Drag reduction in the turbulent pipe flow of polymers

Escudier, M. P.; Presti, Federico Lo; Smith, S. Jerrod

doi:10.1016/s0377-0257(98)00098-6

Cited by 147 publications

(155 citation statements)

References 23 publications

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“…8,14 Evidence suggests that the existence of ECS is a prerequisite for transition (cf. the Introduction).…”

Section: A Existence Of the Ecsmentioning

confidence: 99%

“…Observations of drag-reducing fluids indicate that, at least near the onset Reynolds number for drag reduction, the effects of the polymer are confined primarily to the near-wall buffer layer, 1,[5][6][7][8] which is the most important region for the production and dissipation of turbulent energy. 9 From experia)…”

Section: Introductionmentioning

confidence: 99%

“…12,16,17 These changes become more pronounced as the extensional viscosity of the polymer solution is increased. 8,16,18,19 Due to the importance of the buffer region structures in the production of turbulent energy and the observation that these structures are modified in drag-reducing flows, they are the focus of the present study. To perform the study in a well-controlled way, we make use of an "exact" model of these structures, the family of so-called "exact coherent states" (ECS) recently found in plane shear flows.…”

Section: Introductionmentioning

confidence: 99%

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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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“…8,14 Evidence suggests that the existence of ECS is a prerequisite for transition (cf. the Introduction).…”

Section: A Existence Of the Ecsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Polymer drag reduction in exact coherent structures of plane shear flow

et al. 2004

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“…The central rheological feature of drag-reducing additives is their extensional behavior in solution: for dilute polymer solutions in particular the stresses arising in extensional flow can be orders of magnitude larger than those developed in a shear flow. This fact is well-recognized; nevertheless the mechanism of interaction between polymer stretching and turbulent structure is not well-understood and the goal of the present work is to attempt to shed light on this interaction.A key structural observation from experiments and direct numerical simulations (DNS) of drag-reducing solutions is the modification of the buffer region near the wall [4,5,6,7,8,9,10]. It has long been known that the flow in this region is very structured, containing streamwise vortices that lead to streaks in the streamwise velocity [11]; these structures are thickened in both the wall-normal and spanwise directions during flow of drag reducing solutions [4,5].…”

mentioning

confidence: 99%

“…A key structural observation from experiments and direct numerical simulations (DNS) of drag-reducing solutions is the modification of the buffer region near the wall [4,5,6,7,8,9,10]. It has long been known that the flow in this region is very structured, containing streamwise vortices that lead to streaks in the streamwise velocity [11]; these structures are thickened in both the wall-normal and spanwise directions during flow of drag reducing solutions [4,5].…”

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confidence: 99%

Toward a Structural Understanding of Turbulent Drag Reduction: Nonlinear Coherent States in Viscoelastic Shear Flows

Stone

Waleffe²,

Graham

2002

Phys. Rev. Lett.

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Nontrivial steady flows have recently been found that capture the main structures of the turbulent buffer layer. We study the effects of polymer addition on these "exact coherent states" (ECS) in plane Couette flow. Despite the simplicity of the ECS flows, these effects closely mirror those observed experimentally: structures shift to larger length scales, wall-normal fluctuations are suppressed while streamwise ones are enhanced, and drag is reduced. The mechanism underlying these effects is elucidated. These results suggest that the ECS are closely related to buffer layer turbulence.PACS numbers: 83.60. Yz,83.80.Rs,47.20.Ky,47.27.Cn Rheological drag reduction, the suppression by additives of skin friction in turbulent flow, has received much attention since its discovery in 1947 [1,2,3]. For many polymer-solvent systems, the pressure drop measured in the pipe flow of the solution can be 30 − 50% less than for the solvent alone. The central rheological feature of drag-reducing additives is their extensional behavior in solution: for dilute polymer solutions in particular the stresses arising in extensional flow can be orders of magnitude larger than those developed in a shear flow. This fact is well-recognized; nevertheless the mechanism of interaction between polymer stretching and turbulent structure is not well-understood and the goal of the present work is to attempt to shed light on this interaction.A key structural observation from experiments and direct numerical simulations (DNS) of drag-reducing solutions is the modification of the buffer region near the wall [4,5,6,7,8,9,10]. It has long been known that the flow in this region is very structured, containing streamwise vortices that lead to streaks in the streamwise velocity [11]; these structures are thickened in both the wall-normal and spanwise directions during flow of drag reducing solutions [4,5]. Because of its importance in the production and dissipation of turbulent energy [11], any effort to mechanistically understand rheological drag reduction should address this region.To better understand the effect of the polymer on the buffer layer, we wish to study a model flow that has structures similar to those seen in this region but without the full complexities of time-dependent turbulent flows. Fortunately, a family of such flows exists, in the recently-discovered "exact coherent states" (ECS) found by computational bifurcation analysis in plane Couette and plane Poiseuille flows [12,13,14,15,16]. These are three-dimensional, traveling wave flows (hence steady in a traveling reference frame) that appear via saddle-node bifurcations [35] at a Reynolds number somewhat below the transition value seen in experiments [17,18]. The structure of the ECS captures the counter-rotating staggered streamwise vortices that dominate the structure in the buffer region. From the dynamical point of view, there is evidence that these states form a part of the dynamical skeleton of the turbulent flow: i.e., they are saddle points that underlie the strange attract...

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Drag Reduction

Singh

2004

Encyclopedia of Polymer Science and Technology

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Turbulent drag reduction in fluid flow by additives has been an exotic field of research ever since its reported discovery in 1949. Various technical applications have been envisaged both for polymeric and surfactant drag reduction. Some successful applications include increased flow of oil and other fluids through pipelines, improved fire fighting and irrigation, improved flow in storm sewers, and flow augmentation by drag reducers in pipeline transport of sediments and slurries. Other possible applications include district heating circuits, industrial and agricultural sprays, and slow‐release fertilizers and pesticides. However, the mechanism of drag reduction still eludes exact explanation mainly because of the inability to characterize polymers, surfactants, and their interactions at molecular or micellar levels in turbulent flows. The main features of polymeric and surfactant homogeneous and heterogeneous drag reduction have been investigated by two‐component laser‐Doppler velocity meter in fully developed, well‐mixed, low concentration (1–2 ppm) drag‐reducing channel flows. Advances in computer technology have led to improved accuracies and reliability of experimental techniques and made possible direct numerical simulation of drag‐reducing turbulent flows. The role of extensional viscosity and elasticity of drag reducers is being keenly debated for the origin of drag reduction in theoretical and experimental investigations. A better understanding is emerging. Some synergistic effects have been observed in combining passive drag‐reducing devices such as riblets with polymers surfactants. Similar observations have been made in combination with microbubbles. This article provides an overview of the latest salient developments in materials, mechanisms, and applications in the field of polymeric drag reduction of various forms and geometries.

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Drag reduction in the turbulent pipe flow of polymers

Cited by 147 publications

References 23 publications

Polymer drag reduction in exact coherent structures of plane shear flow

Polymer drag reduction in exact coherent structures of plane shear flow

Toward a Structural Understanding of Turbulent Drag Reduction: Nonlinear Coherent States in Viscoelastic Shear Flows

Drag Reduction

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