Drag Reduction by Additives

An examination is made of the experimental evidence for the reduction of skin friction in dilute solutions of high molecular weight linear polymers below that of the solvent alone. Inferences are drawn about the necessary properties of the polymers and their solvents, and the mechanical properties of the solutions are described. In the detailed flow measurements, those observations requiring explanation are identified. Simple dimensional considerations are applied to isolate the phenomenon in a relatively narrow region outside the viscous sublayer; these same considerations are shown to explain several of the observed anomalies. In an attempt at a deeper explanation, the influence of phenomena such as agglomeration and extension is discussed. It is shown that mechanisms of interaction which suggest themselves, while qualitatively satisfactory, are quantitatively and conceptually in disagreement with experiment, while the experimental results are in disagreement with accepted principles of fluid mechanics. ( Author )