studies. Furthermore, the dimensionless rotation speed of the spheres in the different fluids as function of the elasticity of the medium scales onto a single curve. This scaling with the Weissenberg number was somewhat unexpected given simulation results for different rheological models, where significant differences are observed for selected single relaxation time differential models