Flow past a sphere: Predicting enhanced drag with shear-thinning fluids, dissipative and constant shear-viscosity models

This article tackles the topic of drag detection for flow past a sphere, focusing on response for viscoelastic shear-thinning fluids, in contrast to constant shear-viscosity forms, both with and without extensional viscous dissipative contributions. The work extends that previously of Gardutio et al. [1], where experimental levels of resultant drag-enhancement were captured for Boger-fluids, using a new hybrid dissipative viscoelastic model. This advance was based on Finitely Extensible Non-linear Elastic and White Metzner constructs, where the level of extensional-viscous material time-scale had to be considerably raised to provide strong strain-hardening properties. The new dissipative model drag findings are:- for low-solvent systems, all such models reflect only significant drag-reduction, with barely any distinction from base-level dissipative-factor response. Such systems consistently gave considerably more pronounced decline in drag than for their high-solvent counterparts. Alternatively, under high-solvent systems (as in Boger fluids), the general observation for all four such dissipative models, is that after an initial-decrease in drag, a second-increasing trend can be extracted. This lies in stark contrast to base-level, null dissipative-factor drag findings, where only drag-reduction could be observed. Yet consistently, the inclusion of shear-thinning is reflected in the overall lowering of drag levels. Nevertheless, strong terminating drag-enhancement can be generated under larger dissipative-factor setting for dissipative-EPTT (shear-thinning, strain-hardening/softening), only slightly suppressed from that for dissipative-FENE-CR (constant shear-viscosity, strain-hardening/hardening-plateau). Other dissipative-{FENE-P, LPTT} variants, showed encouraging trends towards drag-enhancement, but unfortunately suffered from premature solution stunting, and hence, were restricted in accessible range of deformation-rates. In addition, an increase in geometry aspect-ratio, generally provokes elevation of drag, but only under high-solvent state, and hence only then, leads to evidence for stimulating drag-enhancement. (C) 2017 Elsevier B.V. All rights reserved.