Laser velocimeter measurement of Reynolds stress and turbulence in dilute polymer solutions
Measurements of Reynolds stress and axial and transverse turbulence intensities have been made in drag-reducing turbulent pipe flow of a dilute solution of high molecular weight polymer and compared to measurements made with pure water. A newly developed laser velocimeter capable of measuring t...
| Summary: | Measurements of Reynolds stress and axial and transverse
turbulence intensities have been made in drag-reducing
turbulent pipe flow of a dilute solution of high molecular
weight polymer and compared to measurements made with pure
water. A newly developed laser velocimeter capable of
measuring these turbulence parameters has been utilized and
is described in detail.
Axial turbulence intensities measured in polymer solution
are consistent with previous polymer results and
viscous sublayer thickening is observed. New results include
demonstration that the turbulent shearing stress is
reduced in the turbulent core by an amount proportional to
the observed decrease in pressure gradient at the wall, and
extrapolates to a wall value in agreement with calculated
local wall shear. Near the wall polymer solution Reynolds
stress is reduced below that measured for water consistent
with observed velocity profiles. Polymer radial turbulence
intensities are comparable with those for water in the
turbulent core, but exhibit similar dramatic suppression
near the wall. These and other recent results strongly
suggest that dilute polymer solution drag reduction is
primarily a wall phenomenon. Polymers appear to have little
or no effect on turbulent flow away from a solid boundary
where turbulent velocities scale with u_τ, the shear
velocity based on the observed wall shear.
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