Statistics and tensor analysis of polymer coil–stretch mechanism in turbulent drag reducing channel flow

Pereira, Anselmo Soeiro; Mompean, Gilmar; Thais, Laurent; Thompson, Roney L.

doi:10.1017/jfm.2017.332

Cited by 32 publications

(40 citation statements)

References 56 publications

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“…Similar to previous investigations, they reported vortical structures close to the low momentum regions and these vortices induce ejection and sweep events. Another coherent structure, hyperbolic structures, have been reported in NS study of Pereira et al In general, vortices (and hyperbolic structures) are responsible for energy dissipation in the self‐sustaining turbulent process and the PIV technique provides an excellent platform for visualizing coherent structures.…”

Section: Piv Studies Of Single‐phase Newtonian Fluid Flowmentioning

confidence: 93%

“…As will be discussed in subsequent sections of this article, these studies classified the spatiotemporal characteristics of fluid flow into active and hibernating turbulence regimes. The duration of each regime is characterized by the Reynolds and Weissenberg number of the flow …”

Section: Piv Studies Of Single‐phase Newtonian Fluid Flowmentioning

confidence: 99%

“…Polymer stresses oppose vortical motion resulting in the weakening of vortices . More recent numerical simulation studies have revealed important coherent structures such as hyperbolic structures (in addition to elliptical vortices) which are significantly weakened by the counter‐stretching action of DRP . These important findings require experimental validation and PIV technique could be used to validate these results.…”

Section: Piv Investigations Of Drag‐reducing Flowsmentioning

confidence: 99%

“…Furthermore, there is need for improvement of both spatial and temporal resolutions of PIV data acquisition especially where transient characteristics is to be measured. Recent numerical simulation studies have revealed important coherent structures such as hyperbolic structures (besides the elliptical vortices) and there is limited experimental investigation to validate this. Although, significant research has been done on the effect of DRAs on turbulence structures such as vortices and the associated ejection and sweep events, very limited studies have been done on the effect of DRAs on low‐speed streaks. Some recent numerical simulation studies have remarked that, in the near‐wall region, polymer does not only release energy to the streaks but also to elliptical and hyperbolic structures . Therefore, the traditional view on the mechanism of energy release by polymer when it relaxes requires further investigation.…”

Section: Research Gapsmentioning

confidence: 99%

“…Numerical simulation of drag‐reducing flows has also been extended to curved conduits with reasonable success. These include the works of Mompean and coworkers on drag‐reduced flows in straight and curved conduits …”

Section: Introductionmentioning

confidence: 99%

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Turbulence statistics and flow structure in fluid flow using particle image velocimetry technique: A review

Ayegba

Edomwonyi‐Otu

2020

Engineering Reports

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Particle image velocimetry (PIV) measurement technique provides an excellent opportunity for investigating instantaneous spatial structures which are not always possible with point measurements techniques like laser Doppler velocimetry. In this review, it was shown that PIV technique provides an effective means of visualizing important structures of Newtonian and drag‐reducing fluid flows. Such structures include large‐scale‐events that constitute an important portion of the Reynolds stress tensor; shear layers of drag‐reducing flows, which have been suggested to constitute the mechanism of drag reduction (DR); and near wall vortices/low speed streaks which constitute the mechanism of turbulence production. PIV investigations of turbulence statistics in Newtonian and drag‐reducing fluid flows were reviewed with the view of providing explanation to DR by additives. Results of turbulence statistics, for Newtonian fluid flow, showed that streamwise velocity fluctuations and turbulence intensity had peak values close to the wall, in a region of high mean velocity gradient, while radial fluctuating velocity and Reynolds stress tensor had peaks further from the wall and at approximately the same detachment from the wall. In single‐ and two‐phase flows in horizontal channels, the velocity profile of polymer solution, in the turbulent regime, show asymmetric behavior. This review highlighted important interfacial characteristics in gas‐liquid flows such as S‐shaped velocity profile as well as the turbulences statistics in each phase and across the interface region. Drag‐reducing agents (DRAs)‐imposed changes on turbulence statistics and flow structures were also examined. PIV studies of drag‐reducing flows showed that DRAs act to dampen wall‐normal‐, streamwise fluctuating velocity, and Reynolds stress tensor. The reduction in Reynolds stress tensor is higher than the reduction of both wall‐normal and streamwise velocity fluctuations and this discrepancy has been associated with the decorrelation of the component of fluctuating velocity. Furthermore, the addition of DRA produces a shift of the peak of wall‐normal velocity fluctuations further from the wall due to increased buffer layer thickness. DRAs do not only act to reduce drag but also to modify the flow structure. The major influence of DRAs on flow structures is seen in the reduced strength and population of vortices close to the wall, increased spacing between low‐speed streaks, reduced frequency of large‐scale events and reduced concentration of small eddies. Effect of DRAs on flow structures depends not only on the level of DR but also on the concentration and molecular weight. The effect of concentration is linked to the elastic properties of the DRA. The influence of DRA on oil‐water flows in similar to its effect on single phase water flow with regards to changes in near wall structures and turbulence statistics. A few research gaps and limitations of the PIV techniques were also highlighted.

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Section: Piv Studies Of Single‐phase Newtonian Fluid Flowmentioning

confidence: 93%

Section: Piv Studies Of Single‐phase Newtonian Fluid Flowmentioning

confidence: 99%

Section: Piv Investigations Of Drag‐reducing Flowsmentioning

confidence: 99%

Section: Research Gapsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Turbulence statistics and flow structure in fluid flow using particle image velocimetry technique: A review

Ayegba

Edomwonyi‐Otu

2020

Engineering Reports

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On the link between experimentally‐measured turbulence quantities and polymer‐induced drag reduction in pipe flows

et al. 2019

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In this study, we investigate the hydrodynamics of polymer-induced drag reduction in horizontal turbulent pipe flows. We provide spatiotemporally resolved information of velocity and its gradients obtained with particle image velocimetry (PIV) measurements in solutions of water with dissolved polyethylene oxide (PEO) of three different molecular weights, at various dilute concentrations and with flow Reynolds numbers from 35, 000 to 210, 000. We find that the local magnitudes of important turbulent flow variables correlate with the measured levels of drag reduction irrespective of the flow Reynolds number, polymer weight and concentration. Contour maps illustrate the spatial characteristics of this correlation. A relationship between the drag reduction and the turbulent flow variables is found. The effects of the polymer molecular weight, its concentration and the Reynolds number on the flow are further examined through joint probability distributions of the fluctuations of the streamwise and spanwise velocity components.

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A review of drag reduction by additives in curved pipes for single‐phase liquid and two‐phase flows

Ayegba

Edomwonyi‐Otu

Yusuf

et al. 2020

Engineering Reports

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The effect of drag‐reducing agents (DRAs) on fluid flows in straight pipes has been well documented. Key among these is the effect of DRAs on turbulence statistics (Reynolds shear stress, turbulence intensity, streamwise and wall‐normal velocity fluctuation among others). These primary effects result in secondary effects such as modification of mean velocity profile and reduction in frictional losses (drag reduction, DR). Interestingly, in curved pipe flows, the characteristic of flow is more complex due to secondary flow, wake effects and under‐developed flow characteristics. Therefore, a review of investigations on the effect of DRAs in curved pipe flows is presented in this paper. The paper highlights the difference between DR in straight and curved conduits as well as the interaction between DRAs and flow characteristics of curved pipe flows. Proposed mechanisms of DR, and factors that influence their effectiveness also received attention. It was shown that significant DR can be achieved in curved pipes. A review of various experimental results revealed that DR by additives in curved pipes is generally lower than in straight pipes but with certain similarities. It decreases with increase in curvature ratio and is more pronounced in the transition and turbulent flow regimes. Maximum DR asymptote differed between straight and curved pipes and between polymer and surfactant. Due to the limited studies in the area of DR for gas‐liquid flow in curved pipes, no definite conclusion could be drawn on the effect of DRAs on such flows. A number of questions remain such as physical interaction between molecules of DRA and flow features such as secondary flow streamlines and wakes. Hence, some research gaps have been identified with recommendations for areas of future researches.

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Statistics and tensor analysis of polymer coil–stretch mechanism in turbulent drag reducing channel flow

Cited by 32 publications

References 56 publications

Turbulence statistics and flow structure in fluid flow using particle image velocimetry technique: A review

Turbulence statistics and flow structure in fluid flow using particle image velocimetry technique: A review

On the link between experimentally‐measured turbulence quantities and polymer‐induced drag reduction in pipe flows

A review of drag reduction by additives in curved pipes for single‐phase liquid and two‐phase flows

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