Drag reduction by herringbone riblet texture in direct numerical simulations of turbulent channel flow

Benschop, H.O.G.; Breugem, Wim-Paul

doi:10.1080/14685248.2017.1319951

Cited by 50 publications

(23 citation statements)

References 96 publications

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“…Instantaneous structure of the flow visualized using isosurfaces of λ2-criterion (λ2 = −0.005) and colored by their rotational direction (video of the simulation visualization is available online in mp4 format on the Cambridge Core website) the flow structures seem to predominantly appear in the regions along the ridges which is in agreement with the observed enhanced turbulence intensity in the region above the ridges. Similar observations in visualisations of the near-wall turbulent structures have been previously reported in flows with spanwise heterogeneity of boundary conditions resultung in formation of secondary flows(Benschop & Breugem 2017;Ni et al 2018) or flows with directly induced large-scale secondary motion(Canton et al 2016). Additionally, one can also observe a local clustering of the detected structures mainly located along the sides of the ridges.…”

supporting

confidence: 87%

The instantaneous structure of secondary flows in turbulent boundary layers

Vanderwel

Stroh²,

Kriegseis³

et al. 2019

J. Fluid Mech.

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Secondary flows can develop in turbulent boundary layers that grow over surfaces with spanwise inhomogeneities. In this article, we demonstrate the formation of secondary flows in both experimental and numerical tests and dissect the instantaneous structure and topology of these secondary motions. We show that the formation of secondary flows is not very sensitive to the Reynolds number range investigated, and direct numerical simulations and experiments produce similar results in the mean flow as well as the dispersive and turbulent stress distributions. The numerical methods capture time-resolved features of the instantaneous flow and provide insight into the near-wall flow structures, that were previously obscured in the experimental measurements. Proper orthogonal decomposition was shown to capture the essence of the secondary flows in relatively few modes and to be useful as a filter to analyse the instantaneous flow patterns. The secondary flows are found to create extended regions of high Reynolds stress away from the wall that comprise predominantly sweeps similar to what one would expect to see near the wall and which are comparable in magnitude to the near-wall stress. Analysis of the instantaneous flow patterns reveals that the secondary flows are the result of a non-homogeneous distribution of mid-size vortices.

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supporting

confidence: 87%

The instantaneous structure of secondary flows in turbulent boundary layers

Vanderwel

Stroh²,

Kriegseis³

et al. 2019

J. Fluid Mech.

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“…Even so, the physical mechanism of the drag reduction by riblets has still been inconclusive. One main reason is the fact that most previous research only focused on the understanding of the riblet effect on the total viscous drag over the wall surface, while few discussed the effects of the microscopic flow structures around riblets, especially the vortex structures concerned with the evolving flow field, on the local distribution of skin-friction (Bechert et al (1997), Garcıá-Mayoral and Jiménez (2011), Martin and Bhushan (2014), Benschop and Breugem (2017)). Further investigating these ignored points will help to get a better understanding on the drag reduction mechanism of riblets.…”

Section: Introductionmentioning

confidence: 99%

Investigation on the Mechanism of Drag Modification over Triangular Riblets

Zhang¹,

Zhang²,

Zhao³

2020

JAFM

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This paper presents experimental and numerical investigations on the modification of local spanwise skinfriction over triangular riblets under the total drag reduction condition. Specifically, the mean and fluctuating vortical flow fields were measured using 2-components X-wires and computed using LES, respectively. Besides, the relationship between local skin-friction along the riblet spanwise and associated vortex evolution was also built using the vortex dynamic method. Based on these results, it was found that, compared with the smooth case, the impaired and enhanced vortex strength, and resultant viscous diffusion/energy dissipation, determined the reduction and augment of the viscous drag force over the local spanwise riblet groove, i.e., decreasing and increasing cases of local drag, respectively. Furthermore, the mean normal diffusion fluxes of normal and spanwise vorticities contributed more to the viscous drag under these two cases. Correspondingly, the relevant flow physics related to these phenomena was discussed in detail.

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“…After millions of years of continuous adaption and evolution, bodies of creatures in nature have formed delicate biological surface structures with drag-reducing characteristics 8 – 11 . For instance, convex hull structures of the head of the dung beetle 12 – 14 , the herringbone riblet textures inspired by the bird feathers 15 , 16 , ridged structures distributed on the mouthpart of the honeybee 17 , 18 , and the super-hydrophobic surface of the skins of many creatures 19 – 22 . In addition, the surface structure of many aquatic animals also had excellent drag-reduction characteristic, which had been applied in many fields and showed great drag-reduction effect.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigations on drag-reduction characteristics of bionic surface with water-trapping microstructures of fish scales

Jiao

Song

et al. 2018

Sci Rep

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Biological surfaces with unique wettability in nature have provided an enormous innovation for scientists and engineers. More specifically, materials possessing various wetting properties have drawn considerable attention owing to their promising application prospects. Recently, great efforts have been concentrated on the researches on wetting-induced drag-reduction materials inspired by biology because of their ability to save energy. In this work, the drag-reduction characteristics of the bionic surface with delicate water-trapping microstructures of fish Ctenopharyngodon idellus scales were explored by experimental method. Firstly, the resistance of smooth surface and bionic surface experimental sample at different speeds was carefully tested through the testing system for operation resistance. Then, the contact angle (CA) of fish scale surface was measured by means of the contact angle measuring instrument. It was discovered that the bionic surface created a rewarding drag-reduction effect at a low speed, and the drag-reduction rate significantly displayed a downward trend with the increase in flow speed. Thus, when the rate was 0.66 m/s, the drag-reduction effect was at the optimum level, and the maximum drag reduction rate was 2.805%, which was in concordance with the simulated one. Furthermore, a contact angle (CA) of 11.5° appeared on the fish scale surface, exhibiting fine hydrophilic property. It further manifested the spreading-wetting phenomenon and the higher surface energy for the area of apical of fish scales, which played an important role in drag-reduction performance. This work will have a great potential in the engineering and transportation field.

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Drag reduction by herringbone riblet texture in direct numerical simulations of turbulent channel flow

Cited by 50 publications

References 96 publications

The instantaneous structure of secondary flows in turbulent boundary layers

The instantaneous structure of secondary flows in turbulent boundary layers

Investigation on the Mechanism of Drag Modification over Triangular Riblets

Experimental investigations on drag-reduction characteristics of bionic surface with water-trapping microstructures of fish scales

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