Vortex shedding in cylinder flow of shear-thinning fluids. III - Pressure measurement

Measurements of pressure on the cylinder surface for the flow of Newtonian and non-Newtonian fluids around a circular cylinder were carried out, from which several parameters were calculated: the form drag coefficient (C-D), the pressure rise coefficient (C-pb - C-pm) and the wake angle (theta(w)). The non-Newtonian fluids were aqueous solutions of CMC and tylose with varying degrees of shear-thinning and elasticity, at weight concentrations of 0.1-0.6% and the experiments encompassed the transition and shear-layer transition regimes. For low Reynolds numbers flows elasticity on the shear layers was responsible for an increase in drag reduction with polymer concentration. Within the shear-layer transition regime the increase of the wake angle and pressure rise coefficient for the more concentrated solutions reduced CD by narrowing the near wake. For the tylose solutions a good correlation was found between the elasticity number and the mean pressure rise coefficient. (C) 2004 Elsevier B.V. All rights reserved.