In this work we present an experimental study of the 3D laminar flow of Newtonian and Boger fluids through square-square expansions with expansion ratios of 1:2.4, 1:4, 1:8 and 1:12. Visualizations of the flow patterns were performed using streak line photography and the velocity field of the flow was measured in detail using Particle Image Velocimetry (PIV). The experimental results obtained with the Newtonian fluid are compared with numerical predictions. The numerical code used is based on a Finite-Volume method and an excellent agreement is found between experimental and numerical results. For all expansion ratios studied, a Moffatt corner vortex is observed downstream of the expansion and an increase in the flow inertia leads to an enhancement of the vortex size. On the other hand, the viscoelastic fluid flow also reveals the existence of a corner vortex downstream of the expansion, which decreases in size and strength when the Deborah number is increased. The vortices in square-square expansion flows exhibit a three-dimensional structure evidenced by a helical flow, which is well predicted by numerical simulation in the Newtonian fluid flow case.
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