Oscillatory pipe flows of a yield-stress fluid

Oscillatory pipe flows of aqueous Carbopol solutions are investigated both experimentally and analytically. Using the PIV technique, the velocity profiles are measured and compared with the numerical solutions based on an elasto-viscoplastic rheological model, in which an elastic spring is serially connected to a regularized Bingham viscoplastic model. The rheological parameters, such as shear modulus of elasticity, yield stress and viscosity, are estimated from steady-shear measurements. Good agreement between the experiments and the model results is observed. It is apparent that the elasticity plays an important role in the unsteady flows of the soft yield-stress fluid studied herein.