%0 Journal Article %1 PérezCamacho2015260 %A Pérez-Camacho, M. %A López-Aguilar, J.E. %A Calderas, F. %A Manero, O. %A Webster, M.F. %D 2015 %J Journal of Non-Newtonian Fluid Mechanics %K myown %P 260 - 271 %R http://dx.doi.org/10.1016/j.jnnfm.2015.01.013 %T Pressure-drop and kinematics of viscoelastic flow through an axisymmetric contraction–expansion geometry with various contraction-ratios %U http://www.sciencedirect.com/science/article/pii/S0377025715000269 %V 222 %X Abstract One of the relevant benchmark problems in pressure-driven flows, that of flow through an axisymmetric expansion–contraction geometry, is addressed in this study. Three fluids have been considered: a Newtonian (theoretically simulated based on the Poiseuille and Samson solutions), Boger and a shear-thinning polymer solution. Particular attention is given to the pressure-drop and kinematics obtained in a flow apparatus specifically designed for various contraction-ratios (2:1:2, 4:1:4, 6:1:6, 8:1:8, 10:1:10). Both viscoelastic fluids present large magnitudes of normal stress under simple shear flow. The three fluids have the same viscosity at low shear-rates. The Boger fluid (polyacrylamide in a syrup-water solution) possesses a constant viscosity over a wide range of shear-rates. The shear-thinning fluid also has a wide range of first Newtonian plateau before the onset of shear-thinning. Findings for the Boger fluid reflect, initially, a decreasing pressure-drop below the Newtonian reference line (excess pressure-drop “epd” lower than unity), followed by values larger than one as the contraction-ratio increases. This can be explained on the basis of the extensional viscosity behaviour in the contraction section of the geometry. The shear-thinning polymer solution (HASE-type associative polymer) shows a reduction in epd below the Newtonian curve for small contraction-ratios (due to shear-thinning). However, in more abrupt contractions, the extensional flow behaviour dominates the shear-thinning effects: first attaining a Newtonian equivalent value (producing an epd of one), and then, showing values larger than unity as the contraction-ratio becomes more severe. Kinematic fields illustrated by flow visualization reveal several different sizes of the corner-vortex, which are related to the relative contributions from the first normal stress difference (N1) and extensional stress throughout the geometry. Transitions from lip-to-corner vortex are related to the transition from shear-dominated to extension-dominated flows. Experimental data, for the Boger fluid on 4:1:4 contraction-ratio, are contrasted against numerical simulation results for a constant-shear-viscosity/extension-hardening FENE-CR model. Trends demonstrate qualitative agreement on epd and vortex activity, which also reveal an interesting interplay between \N1\ and extensional viscosity.

@article{PérezCamacho2015260, abstract = {Abstract One of the relevant benchmark problems in pressure-driven flows, that of flow through an axisymmetric expansion–contraction geometry, is addressed in this study. Three fluids have been considered: a Newtonian (theoretically simulated based on the Poiseuille and Samson solutions), Boger and a shear-thinning polymer solution. Particular attention is given to the pressure-drop and kinematics obtained in a flow apparatus specifically designed for various contraction-ratios (2:1:2, 4:1:4, 6:1:6, 8:1:8, 10:1:10). Both viscoelastic fluids present large magnitudes of normal stress under simple shear flow. The three fluids have the same viscosity at low shear-rates. The Boger fluid (polyacrylamide in a syrup-water solution) possesses a constant viscosity over a wide range of shear-rates. The shear-thinning fluid also has a wide range of first Newtonian plateau before the onset of shear-thinning. Findings for the Boger fluid reflect, initially, a decreasing pressure-drop below the Newtonian reference line (excess pressure-drop “epd” lower than unity), followed by values larger than one as the contraction-ratio increases. This can be explained on the basis of the extensional viscosity behaviour in the contraction section of the geometry. The shear-thinning polymer solution (HASE-type associative polymer) shows a reduction in epd below the Newtonian curve for small contraction-ratios (due to shear-thinning). However, in more abrupt contractions, the extensional flow behaviour dominates the shear-thinning effects: first attaining a Newtonian equivalent value (producing an epd of one), and then, showing values larger than unity as the contraction-ratio becomes more severe. Kinematic fields illustrated by flow visualization reveal several different sizes of the corner-vortex, which are related to the relative contributions from the first normal stress difference (N1) and extensional stress throughout the geometry. Transitions from lip-to-corner vortex are related to the transition from shear-dominated to extension-dominated flows. Experimental data, for the Boger fluid on 4:1:4 contraction-ratio, are contrasted against numerical simulation results for a constant-shear-viscosity/extension-hardening FENE-CR model. Trends demonstrate qualitative agreement on epd and vortex activity, which also reveal an interesting interplay between \{N1\} and extensional viscosity. }, added-at = {2016-03-09T19:44:50.000+0100}, author = {Pérez-Camacho, M. and López-Aguilar, J.E. and Calderas, F. and Manero, O. and Webster, M.F.}, biburl = {https://www.bibsonomy.org/bibtex/2bd4e91fcaea80edf8e0d70d5102bc967/faustocg}, doi = {http://dx.doi.org/10.1016/j.jnnfm.2015.01.013}, interhash = {eadc945ce8d6feea3c7ef29b5510ad66}, intrahash = {bd4e91fcaea80edf8e0d70d5102bc967}, issn = {0377-0257}, journal = {Journal of Non-Newtonian Fluid Mechanics }, keywords = {myown}, note = {Rheometry (and General Rheology): Festschrift dedicated to Professor K Walters \{FRS\} on the occasion of his 80th birthday }, pages = {260 - 271}, timestamp = {2016-03-09T19:44:50.000+0100}, title = {Pressure-drop and kinematics of viscoelastic flow through an axisymmetric contraction–expansion geometry with various contraction-ratios }, url = {http://www.sciencedirect.com/science/article/pii/S0377025715000269}, volume = 222, year = 2015 }