A wind tunnel study of flows over idealised urban surfaces with roughness sublayer corrections

Ho, Yat-Kiu

doi:10.1007/s00704-016-1877-8

Cited by 20 publications

(2 citation statements)

References 70 publications

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“…One of the examples is the TKE redistribution from vertical to spanwise components, resulting in decreasing anisotropy and turbulence scales [63,64]. While the RSL dynamics were examined in details in our previous study [65], such as the velocity profiles and length scale in RSL, this paper focuses on the practical significance of RSL particularly related to the street-level ventilation estimate.…”

Section: Street-level Ventilation Estimatementioning

confidence: 99%

Street-Level Ventilation in Hypothetical Urban Areas

2017

Atmosphere

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Street-level ventilation is often weakened by the surrounding high-rise buildings. A thorough understanding of the flows and turbulence over urban areas assists in improving urban air quality as well as effectuating environmental management. In this paper, reduced-scale physical modeling in a wind tunnel is employed to examine the dynamics in hypothetical urban areas in the form of identical surface-mounted ribs in crossflows (two-dimensional scenarios) to enrich our fundamental understanding of the street-level ventilation mechanism. We critically compare the flow behaviors over rough surfaces with different aerodynamic resistance. It is found that the friction velocity u τ is appropriate for scaling the dynamics in the near-wall region but not the outer layer. The different freestream wind speeds (U ∞ ) over rough surfaces suggest that the drag coefficient C d (= 2u 2 τ /U 2 ∞ ) is able to characterize the turbulent transport processes over hypothetical urban areas. Linear regression shows that street-level ventilation, which is dominated by the turbulent component of the air change rate (ACH), is proportional to the square root of drag coefficient ACH ∝ C 1/2 d . This conceptual framework is then extended to formulate a new indicator, the vertical fluctuating velocity scale in the roughness sublayer (RSL) w RSL , for breathability assessment over urban areas with diversified building height. Quadrant analyses and frequency spectra demonstrate that the turbulence is more inhomogeneous and the scales of vertical turbulence intensity w w 1/2 are larger over rougher surfaces, resulting in more efficient street-level ventilation.

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Section: Street-level Ventilation Estimatementioning

confidence: 99%

Street-Level Ventilation in Hypothetical Urban Areas

2017

Atmosphere

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“…However, each of the assumptions has its drawbacks. For applications in urban context especially at the nearground level, the log-law wind profile's validity is dubious, as the roughness of urban areas would significantly alter the atmospheric boundary layer's (ABL) layered structure which makes the log-law wind profile less accurate [1,2]. The power-law wind profile is an empirical assumption that describes the ground surface roughness's influence on the wind profile, of which the validity in describing the near-ground wind profile is also dubious.…”

Section: Introductionmentioning

confidence: 99%

Mean Wind Velocity Distribution at Near-ground Level Obtained Through Field Measurements

Zhong

Liu²,

Liang³

2022

E3S Web Conf.

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Mean wind velocity profiles enable researchers to conduct efficient and accurate analyses of a wide variety of urban microclimatic problems, such as pollution dispersion, heat island effect and pedestrian wind comfort. However, due to the heterogeneity in the complex urban context, the wind profile at near-ground level within the real urban context remains insufficiently investigated. The present study aims to measure the near-ground level mean wind profiles in an industrial park. To this practical end, a sonic anemometer was equipped to a height adjustable bar on a mobile measurement platform. Through adjusting the sonic anemometer’s height, the mean wind velocities at different heights of the near-ground level were measured. Results indicate that the mean wind velocities’ variation along the near-ground heights measured at the site exposed to open and flat upwind areas can be reasonably captured by the power-law profile, while the other two conventional profiles, i.e. the log-law and the exponential profiles, show different levels of inaccuracy.

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Large-Eddy Simulation of Reactive Plume Dispersion Over Hypothetical Urban Areas

Liu

2019

Direct and Large-Eddy Simulation XI

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A wind tunnel study of flows over idealised urban surfaces with roughness sublayer corrections

Cited by 20 publications

References 70 publications

Street-Level Ventilation in Hypothetical Urban Areas

Street-Level Ventilation in Hypothetical Urban Areas

Mean Wind Velocity Distribution at Near-ground Level Obtained Through Field Measurements

Large-Eddy Simulation of Reactive Plume Dispersion Over Hypothetical Urban Areas

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