The Effects Of A Drag Reducing Polymer On The Turbulent Boundary Layer Of A Submerged Flat Plate

The primary objective of an experimental investigation was to study the effect that a drag-reducing polymer has on the turbulent boundary layer of a submerged flat plate using a Laser-Doppler flowmeter. Data are presented showing the time effects caused by polymer solution drag-reduction degradation on the mean velocity and axial fluctuating-velocity profiles. The importance of the data is that it provides a connection between the apparently diverse results reported previously for the velocity profiles at conditions of high and low drag-reduction effectiveness. The polymer molecules' effect on the boundary layer structure is apparently progressively restricted to the near wall region with decreasing drag reduction in agreement with the mean velocity profiles. (Author).

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An experimental investigation was made into the effects of injecting non-Newtonian fluids into the turbulent boundary layer of a flat plate. The ejection of weakly viscoelastic solutions of a macromolecular polymer at the leading edge of the plate decreased its drag coefficient by as much as 50%; the Reynolds number of the plate was 1.8 x 10 to the 6th power. It was found that for a given ejection rate and free stream velocity there was a solution concentration for which the drag coefficient was a minimum. It is conjectured that the relatively sharp loss of effectiveness for higher concentrations may be due to insufficient mixing of the additive into the turbulent boundary layer. Ejection of neutrally buoyant spherical particles, not too much larger than the macromolecules, had no effect on the drag of the plate, indicating that the drag reduction is probably associated with the viscoelastic properties of the solutions studied. (Author).