Rolie-Poly fluid flowing through constrictions: Two distinct instabilities

Elastic instabilities of entangled polymer melts are common in industrial processes but the physics responsible is not well understood. We present a numerical linear stability study of a molecular based constitutive model which grants us physical insight into the underlying mechanics involved. Two constriction flows are considered – one shear dominated, the other extension dominated – and two distinct instabilities are found. The influence of the molecular structure and the behaviour of the polymer dynamics are investigated and in both cases chain relaxation and orientation play a crucial role. This suggests a molecular-based physical interpretation of the underlying mechanisms responsible for flow instabilities.

► Numerical simulation of the perturbed Rolie-Poly equation for linear stability (normal mode) analysis. ► Critical parameters for the onset of instability in monodispersed poymeric materials. ► Physical explanation of elastic instabilities in shear dominated and extension dominated flows.