  We present the dynamic velocity profiles of a Newtonian fluid (glycerol) and
a viscoelastic Maxwell fluid (CPyCl/NaSal in water) driven by an oscillating
pressure gradient in a vertical cylindrical pipe. The frequency range explored
has been chosen to include the first three resonance peaks of the dynamic
permeability of the viscoelastic fluid / pipe system. Three different optical
measurement techniques have been employed. Laser Doppler Anemometry has been
used to measure the magnitude of the velocity at the centre of the liquid
column. Particle Image Velocimetry and Optical Deflectometry are used to
determine the velocity profiles at the bulk of the liquid column and at the
liquid--air interface respectively. The velocity measurements in the bulk are
in good agreement with the theoretical predictions of a linear theory. The
results, however, show dramatic differences in the dynamic behaviour of
Newtonian and viscoelastic fluids, and demonstrate the importance of resonance
phenomena in viscoelastic fluid flows, biofluids in particular, in confined
geometries.
