Effect of the Reynolds number on viscoelastic fluid flows through axisymmetric sudden contraction

Abstract

Viscoelastic fluid flows through sudden contractions can be found in several industrial applications, such as polymer extrusion and processing, polymer solution flows, and food and paints processing. However, this kind of flow has not yet been studied within the whole extent of laminar flows. In the current work, a numerical study of viscoelastic fluid flow through an axisymmetric 4:1 sudden contraction is conducted. The approach employs the exponential PTT model, the Reynolds number is varied from 0.0005 to 250, the Weissenberg number from 0.01 to 100 and two values for the extensional parameter e are used, 0.02 and 0.25. The results show that for Re > 25 and low Weissenberg numbers the Couette correction and the size of the corner vortices are almost independent of the Weissenberg number and of the extensional parameter. For lower values of Re, however, the size of the corner vortices is strongly dependent of We and e for We ≥ 0.1. The recirculation zones are larger for e = 0.02 than for e = 0.25, since an increase of the extensional viscosity hinders the fluid passage through the contraction, creating larger vortices. The Couette correction varies linearly with the Reynolds number within the whole range of the Weissenberg number investigated. It can be concluded that while the rheological properties of viscoelastic fluids affect significantly creeping flow patterns, inertial forces reduce the effect of these properties as the Reynolds number increases.