Studies of Viscous Drag Reduction with Polymers Including Turbulence Measurements and Roughness Effects
Recent results of turbulence measurements in very effective drag-reducing fluids are presented. Effects of the polymer on turbulence intensity are found to not be directly related to friction reduction. Turbulence intensity is found to be a function of Reynolds number, polymer concentration, and location in the flow field and may be locally higher or lower than for Newtonian flow. Turbulence spectral measurements show moderate effects in both macroscale and microscale for polymer solutions suggesting a possible elasticity effect which is not related to the drag-reduction phenomenon.
Friction factors for flow of a very effective drag-reducing dilute polymer solution in uniformly rough pipes are presented. The onset of “fully rough” effects is found to occur at higher Reynolds numbers in the polymer solution than in water in accordance with predictions based on the sublayer thickening effect of the polymer. The friction factors are found to be less for the polymer than for water in the roughness transition regime, but there is an indication that in the fully rough regime no drag-reduction will be realized. The data are analyzed in terms of a roughness function based on the effects of the polymer and the roughness on the law of the wall velocity profile.
KeywordsTurbulence Intensity Friction Factor Drag Reduction Friction Reduction Roughness Effect
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