Finite Element Simulation of Unsteady Viscoelastic Flow by Using Leonov Model

Many numerical simulations for viscoelastic fluids have been carried out. Most of them deal with steady flows and there are few analyses dealing with unsteady flows. Transient behavior of viscoelastic flows in unsteady state is more complex than that of Newtonian flows. Further, such a behavior is often observed in polymer processing, such as injection molding and has an influence on the quality of products. In this respect, it is important to understand the properties of viscoelastic fluids in unsteady flow.In the present paper, unsteady viscoelastic flows were studied using the finite element method. The Leonov model has been used to represent the rheological behavior of viscoelastic fluid. We numerically analyzed a start-up flow problem in channels with 4:1 and 8:3 abrupt contraction for polystyrene STYRON 678 at 190°C, and obtained the predictions of transient behavior of velocity and stress fields. In the present paper, the results of velocity field are reported and in the second, stress field will be reported.The results obtained from the simulation are as follows, (1) overshoot in velocity near the contraction is predicted, and (2) vortex occurs in the corner region and the size of the vortex changes with time.