Flow visualization is performed on an elastically-dominated instabilit
y in several similar Boger fluids in Taylor-Couette flow The onset and
evolution of secondary flow are observed over a range of shear rates
using reflective mica platelet seeding. Sequences of ambiently and she
et-illuminated images were digitally processed. Rotation of the inner
cylinder was ramped from rest to its final value over a time on the or
der of a polymer relaxation time. Dilute solutions of high molecular w
eight polyisobutylene in oligomeric polybutene manifest a flow transit
ion at a Deborah number, De(s) = lambda(s) gamma approximate to 1.5 wi
th a Taylor number of 0.00022 in a cell with dimensionless gap ratio d
elta = 0.0963. At this transition, simple azimuthal shearing is replac
ed by steady, roughly square, axisymmetric counter-rotating vortices g
rossly similar to the well-known Taylor vortex flow that is observed a
t De(s) = 0, Ta = 3612. At De(s) = 3.75, Ta = 0.0014, an axisymmetric
oscillatory secondary flow develops initially but is replaced by the s
teady vortices. At De(s) = 7.5, Ta = 0.0054, the oscillatory and vorte
x flow coexist and possess an irregular cellular cross-section. A wide
span of growth rates is observed: the ratio of onset to polymer relax
ation time ranges from 170 000 at De(s) = 1.5 to 0(10) at De(s) > 5. T
he role of inertia was explored through changing the solvent viscosity
. A transition similar to the one that occurs at De(s) = 3.75, Ta = 0.
0014, from the base azimuthal shearing flow to axisymmetric vortices,
was also observed with a much lower viscosity fluid at De(s) = 3.3, Ta
= 74.