Further Investigations on the Modelling of Gravity-Drawn Boger Fluid Jets

Abstract

The flow field generated by a viscoelastic jet stretching under its own weight has been used to study the elongational behaviour of a number of constant viscosity elastic fluids (Boger fluids). Previous studies have shown that the Oldroyd-B model failed to describe the jets adequately. An attempt is made here to evaluate the performance of a number of more complicated constitutive models in predicting the jet profiles. The models reported in this study include the FENE-P, PTT, Giesekus and multiple-relaxation-time (MRT) KBKZ equations. As in the earlier studies, the fluid parameters are estimated from the measured shear properties and are used to predict the jet profiles. The jet profile calculation is simplified by making the standard one-dimensional approximation. The use of the MRT KBKZ-type constitutive equation for modelling Boger fluids is recommended in preference to the more traditional Oldroyd-Maxwell and other single-time-constant equations.