Visualization studies of viscoelastic flow in a 4:1 square/square contraction

Abstract

Visualizations of the 3-D flow in a 4:1 sudden square-square contraction for a viscoelastic shear-thinning fluid underconditions of negligible inertia show provocative flow patterns. Whereas for a Newtonian fluid the vortex length remainsunchanged, with the non-Newtonian fluid there is a dramatic increase in vortex length with fluid elasticity leading to unstableperiodic flow at higher flow rates. In the steady flow regime the vortices are not closed and fluid particles enter the middle-planevortex, rotate towards its eye, drift to the corner plane vortex, rotate to its periphery and exit to the downstream duct, a dynamicprocess that is opposite that found with Newtonian fluids. The periodic flow was characterised by a constant Strouhal number of 0.5.