N1 stresses in extensional flows

The possible role of shear-generated normal stresses in flows which appear to be extensional in nature is rarely considered. But in a recent article we showed that, in flows of Boger fluids through arrays of rods, the increased flow resistance caused by elasticity was related to the property N1 and not to extensional stresses. In the present paper, that flow is examined further and several other complex flows, normally associated with extensional stresses, are investigated to assess the normal stresses generated by shearing, specifically: flow in a converging channel, the tubeless siphon, and flows around a sphere and cylinder. From experimental results obtained in these flows and from modeling, the normal stresses due to shearing and extension are evaluated and compared. The comparisons show that shear-generated stresses are at least comparable with those generated by extension.