ENTRY FLOW AND CONSTITUTIVE MODELING OF FLUID S1

Experimental observations of the flow through an axisymmetric 4:1 cont raction for the shear-thinning test fluid S1 are presented. In order t o provide the basis for comparison with numerical simulations of the f low, the linear viscoelastic spectrum and the nonlinear parameters for three constitutive models are also obtained, based on the rheological characterisation of the fluid by Ooi and Sridhar [J. Non-Newtonian Fl uid Mech. 52 (1994) 121-135]. The Phen-Thien-Tanner model provides the best fit to the data, but a good fit can also be obtained for the Gie sekus model if the fit to the extensional stress growth coefficient is restricted to low strains. The results of flow visualisation experime nts are presented for the flow of S1 through a 4:1 axisymmetric contra ction with either an abrupt entry or a rounded re-entrant corner. The dimensionless vortex size increased with Weissenberg number for each g eometry, with a larger vortex observed for the abrupt entry geometry f or identical flow conditions. No elastic lip vortex or flow instabilit y was observed for We less than or equal to 5.0. (C) 1997 Elsevier Sci ence B.V.