Flow over cube arrays of different packing densities

Cheng, Hong Ping; Hayden, Paul; Robins, Alan; Castro, Ian P.

doi:10.1016/j.jweia.2007.01.004

Cited by 147 publications

(177 citation statements)

References 28 publications

(48 reference statements)

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“…Using the above definition applied to the mean velocity profiles, we found that the RSL height varied between z * = 2.16 H b to z * = 3.43 H b . This is consistent with previous studies (see, e.g., Cheng et al, 2007). The lowest values are, of course, for the SimpleC model, where we also observed an influence of the wind direction (lowest value for 0°, highest value for 45°).…”

Section: Discussionsupporting

confidence: 93%

“…Most of the systematic studies on building arrays involve the use of cuboidal obstacles (Cheng and Castro, 2002;Cheng et al, 2007) or relatively deep and long street canyons (Kastner- Klein and Plate, 1999;Salizzoni et al, 2009). The few papers that consider a more realistic urban form usually tend to focus on diagonally symmetric buildings (width = length), so that fewer wind directions are needed to completely characterise flow and dispersion (Garbero et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

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Influence of urban morphology on air flow over building arrays

Carpentieri

Robins

2015

Journal of Wind Engineering and Industrial Aerodynamics

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Section: Discussionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Influence of urban morphology on air flow over building arrays

Carpentieri

Robins

2015

Journal of Wind Engineering and Industrial Aerodynamics

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“…The roughness sublayer is the region of flow near the wall where the flow is very strongly influenced by the presence of roughness elements or surface features, leading to spatial inhomogeneities in the flow field (Cheng et al 2007). The thickness of the roughness sublayer can be measured based on the dispersive stresses of the flow field (Pokrajac et al 2007;Florens et al 2013), u i = u i − u i xy , i.e.…”

Section: Roughness Sublayermentioning

confidence: 99%

Reynolds-number dependence of the near-wall flow over irregular rough surfaces

2016

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The Reynolds-number dependence of turbulent channel flow over two irregular rough surfaces, based on scans of a graphite and a grit-blasted surface, is studied by direct numerical simulation. The aim is to characterise the changes in the flow in the immediate vicinity of and within the rough surfaces, an area of the flow where it is difficult to obtain experimental measurements. The average roughness heights and spatial correlation of the roughness features of the two surfaces are similar, but the two surfaces have a significant difference in the skewness of their height distributions, with the graphite sample being positively skewed (peak-dominated) and the grit-blasted surface being negatively skewed (valley-dominated). For both cases, numerical simulations were conducted at seven different Reynolds numbers, ranging from Re τ = 90 to Re τ = 720. The positively skewed surface gives rise to higher friction factors than the negatively skewed surface in all cases. For the highest Reynolds numbers, the flow has values of the roughness function U + well in excess of 7 for both surfaces and the bulk flow profile has attained a constant shape across the full height of the channel except for the immediate vicinity of the roughness, which would indicate fully rough flow. However, the mean flow profile within and directly above the rough surface still shows considerable Reynolds-number dependence and the ratio of form to viscous drag continues to increase, which indicates that at least for some types of rough surfaces the flow retains aspects of the transitionally rough regime to values of U + or k + well in excess of the values conventionally assumed for the transitionally to fully rough threshold. This is also reflected in the changes that the near-wall flow undergoes as the Reynolds number increases: the viscous sublayer, within which the surface roughness is initially buried, breaks down and regions of reverse flow intensify. At the highest Reynolds numbers, a layer of near-wall flow is observed to follow the contours of the local surface. The distribution of thickness of this 'blanketing' layer has a mixed scaling, showing that viscous effects are still significant in the near-wall flow.

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“…In our investigation, the average across the streamwise direction and over a single repetitive unit yielded, within experimental uncertainty, the same results. Furthermore, Cheng et al (2007) also argued that for boundary-layer flows over staggered arrays of cubical elements, the ρuv underestimates the surface stress by some 25%. Therefore, a corrected estimate should be used, defined as (Reynolds & Castro 2008),…”

Section: Indirect Estimate Of Skin-frictionmentioning

confidence: 99%

“…These studies include both numerical and physical experiments (Cheng & Castro 2002b;Coceal & Belcher 2004;Kanda et al 2004;Cheng et al 2007;Hagishima et al 2009;Santiago et al 2008;Leonardi & Castro 2010 among various others). Open symbols in figure 2(a) show the cases examined in these studies.…”

Section: Introductionmentioning

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.

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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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Flow over cube arrays of different packing densities

Cited by 147 publications

References 28 publications

Influence of urban morphology on air flow over building arrays

Influence of urban morphology on air flow over building arrays

Reynolds-number dependence of the near-wall flow over irregular rough surfaces

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

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