Aerodynamic Properties of Rough Surfaces with High Aspect-Ratio Roughness Elements: Effect of Aspect Ratio and Arrangements

Sadique, Jasim; Yang, Xiang; Meneveau, Charles; Mittal, Rajat

doi:10.1007/s10546-016-0222-1

Cited by 41 publications

(35 citation statements)

References 63 publications

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“…Such an effect was noted by Sadique et al (2017), who examined the meanvelocity profiles in turbulent flows over high-aspect-ratio prismatic posts. Sadique et al (2017) found that the mean-velocity profile over such geometries became independent of the element heights at large element aspect ratios. They concluded that the overlying flow only interacted with the region near the element tips, and that the height below this 'active' region was dormant, and did not have a significant effect on the overlying flow.…”

Section: Introductionmentioning

confidence: 73%

Turbulent flows over dense filament canopies

Sharma

García-Mayoral

2020

J. Fluid Mech.

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Turbulent flows over dense canopies consisting of rigid filaments of small size are investigated using direct numerical simulation. The effect of the height and spacing of the canopy elements on the overlying turbulence is studied. In these dense canopies, the element spacing is the key parameter determining the penetration of turbulent fluctuations within the canopy and the height of the roughness sublayer. The flow within and above the canopy is found to become independent of the filament height at large element heightto-spacing ratios, h/s 6. We also study the effect of the canopy parameters on the Kelvin-Helmholtz-like instability typically associated with dense-canopy flows. We find that the instability is inhibited in canopies with small element height-to-spacing ratios, h/s ∼ 1, due to the blocking effect of the wall at the base of the canopy, while a stronger signature of the instability can be observed as the height is increased. Canopies with very small element spacings, s + 10, also inhibit the instability, owing to the large drag they exert on the fluctuations. The streamwise wavelength of the instability depends on the canopy shear-layer thickness, and we show that, for the present dense canopies, this thickness also scales with the element spacing. Some of the effects of the canopy parameters on the instability can be captured by a linear stability analysis.

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Section: Introductionmentioning

confidence: 73%

Turbulent flows over dense filament canopies

Sharma

García-Mayoral

2020

J. Fluid Mech.

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“…There has been some effort to address this (see, for example, Huq et al 2007, who showed that mean flow profiles can be quite different for canopies of buildings with h/w = 3, compared with canopies of cubes). Very recently, Sadique et al (2016) have used LES specifically to explore the effect of h/w by varying it from unity to seven for various λ p . They showed that the phenomenological (wake-sheltering) model of , mentioned above and suitably extended to cope with tall obstacles, succeeds quite well in predicting z o for the above-canopy flow, but they did not explore the canopy region in detail.…”

Section: Further Discussion and Conclusionmentioning

confidence: 99%

Are Urban-Canopy Velocity Profiles Exponential?

Castro

2017

Boundary-Layer Meteorol

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Using analyses of data from extant direct numerical simulations and large-eddy simulations of boundary-layer and channel flows over and within urban-type canopies, sectional drag forces, Reynolds and dispersive shear stresses are examined for a range of roughness densities. Using the spatially-averaged mean velocity profiles these quantities allow deduction of the canopy mixing length and sectional drag coefficient. It is shown that the common assumptions about the behaviour of these quantities, needed to produce an analytical model for the canopy velocity profile, are usually invalid, in contrast to what is found in typical vegetative (e.g. forest) canopies. The consequence is that an exponential shape of the spatially-averaged mean velocity profile within the canopy cannot normally be expected, as indeed the data demonstrate. Nonetheless, recent canopy models that allow prediction of the roughness length appropriate for the inertial layer's logarithmic profile above the canopy do not seem to depend crucially on their (invalid) assumption of an exponential profile within the canopy.

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“…Several basal shapes of wind reduction region (triangle, rectangular, and half‐ellipse) in the lee of plants (Leenders et al, ; Okin, ; Raupach, ) have been proposed. Recent observations (Leenders et al, ; Mayaud et al, ) and simulations (Sadique, Yang, Meneveau, & Mittal, ; Yang et al, ), however, indicated that the half‐ellipse shape proposed by Leenders et al () is likely to be more reasonable for porous shrub vegetation element. The semiminor axis of the half‐ellipse is set to be D /2.…”

Section: Methodsmentioning

confidence: 97%

Potential differences in seed dispersals of low‐height vegetation between single element and windbreak‐like clumps

2019

Ecology and Evolution

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Wind speed is one of the most important factors for seed wind dispersal. A wind speed reduction region, which could be influenced by vegetation arrangement, will form in the lee of vegetation and therefore affects the seed dispersal. Here, by taking shrub as an example, quantitative differences in seed dispersals of low vegetation between single element and windbreak‐like clumps are numerically investigated. The local variation of stream‐wise wind speed is focused. Empirically parameterized functions of leeward wind distributions are employed. It reveals that the accumulative probability of dispersed seeds from a point source with considering leeward wind reduction could be well fitted by a logistic function. For a fixed release height or vegetation porosity, accumulative probabilities for single element and those for windbreak‐like clumps would intersect at a leeward location. This intersection location decreases linearly with release height but exponentially with porosity. The fitting parameter r 0 (the center of logistic function) for single element increases as the same manner for windbreak‐like clumps, with regard to the increase of release height, porosity, and height. But, the increasing rates for single element are higher than those for windbreak‐like clumps. The fitting parameter p (the power index of logistic function) for single element is generally larger than that for windbreak‐like clumps. With the increase of release height, p decreases at first but increases then for single element, while it shows opposite trend for windbreak‐like clumps. p decreases with porosity for both single element and windbreak‐like clumps. But, the decreasing rate for single element is lower than that for windbreak‐like clumps. p increases exponentially with height for windbreak‐like clumps, while it almost keeps constant for single element. These results suggest the potential importance of vegetation arrangement on seed dispersal and therefore possibly provide additional reason for the disagreement among observed dispersal kernels.

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Aerodynamic Properties of Rough Surfaces with High Aspect-Ratio Roughness Elements: Effect of Aspect Ratio and Arrangements

Cited by 41 publications

References 63 publications

Turbulent flows over dense filament canopies

Turbulent flows over dense filament canopies

Are Urban-Canopy Velocity Profiles Exponential?

Potential differences in seed dispersals of low‐height vegetation between single element and windbreak‐like clumps

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