NUMERICAL-SIMULATION OF CONFINED FLOW OF POLYETHYLENE MELTS AROUND A CYLINDER IN A PLANAR CHANNEL

Numerical simulations have been undertaken for the flow of three polye thylene melts, two low-density (LDPE) and a linear low-density (LLDPE) , around a cylinder placed between parallel plates. Polyethylene melts have been the subject of previous extensive rheological characterizat ions. The flow geometry corresponds to a 2:1 and a 1.6:1 gap/diameter ratio used in experimental studies for flow-induced birefringence (FIB ) measurements. The constitutive equation of this work is an integral- type K-BKZ model with a relaxation spectrum, which fits well experimen tal data for the shear viscosities and the normal stresses as measured in shear flow. The model has been properly modified to account for st rain-thickening in planar extensional flows, such as those studied her e. Stable numerical solutions have been obtained for a wide range of f low rates and used to compare the K-BKZ model predictions with the exp erimental observations for FIB. Good agreement is obtained for the bir efringence predictions in all cases, provided that the right amount of strain-thickening has been assumed for the planar extensional viscosi ty. The simulations are also in agreement with previous simulations fo r the same problem using multi-mode differential constitutive models. The drag force exerted by the fluid on the cylinder has been calculate d and reported to be a decreasing function of the flow rate. (C) 1998 Elsevier Science B.V. All rights reserved.