Observations of turbulent secondary flows in a rough-wall boundary layer

Barros, Julio; Christensen, Kenneth T.

doi:10.1017/jfm.2014.218

Cited by 128 publications

(152 citation statements)

References 21 publications

Supporting

Mentioning

131

Contrasting

Order By: Relevance

“…The mean-flow heterogeneity in both cases were here found to be in correspondence of the periodic spanwise roughness spacing. However, although some of the cases herein in examination resemble Barros & Christensen (2014)'s geometry (in particular case LP6), the current investigation found no trace of this heterogeneity in the freestream. This is in disagreement with the aforementioned studies and it is perhaps due to the fact that the spanwise spacing between elements in the cases examined in the current study is not significant enough to induce this characteristic behaviour.…”

Section: Effect Of Surface Morphology On the Roughness Sublayercontrasting

confidence: 72%

“…This heterogeneity extend outside the RSL all the way to the freestream. This phenomenon is due to the presence of spanwise-wall-normal mean secondary flow in the form of mean streamwise vorticity associated with counter-rotating boundary layer-scale circulations (Barros & Christensen 2014). The latter induces regions of high and low momentum (HMPs and LMPs respectively).…”

Section: Effect Of Surface Morphology On the Roughness Sublayermentioning

confidence: 99%

See 1 more Smart Citation

Effects of frontal and plan solidities on aerodynamic parameters and the roughness sublayer in turbulent boundary layers

Placidi

Ganapathisubramani

2015

J. Fluid Mech.

View full text Add to dashboard Cite

Citation: Placidi, M. & Ganapathisubramani, B. (2015). Effects of frontal and plan solidities on aerodynamic parameters and the roughness sublayer in turbulent boundary layers. Journal of Fluid Mechanics, 782, pp. 541-566. doi: 10.1017Mechanics, 782, pp. 541-566. doi: 10. /jfm.2015 This is the accepted version of the paper.This version of the publication may differ from the final published version. Experiments were conducted in the fully-rough regime on surfaces with large relative roughness height (h/δ ≈ 0.1, where h is the roughness height and δ is the boundary layer thickness). The surfaces were generated by distributed LEGO TM bricks of uniform height, arranged in different configurations. Measurements were made with both floating-element drag-balance and high-resolution particle image velocimetry on six configurations with different frontal solidity, λ F , at fixed plan solidity, λ P , and vice versa, for a total of twelve rough-wall cases. Results indicate that the drag reaches a peak value λ F ≈ 0.21 or a constant λ P = 0.27, whilst it monotonically decreases for increasing values of λ P for a fixed λ F = 0.15. This is in contrast with previous studies in the literature based on cube roughness that show a peak in drag for both λ F and λ P variations. The influence of surface morphology on the depth of the roughness sublayer (RSL) is also investigated. Its depth is found to be inversely proportional to the roughness length, y 0 . A decrease in y 0 is usually accompanied by a thickening of the the RSL and vice-versa. Proper orthogonal decomposition analysis was also employed. The shapes of the most energetic modes calculated using the data across the entire boundary layer are found to be selfsimilar across the twelve rough-walls cases, however, when the analysis is restricted to the roughness sublayer, differences that depend on the wall morphology are apparent. Moreover, the energy content of the POD modes within the RSL suggest that the effect of increased frontal solidity is to redistribute the energy towards the larger-scales (i.e. larger portion of energy is within the first few modes) whilst the opposite is found for variation of plan solidity. Permanent

show abstract

Section: Effect Of Surface Morphology On the Roughness Sublayercontrasting

confidence: 72%

Section: Effect Of Surface Morphology On the Roughness Sublayermentioning

confidence: 99%

Effects of frontal and plan solidities on aerodynamic parameters and the roughness sublayer in turbulent boundary layers

Placidi

Ganapathisubramani

2015

J. Fluid Mech.

View full text Add to dashboard Cite

show abstract

“…In fact, the layer of gravel was not uniformly glued on the channel bed and, therefore, different topographical scales were arranged in a highly irregular manner. Several studies showed how the formation of these vortical structures are influenced by the roughness height (e.g., [38][39][40]). In general, the identified LMR and HMR patterns tend to occur at spanwise locations of recessed and elevated roughness (relative to the mean elevation), respectively, with the swirling motions residing at spanwise locations of intense spanwise gradients in topographical height [39].…”

Section: Analysis Of the Experimental Datamentioning

confidence: 99%

Effect of the Junction Angle on Turbulent Flow at a Hydraulic Confluence

Penna

Marchis

Canelas

et al. 2018

Water

View full text Add to dashboard Cite

Despite the existing knowledge concerning the hydrodynamic processes at river junctions, there is still a lack of information regarding the particular case of low width and discharge ratios, which are the typical conditions of mountain river confluences. Aiming at filling this gap, laboratory and numerical experiments were conducted, comparing the results with literature findings. Ten different confluences from 45 • to 90 • were simulated to study the effects of the junction angle on the flow structure, using a numerical code that solves the 3D Reynolds Averaged Navier-Stokes (RANS) equations with the k-turbulence closure model. The results showed that the higher the junction angle, the wider and longer the retardation zone at the upstream junction corner and the separation zone, and the greater the flow deflection at the entrance of the tributary into the post-confluence channel. Furthermore, it was shown that the maximum streamwise velocity does not necessarily increase with the junction angle and that it is not always located in the contraction section.

show abstract

“…Terrain with heterogeneities along the spanwise direction has been shown to generate secondary flows that manifest as large counter-rotating vortices with axes aligned in the streamwise direction [32,33]. These secondary flows create low-and high-momentum pathways that impact the entire boundary layer thickness and can have serious implications for wind resources as they result in inhomogeneities in the mean wind velocity and turbulence properties.…”

Section: Spanwise Heterogeneity In Surface Terrainmentioning

confidence: 99%

Wind resource assessment in heterogeneous terrain

Vanderwel

Placidi

Ganapathisubramani

2017

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

High-resolution particle image velocimetry data obtained in rough-wall boundary layer experiments are re-analysed to examine the influence of surface roughness heterogeneities on wind resource. Two different types of heterogeneities are examined: (i) surfaces with repeating roughness units of the order of the boundary layer thickness (Placidi & Ganapathisubramani. 2015 J. Fluid Mech. 782 , 541–566. ( doi:10.1017/jfm.2015.552 )) and (ii) surfaces with streamwise-aligned elevated strips that mimic adjacent hills and valleys (Vanderwel & Ganapathisubramani. 2015 J. Fluid Mech. 774 , 1–12. ( doi:10.1017/jfm.2015.228 )). For the first case, the data show that the power extraction potential is highly dependent on the surface morphology with a variation of up to 20% in the available wind resource across the different surfaces examined. A strong correlation is shown to exist between the frontal and plan solidities of the rough surfaces and the equivalent wind speed, and hence the wind resource potential. These differences are also found in profiles of and (where U is the streamwise velocity), which act as proxies for thrust and power output. For the second case, the secondary flows that cause low- and high-momentum pathways when the spacing between adjacent hills is beyond a critical value result in significant variations in wind resource availability. Contour maps of and show a large difference in thrust and power potential (over 50%) between hills and valleys (at a fixed vertical height). These variations do not seem to be present when adjacent hills are close to each other (i.e. when the spacing is much less than the boundary layer thickness). The variance in thrust and power also appears to be significant in the presence of secondary flows. Finally, there are substantial differences in the dispersive and turbulent stresses across the terrain, which could lead to variable fatigue life depending on the placement of the turbines within such heterogeneous terrain. Overall, these results indicate the importance of accounting for heterogeneous terrain when siting individual turbines and wind farms. This article is part of the themed issue ‘Wind energy in complex terrains’.

show abstract

Observations of turbulent secondary flows in a rough-wall boundary layer

Cited by 128 publications

References 21 publications

Effects of frontal and plan solidities on aerodynamic parameters and the roughness sublayer in turbulent boundary layers

Effects of frontal and plan solidities on aerodynamic parameters and the roughness sublayer in turbulent boundary layers

Effect of the Junction Angle on Turbulent Flow at a Hydraulic Confluence

Wind resource assessment in heterogeneous terrain

Contact Info

Product

Resources

About