Instabilities in viscoelastic flow through an axisymmetric sudden contraction

Kinematics and dynamics of the viscoelastic flow in an axisymmetric 4:1 sud den contraction geometry are studied for a highly elastic polyisobutylene ( PIB) based polymer solution (referred to as PIB-Boger fluid). The critical conditions for the onset of the elastic instabilities and the dynamics of t he resulting secondary flows are measured for various flow rates. The spati o-temporal characteristics of the flow are determined by instantaneous pres sure measurements and streakline photography. The nonlinear dynamics of the global flow field both upstream and downstream of the contraction plane ar e systematically examined. New dynamic flow behavior and elastic instabilit ies downstream of the contraction plane are reported. It is shown that the instantaneous pressure measurements along with flow visualization can be us ed as an effective tool to characterize viscoelastic flows in complex geome tries. (C) 1999 Elsevier Science B.V. All rights reserved.