Scaling of turbulent structures in riblet channels up to Re
 τ ≈ 550

García-Mayoral, Ricardo; Jiménez, Javier

doi:10.1063/1.4757669

Cited by 43 publications

(60 citation statements)

References 33 publications

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“…They established that the riblet-induced spanwise rollers, which are responsible for the drag-reducing break-down, scale in viscous units [12]. This result is consistent with the assumption that the riblet effect is limited to the viscous and buffer layers [13].…”

supporting

confidence: 78%

“…6) are both approximately conserved A longer computational domain would be necessary to determine accurately whether or not the drag reduction remains constant when the comparison is done with respect to one of those two Reynolds numbers. García-Mayoral and Jiménez [12] have already predicted a weak dependence of c f with Re τ , invoking that the riblet influence is restricted to the buffer layer.…”

Section: Reduction Of the Wall Frictionmentioning

confidence: 96%

“…6, right) remains almost equal to that of the smooth wall at the same Re τ . According to its definition (12), this implies that the weighted integral of u v + across the boundary layer is approximately conserved. This suggests that the inner-scaled intensity of the Reynolds shear stress is not massively affected by the riblets.…”

Section: Analysis Of the Riblet Effects Through A Friction Decompositionmentioning

confidence: 98%

“…While most of the previous numerical studies have focused on channel flows [4,5,[10][11][12], only few numerical simulations of zero-pressure gradient boundary layers over riblets have been conducted for transitional flow [21,22], supersonic flow [23] or flow over spanwise rods [24]. To the authors's knowledge, no available data exists for fully-turbulent subsonic ZPGTBL over drag-reducing riblets.…”

mentioning

confidence: 96%

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Riblet Flow Model Based on an Extended FIK Identity

Bannier

Garnier

Sagaut

2015

Flow Turbulence Combust

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International audienceLarge Eddy Simulations of zero-pressure-gradient turbulent boundary layers over riblets have been conducted. All along the controlled domain, riblets maintain a significant 11 % drag reduction with respect to the flat plate at the same R e τ (from 250 to 450). To compare the flows above riblets and a reference smooth wall, an appropriate vertical shift between the two surfaces is required. In the present study, the “vertical origin” is set using the identity of Fukagata, Iwamoto and Kasagi (FIK) in Phys. Fluids, vol. 14, 2002, L73. This identity, which provides a physically meaningful decomposition of the skin friction, has been extended to complex wall surfaces and constitutes the basis for the derivation of a new virtual origin. Using this FIK-based origin, it is shown that the complex interactions between the riblets and the near-wall turbulent structures can be taken into account by a simple shift of the two axes of the mean and turbulent velocity profiles. The appropriate upward shift Δu +, typical for drag reduction, is directly dependent on the skin friction on the riblets and on the reference smooth plate at the same R e τ

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supporting

confidence: 78%

Section: Reduction Of the Wall Frictionmentioning

confidence: 96%

Section: Analysis Of the Riblet Effects Through A Friction Decompositionmentioning

confidence: 98%

mentioning

confidence: 96%

See 2 more Smart Citations

Riblet Flow Model Based on an Extended FIK Identity

Bannier

Garnier

Sagaut

2015

Flow Turbulence Combust

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“…That does not happen above the buffer layer, and is inhibited near the wall by the impermeability boundary condition but, if that condition is relaxed by porosity 63 or by other means, 50 the Kelvin-Helmholtz instability reappears, with vertical eigenfunctions that remain localized below x + 2 ≈ 30. 50,64 We have also analyzed the bursts in simulations of fully turbulent flows in computational boxes that are minimal with respect to the structures of the logarithmic layer. We have shown that they share many features with the linearized bursts, especially for the wall-normal velocity u 2 .…”

Section: Discussionmentioning

confidence: 99%

How linear is wall-bounded turbulence?

2013

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The relevance of Orr's inviscid mechanism to the transient amplification of disturbances in shear flows is explored in the context of bursting in the logarithmic layer of wall-bounded turbulence. The linearized problem for the wall normal velocity is first solved in the limit of small viscosity for a uniform shear and for a channel with turbulent-like profile, and compared with the quasiperiodic bursting of fully turbulent simulations in boxes designed to be minimal for the logarithmic layer. Many properties, such as time and length scales, energy fluxes between components, and inclination angles, agree well between the two systems. However, once advection by the mean flow is subtracted, the directly computed linear component of the turbulent acceleration is found to be a small part of the total. The temporal correlations of the different quantities in turbulent bursts imply that the classical model, in which the wall-normal velocities are generated by the breakdown of the streamwise-velocity streaks, is a better explanation than the purely autonomous growth of linearized bursts. It is argued that the best way to reconcile both lines of evidence is that the disturbances produced by the streak breakdown are amplified by an Orr-like transient process drawing energy directly from the mean shear, rather than from the velocity gradients of the nonlinear streak. This, for example, obviates the problem of why the cross-stream velocities do not decay once the streak has broken down. C

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Direct numerical simulation of turbulent flow over wide‐rib rectangular grooves

et al. 2017

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The turbulent flow over the wide‐rib rectangular grooves, the motions and variations of near‐wall streamwise vortices with time, and the interaction between microgroove and near‐wall streamwise vortices were investigated by direct numerical simulation method (DNS). The distributions of radius, density, and swirling strength of streamwise vortex were also studied quantitatively by using swirling‐strength criterion. It was found that the distribution of vortex radius in smooth channels can approximately be divided into three parts. The vortex radii are smaller in grooved channels than in smooth channels and almost the same when y+ > 40 for all grooved cases. Moreover, a simple prediction method was proposed to estimate the optimal height and spacing of drag‐reducing microgrooves for different fluids, and they were about 10 and 17 wall units for water, respectively. Furthermore, using the same frictional velocity uτ to normalize the shear stress is more suitable for the quantitative comparison and analysis of different longitudinal microgrooves. The drag‐reducing mechanism of longitudinal microgrooves could be considered as the competition results between the “restriction or blockage effect” of microgroove on the near‐wall vortices (causing a drag‐reducing effect) and the “tip effect” of microgrooves caused by the scouring of higher speed fluid near the groove tip (causing a drag‐increasing effect). A large number of small streamwise secondary vortices with small swirling strength within the groove valley, which are induced by microgrooves, may be the essential reason of drag reduction by microgrooves.

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Scaling of turbulent structures in riblet channels up to Re τ ≈ 550

Abstract: Articles you may be interested inEffect of the computational domain on direct simulations of turbulent channels up to Re τ = 4200

Cited by 43 publications

References 33 publications

Riblet Flow Model Based on an Extended FIK Identity

Riblet Flow Model Based on an Extended FIK Identity

How linear is wall-bounded turbulence?

Direct numerical simulation of turbulent flow over wide‐rib rectangular grooves

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