An Experimental Study Of Polymer Drag Reduction And Boundary Layer Diffusion Characteristics For Incompressible Flow Over A Flat Plate

Drag reduction by injection of high molecular weight polymers into boundary layers has been demonstrated repeatedly in the past. However, from a volume utilization tradeoff standpoint, the quantities of polymer required make the gains achieved by this process marginal. While indicating reduced polymer requirements for drag reduction, limited data obtained from pipe flow and external boundary layer flow experiments are conflicting and hard to interpret. Ambiguities in measurement techniques due to polymer effects on commonly used instrumentation and opposing features of varied flow facilities have also contributed to making these earlier works contradictory and difficult to resolve. Experiments performed in this research indicate that turbulence intensity distributions are altered by the addition of polymer in such a way that the peak of turbulence production is lowered and its location moved away from the wall. The transition region is delayed and extended by the addition of polymer to the boundary layer. The laminar sublayer of boundary layer profiles appears to have thickened due to the addition of polymer. When compared to the law of the wall corrected for developing flow, the velocity profiles also show evidence of a thickened sublayer.

Drag reduction by ejection of high molecular weight polymers on free-running bodies of revolution has been demonstrated repeatedly. The quantities of polymer required have made the gains achieved marginal from a volume utilization tradeoff. The ejection process is hypothesized to be the controlling factor. Limited data obtained in pipe flow and flat plate flow experiments on ejection into developing boundary layers indicate a drastic reduction in polymer requirements for equivalent percent drag reductions. Extension to axisymmetric flow could result in significant achievable gains to volume utilization. This study examines these polymer ejection processes through measurement of wall and boundary layer concentration profiles and through a photographic study of the boundary layer. Tests performed with fresh water ejection and solutions of the drag reducing polymer, Polyox WSR-301, lead to the hypothesis that optimal ejection for minimum polymer usage requires ejection into a laminar boundary layer prior to turbulent flow transition. Analytical routines are developed which predict boundary layer parameters and polymer wall concentrations for this postulated optimal ejection process or the suboptimal case. Limited verification of the model is made. (Author).

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).