An Experimental Study of Polymer Drag Reduction and Boundary Layer Diffusion Characteristics for Incompressible Flow Over a Flat Plate.

Abstract : 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.