Rough-wall boundary layers: mean flow universality

Castro, Ian P.

doi:10.1017/s0022112007006921

Cited by 169 publications

(148 citation statements)

References 24 publications

(41 reference statements)

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“…In particular, figure 6(a) shows results for the indirect method (via equation 2.1) and figure 6(b) using the direct method (friction-balance) for skin-friction estimation. This type of plot was first proposed by Castro (2007) and will allow us to estimate if the current data agrees with previous findings. Most of the results from rough-wall studies have been found to scatter around the two curves (for different values of wake parameter Π) shown in figure 6 (Castro 2007).…”

Section: Effect Of Surface Morphology On Aerodynamic Parameterssupporting

confidence: 61%

“…where the Reynolds shear stress is evaluated from the plateau region in the roughness sublayer (as in Flack et al 2005 andCastro 2007). Both these above-mentioned approaches yield a U τ value that is within 5% of each other.…”

Section: Indirect Estimate Of Skin-frictionmentioning

confidence: 99%

“…It is important to highlight that, although is of common practice, fitting velocity profiles to determine the unknowns in equation 1.1, bares great uncertainty. This is due to the difficulties, particularly at the large h/δ, in determining both the skin friction velocity and the log-law boundaries (Acharya et al 1986;Castro 2007;Segalini et al 2013). The reduction of the wall-normal range of the logarithmic layer, due to the increasing importance of the RSL is another important factor to take into account.…”

Section: Determination Of Aerodynamic Parametersmentioning

confidence: 99%

“…viscous effects). There is general consensus in the literature that fully-rough conditions are attained when y + 0 > 2 (Castro 2007) to h + s > 70 ). Here h s is the equivalent sand-grain roughness as in Nikuradse (1933).…”

Section: Effect Of Surface Morphology On Aerodynamic Parametersmentioning

confidence: 99%

“…Additionally, effects of large roughness elements on these correlations remain unresolved. Castro (2007) pointed out that, although there is a substantial literature on rough-wall flows and there have been a number of attempts to develop useful correlations relating the surface friction to boundary-layer parameters over a wide range of surface roughness, such correlations have mainly considered only small h/δ and it is not known how adequate they are at larger values of h/δ or what the critical value h/δ should be.…”

Section: Introductionmentioning

confidence: 99%

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

Placidi

Ganapathisubramani

2015

J. Fluid Mech.

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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

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Section: Effect Of Surface Morphology On Aerodynamic Parameterssupporting

confidence: 61%

Section: Indirect Estimate Of Skin-frictionmentioning

confidence: 99%

Section: Determination Of Aerodynamic Parametersmentioning

confidence: 99%

Section: Effect Of Surface Morphology On Aerodynamic Parametersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Placidi

Ganapathisubramani

2015

J. Fluid Mech.

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Remote determination of the velocity index and mean streamwise velocity profiles

Johnson

Cowen

2017

Water Resources Research

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When determining volumetric discharge from surface measurements of currents in a river or open channel, the velocity index is typically used to convert surface velocities to depth‐averaged velocities. The velocity index is given by, k=Ub/Usurf, where Ub is the depth‐averaged velocity and Usurf is the local surface velocity. The USGS (United States Geological Survey) standard value for this coefficient, k = 0.85, was determined from a series of laboratory experiments and has been widely used in the field and in laboratory measurements of volumetric discharge despite evidence that the velocity index is site‐specific. Numerous studies have documented that the velocity index varies with Reynolds number, flow depth, and relative bed roughness and with the presence of secondary flows. A remote method of determining depth‐averaged velocity and hence the velocity index is developed here. The technique leverages the findings of Johnson and Cowen (2017) and permits remote determination of the velocity power‐law exponent thereby, enabling remote prediction of the vertical structure of the mean streamwise velocity, the depth‐averaged velocity, and the velocity index.

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Optimal turbine spacing in fully developed wind farm boundary layers

2011

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As wind farms become larger, the asymptotic limit of the ‘fully developed’, or ‘infinite’, wind farm has been receiving an increased interest. This limit is relevant for wind farms on flat terrain whose length exceeds the height of the atmospheric boundary layer by over an order of magnitude. Recent computational studies based on large eddy simulation have identified various mean velocity equilibrium layers and have led to parameterizations of the effective roughness height that allow the prediction of the wind velocity at hub height as a function of parameters such as wind turbine spacing and loading factors. In the current paper, we employ this as a tool in making predictions of optimal wind turbine spacing as a function of these parameters, as well as in terms of the ratio of turbine costs to land surface costs. For realistic cost ratios, we find that the optimal average turbine spacing may be considerably higher than that conventionally used in current wind farm implementations. Copyright © 2011 John Wiley & Sons, Ltd.

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Rough-wall boundary layers: mean flow universality

Cited by 169 publications

References 24 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

Remote determination of the velocity index and mean streamwise velocity profiles

Optimal turbine spacing in fully developed wind farm boundary layers

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