The simulation results on viscoelastic fluid flows in sudden expansion geometry with different expansion ratios are presented.Oldroyd-B,linear Phan-Thien-Tanner(L-PTT)and Finitely Extensible Nonlinear Elastic(FENE-P)based constitutive equations were applied in two-dimensional Cartesian coordinates.The governing equations in transient and fully developed regions were solved using open source software called OpenFOAM.The flow patterns,including velocity profiles,shear stresses and first normal stress differences in some horizontal and vertical sections are illustrated.In addition,effects of the fluid type,flow dynamics and expansion ratio on the flow and vortex patterns in transient and fully developed regions are presented and discussed.The presented results show that existences of vortices cause the inverse velocity and negative stresses in expansion regions of the channel which increase with increment of expansion ratio and Weissenberg number(We).Furthermore,some dead spaces can be observed at channel expansion regions close to the wall which are also increased.The results also show that at low We numbers all fluids show close behavior while at high We numbers the FENE-P fluid behavior shows high divergence from that of the two other fluids.