A tracer dispersion study of the drag-reduction effect in a turbulent pipe flow

Abstract

Remarkable differences in dispersion of a tracer material injected into turbulent pipe flows of water and water containing as little as 2·5 parts per million by weight of a soluble high-molecular-weight drag-reducing polyoxyethylene additive have been measured. Analysis of the tracer response curves in terms of a simple one-parameter model shows that the observed results are compatible with a drag-reduction mechanism based on thickening of the viscous sublayer adjoining the wall. Other experiments, reported briefly, suggest that polymer adsorption on to the wall is responsible for this thickening.

The Drag Reduction Phenomenon. Observed Characteristics, Improved Agents, and Proposed Mechanisms

“…Some workers (12,15,57) have postulated that an adsorbed layer of polymer molecules at the interface of flowing liquid and wall continues to function in a drag-reduction sense when the bulk of the polymer solution has been displaced by the base solvent. The suggestion that adsorbed polymer layers play an important role in the drag reduction mechanism is at first glance a thoroughly intriguing one and interest in it still persists (3,10).…”

“…(4) Percent drag reduction is greatest in the most viscous solvent when comparisons are made at similar Reynolds number and solvent power. Some limited success in correlating solvent, viscosity, and temperature effects was obtained by casting the results in a time-based correlation where the time of the disk system (1/rpm) is combined with the polymer relaxation time (a[yo(br ~1)]/TkC), that is %DR = K>(rpm)^^1 } (Re ~X lp5) (10) where K = a constant, = solvent viscosity, = reduced viscosity, Re = Reynolds number, T = temperature, and C = concentration. Such a correlation, however, while certainly not novel provides the barest suggestion that solvent effects might be accounted for by cataloging polymer reduced viscosities or intrinsic viscosities together with some sort of drag reduction index such as intrinsic concentration.…”

Flow of dilute polymer solutions about circular cylinders

“…Although extensive theoretical and experimental work has been carried out with steady pipe flows (e.g. Virk 1971;Bryson, Arunachalam & Fulfords 1971;Kerekes & Douglas 1972), where the resistance is due to turbulent skin friction alone, relatively few studies have been conducted on the effect of additives on the flow about bluff bodies.…”

Drag reduction in turbulent flow due to additives: a report on Euromech 52

“…Molecular entanglements tended to decrease drag reduction, as did degradation. The thickness of the adsorbed layer of molecules on the solid surface was found to be very small, approximately 200 A, suggesting that the drag reduction cannot be due to wall flexibility caused by the adsorbed polymer layer as suggested by Bryson, Arunachalan & Fulford (1971). E. H. Dunlop (London) presented pipe-flow drag-reduction measurements for polystyrene in toluene.…”