In addition to their shear-thinning behavior, polymer melts are characterized by first and second normal stress differences, which are responsible for the occurrence of secondary motions. Viscoelastic flows through straight ducts exhibit secondary motions which cannot be explained solely by the first normal stress difference. The effect of second normal stress difference was analyzed by observing the coextrusion of two polymer melts, each with a different pigmentation, in a square duct. The development of secondary motions was observed by tracking the motion of the interface between both fluids. In this work a new solver for the OpenFOAM CFD toolbox is used, which handles viscoelastic two-phase flows. A derivative of the volume-of-fluid (VOF) methodology is used to describe the interface.