Numerical Analysis of Viscoelastic Start-up Flow through a Slit

Part 1: Change of Velocity and Stress Fields with Time

Abstract

The transient flow behavior of viscoelastic fluids is studied. In the present paper, a start-up flow which is a typical unsteady flow is examined and the flow through a slit is numerically solved with FEM. The Leonov model is applied to describe the rheological properties of the viscoelastic fluids. The numerical simulations are carried out using two Weissenberg numbers in order to study the effect of elastic property of the fluid. The present simulation predicts viscoelastic phenomena such as the stress relaxation, the Barus effect and the growth of flow field with time. The difference of the flow patterns on the upstream and downstream sides of the slit becomes apparent with time because the stress is not perfectly relaxed in the slit region. This phenomenon appears more apparently at the higher Weissenberg number.