Influence of drag-reducing polymers on turbulence: effects of Reynolds number, concentration and mixing

Warholic, M. D.; Massah, H.; Hanratty, Thomas J.

doi:10.1007/s003480050371

Cited by 298 publications

(364 citation statements)

References 17 publications

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“…These trends are opposite to those observed in polymer-induced drag reduction, see e.g. Warholic et al (1999a).…”

Section: Turbulence Modulationcontrasting

confidence: 79%

“…In polymer solutions there is an increase in the peak value of u rms , while v rms and w rms are reduced everywhere, also close to the wall; see e.g. Warholic et al (1999a). This further indicates the structural difference between the present type of drag reduction and polymer-induced drag reduction.…”

Section: Shear Stress Budgetsmentioning

confidence: 82%

“…This is different with polymer-induced drag-reduced flow, which shows a parallel upward shift of the logarithmic profile; see e.g. Warholic, Massah & Hanratty (1999a).…”

Section: Particle Concentrationmentioning

confidence: 85%

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Turbulent drag reduction using fluid spheres

Gillissen

2013

J. Fluid Mech.

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Using direct numerical simulations of turbulent Couette flow, we predict drag reduction in suspensions of neutrally buoyant fluid spheres, of diameter larger than the Kolmogorov length scale. The velocity fluctuations are enhanced in the streamwise direction, and reduced in the cross-stream directions, which is similar to the more studied case of drag reduction using polymers. Despite these similarities, the drag reduction mechanism is found to originate in the logarithmic region, while the buffer region contributes to a slight drag increase, which is opposite to polymer-induced drag reduction. Another striking difference is the reduction of the turbulent energy at the large scales and an enhancement at the small scales.

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“…These trends are opposite to those observed in polymer-induced drag reduction, see e.g. Warholic et al (1999a).…”

Section: Turbulence Modulationcontrasting

confidence: 79%

Section: Shear Stress Budgetsmentioning

confidence: 82%

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Turbulent drag reduction using fluid spheres

Gillissen

2013

J. Fluid Mech.

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“…The log-layer mean velocity gradient (inverse von Kármán constant) is significantly higher than the Newtonian value over a large fraction of the channel. 1 Furthermore, as the level of drag reduction increases, the streamwise velocity fluctuations (scaled with u ) peak and then decrease, 51,52 a result that suggests that at high drag reduction a change in the basic turbulence production Polymer drag reduction in exact coherent structuresmechanism occurs. The relevance of the viscoelastic ECS in this regime is not clear.…”

Section: Discussionmentioning

confidence: 99%

Polymer drag reduction in exact coherent structures of plane shear flow

et al. 2004

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Recently discovered traveling-wave solutions to the Navier-Stokes equations in plane shear geometries provide model flows for the study of turbulent drag reduction by polymer additives. These solutions, or "exact coherent states" (ECS), qualitatively capture the dominant structure of the near-wall buffer region of shear turbulence, i.e., counter-rotating pairs of streamwise-aligned vortices flanking a low-speed streak in the streamwise velocity. The optimum length scales for the ECS match well the length scales of the turbulent coherent structures and evidence suggests that the ECS underlie the dynamics of these structures. We study here the effect of viscoelasticity on these states. The changes to the velocity field for the viscoelastic ECS, where the FENE-P model calculates the polymer stress, mirror the modifications seen in experiments of fully turbulent flows of polymer solutions at low to moderate levels of drag reduction: drag is reduced, streamwise velocity fluctuations increase while wall-normal fluctuations decrease, and smaller wavelength structures are suppressed. These modifications to the ECS are due to the suppression of the streamwise vortices. The polymer molecules become highly stretched in the wavy, streamwise streaks, where the flow is predominately elongational, then relax as they move from the streaks into and around the streamwise vortices, where the flow is predominately rotational. This relaxation of the polymer molecules produces a force that directly opposes the fluid motion in the vortices, weakening them. Since the pressure fluctuations have their greatest magnitude (i.e., they are most negative) in the cores of the vortices, a reduction in vortex strength leads to a decrease in the magnitude of the pressure fluctuations. The pressure fluctuations redistribute energy from the streamwise velocity fluctuations to the Reynolds shear stress, so a decrease in their magnitude leads to a reduction in turbulent drag. For the viscoelastic ECS, we also find that after the onset of drag reduction (at Weissenberg number, WeϷ 7) there is a dramatic increase in the critical wall-normal length scale at which the ECS can exist. This sharp increase in length scale mirrors experimental observations and is also consistent with the observed shift to higher Reynolds numbers of the transition to turbulence in polymer solutions.

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“…Consequently, the Reynolds shear stress at the wall decreases, thus leading to a reduction in drag. 38 Warholic et al 39 also reported that based on their experimental data, "the log-layer is displaced upward and thickness of viscous wall region increases with increasing drag-reduction." By examining the velocity in the near-wall region, Yang and Dou 36 found that the thickening of the viscous sublayer, i.e., ␦ + in Eq.…”

Section: ͑28͒mentioning

confidence: 98%

Modeling of viscoelastic turbulent flow in channel and pipe

Yang

Dou

2008

Physics of Fluids

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This paper investigates turbulent flows with or without polymer additives in open channels and pipes. Equations of mean velocity, root mean square of velocity fluctuations, and energy spectrum are derived, in which the shear stress deficit model is used and the non-Newtonian properties are represented by the viscoelasticity ␣ * . The obtained results show that, with ␣ * increment, ͑1͒ the streamwise velocity fluctuations is increased, ͑2͒ the wall-normal velocity fluctuation is attenuated, ͑3͒ the Reynolds stress is reduced, and ͑4͒ there is a redistribution of energy from high frequencies to the low frequencies for the streamwise component, but dimensionless distribution over all frequencies almost remains the same as that in Newtonian fluid flows. Good agreement between the derived equations and experimental data in small drag-reduction regime is achieved, which indicates that the present model is workable for Newtonian/non-Newtonian fluid turbulent flows.

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Influence of drag-reducing polymers on turbulence: effects of Reynolds number, concentration and mixing

Cited by 298 publications

References 17 publications

Turbulent drag reduction using fluid spheres

Turbulent drag reduction using fluid spheres

Polymer drag reduction in exact coherent structures of plane shear flow

Modeling of viscoelastic turbulent flow in channel and pipe

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