Drag of an isolated cylinder and interactions between two cylinders in yield stress fluids

The drag force of two interacting cylinders moving at very low controlled velocity in yield stress fluids was measured. The influence of the distance separating them was evaluated. The two cylinders are parallel, one in the wake of the other. The drag force on an isolated cylinder was studied and is used as reference. Correlations for predicting the drag coefficient and stability criterion are proposed. Special attention was paid to the fluid–cylinder interfaces, as they govern the adherence and slip of the fluid at the wall. Their influence on the drag coefficient was quantified. The experimental results are compared with the theoretical or numerical predictions for a yield stress fluid. These results show that the yield stress reduces the extent of the interactions in comparison with the Newtonian fluid case.