Drag reduction by additives: a review

Nieuwstadt, F. T. M.; Toonder, Jaap M.J. den

doi:10.1007/978-3-7091-2574-8_10

Cited by 25 publications

(11 citation statements)

References 52 publications

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“…However, drag reduction in the suspensions of rigid fibers was also observed in [25,26], similarly to what was reported for dilute polymer solutions [27,28]. A review of the phenomenon of drag reduction was provided by Nieuwstadt and den Toonder [29]. While drag reduction was observed also with spherical particles [30], very few other evidences were reported in the literature.…”

Section: Introductionsupporting

confidence: 65%

Effect of particle shape on fluid statistics and particle dynamics in turbulent pipe flow

2018

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Anisotropic particles are present in many natural and industrial flows. Here we perform direct numerical simulation (DNS) of turbulent pipe flows with dispersed finite-size prolate spheroids simulated by means of the lattice Boltzmann method (LBM). We consider three different particle shapes: spheroidal (aspect ratio 2 and 3) and spherical. These three simulations are complemented with a reference simulation of a single-phase flow. For the sake of comparison, all simulations, laden or unladen have the same energy input. The flow geometry used is a straight pipe with length eight times its radius where the fluid is randomly seeded with 256 finite-size particles. The volume fraction of particles in the flow has been kept fixed at 0.48% by varying the major and minor axis of each particle such that their volume remains the same. We studied the effect of different particle shapes on particle dynamics and orientation, as well as on the flow modulation. We show that the local accumulation of spheres close to the wall decreases for spheroids with increasing aspect ratio. These spheroidal particles rotate slower than spheres near to the wall and tend to stay with their major axes aligned to the flow streamwise direction. Despite the lower rotation rates, a higher intermittency in the rotational rates was observed for spheroids and this increase at increasing the aspect ratio. The drag reduction observed for particles with higher aspect ratio have also been investigated using the one-dimensional energy and dissipation spectra. These results point to the relevance of particle shapes on their dynamics and their influence on the turbulent flow.

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Section: Introductionsupporting

confidence: 65%

Effect of particle shape on fluid statistics and particle dynamics in turbulent pipe flow

2018

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“…This is a significant new finding, in view of the fact that streaks and streak spacing are usually difficult to alter even in cases where a very large amount of drag reduction has been obtained. For example, in drag reduction using polymers the increase in streak spacing is proportional to the percentage of drag reduction (Tiederman 1990;Sureshkumar, Beris & Handler 1997;Nieuwstadt & DenToonder 2001). In order to contrast this finding with the turbulence structure resulting from other drag reducing techniques, we plot in figure 24 the wall streaks visualized in simulations of turbulent flow over streamwise riblets (Chu & Karniadakis 1993).…”

Section: Modifications Of Near-wall Structuresmentioning

confidence: 99%

Drag reduction in wall-bounded turbulence via a transverse travelling wave

2002

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Computational experiments based on direct numerical simulation of wall-bounded flow reveal that turbulence production can be suppressed by the action of a transverse travelling wave. Flow visualizations show that the near-wall flow structure is altered substantially, compared to other turbulence control techniques, leading to a large amount of shear stress reduction (i.e., more than 30%). The travelling wave can be induced by a spanwise force that is confined within the viscous sublayer, it has its maximum at the wall, and decays exponentially away from it. We demonstrate the robustness of this approach, and its application in salt water using arrays of electro-magnetic tiles that can produce the required travelling wave excitation. We also study corresponding results from spanwise oscillations using a similar force, which also leads to large drag reduction. Although the turbulence statistics for the two approaches are similar, the near-wall structures appear to be different: in the spanwise oscillatory excitation there is a clear presence of wall-streaks whereas in the travelling wave excitation these streaks have disappeared. From the fundamental point of view, the new finding of this work is that appropriate enhancement of the streamwise vortices leads to weakening of the streak intensity, as measured by the normal vorticity component, and correspondingly substantial suppression of turbulence production. From the practical point of view, our findings provide guidance for designing different surface-based actuation techniques including piezoelectric materials, shape memory alloys, and electro-magnetic tiles.

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“…However, their work showed that the dynamics of these polymers upon approaching the asymptote are different. They found that the degree of drag reduction for a rigid polymer is dependent only on the concentration while it is well known that for a flexible polymer, it is a function of concentration, Reynolds number and the Deborah number [1][2][3][4][5]. For flexible polymers, the asymptote is reached even for low concentrations and then a crossover back to the Newtonian core is found.…”

Section: Introductionmentioning

confidence: 97%

“…The phenomenon of drag reduction, often referred to as "Tom's phenomenon", has been the subject of extensive reviews by Lumley [1], Virk [2], Berman [3], Hoyt [4], Nieuwstadt and den Toonder [5], Graham [6] and many others, and the behaviour of flexible polymer solutions as drag-reducing agents is now fairly well understood. A notional limit of drag reduction of 40% has been found below which, the flow is categorized as "low" drag-reducing and above which, "high" drag-reducing (e.g.…”

Section: Introductionmentioning

confidence: 99%