Motion and stability of cones in a yield stress fluid

This experimental study focuses on the creeping flow of a shear thinning yield stress fluid around conical obstacles. The flow has been analyzed in steady state and with adherence conditions. Firstly, the influences of the cone apex angle and of the Oldroyd number, that is the ratio between plastic and viscous effects, on the drag coefficient have been analyzed. Correlations have been proposed to model the evolution of this coefficient as a function of these two parameters. The analysis provides a new alternative for measuring the yield stress. Then, the kinematic fields around the cones have been analyzed. These fields enable to describe the rigid zones and the sheared zone developing around the lateral edge of the cones as a function of the cone apex angle. Moreover, the wall shear stresses estimated from the particle image velocimetry measurements have enabled to quantify the contribution of the lateral drag force in the drag force. © 2014 American Institute of Chemical Engineers AIChE J, 61: 709–717, 2015