Experimental study on drag-reduction effect due to sinusoidal riblets in turbulent channel flow

Sasamori, Monami; Mamori, Hiroya; Iwamoto, Kaoru; Murata, Akira

doi:10.1007/s00348-014-1828-z

Cited by 55 publications

(35 citation statements)

References 17 publications

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“…By applying the feedback control using the adjoint equations (Bewley et al 2001;Kasagi et al 2012) to heat transfer in turbulent channel flow with blowing and suction on the wall, Hasegawa & Kasagi (2011) and Yamamoto et al (2013) have numerically achieved the dissimilarity even when the Prandtl number is equal to unity. Experimentally, several practicable passive or active control techniques have been developed using riblet (Sasamori et al 2014), permeable wall (Suga et al 2011), micro actuator and sensor (Kasagi et al 2009), and so on. Hence, the accomplishment of dissimilar heat transfer enhancement by flow control might be expected in the near future.…”

Section: Introductionmentioning

confidence: 99%

Optimal heat transfer enhancement in plane Couette flow

2017

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Optimal heat transfer enhancement has been explored theoretically in plane Couette flow. The velocity field to be optimised is time-independent and incompressible, and temperature is determined in terms of the velocity as a solution to an advection-diffusion equation. The Prandtl number is set to unity, and consistent boundary conditions are imposed on the velocity and the temperature fields. The excess of a wall heat flux (or equivalently total scalar dissipation) over total energy dissipation is taken as an objective functional, and by using a variational method the Euler-Lagrange equations are derived, which are solved numerically to obtain the optimal states in the sense of maximisation of the functional. The laminar conductive field is an optimal state at low Reynolds number Re ∼ 10 0 . At higher Reynolds number Re ∼ 10 1 , however, the optimal state exhibits a streamwise-independent two-dimensional velocity field. The two-dimensional field consists of large-scale circulation rolls that play a role in heat transfer enhancement with respect to the conductive state as in thermal convection. A further increase of the Reynolds number leads to a three-dimensional optimal state at Re 10 2 . In the three-dimensional velocity field there appear smaller-scale hierarchical quasi-streamwise vortex tubes near the walls in addition to the large-scale rolls. The streamwise vortices are tilted in the spanwise direction so that they may produce the anticyclonic vorticity antiparallel to the mean-shear vorticity, bringing about significant three-dimensionality. The isotherms wrapped around the tilted anticyclonic vortices undergo the cross-axial shear of the mean flow, so that the spacing of the wrapped isotherms is narrower and so the temperature gradient is steeper than those around a purely streamwise (twodimensional) vortex tube, intensifying scalar dissipation and so a wall heat flux. Moreover, the tilted anticyclonic vortices induce the flow towards the wall to push low-(or high-) temperature fluids on the hot (or cold) wall, enhancing a wall heat flux. The optimised three-dimensional velocity fields achieve a much higher wall heat flux and much lower energy dissipation than those of plane Couette turbulence.

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Section: Introductionmentioning

confidence: 99%

Optimal heat transfer enhancement in plane Couette flow

2017

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“…With a simplified riblet geometry, a maximum DR of almost 10% has been obtained [5]. In the search for even higher values of DR, many variations on the standard riblet geometries have been investigated [19], such as hierarchical or compound riblets [91], riblets on a spanwise traveling surface wave [47], oscillating riblets [88,37,83], riblets in a wave-like pattern (either in phase [36] or out of phase [69]) and riblets combined with drag-reducing polymers [12]. The rationale behind these alternatives is to further reduce drag by somehow incorporating other drag-reducing methods, such as oscillating walls or polymer addition.…”

Section: Introductionmentioning

confidence: 99%

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

Benschop

Breugem

2017

Journal of Turbulence

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A bird-feather-inspired herringbone riblet texture was investigated for turbulent drag reduction. The texture consists of blade riblets in a converging/diverging or herringbone pattern with spanwise wavelength f . The aim is to quantify the drag change for this texture as compared to a smooth wall and to study the underlying mechanisms. To that purpose, direct numerical simulations of turbulent flow in a channel with height L z were performed. The FukagataIwamoto-Kasagi identity for drag decomposition was extended to textured walls and was used to study the drag change mechanisms. For f /L z ࣡ O(10), the herringbone texture behaves similarly to a conventional parallel-riblet texture in yaw: the suppression of turbulent advective transport results in a slight drag reduction of 2%. For, the drag increases strongly with a maximum of 73%. This is attributed to enhanced mean and turbulent advection, which results from the strong secondary flow that forms over regions of riblet convergence/divergence. Hence, the employment of convergent/divergent riblets in the texture seems to be detrimental to turbulent drag reduction.

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“…It can be obviously seen that for the smooth surface, as time goes on, the near‐wall streamwise vortices can frequently and directly scour the wall on a large scale, resulting in the shear stress with a large zone as shown in Figure a. However, for the drag‐reducing case presented in Figures b1–b5, the streamwise vorticity of

ω_{x}^{+} = 0.1

almost cannot intrude into the groove valley and is just above the groove, indicating that the motions of near‐wall fluid in y direction (the normal motions) are mild and the momentum exchange is weaker within the groove valley, which is the main reason for the significant suppression of turbulent fluctuations within the groove valley found by other researchers in their drag‐reducing microgrooves. Moreover, it can also be visually found that the higher shear stress caused by the scour of high‐speed fluid only occurs in a small region near the groove tips, and the fluid is “quiet” within the groove valley, resulting in a lower shear stress with a large region.…”

Section: Resultsmentioning

confidence: 99%

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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Experimental study on drag-reduction effect due to sinusoidal riblets in turbulent channel flow

Cited by 55 publications

References 17 publications

Optimal heat transfer enhancement in plane Couette flow

Optimal heat transfer enhancement in plane Couette flow

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

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

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