START-UP OF FLOW OF A FENE-FLUID THROUGH A 4 1/4 CONSTRICTION IN A TUBE/

The flow of a FENE-fluid through a 4:1:4 constriction in a tube is com puted by a split Lagrangian-Eulerian finite element method. In steady flow it is found that the upstream vortex grows with increasing Debora h number, while the down-stream vortex diminishes and disappears. The steady pressure drop decreases with Deborah number unless the finite e xtensibility L is quite small. Starting from rest at high Deborah numb er, the upstream vortex grows in two stages, each with their own time scales. A simple model of this growth is proposed. (C) 1997 Elsevier S cience B.V.