THE PUBLISHING HOUSE PROCEEDINGS OF THE ROMANIAN ACADEMY, Series A, OF THE ROMANIAN ACADEMY Volume 8, Number 3/2007, pp. 000-000 EXPERIMENTAL AND NUMERICAL STUDIES OF WEAKLY ELASTIC VISCOUS FLUIDS IN A HELE-SHAW GEOMETRY

The paper is focused to the experimental investigations of weakly elastic viscous flows in complex geometries, with application in biofluid mechanics. The test samples, polyacrylamide solutions in water characterized by very low relaxation times ( λ < 0.01 s), have similar shear rheology with blood at medium and high shear rates. The flow configuration is a special designed “T” branch Hele – Shaw geometry, characterized by relevant separation areas. The influence of polymer concentration and Reynolds number (Re) on the vortical structures are investigated. Experiments and numerical simulations of the Newtonian and shear thinning viscous fluid are performed at Re < 1000. The analyses of vortices evidence the increasing of their magnitude with polymer concentration and qualitative changes in the vorticity distribution within the separation areas of weakly elastic flows, in comparison to pure Newtonian ones. The present numerical results are qualitatively similar to experiments, up to a Reynolds critical number Recr ≅ 650. The generalized Newtonian models, which fit the shear thinning behaviour of the samples, are not able to reproduce also quantitatively the experimental evidences, so elasticity (even if is present in a very small amount) plays a relevant role in defining the flow structure within separation areas.