Laminar flow in three-dimensional square-square expansions

► We study the three-dimensional laminar flow through square-square expansions. ► The flow of Newtonian and viscoelastic fluids is compared. ► Flow patterns visualized using streak photography and velocity field measured with PIV. ► Comparison between experiments and numerical simulations is presented. ► Flow inversion due to inertia is predicted numerically in agreement with experiments.