Newtonian and non-Newtonian flow in a channel obstructed by an antisymmetric array of cylinders

Abstract

Consideration is given to the flow of Newtonian and non-Newtonian elastic liquids in a channel obstructed by an antisymmetric array of cylinders. Experiments are carried out on Newtonian maltose-syrup/water mixtures and a variety of non-Newtonian liquids, including constant-viscosity Boger fluids and shear-thinning aqueous polymer solutions. In one case, the polymer is polyacrylamide and the shear thinning is accompanied by high normal stresses and high extensional-viscosity levels. In another case, the polymer is the more rigid xanthan gum and the normal-stress and extensional-viscosity levels are accordingly much lower. The details of the flow are investigated by means of a laser technique, which permits an overall picture to be obtained with relative ease. The resistance to flow caused by the positioning of the cylindrical obstructions is also investigated through the pressure gradient/flow rate data. It is concluded that the tortuous geometry and rheology combine to produce significant viscoelastic effects with regard to both the general flow field and 'resistance to flow'. A finite element technique is employed to simulate numerically the observed flows. Significant success is claimed in qualitatively reproducing the viscoelastic behaviour in the model geometry. The quantitative agreement between experiment and theory is considered to be satisfactory, within the acknowledged limitations of present-day viscoelastic simulations. © 1991.