Birefringence and LDV Studies ofViscoelastic Flow Through a Planar Contraction

LIDIA MARÍA QUINZANI; ROBERT ARMSTRONG; ROBERT BROWN

JOURNAL OF NON-NEWTONIAN FLUID MECHANICS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1994 vol. 52 p. 1 - 36

0377-0257

Laser-Doppler velocimetry (LDV) and flow-induced birefringence(FIB) are used to measure the velocity and stress fields of a rheologicallywell characterized viscoelastic solution flowing through a 3.97: 1 planarabrupt contraction. The FIB system is designed to give accurate, spatiallyresolved measurements of the birefringence through the contraction flow. Thefluid is a 5.0 wt.% solution of polyisobutylene in tetradecane that exhibitsshearthinning of both the viscosity and the first normal stress coefficient.Shear rate-dependent Deborah numbers for the contraction flow are accessible inthe range 0 < De(j) 5 0.8. Measurements show the evolution of the shear stressand first normal stress difference throughout the converging flow upstream ofthe contraction plane as well as downstream of the contraction. Measurements ofthe stresses along lines emanating from the reentrant corner of the contractionfollow the power-law scalings given by the analysis of the flow of Newtonianand power-law fluids near a corner, suggesting that the shear thinning of thefluid reduces the importance of ?elasticity? near the corner.