Viscoelastic contraction flows: comparison of axisymmetric and planar configurations

This is an experimental study, which investigates the behaviour of two constant-viscosity polymer solutions (so called Boger fluids) in both axisymmetric and planar contractions. To provide a means of investigating the role of fluid elasticity, experiments are also carried out on Newtonian liquids with the same shear viscosity as the Boger fluids. In the axisymmetric contractions, the experimental results are as expected, with so called vortex enhancement in the Boger fluids, associated with increased pressure losses due to viscoelasticity. Behaviour in the planar contractions for the same liquids is provocatively different from that found in the axisymmetric geometries. Now, vortex enhancement is absent. Furthermore, it is impossible to distinguish between the pressure-drop/flow-rate data for the Boger and Newtonian fluids. (C) 2002 Published by Elsevier Science B.V.