Numerical study of the flow of polystyrene melts in contraction flow using Rolie-Poly model

This paper is concerned with simulating the viscoelastic flow of polystyrene melts in different contraction geometries based on single mode Rolie-Poly constitutive model. The 4:1 abrupt contraction flow of polystyrene melt is considered as a benchmark problem for validating the capabilities of Rolie-Poly model and numerical method and algorithm used in this work. Numerical results of the stress and velocity field illustrate that the present two-dimensional model and numerical method can reproduce predictions made by other published experimental and simulative results. To explore the rheological behaviors of the flowing polystyrene melt in different contraction geometries, the effect of die converging angle, contraction ratio and apparent shear rate on the flow field are discussed in detail. We compared some numerical results with the published experimental results, and reasonable matching between them was found. The present numerical results indicate that the die converging angle, contraction ratio and apparent shear rate are three important factors that are affecting the rheological behaviors of polystyrene melt in contraction flow. The magnitude of maximum PSD, first normal stress difference, and stretch ratio decrease with decreasing the converging angles, and largely reduced with a smooth entry shape. It shows that the shape of the convergence plays a major role in the foundation of extensional stress field, and a possible way to decrease the stress concentration at the contraction entrance of a die is to introduce a smooth entry shape. Numerical predictions of the distributions of principal stress difference (PSD), first normal stress difference, stretch ratio, shear stress, velocity, and so on in the flow field are also presented; the information contributes to a better understanding of the dynamic response of polymer melt forced into contraction geometries. Graphical abstract