Drag Reduction in Turbulent Flow

The friction coefficient of simple fluids in highly turbulent flows can be dramatically lowered by addition of rather small quantities of polymer. Fabula has shown, for example, that extremely small amounts of poly(ethylene oxide) in water reduce the pressure drop for a given flow rate to as little as one-fourth that 

FIG U RE 7.25 Decrease in stress (drag reduction) at constant average velocity 0 by addition of small amounts of high-molecular-weight polyfethylene oxide). (Data from Hoyt, J. W., Drag reduction, in Encyclopedia of Polymer Science and Engineering, vol. 5, 2nd edn., Wiley, New York, 129, 1986.) 

FIGURE 7.26 Apparatus for performing turbulent flow measurements using polymer solutions. 

FIGURE 7.27 Typical flow data for dilute solutions of polyacrylamide in water. The plot shows results obtained by several groups of students. The concentration c of the solutions increase from left to right in the flgure. 

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Lumley JL (1973) Drag reduction in turbulent flow by polymer additives J Polym Sci Macromol Rev 7 263... 

Drag reduction in turbulent flows of dilute high-polymer of surfactant solutions is a striking... 

DRAG REDUCTION IN TURBULENT FLOW. Dilute solutions of polymers in water or other solvents sometimes give the peculiar effect of a reduction in drag in turbulent flow. The phenomenon was first noted by Toms and has prompted many theoretical studies and some practical applications. As shown in Fig. 5.11, the friction factor can be significantly below the normal value for turbulent flow with only a few parts per million of polymer in water, and at 50 to 100 ppm, the drag reduction may be as much as 70 percent. Similar effects have been shown for some polymers in organic solvents. 

POLYMER AND SURFACTANT DRAG REDUCTION IN TURBULENT FLOWS... 

Graham, M. D., Drag reduction in turbulent flow of polymer solutions, in Rheology Reviews 2004. British Society of Rheology, Binding, D. M., and Walters, K., Eds., 143-170 (2004). 

Ruckenstein, E On the Mechanism of Drag Reduction in Turbulent Flow of Viscoelastic Liquids. Chem. Eng. Sci. 26 (1971) 1075. 

Equation (10) cannot be applied until A, the equivalent relaxation time for the fluid, is known. However, A is defined by the linear Maxwell model, and actual polymer solutions exhibit marked nonlinear viscoelastic properties [5,6,7]. For both fresh and shear degraded solutions of Separan AP 30 polyacrylamide, which exhibit pronounced drag reduction in turbulent flow, Chang and Darby [8] have measured the nonlinear viscosity and first normal stress functions, and Tsai and Darby [6] have reported transient elastic properties of similar solutions, A nonlinear hereditary integral function containing six parameters has been proposed to represent the measured properties [8], The apparent viscosity function predicted by this model is ... 

Yang, S.-Q. (2009). Drag reduction in turbulent flow with polymer additives. Journal of Fluids Engineering 131(5) 051301. 

Brit. Hydromechanics Research Assn., 1976, 17 Drag reduction in fluid flows, Sellin H.J Moses R, Horwood Ellis, 1989, 39.95 Drag reduction in turbulent flows by additives, Gyr A Bewersdorff H-W, Kluwer, 1995, 79 Emerging techniques in drag reduction, Kwing-So C, Prasad K.K Truong T.V,... 

Dean, B., Bhushan, B., 2010. Shark-skin surfaces for fluid-drag reduction in turbulent flow a review. Philos.Trans. A Math. Phys. Eng. Sci. 368, 4775. 

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