Turbulence Over Urban-type Roughness: Deductions from Wind-tunnel Measurements

Castro, Ian P.; Cheng, Hong Ping; Reynolds, Ryan T.

doi:10.1007/s10546-005-5747-7

Cited by 177 publications

(156 citation statements)

References 33 publications

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“…Our results are consistent with those of Castro et al (2006) who found that spanwise integral length scales obtained from twopoint correlations increased with height. Tomkins and Adrian (2003) also observed a linear scaling of eddy sizes in the corresponding log region over smooth walls, but the eddy sizes there were several times smaller than the present ones.…”

Section: Coherent Structures Above the Buildingssupporting

confidence: 93%

“…Moreover, as noted above, the Reynolds number dependence for this type of flow is weak (Xie and Castro, 2006). The adequacy of the grid was confirmed by a close comparison of the statistics with those for a test run at double the resolution but on a smaller domain of 4 h × 4 h × 4 h. Figure 2 demonstrates the good agreement obtained with the wind-tunnel data of Cheng and Castro (2002) and Castro et al (2006). Further comparisons are presented in Coceal et al (2006).…”

Section: Numerical Methods and Geometrysupporting

confidence: 65%

“…The present dimensions of the domain are chosen to be much larger than these integral length scales. The domain height H = 8 h is comparable to the boundary layer height δ = 7.5 h in the wind tunnel experiment of Cheng and Castro (2002) and Castro et al (2006).…”

Section: Numerical Methods and Geometrymentioning

confidence: 54%

“…The computational domain has streamwise, lateral and vertical dimensions of 16 h, 12 h and 8 h respectively. This choice of domain size was guided by the results of wind tunnel measurements made by Castro et al (2006) over the same geometry. These authors deduced integral lengthscales in the streamwise, lateral and vertical directions of L x = 3 h, L y = h and L z = h in the inertial sublayer.…”

Section: Numerical Methods and Geometrymentioning

confidence: 99%

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Unsteady dynamics and organized structures from DNS over an idealized building canopy

Coceal

Dobre

Thomas

2007

Intl Journal of Climatology

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Abstract:A numerical study is performed to elucidate the dominant turbulent processes that occur in urban areas. Comprehensive data from direct numerical simulations (DNS) over idealized three-dimensional arrays of buildings are analysed to study the unsteady and organized aspects of the turbulent flow. The accuracy of the DNS is evaluated by comparing turbulence statistics with a high quality wind-tunnel dataset. The simulation results are studied using flow visualization as well as statistical methods including quadrant analysis, space-time two-point correlations and conditional averaging. Three regimes of the flow are identified. First, the rough wall flow above the buildings has turbulent organized structures that resemble the 'hairpin vortices' and 'low momentum regions' that are well known to occur in the turbulent boundary layer over smooth walls. These hairpin-like vortices contribute dominantly to vertical momentum transport. Secondly, shear layers develop over the tops of the buildings and shed structures that may sometimes impinge upon downstream buildings and drive a robust recirculation within the building canopy. These unsteady canopy-top shear layers and their interaction with the larger eddies above provide important mechanisms for coupling with the flow within the canopy. Thirdly, the flow within the building canopy is the result of complicated interactions between the above and eddies shed off the vertical edges of the buildings, and their distortion caused by impacting buildings. Mean flow patterns around the buildings are important and lead to significant dispersive stresses. Implications for scalar transport and dispersion are briefly discussed.

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Section: Coherent Structures Above the Buildingssupporting

confidence: 93%

Section: Numerical Methods and Geometrysupporting

confidence: 65%

Section: Numerical Methods and Geometrymentioning

confidence: 54%

Section: Numerical Methods and Geometrymentioning

confidence: 99%

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Unsteady dynamics and organized structures from DNS over an idealized building canopy

Coceal

Dobre

Thomas

2007

Intl Journal of Climatology

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“…A few minor differences are found due to the different building geometry, for example, R u,x falls to 0.2 at δx = 6h and R u,y falls to −0.25 at δy = 2.8h for the flows over an array of staggered 3D cubes. Nevertheless, the LES-calculated R φ,x i behaviours are generally in line with those of the wind-tunnel experiment (Castro et al 2006) and with DNS (Coceal et al 2007). …”

Section: Two-point Correlationssupporting

confidence: 83%

Large-Eddy Simulation of Flow and Pollutant Transports in and Above Two-Dimensional Idealized Street Canyons

Cheng

Liu

2011

Boundary-Layer Meteorol

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A large-eddy simulation (LES) model, using the one-equation subgrid-scale (SGS) parametrization, was developed to study the flow and pollutant transport in and above urban street canyons. Three identical two-dimensional (2D) street canyons of unity aspect ratio, each consisting of a ground-level area source of constant pollutant concentration, are evenly aligned in a cross-flow in the streamwise direction x. The flow falls into the skimming flow regime. A larger computational domain is adopted to accurately resolve the turbulence above roof level and its influence on the flow characteristics in the street canyons. The LES calculated statistics of wind and pollutant transports agree well with other field, laboratory and modelling results available in the literature. The maximum wind velocity standard deviations σ i in the streamwise (σ u ), spanwise (σ v ) and vertical (σ w ) directions are located near the roof-level windward corners. Moreover, a second σ w peak is found at z ≈ 1.5h (h is the building height) over the street canyons. Normalizing σ i by the local friction velocity u * , it is found that σ u /u * ≈ 1.8, σ v /u * ≈ 1.3 and σ w /u * ≈ 1.25 exhibiting rather uniform values in the urban roughness sublayer. Quadrant analysis of the vertical momentum flux u w shows that, while the inward and outward interactions are small, the sweeps and ejections dominate the momentum transport over the street canyons. In the x direction, the two-point correlations of velocity R v,x and R w,x drop to zero at a separation larger than h but R u,x (= 0.2) persists even at a separation of half the domain size. Partitioning the convective transfer coefficient T of pollutant into its removal and re-entry components, an increasing pollutant re-entrainment from 26.3 to 43.3% in the x direction is revealed, suggesting the impact of background pollutant on the air quality in street canyons.

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Estimating aerodynamic roughness over complex surface terrain

et al. 2013

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[1] Surface roughness plays a key role in determining aerodynamic roughness length (z o ) and shear velocity, both of which are fundamental for determining wind erosion threshold and potential. While z o can be quantified from wind measurements, large proportions of wind erosion prone surfaces remain too remote for this to be a viable approach. Alternative approaches therefore seek to relate z o to morphological roughness metrics. However, dust-emitting landscapes typically consist of complex small-scale surface roughness patterns and few metrics exist for these surfaces which can be used to predict z o for modeling wind erosion potential. In this study terrestrial laser scanning was used to characterize the roughness of typical dust-emitting surfaces (playa and sandar) where element protrusion heights ranged from 1 to 199 mm, over which vertical wind velocity profiles were collected to enable estimation of z o . Our data suggest that, although a reasonable relationship (R 2 > 0.79) is apparent between 3-D roughness density and z o , the spacing of morphological elements is far less powerful in explaining variations in z o than metrics based on surface roughness height (R 2 > 0.92). This finding is in juxtaposition to wind erosion models that assume the spacing of larger-scale isolated roughness elements is most important in determining z o . Rather, our data show that any metric based on element protrusion height has a higher likelihood of successfully predicting z o . This finding has important implications for the development of wind erosion and dust emission models that seek to predict the efficiency of aeolian processes in remote terrestrial and planetary environments.

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Turbulence Over Urban-type Roughness: Deductions from Wind-tunnel Measurements

Cited by 177 publications

References 33 publications

Unsteady dynamics and organized structures from DNS over an idealized building canopy

Unsteady dynamics and organized structures from DNS over an idealized building canopy

Large-Eddy Simulation of Flow and Pollutant Transports in and Above Two-Dimensional Idealized Street Canyons

Estimating aerodynamic roughness over complex surface terrain

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