Studies of Viscous Drag Reduction with Polymers Including Turbulence Measurements and Roughness Effects

Spangler, J. G.

doi:10.1007/978-1-4899-5579-1_6

Cited by 24 publications

(4 citation statements)

References 12 publications

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“…Since the tube diameter is 0*63cm, it is impossible t o measure the initial mean velocity profile in great detail. However, past measurements in pipe flows (Spangler 1969) indicate that the chief effect of the polymer upon the mean velocity is the thickening of the viscous sublayer and that the most significant effect upon the turbulence intensity occurs very near the wall. These differences apparently have an effect upon the early development of the jet, since no polymer effect was observed when the initial velocity profiles were uniform.…”

Section: Resultsmentioning

confidence: 99%

Laser-Doppler measurements on a round turbulent jet in dilute polymer solutions

Barker

1973

J. Fluid Mech.

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A laser-Doppler velocimeter suitable for the measurement of mean and fluctuating flow velocities in water is described. Results of a study using this system in an axisymmetric turbulent jet of water and dilute polymer solutions are given. The laser-Doppler technique is better suited for such measurements than either Pitot tubes or heat-transfer gauges because the Doppler velocity measurements are independent of the physical properties of the fluid. Previous velocity measurements in polymer jets have suffered from the effects of the additives upon the sensors.Turbulent round jets with Reynolds numbers between 5000 and 50000 were studied. Por a jet issuing from a convergent nozzle the additives were found to have no effect upon the mean axial velocity or turbulence intensity at any point in the jet. However, for a jet issuing from a long length of circular pipe, the additives reduced the centre-line velocity and increased the turbulence level in the early part of the jet. Thus the principal effect of a polymer additive upon tlie jet appears to result from its effect upon the initial conditions.

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Section: Resultsmentioning

confidence: 99%

Laser-Doppler measurements on a round turbulent jet in dilute polymer solutions

Barker

1973

J. Fluid Mech.

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“…Wells and Spangler (1967) injected a polymer solution into a turbulent water flow at both the wall and the axis of a pipe; in the former case, the wall shear stress was reduced almost directly downstream of the injection point, whereas in the latter case the drag reduction was observed relatively much further downstream, presumably only after the macromolecules had diffused to the wall region. Mean velocity profiles, shown.in Figure 9, indicate that, at low drag reduction, the region affected is closer to the wall than y+ N 50, whereas rough pipe experiments ( McNally, 1968;Spangler, 1969;Virk, 1971) show that onset is unaffected by the presence (hydraulically smooth flow) or absence (fully rough flow) of a viscous sublayer, which suggests that the region of interest is further from the wall than y+ -N 5; together, these implicate 5 < y + < 50 as the region affected by the macromolecules. Turbulence measurements (Figure l l a ) also suggest that the region affected is roughly 10 < y+ < 100.…”

Section: Physical Frameworkmentioning

confidence: 92%

Drag reduction fundamentals

1975

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Drag reduction by dilute solutions of linear, random-coiling macromolecules in turbulent pipe flow is reviewed. The experimental evidence is emphasized in three sections concerned with the graphical display of established features of the phenomenon, data correlation and analysis, and the physical mechanism of drag reduction. P. S. VlRK Deportment of Chemical Engineering Indian Institute of TechnologyMadras 600036, India SCOPEOur objective is to acquaint the reader with the phenomenon of drag reduction, in which the skin friction caused by turbulent flow of an ordinary liquid is reduced by additives. This phenomenon, discovered ahnut 1947, has received attention because it suggests practical benefits, such as increased pipeline capacities and faster ships, and is also theoretically stimulating, in the areas of wall turbulence and molecular rheology . This review, restricted to drag reduction by polymer solutions in pipe flow, has three sections: (1) the experimental evidence, (2) correlation and analysis, and (3) mechanism. Section 1 presents experimentally established results showing the flow regimes exhibited by polymer solutions, the relationships among flow and macromolecular parameters, and the changes in mean and turbulent flow structures which accompany drag reduction. The conclusions of Section 1 are documented in Section 2. The latter concerns the empirical correlation of experimental results, with analysis (and tabulations) of the data used for this purpose. Section 2 also provides for discussion of evidence not fully enough established to be included in Section 1. Finally, in Section 3 an attempt is made to physically interpret the experimental results, to infer the nature of the polymer-turbulence interaction responsible for drag reduction and its effect on the energy balances of turbulent pipe flow. CONCLUSIONS AND SIGNIFICANCE1. Gross Flow. Drag reduction by dilute polymer solutions in turbulent pipe flow appears bounded between two universal asymptotes, namely, the Prandtl-Karman law [Equation (2)] for Newtonian turbulent flow and a maximum drag reduction asymptote [Equation (4)]. Between these limits is a polymeric regime in which the observed friction factor relations are approximately linear on Prandtl-Karman coordinates and can be characterized by two parameters-the wall shear stress at the onset of drag reduction and the slope increment by which the polymer solution slope exceeds Newtonian. For a given polymer species-solvent pair: The onset wall shear stress is essentially independent of pipe diameter, polymer concentration, and solvent viscosity, and varies inversely as the two to three power of polymer radius of gyration [Equations (19) and ( 5 ) ] . The slope increment is essentially independent of pipe diameter, varies as the square root of polymer concentration, and as the three-halves power of the number of chain links in the polymer backbone [Equation (S)], and seems unaffected by decreases in polymer excluded volume.2. Mean Velocity Profiles. On law of the wall coordinates, these posse...

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“…It was found that the intensity level of the turbulence near the wall increased with injection, and the spectrum showed more energy at low wave-numbers and less a t high wave-numbers compared to that in water. Spangler (1969) obtained measurements similar to those of Virk et al (1967) in a pipe, but with a different polymer (an ionic copolymer of polyacrylamide and polyacrylic acid), and used an impact tube from which instantaneous velocity measurements were inferred. The intensity level at the centre-line of the pipe was increased up to three times that in water, the effect decreasing with increasing mean velocity.…”

Section: A Friehe and W H Schwarxmentioning

confidence: 99%

Grid-generated turbulence in dilute polymer solutions

Friehe

Schwarz

1970

J. Fluid Mech.

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Measurements were made of some of the properties of grid-generated, turbulence for several concentrations of a drag-reducing polymer additive in water. Reference measurements of the grid pressure drops, streamwise intensities and one-dimensional spectra in pure water agreed with previous measurements obtained in Newtonian fluids. Corresponding results for the polymer solutions showed that the grid pressure drops were generally lowered, the turbulence intensity levels were increased and the one-dimensional energy spectra were unchanged compared to the results in water. A dimensionless rate of decay correlation was introduced which removed the dependence of the rate of decay on the initial conditions of grid-generated turbulence for Newtonian fluids: the polymer solution decay results did not follow this correlation, indicating that the decay process is different in these fluids. The one-dimensional energy spectra of the turbulence in the polymer solutions were of the same shape as those in Newtonian fluids, and were normalized with modified Kolmogoroff variables using an effective viscosity (Lumley 1964) and the viscous dissipation in order to provide a quantitative comparison to Newtonian spectra. All of the normalized spectra in the polymer solutions collapsed to a single curve which coincided with the normalized Newtonian spectral curve. It was also found that the rate of decay was less than the viscous dissipation in the polymer solutions, in accordance with recent theoretical predictions.

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Studies of Viscous Drag Reduction with Polymers Including Turbulence Measurements and Roughness Effects

Cited by 24 publications

References 12 publications

Laser-Doppler measurements on a round turbulent jet in dilute polymer solutions

Laser-Doppler measurements on a round turbulent jet in dilute polymer solutions

Drag reduction fundamentals

Grid-generated turbulence in dilute polymer solutions

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