Pedestrian-Level Urban Wind Flow Enhancement with Wind Catchers

Abstract

Dense urban areas restrict air movement, causing airflow in urban street canyons to be much lower than the flow above buildings. Boosting near-ground wind speed can enhance thermal comfort in warm climates by increasing skin convective heat transfer. We explored the potential of a wind catcher to direct atmospheric wind into urban street canyons. We arranged scaled-down models of buildings with a wind catcher prototype in a water channel to simulate flow across two-dimensional urban street canyons. Velocity profiles were measured with Acoustic Doppler Velocimeters. Experiments showed that a wind catcher enhances pedestrian-level wind speed in the target canyon by 2.5 times. The flow enhancement is local to the target canyon with little effect in other canyons. With reversed flow direction, a "reversed wind catcher" has no effect in the target canyon but reduces the flow in the immediate downstream canyon. The reversed wind catcher exhibits a similar blockage effect of a tall building amid an array of lower buildings. Next, we validated Computational Fluid Dynamics (CFD) simulations of all cases with experiments and extended the study to reveal impacts on three-dimensional ensembles of buildings. A wind catcher with closed sidewalls enhances maximum pedestrian-level wind speed in three-dimensional canyons by four times. Our results encourage better designs of wind catchers to increase wind speed in targeted areas.

Recent Advances in Urban Ventilation Assessment and Flow Modelling

“…Chew et al [12] studied pedestrian-level wind enhancement in urban street canyons with wind catchers. Water channel experiments with idealized models of street canyons revealed that a wind catcher could enhance pedestrian-level wind speed by up to 2.5 times in two-dimensional canyons.…”

Buoyant flows in street canyons: Comparison of RANS and LES at reduced and full scales

“…2(b). The characteristic advection timescale, τ, is defined as H/Uref [38], where Uref is the reference freestream velocity taken at z/H = 2.5, following the recommendation in the literature [11][12][13]. For the URANS simulation and LES, the time step size was fixed at 0.01τ [18,39].…”

“…The Reynolds number, Re, is defined as HUref/ν, where H is the canyon height, Uref is a reference velocity taken 2H or higher [11][12][13], and ν is the kinematic viscosity. In full-scale built environments, buildings have H on the order of 10 1 to 10 2 m. With a reference wind speed of 2 m/s, the corresponding Re is on the order of 10 6 to 10 7 .…”

“…This criterion states that beyond a critical Re, the overall flow pattern is independent of Re. Many studies of street canyon flows have adopted a critical Re of 1×10 4 [12][13][14][15]. This means that reduced-scale experiments are expected to reproduce the flow fields at full scale, as long as the Re exceeds 1×10 4 .…”

Impacts of Traffic Tidal Flow on Pollutant Dispersion in a Non-Uniform Urban Street Canyon

“…This has been defined as a relatively narrow street space formed by successive buildings on both sides of a city street [5]. Relevant studies mainly relied on field measurements [6,7], wind tunnel experiments [8][9][10], and numerical simulations [11][12][13]. Based on previous studies, important factors that influence the flow patterns and the dispersion mechanism of pollutant can be grouped into the following categories: Inflow conditions (such as wind speed, wind direction [14][15][16], turbulence intensity [17]); Geometric conditions of building structures (such as building aspect ratio [18,19] and the street canyon aspect ratio [20,21]); Ground surface and building surface conditions (such as building surface roughness and hot or cold conditions [22][23][24][25]); The impact of turbulences caused by vehicle movement [11].…”