Rc. Yalamanchili et al., AN EXPERIMENTAL INVESTIGATION OF THE FLOW OF DILUTE POLYMER-SOLUTIONSTHROUGH CORRUGATED CHANNELS, Journal of non-Newtonian fluid mechanics, 58(2-3), 1995, pp. 243-277
Measurements of the velocity using Laser Doppler Velocimetry and norma
l stress are made for the flow of dilute polymer solutions through a c
hannel with corrugated top and bottom plates. (Since we are dealing wi
th non-Newtonian fluids, there can be significant contributions to the
normal stress from non-linear terms in the constitutive expression, e
ven when the flow is slow. The measurements being made are the normal
stresses and not the ''pressure''.) The surfaces of the plates are sin
usoidal. A Reynolds number based on half the average plate spacing as
the length scale and the characteristic velocity as the velocity scale
was used and the range of Reynolds numbers studied was 50 < Re < 1000
. The centerline velocities indicate that the experiments were perform
ed in the inertial regime, as confirmed by the asymmetry of the center
line velocities along the channel length. The velocity profiles at the
trough near the wall, for a channel with wavelength of 2.54 cm, indic
ate the presence of secondary flow. Sinusoidal plates with nearly iden
tical aspect ratios (ali,) allowed for dramatic changes in the way in
which the friction factor varied with Reynolds number, in that, in one
case the friction factor associated with the fluid without polymer wa
s higher than the friction factor associated with the fluid with polym
er, while in others it was just the opposite. This would call into que
stion the use of aspect ratio as an appropriate parameter for studying
such problems. Changes in plate wavelength either increased or decrea
sed the friction factor depending on the Reynolds number. Increasing p
late amplitude increased the friction factor of the fluid for the rang
e of values for the Reynolds number that was considered. The amplitude
associated with the dimensionless normal stress increased with decrea
sing wavelength, for particular Reynolds numbers, irrespective of the
fluid studied. Increasing the polymer concentration in the fluid decre
ased the difference in the amplitude of the dimensionless normal stres
s, the Reynolds number being fixed. Increasing the plate amplitude inc
reased the amplitude of the normal stress. while an increase in plate
wavelength decreased the amplitude of the normal stress.