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Journal articles on the topic 'Drag reduction'

Author: Grafiati

Published: 4 June 2021

Last updated: 7 July 2024

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1

García-Mayoral, Ricardo, and Javier Jiménez. "Drag reduction by riblets." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369, no. 1940 (April 13, 2011): 1412–27. http://dx.doi.org/10.1098/rsta.2010.0359.

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The interaction of the overlying turbulent flow with riblets, and its impact on their drag reduction properties are analysed. In the so-called viscous regime of vanishing riblet spacing, the drag reduction is proportional to the riblet size, but for larger riblets the proportionality breaks down, and the drag reduction eventually becomes an increase. It is found that the groove cross section A + g is a better characterization of this breakdown than the riblet spacing, with an optimum . It is also found that the breakdown is not associated with the lodging of quasi-streamwise vortices inside the riblet grooves, or with the inapplicability of the Stokes hypothesis to the flow along the grooves, but with the appearance of quasi-two-dimensional spanwise vortices below y + ≈30, with typical streamwise wavelengths . They are connected with a Kelvin–Helmholtz-like instability of the mean velocity profile, also found in flows over plant canopies and other surfaces with transpiration. A simplified stability model for the ribbed surface approximately accounts for the scaling of the viscous breakdown with A + g .

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2

Watanabe, Osamu. "Drag Reduction by Microbubbles." Proceedings of the Fluids engineering conference 2000 (2000): 176. http://dx.doi.org/10.1299/jsmefed.2000.176.

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3

GILLISSEN, J. J. J., B. J. BOERSMA, P. H. MORTENSEN, and H. I. ANDERSSON. "Fibre-induced drag reduction." Journal of Fluid Mechanics 602 (April 25, 2008): 209–18. http://dx.doi.org/10.1017/s0022112008000967.

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We use direct numerical simulation to study turbulent drag reduction by rigid polymer additives, referred to as fibres. The simulations agree with experimental data from the literature in terms of friction factor dependence on Reynolds number and fibre concentration. An expression for drag reduction is derived by adopting the concept of the elastic layer.

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4

HŒPFFNER, JÉRÔME, and KOJI FUKAGATA. "Pumping or drag reduction?" Journal of Fluid Mechanics 635 (September 10, 2009): 171–87. http://dx.doi.org/10.1017/s0022112009007629.

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Two types of wall actuation in channel flow are considered: travelling waves of wall deformation (peristalsis) and travelling waves of blowing and suction. The flow response and its mechanisms are analysed using nonlinear and weakly nonlinear computations. We show that both actuations induce a flux in the channel in the absence of an imposed pressure gradient and can thus be characterized as pumping. In the context of flow control, pumping and drag reduction are strongly connected, and we seek to define them properly based on these two actuation examples. Movies showing the flow motion for the two types of actuation are available with the online version of this paper (journals.cambridge.org/FLM).

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5

Bushnell, D. M., and K. J. Moore. "Drag Reduction in Nature." Annual Review of Fluid Mechanics 23, no. 1 (January 1991): 65–79. http://dx.doi.org/10.1146/annurev.fl.23.010191.000433.

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6

Bushnell, Dennis M. "SHOCK WAVE DRAG REDUCTION*." Annual Review of Fluid Mechanics 36, no. 1 (January 2004): 81–96. http://dx.doi.org/10.1146/annurev.fluid.36.050802.122110.

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7

Hewitt, Geoffrey F., A. Bismarck, J. M. Griffen, L. Chen, and John Christos Vassilicos. "2.14.1 DRAG REDUCTION: INTRODUCTION." Heat Exchanger Design Updates 11, no. 3 (2004): 5. http://dx.doi.org/10.1615/heatexchdesignupd.v11.i3.10.

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8

Hewitt, Geoffrey F., A. Bismarck, J. M. Griffen, L. Chen, and John Christos Vassilicos. "2.14.2 POLYMER DRAG REDUCTION." Heat Exchanger Design Updates 11, no. 3 (2004): 25. http://dx.doi.org/10.1615/heatexchdesignupd.v11.i3.20.

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9

Bismarck, A., L. Chen, J. M. Griffen, John Christos Vassilicos, and Geoffrey F. Hewitt. "2.14.3 SURFACTANT DRAG REDUCTION." Heat Exchanger Design Updates 11, no. 3 (2004): 5. http://dx.doi.org/10.1615/heatexchdesignupd.v11.i3.30.

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10

Abdul Bari, Hayder A., Siti Nuraffini Kamaruliza, and Rohaida Che Man. "Investigating Drag Reduction Characteristic using Okra Mucilage as New Drag Reduction Agent." Journal of Applied Sciences 11, no. 14 (July 1, 2011): 2554–61. http://dx.doi.org/10.3923/jas.2011.2554.2561.

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11

Bushnell, D. M. "Aircraft drag reduction—a review." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 217, no. 1 (January 1, 2003): 1–18. http://dx.doi.org/10.1243/095441003763031789.

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The paper summarizes the state of the art in aeronautical drag reduction across the speed range for the “conventional” drag components of viscous drag, drag due to lift and wave drag. It also describes several emerging drag-reduction approaches that are either active or reactive/interactive and the drag reduction potentially available from synergistic combinations of advanced configuration aerodynamics, viscous drag-reduction approaches, revolutionary structural concepts and propulsion integration.

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12

Chuan Eun, Lay, Azmin Shakrine Mohd Rafie, Surjatin Wiriadidjaja, and Omar Faruqi Marzuki. "An overview of passive and active drag reduction methods for bluff body of road vehicles." International Journal of Engineering & Technology 7, no. 4.13 (October 9, 2018): 53. http://dx.doi.org/10.14419/ijet.v7i4.13.21328.

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This paper is an overview of results done on bluff body road vehicle’s base drag reduction either by experimental or numerical methods. Two categories of devices are divided that prove certain degrees of effectiveness in reducing the base drag, namely passive and active. The reduction of drag coefficient achieved in existing research ranging from 5% to 50%, which varies for each method and device. However, the higher the achieved drag reduction is, the greater the compensation required is. The compensation comes in various forms to achieve the desirable drag reduction. For passive drag reduction, hump shaped bluff body with boat-tail shows significant drag reduction by 50.9% compared to the other methods. Meanwhile, one of the potential of active drag reductions is by utilizing rotating cylinder. The rotating can reduce the drag on the bluff body by influencing the separation of boundary layer. The drag can be further reduced by enhancing the rotating cylinder with surface roughness and rotation speed. A notable 23% reduction of drag coefficient using rough surface on bluff body vehicle’s is achieved compared to the smooth surface.

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13

Jaafar, A., and R. J. Poole. "Drag Reduction of Biopolymer Flows." Journal of Applied Sciences 11, no. 9 (April 15, 2011): 1544–51. http://dx.doi.org/10.3923/jas.2011.1544.1551.

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14

Doi, Yasuaki, Kazu-hiro Mori, and Takio Hotta. "Frictional Drag Reduction by Microbubbles." Journal of the Society of Naval Architects of Japan 1991, no. 170 (1991): 55–63. http://dx.doi.org/10.2534/jjasnaoe1968.1991.170_55.

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15

Babenko, V. V. "Hydrobionic Principles of Drag Reduction." International Journal of Fluid Mechanics Research 30, no. 2 (2003): 125–46. http://dx.doi.org/10.1615/interjfluidmechres.v30.i2.10.

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16

Tong, P., W. I. Goldburg, J. S. Huang, and T. A. Witten. "Anisotropy in turbulent drag reduction." Physical Review Letters 65, no. 22 (November 26, 1990): 2780–83. http://dx.doi.org/10.1103/physrevlett.65.2780.

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17

Gao, Ge, and W. L. Chow. "Drag reduction in accelerating flow." AIAA Journal 30, no. 8 (August 1992): 2155–56. http://dx.doi.org/10.2514/3.11194.

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18

MORI, Tatsuki, Naoto KATO, and Hiroaki HASEGAWA. "Drag Reduction Effect of Microbubbles." Proceedings of Conference of Kanto Branch 2019.25 (2019): 19H12. http://dx.doi.org/10.1299/jsmekanto.2019.25.19h12.

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19

Bonn, Daniel, Yacine Amarouchène, Christian Wagner, Stéphane Douady, and Olivier Cadot. "Turbulent drag reduction by polymers." Journal of Physics: Condensed Matter 17, no. 14 (March 25, 2005): S1195—S1202. http://dx.doi.org/10.1088/0953-8984/17/14/008.

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20

Storm, D. A., R. J. McKeon, H. L. McKinzie, and C. L. Redus. "Drag Reduction in Heavy Oil." Journal of Energy Resources Technology 121, no. 3 (September 1, 1999): 145–48. http://dx.doi.org/10.1115/1.2795973.

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Transporting heavy crude oil by pipeline requires special facilities because the viscosity is so high at normal field temperatures. In some cases the oil is heated with special heaters along the way, while in others the oil may be diluted by as much as 30 percent with kerosene. Commercial drag reducers have not been found to be effective because the single-phase flow is usually laminar to only slightly turbulent. In this work we show the effective viscosity of heavy oils in pipeline flow can be reduced by a factor of 3–4. It is hypothesized that a liquid crystal microstructure can be formed so that thick oil layers slip on thin water layers in the stress field generated by pipeline flow. Experiments in a 1 1/4-in. flow loop with Kern River crude oil and a Venezuela crude oil BCF13 are consistent with this hypothesis. The effect has also been demonstrated under field conditions in a 6-in. flow loop using a mixture of North Sea and Mississippi heavy crude oils containing 10 percent brine.

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21

MATSUZAKI, Takeshi. "Drag Reduction of Racing Swimsuit." Journal of the Society of Mechanical Engineers 108, no. 1039 (2005): 436–37. http://dx.doi.org/10.1299/jsmemag.108.1039_436.

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22

Nakamura, Kunio. "Turbulent drag reduction by polymers." Kobunshi 34, no. 2 (1985): 86–89. http://dx.doi.org/10.1295/kobunshi.34.86.

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23

MURAI, Yuichi. "Frictional Drag Reduction Using Microbubbles." Journal of the Society of Mechanical Engineers 115, no. 1127 (2012): 688–91. http://dx.doi.org/10.1299/jsmemag.115.1127_688.

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24

Mohammadi, A., and J. M. Floryan. "Groove optimization for drag reduction." Physics of Fluids 25, no. 11 (November 2013): 113601. http://dx.doi.org/10.1063/1.4826983.

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25

Gad-el-Hak, Mohamed. "Compliant coatings for drag reduction." Progress in Aerospace Sciences 38, no. 1 (January 2002): 77–99. http://dx.doi.org/10.1016/s0376-0421(01)00020-3.

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26

Choi, Hyoung J., and Myung S. Jhon. "Polymer-Induced Turbulent Drag Reduction." Industrial & Engineering Chemistry Research 35, no. 9 (January 1996): 2993–98. http://dx.doi.org/10.1021/ie9507484.

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27

Hoyt, J. W. "Drag reduction in polysaccharide solutions." Trends in Biotechnology 3, no. 1 (January 1985): 17–21. http://dx.doi.org/10.1016/0167-7799(85)90071-x.

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28

Bandyopadhyay, Promode R. "Stokes Mechanism of Drag Reduction." Journal of Applied Mechanics 73, no. 3 (September 20, 2005): 483–89. http://dx.doi.org/10.1115/1.2125974.

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The mechanism of drag reduction due to spanwise wall oscillation in a turbulent boundary layer is considered. Published measurements and simulation data are analyzed in light of Stokes’ second problem. A kinematic vorticity reorientation hypothesis of drag reduction is first developed. It is shown that spanwise oscillation seeds the near-wall region with oblique and skewed Stokes vorticity waves. They are attached to the wall and gradually align to the freestream direction away from it. The resulting Stokes layer has an attenuated nature compared to its laminar counterpart. The attenuation factor increases in the buffer and viscous sublayer as the wall is approached. The mean velocity profile at the condition of maximum drag reduction is similar to that due to polymer. The final mean state of maximum drag reduction due to turbulence suppression appears to be universal in nature. Finally, it is shown that the proposed kinematic drag reduction hypothesis describes the measurements significantly better than what current direct numerical simulation does.

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29

Wang, Jiadao, Bao Wang, and Darong Chen. "Underwater drag reduction by gas." Friction 2, no. 4 (December 2014): 295–309. http://dx.doi.org/10.1007/s40544-014-0070-2.

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30

Yu, Bo, Jacques L. Zakin, Yasuo Kawaguchi, Jinjia Wei, Fengchen Li, and Yi Wang. "Advances in Turbulent Drag Reduction." Advances in Mechanical Engineering 7, no. 2 (December 17, 2014): 862424. http://dx.doi.org/10.1155/2014/862424.

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31

Drappier, J., T. Divoux, Y. Amarouchene, F. Bertrand, S. Rodts, O. Cadot, J. Meunier, and Daniel Bonn. "Turbulent drag reduction by surfactants." Europhysics Letters (EPL) 74, no. 2 (April 2006): 362–68. http://dx.doi.org/10.1209/epl/i2005-10519-x.

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32

OGATA, Satoshi, and Keigo SHIMIZU. "Drag Reduction by Hydrophobic Microstructures." Journal of Environment and Engineering 6, no. 2 (2011): 291–301. http://dx.doi.org/10.1299/jee.6.291.

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33

FUKAGATA, Koji. "Drag Reduction by Wavy Surfaces." Journal of Fluid Science and Technology 6, no. 1 (2011): 2–13. http://dx.doi.org/10.1299/jfst.6.2.

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34

Hoyt, J. W., and R. H. J. Sellin. "Polymer ?threads? and drag reduction." Rheologica Acta 30, no. 4 (1991): 307–15. http://dx.doi.org/10.1007/bf00404191.

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35

Tsai, Peichun Amy. "Slippery interfaces for drag reduction." Journal of Fluid Mechanics 736 (November 1, 2013): 1–4. http://dx.doi.org/10.1017/jfm.2013.376.

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AbstractInspired by natural interfaces with surprising transport properties, innovative modifications of surfaces have been engineered to reduce drag. The common theme across these new developments is the presence of lubricant patches or layers that decrease the direct contact of viscous liquid with non-slippery solid walls. For laminar flow, the traditional assumption regarding the lubricant layer is a constant shear rate or a steady pressure gradient, implying a net flow rate of the lubricant film. By challenging this assumption, Busse et al. (J. Fluid Mech., vol. 727, 2013, pp. 488–508) rigorously found that the hydrodynamic slip is reduced by the presence of a reversal of lubricant flow close to the wall. The analytical results for velocity field and change in drag provide insight into the optimal design of slippery surfaces with lubricant layers for drag reduction.

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36

Floryan, Daniel, and J. M. Floryan. "Drag reduction in heated channels." Journal of Fluid Mechanics 765 (January 23, 2015): 353–95. http://dx.doi.org/10.1017/jfm.2014.683.

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AbstractIt is known that the drag for flows driven by a pressure gradient in heated channels can be reduced below the level found in isothermal channels. This reduction occurs for spatially modulated heating and is associated with the formation of separation bubbles which isolate the main stream from direct contact with the solid wall. It is demonstrated that the use of a proper combination of spatially distributed and spatially uniform heating components results in an increase in the horizontal and vertical temperature gradients which lead to an intensification of convection which, in turn, significantly increases the drag reduction. An excessive increase of the uniform heating leads to breakup of the bubbles and the formation of complex secondary states, resulting in a deterioration of the system performance. This performance may, under certain conditions, still be better than that achieved using only spatially distributed heating. Detailed calculations have been carried out for the Prandtl number $\mathit{Pr}=0.71$ and demonstrate that this technique is effective for flows with a Reynolds number $\mathit{Re}<10$; faster flows wash away separation bubbles. The question of net gain remains to be settled as it depends on the method used to achieve the desired wall temperature and on the cost of the required energy. The presented results provide a basis for the design of passive flow control techniques utilizing heating patterns as controlling agents.

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37

IGARASHI, Tamotsu. "Drag Reduction of a Square Prism. 3rd Report. Aerodynamic Mechanism of Reduction of Drag." Transactions of the Japan Society of Mechanical Engineers Series B 64, no. 625 (1998): 2928–34. http://dx.doi.org/10.1299/kikaib.64.2928.

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38

IGARASHI, Tamotsu, and Yoshihiko SHIBA. "DRAG REDUCTION FOR D-SHAPE AND I-SHAPE CYLINDERS : AERODYNAMIC MECHANISM OF REDUCTION OF DRAG(Flow around Cylinder 1)." Proceedings of the International Conference on Jets, Wakes and Separated Flows (ICJWSF) 2005 (2005): 451–56. http://dx.doi.org/10.1299/jsmeicjwsf.2005.451.

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39

Zhang, Li, Zhenghong Gao, and Yiming Du. "Study on Cruise Drag Characteristics of Low Drag Normal Layout Civil Aircraft." Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 38, no. 3 (June 2020): 580–88. http://dx.doi.org/10.1051/jnwpu/20203830580.

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This paper focus on the wing shape related drag reduction measures of normal layout civil aircraft, through the drag reduction to improve the aircraft performance. Mainly by the laminar flow wing to reduce skin drag and weak shock wave wing to reduce shock drag, to keep a section of laminar zone on the wing leading edge to reduce skin drag, the wing profile's pressure distribution transit from the middle part's tonsure pressure zone to the trailing edge's inverse pressure gradient zone gentle to reduce the shock drag. The wing body junction plus the body belly fairing to increase the junction flow velocity, through increase flow velocity to weak the boundary layer stacked at the junction, improve the drag performance. The blended winglet to reduce the wing tip induced drag, study the shape parameters impact on the drag reduction, longitudinal moment and directional moment, attain the winglet model with drag reduction effect, suitable pitching moment and directional moment. For the wing body fairing have significant impact on the wing shape lower surface pressure distribution, the winglet have important impact on the wing tip flow, so the single part drag reduction measure is not feasible, need to carry out integrated drag reduction study on the wing related three drag reduction measures, and study the drag reduction measure's drag reduction decrement, put a reference for the normal layout civil aircraft's drag reduction. Through the above drag reduction measure's assessment attain the effect of drag reduction and rising the normal layout civil aircraft's cruise ratio, improving the cruise performance.

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40

Gillissen, J. J. J. "Turbulent drag reduction using fluid spheres." Journal of Fluid Mechanics 716 (January 25, 2013): 83–95. http://dx.doi.org/10.1017/jfm.2012.510.

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AbstractUsing 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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41

Zhang, Xue Peng, Yong Hua Wang, and Lu Quan Ren. "Wind Tunnel Test for Drag Reduction of Airfoil Bionic Soft Surface." Applied Mechanics and Materials 461 (November 2013): 767–78. http://dx.doi.org/10.4028/www.scientific.net/amm.461.767.

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The soft surface of birds and aquatic organisms in the nature can effectively reduce the drag. Inspired by the fact,in this paper, an attempt is made to stick silicone rubber soft surface on the surfaces of NACA 4412 and NACA 6409 airfoils. The drags, lifts and lift-drag ratios of airfoils with soft and rigid surfaces in 5 different thickness were compared through wind tunnel test under the condition of α = 0 °. The results show that most of the bionic soft surfaces play the role of reducing the aerodynamic drag, and also increasing the lift at the same time, in which the soft surface of 0.6mm had the most significant effect of drag reduction and lift increasing.

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42

SREENIVASAN, KATEPALLI R., and CHRISTOPHER M. WHITE. "The onset of drag reduction by dilute polymer additives, and the maximum drag reduction asymptote." Journal of Fluid Mechanics 409 (April 25, 2000): 149–64. http://dx.doi.org/10.1017/s0022112099007818.

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Drag reduction due to dilute addition of high polymers has been known for about fifty years. In spite of this long history, many aspects of the problem remain poorly understood. Two of its features for pipe flow are considered here in the context of the elastic theory of de Gennes: the onset of drag reduction and the so-called maximum drag reduction (MDR) asymptote. A cautious conclusion is that a version of the theory agrees qualitatively with existing experiments.

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43

Szodrai, Ferenc. "Quantitative Analysis of Drag Reduction Methods for Blunt Shaped Automobiles." Applied Sciences 10, no. 12 (June 23, 2020): 4313. http://dx.doi.org/10.3390/app10124313.

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In fluid mechanics, drag related problems aim to reduce fuel consumption. This paper is intended to provide guidance for drag reduction applications on cars. The review covers papers from the beginning of 2000 to April 2020 related to drag reduction research for ground vehicles. Research papers were collected from the library of Science Direct, Web of Science, and Multidisciplinary Digital Publishing Institute (MDPI). Achieved drag reductions of each research paper was collected and evaluated. The assessed research papers attained their results by wind tunnel measurements or calculating validated numerical models. The study mainly focuses on hatchback and notchback shaped ground vehicle drag reduction methods, such as active and passive systems. Quantitative analysis was made for the drag reduction methods where relative and absolute drag changes were used for evaluations.

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44

IGARASHI, Tamotsu, and Yoshihiko SHIBA. "Drag Reduction for D-Shape and I-Shape Cylinders (Aerodynamic Mechanism of Reduction of Drag)." JSME International Journal Series B 49, no. 4 (2006): 1036–42. http://dx.doi.org/10.1299/jsmeb.49.1036.

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45

ELBING, BRIAN R., ERIC S. WINKEL, KEARY A. LAY, STEVEN L. CECCIO, DAVID R. DOWLING, and MARC PERLIN. "Bubble-induced skin-friction drag reduction and the abrupt transition to air-layer drag reduction." Journal of Fluid Mechanics 612 (October 10, 2008): 201–36. http://dx.doi.org/10.1017/s0022112008003029.

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To investigate the phenomena of skin-friction drag reduction in a turbulent boundary layer (TBL) at large scales and high Reynolds numbers, a set of experiments has been conducted at the US Navy's William B. Morgan Large Cavitation Channel (LCC). Drag reduction was achieved by injecting gas (air) from a line source through the wall of a nearly zero-pressure-gradient TBL that formed on a flat-plate test model that was either hydraulically smooth or fully rough. Two distinct drag-reduction phenomena were investigated; bubble drag reduction (BDR) and air-layer drag reduction (ALDR).The streamwise distribution of skin-friction drag reduction was monitored with six skin-friction balances at downstream-distance-based Reynolds numbers to 220 million and at test speeds to 20.0ms−1. Near-wall bulk void fraction was measured at twelve streamwise locations with impedance probes, and near-wall (0 < Y < 5mm) bubble populations were estimated with a bubble imaging system. The instrument suite was used to investigate the scaling of BDR and the requirements necessary to achieve ALDR.Results from the BDR experiments indicate that: significant drag reduction (>25%) is limited to the first few metres downstream of injection; marginal improvement was possible with a porous-plate versus an open-slot injector design; BDR has negligible sensitivity to surface tension; bubble size is independent of surface tension downstream of injection; BDR is insensitive to boundary-layer thickness at the injection location; and no synergetic effect is observed with compound injection. Using these data, previous BDR scaling methods are investigated, but data collapse is observed only with the ‘initial zone’ scaling, which provides little information on downstream persistence of BDR.ALDR was investigated with a series of experiments that included a slow increase in the volumetric flux of air injected at free-stream speeds to 15.3ms−1. These results indicated that there are three distinct regions associated with drag reduction with air injection: Region I, BDR; Region II, transition between BDR and ALDR; and Region III, ALDR. In addition, once ALDR was established: friction drag reduction in excess of 80% was observed over the entire smooth model for speeds to 15.3ms−1; the critical volumetric flux of air required to achieve ALDR was observed to be approximately proportional to the square of the free-stream speed; slightly higher injection rates were required for ALDR if the surface tension was decreased; stable air layers were formed at free-stream speeds to 12.5ms−1 with the surface fully roughened (though approximately 50% greater volumetric air flux was required); and ALDR was sensitive to the inflow conditions. The sensitivity to the inflow conditions can be mitigated by employing a small faired step (10mm height in the experiment) that helps to create a fixed separation line.

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46

Deutsch, S., M. Moeny, A. A. Fontaine, and H. Petrie. "Microbubble drag reduction in rough walled turbulent boundary layers with comparison against polymer drag reduction." Experiments in Fluids 37, no. 5 (September 29, 2004): 731–44. http://dx.doi.org/10.1007/s00348-004-0863-6.

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47

Wang, Yi, Yan Wang, and Zhe Cheng. "Direct Numerical Simulation of Gas-Liquid Drag-Reducing Cavity Flow by the VOSET Method." Polymers 11, no. 4 (April 2, 2019): 596. http://dx.doi.org/10.3390/polym11040596.

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Drag reduction by polymer is an important energy-saving technology, which can reduce pumping pressure or promote the flow rate of the pipelines transporting fluid. It has been widely applied to single-phase pipelines, such as oil pipelining, district heating systems, and firefighting. However, the engineering application of the drag reduction technology in two-phase flow systems has not been reported. The reason is an unrevealed complex mechanism of two-phase drag reduction and lack of numerical tools for mechanism study. Therefore, we aim to propose governing equations and numerical methods of direct numerical simulation (DNS) for two-phase gas-liquid drag-reducing flow and try to explain the reason for the two-phase drag reduction. Efficient interface tracking method—coupled volume-of-fluid and level set (VOSET) and typical polymer constitutive model Giesekus are combined in the momentum equation of the two-phase turbulent flow. Interface smoothing for conformation tensor induced by polymer is used to ensure numerical stability of the DNS. Special features and corresponding explanations of the two-phase gas-liquid drag-reducing flow are found based on DNS results. High shear in a high Reynolds number flow depresses the efficiency of the gas-liquid drag reduction, while a high concentration of polymer promotes the efficiency. To guarantee efficient drag reduction, it is better to use a high concentration of polymer drag-reducing agents (DRAs) for high shear flow.

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48

Golovin, Kevin B., James W. Gose, Marc Perlin, Steven L. Ceccio, and Anish Tuteja. "Bioinspired surfaces for turbulent drag reduction." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 374, no. 2073 (August 6, 2016): 20160189. http://dx.doi.org/10.1098/rsta.2016.0189.

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In this review, we discuss how superhydrophobic surfaces (SHSs) can provide friction drag reduction in turbulent flow. Whereas biomimetic SHSs are known to reduce drag in laminar flow, turbulence adds many new challenges. We first provide an overview on designing SHSs, and how these surfaces can cause slip in the laminar regime. We then discuss recent studies evaluating drag on SHSs in turbulent flow, both computationally and experimentally. The effects of streamwise and spanwise slip for canonical, structured surfaces are well characterized by direct numerical simulations, and several experimental studies have validated these results. However, the complex and hierarchical textures of scalable SHSs that can be applied over large areas generate additional complications. Many studies on such surfaces have measured no drag reduction, or even a drag increase in turbulent flow. We discuss how surface wettability, roughness effects and some newly found scaling laws can help explain these varied results. Overall, we discuss how, to effectively reduce drag in turbulent flow, an SHS should have: preferentially streamwise-aligned features to enhance favourable slip, a capillary resistance of the order of megapascals, and a roughness no larger than 0.5, when non-dimensionalized by the viscous length scale. This article is part of the themed issue ‘Bioinspired hierarchically structured surfaces for green science’.

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Zhang, B. F., K. Liu, Y. Zhou, S. To, and J. Y. Tu. "Active drag reduction of a high-drag Ahmed body based on steady blowing." Journal of Fluid Mechanics 856 (October 4, 2018): 351–96. http://dx.doi.org/10.1017/jfm.2018.703.

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Active drag reduction of an Ahmed body with a slant angle of $25^{\circ }$, corresponding to the high-drag regime, has been experimentally investigated at Reynolds number $Re=1.7\times 10^{5}$, based on the square root of the model cross-sectional area. Four individual actuations, produced by steady blowing, are applied separately around the edges of the rear window and vertical base, producing a drag reduction of up to 6–14 %. However, the combination of the individual actuations results in a drag reduction 29 %, higher than any previous drag reductions achieved experimentally and very close to the target (30 %) set by automotive industries. Extensive flow measurements are performed, with and without control, using force balance, pressure scanner, hot-wire, flow visualization and particle image velocimetry techniques. A marked change in the flow structure is captured in the wake of the body under control, including the flow separation bubbles, over the rear window or behind the vertical base, and the pair of C-pillar vortices at the two side edges of the rear window. The change is linked to the pressure rise on the slanted surface and the base. The mechanisms behind the effective control are proposed. The control efficiency is also estimated.

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Hoyer, Klaus W., and Albert Gyr. "Heterogeneous Drag Reduction Concepts and Consequences." Journal of Fluids Engineering 120, no. 4 (December 1, 1998): 818–23. http://dx.doi.org/10.1115/1.2820743.

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This paper deals with the nature of the heterogeneous drag reduction which occurs in turbulent pipe flows when a concentrated polymer solution is injected into the pipe center. According to earlier concepts, the achieved drag reduction is due to a direct, large-scale interaction of the viscoelastic polymer thread with the turbulent flow field. The authors prove that the heterogeneous drag reduction originates exclusively from agglomerates of dissolved polymer molecules present in the flow.

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