Pedestrian-level Wind Speed Research Articles

Climate Modelling and Analytics for Urban Heat Risks Mitigation and Adaptation

This study highlights the need for climate-sensitive urban planning and design in the face of climate change, with a specific focus on Singapore. Rapid urbanization has led to significant warming trends, increased heat stress, and heightened electricity demand for cooling. The Urban Climate Design Lab (UCDL) at the National University of Singapore employs a multidisciplinary approach, merging urban planning, architecture, and urban climate science. The research introduces GIS-based tools to evaluate the microclimate impact of new developments, replacing time-consuming simulations and wind tunnel experiments. These tools encompass: 1) The Urban Wind Environment Model, assessing urban permeability for natural ventilation; 2) The Fine-Scale Wind Environment Model, providing high-resolution pedestrian-level wind speed data. 3) The Urban Tree-Airflow Model, aiding tree placement and species selection for optimal cooling. 4) The Anthropogenic Heat Dispersion Model, estimating the impact of human-generated heat emissions. These GIS tools are integrated into the open-access UCDL Microclimate Digital Platform, facilitating knowledge transfer and empowering stakeholders in climate-sensitive urban planning. The platform offers various climate models and visualization capabilities to enhance evidence-based decision-making for urban climate sustainability and resilience. In the future, the platform will expand its offerings, becoming a valuable resource for urban planners, engineers, health practitioners, environmental experts, and residents adapting to a changing climate.

Outdoor ventilation evaluation and optimization based on spatial morphology analysis in Macau

Owing to Macau's high urban development intensity, outdoor ventilation is important to enhance human comfort. In this study, four morphological indices as frontal area index (FAI), site coverage (SC), building height (BH) and floor area ratio (FAR) were mapped and analyzed by establishing a refined three-dimensional urban digital model. Then indicator analysis, numerical simulation and LST retrieval were comprehensively used to assess the present outdoor ventilation conditions of Macau. The results showed that Macau's overall spatial morphology was not conducive to ventilation. In hot season, the cool sea breeze was obstructed by high-rise buildings in coastal area of the northern peninsula and difficult to infiltrate into the inner city. In cold season, the high pedestrian level wind speed of urban blocks in coastal areas of southern island was not good for wind protection. In Macau's northern peninsula, three potential wind corridors that connecting several existing open spaces are suggested. In southern island, a clustered urban development mode is proposed to create a wind corridor network. In addition, the existing heat islands in the windward side of wind corridors can be reduced by optimizing land surface. For pedestrian-level ventilation, the wind speed of traditional neighborhoods can be enhanced by reducing site coverage and introducing high-rise buildings during urban renewal. Wind protection methods should be considered in existing coastal urban areas, and low-rise high-density development mode is recommended for coastal new town planning in southern island. This research presents an opportunity to assist urban planners and researchers in developing a comprehensive understanding of Macau's ventilation condition, and provides theoretical support for planning practices for Macau and cities with comparable conditions.

Effects of void deck on the airflow and pollutant dispersion in 3D street canyons.

In general, urban canyons are the areas most clearly affected by traffic pollutants since the ability of the canyon to self-ventilate is inhibited due to blockage of buildings or other urban structures. However, previous studies have aimed to improve the pedestrian-level wind speed with void deck in single buildings or short canyons. This study investigated the effects of void deck height and location, and the building height on the airflow field and the traffic pollutant diffusion in a long canyon with L/H = 10, validated by wind-tunnel experiment data. The results show that the void decks have a significant effect on the airflow and pollutant distribution inside the canyon. Air exchange rates (ACH) of the canyons with the void deck are much larger than that of regular canyons, and the perturbation changes of turbulence (ACH′) decrease. For the windward void deck, purging flow rate (PFR) and normalized net escape velocity (NEV*) increase by 6.4 times compared to the regular canyon, and for the leeward void deck, increase by 13 times. In particular, when the void decks are at both buildings, they are increased by 38.3 times. Also, for the canyons with the void deck, traffic pollutants are removed out of the canyon by the strong airflow through the void deck. Therefore, unlike the regular canyons, as the void deck and the building height increases, the strength of the airflow through the void deck becomes stronger, and as a result, the mean pollutant concentration is significantly reduced at both walls and the pedestrian respiration level. The mean pollutant concentration on the wall of the building with the void deck and on the pedestrian respiration plane close to it is near zero. These findings can help ease traffic pollution inside the street canyons composed of high-rise buildings, especially in tropical cities.

Tall-building effects on pedestrian-level flow and pollutant dispersion: Large-eddy simulations

The urban environmental impact of tall buildings has increasingly become an important topic of investigation, with the rapid pace of tall-building constructions around the world. In this study, the effects of a tall building on pedestrian-level flow and pollutant dispersion are investigated using the parallelized large-eddy simulation model (PALM). Numerical simulations are conducted by changing the tall-building height in the configuration of a tall building surrounded by low-rise cubical buildings. As the tall-building height increases, the time- and area-averaged pedestrian-level wind speed and pollutant concentration increases and decreases, respectively. Both the rates of changes in the average wind speed and pollutant concentration decrease with increasing tall-building height. The trend of the average wind speed is attributable to an increasing tendency of oncoming flows to pass by the sides of the tall building rather than going down as the tall-building height increases. The trend of the average pollutant concentration is associated with that of the average wind speed. Instantaneous flow and pollutant dispersion are also analyzed. In the upstream region of the tall building, bulks of polluted air are repeatedly transported from further upstream regions and enter the canyon right in front of the tall building, temporarily increasing the pedestrian-level pollutant concentration near the windward wall of the tall building. In the downstream region of the tall building, at the pedestrian level, two counter-rotating vortices appear in the canyon just behind the tall building. Each of these vortices repeatedly develops at one of the two leeward corners of the tall building, moves downstream while changing its size, and disappears after reaching the windward wall of the neighboring low-rise building. These coherent vortices considerably affect the spatiotemporal variation of pedestrian-level pollutant concentration in the canyon just behind the tall building.

Pedestrian Wind Analysis for Indian Sub-Continent

Urbanization in India is causing local wind and climate changes near high-rise buildings, affecting the urban wind climate pedestrian-level winds to dangerous and uncomfortable levels. Hence, today's architectural planning Wind comfort has to not only consider the wind load and internal conditions, but also must consider the outdoor wind building design environment. This study reviewed the methods of evaluating pedestrian-level wind weather, different Wind tunnel test standards of wind comfort, and various techniques for evaluating pedestrian-level wind speed. In the CFD Numerical following section, a brief overview of the current research on this topic and the way forward in India is Modeling related to the design and configuration of windward buildings at the pedestrian level. After analysing the previous documents, the authors recommend it is very necessary to homogenize the various wind standards, as it might have different consequences for planers. Among the various wind tunnel experimental technologies, compared to the hot wire wind speed measurement method, the Irwin probe’s accuracy and simplicity is justified, and can be installed in multiple positions to measure wind speed horizontal of pedestrians at the same time. For the numerical simulation, several researchers have used the Renault medium Navier stokes-based technique, although the precision of this technique is not as good as the simulation of large eddies and the simulation of separate eddies. However, this technology is not only precise but also costs less due to its requirement of less computing resources.

Urban ventilation assessment with improved vertical wind profile in high-density cities – Investigations in nighttime extreme heat

Climate change and heatwaves challenge urban dwellers’ thermal comfort and health. In Hong Kong, more frequent and intensive extreme heat has been observed recently. This study uses Light Detection and Ranging (LiDAR) to observe vertical wind profiles and calibrate numerical simulation methods for urban ventilation assessment in nighttime extreme heat (i.e. hot nights (HNs)) at a high-density site. A cross-comparison is conducted to the characteristics between the observed HN-averaged wind profiles and commonly-used 24-h-period-averaged wind profiles in summer. The observation reveals a weaker wind environment in HNs than 24-h-periods, and the weakest condition is found in HNs during prolonged extreme heat where the impacts of weakened advection surpass enhanced thermal buoyancy. Furthermore, CFD simulations are conducted to evaluate the deviations on urban ventilation assessment caused by the lack of consideration of nighttime extreme heat when setting inlet wind profiles and site thermal conditions. In the simulation results, the 24-h-period-averaged wind profiles cause significant deviations on pedestrian-level wind speed and velocity ratio (empirical model (>45%); LiDAR observation (>20%)). Considerable deviations are found when unstable thermal stratification is ignored (>20%). Consistent deviations on vertical turbulent flow structures induced by the inexplicit coupling between thermal buoyancy and advection are found. The findings call for urgent attention to the wind conditions in HNs since they are most needed for releasing heat stress and urban overheating. It is recommended to include explicit buoyancy effects in both measurement and modeling works to optimize urban ventilation assessment for tackling extremely high-temperature and weak-wind conditions.

Integrated impacts of tree planting and aspect ratios on thermal environment in street canyons by scaled outdoor experiments

Urban tree planting has the potential to reduce urban heat island intensity and building energy consumption. However, the heterogeneity of cities makes it difficult to quantitatively assess the integrated impacts of tree planting and street layouts. Scaled outdoor experiments were conducted to investigate the influence of tree plantings on wind and thermal environments in two-dimensional (2D) north-south oriented street canyons with various aspect ratios (building height/street width, AR = H/W = 1, 2, 3; H = 1.2 m). The effects of tree species with similar leaf area index (C. kotoense, big crown; C. macrocarpa, small crown), tree planting densities (ρ = 1, 0.5), and arrangements (double-row, single-row) were considered.Vegetation reduces pedestrian-level wind speed by 29%–70%. For ρ = 1 and single-row arrangement, C. kotoense (big crown) has a better shading effect and decreases wall and air temperature during the daytime by up to 9.4 °C and 1.2 °C, respectively. In contrast, C. macrocarpa (small crown) leads to a temperature increase at the pedestrian level. Moreover, C. kotoense raises the air and wall temperature of the upper urban canopy layer and increases the street albedo during the daytime because of the solar radiation reflected by trees. C. kotoense/C. macrocarpa produces the maximum daytime cooling/warming and nighttime warming of air temperature when H/W = 2 owing to its weaker convective heat transfer. When H/W = 3, the building shade dominates the shading cooling and tree cooling is less significant. When ρ = 1, double-row trees (C. kotoense) reduce wall and air temperatures by up to 10.0 °C and 1.0 °C during the daytime. However, reducing ρ from 1 to 0.5 weakens the capacity of daytime cooling by C. kotoense and the warming effect by C. macrocarpa. Our study quantifies the influence of tree planting and aspect ratios on the thermal environment, which can provide meaningful references for urban tree planting and produce high-quality validation data for numerical modeling.

CFD evaluation of building geometry modifications to reduce pedestrian-level wind speed

High-rise buildings can significantly increase the wind speed at pedestrian level, and knowledge of building aerodynamics and pedestrian-level wind (PLW) conditions is therefore imperative in their design. This study aims at evaluating different building geometry modifications to reduce PLW speed around an isolated high-rise building. Numerical simulations with computational fluid dynamics (CFD) are performed to evaluate the effect of canopies, podiums and permeable floors. To the best knowledge of the authors, a systematic study on the impact of these modifications on PLW conditions using validated CFD simulations has not been reported before. Grid-sensitivity analyses are performed and sub-configuration validation is applied using wind-tunnel measurements from the literature. It is shown that a canopy or a podium can significantly reduce the area-averaged PLW speed (up to 29%) and maximum PLW speed (up to 36%) around the high-rise building. In general, the PLW speeds decrease with increasing canopy or podium size. The introduction of a permeable floor to the building can reduce the maximum and area-averaged mean wind speed. However, when low-floor building layers are removed, adverse effects are noted, i.e. the average PLW speed increases (up to 21%) and the lower-speed wake region behind the building is reduced in size.

Pedestrian-level wind speed enhancement with void decks in three-dimensional urban street canyons

Cities suffer from low wind speeds due to the blockage effects of urban structures. Low wind speeds inhibit a city's ability to self-ventilate and reduce thermal comfort in tropical cities. Building porosity has been shown to be an effective architectural feature to channel winds into the pedestrian level. However, previous studies have focused on building porosity in single buildings or two-dimensional urban street canyons. We extended the investigations of building porosity to three-dimensional urban street canyons with computational fluid dynamics simulations. Validated numerical models were used to conduct parametric studies on void decks (empty spaces at the ground floors). By allowing winds to flow through them, void decks can enhance pedestrian-level wind speeds by more than twofold compared to the reference case without void decks. The wind enhancement effect is the strongest at the first canyon and decreases downstream. The effectiveness of a void deck is greatly improved by increasing the void deck height. The average wind speed in the first canyon increases from 13 percent to 59 percent (of the freestream wind speed) by increasing the void deck height from 2 m to 6 m. On the other hand, the building height and canyon (height-to-width) aspect ratio have a much smaller influence on void-deck effectiveness. Non-uniform building height in an array of buildings also has a minor influence on the effectiveness. Therefore, void decks are equally effective to enhance pedestrian-level wind speeds in urban areas with tall buildings and buildings with non-uniform height.

Pedestrian-level wind speed enhancement in urban street canyons with void decks

Low wind speeds can inhibit passive ventilation and reduce thermal comfort in tropical cities. We use both experimental and numerical approaches to investigate pedestrian-level wind speed enhancement with void decks (empty spaces at the ground floors) in urban street canyons. Water channel experiments show that void decks allow wind to pass through them, thereby enhancing pedestrian-level wind speeds up to twofold. Computational fluid dynamics models validated with the experiments were used to conduct two parametric studies. The first study varied the void deck height and showed that the wind enhancement effects increase with taller void decks, as expected. The second study varied the canyon aspect ratio and showed that variations in the canyon aspect ratio had less influence on wind enhancement compared to the variations in the void deck height. This is because a void deck induces a secondary vortex, which counter-rotates with the vortex driven by the freestream. Increasing the canyon aspect ratio stretches the vortices vertically but does not alter the (normalized) flow fields. Our findings reveal the potential of void decks to channel wind into street canyons, including narrow (high height-to-width aspect ratio) canyons, which suffer from poor ventilation. The enhanced wind speeds are beneficial for pollutant dispersion and outdoor thermal comfort in tropical cities.

Pedestrian-Level Urban Wind Flow Enhancement with Wind Catchers

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.

Pedestrian-level wind environment on outdoor platforms of a thousand-meter-scale megatall building: Sub-configuration experiment and wind comfort assessment

A thousand-meter-scale megatall building is consisted of three peripheral elliptical towers and one central circular tower, together with 10 outdoor platforms along the height with an interval of 100 m to connect the four towers. As there is no shelter between every two adjacent platforms, pedestrians will feel uncomfortable or unsafe due to large approaching wind speed when strolling or walking across the platforms. Therefore, the pedestrian-level wind environment on outdoor platforms is studied via the combination of wind tunnel tests and CFD simulations. Firstly, wind environment experiment of a sub-configuration of the megatall building is carried out, and characteristics of the pedestrian-level wind environment are analyzed. Then, distributions of the pedestrian-level wind speeds of a full model of the megatall building are compared to that of the sub-configuration via CFD simulations, and an adjustment coefficient is introduced to establish the link of wind speeds between these two models. Lastly, based on the statistical meteorological data provided by the Dalian Meteorological Service Center and the aerodynamic information above, assessment of the pedestrian-level wind comfort and wind danger of the outdoor platforms is implemented using both the Lawson criterion and the NEN 8100 criterion. The results show that quality of the wind environment is very poor on most zones of the platforms, especially in the passageways of two adjacent towers due to the “funneling effects”, and some effective measures should be explored to improve it. This study contributes to further understanding of characteristics of the pedestrian-level wind environment of outdoor platforms high up on megatall buildings via sub-configuration experiment and full model simulations.

A modelling-mapping approach for fine-scale assessment of pedestrian-level wind in high-density cities

This study develops an approach to model the pedestrian-level wind speed at high spatial resolution within urban areas. The aerodynamic properties of urban areas are a necessary component in the current urban planning and design. However current numerical modelling methods, such as Computational Fluid Dynamics (CFD), cannot balance modelling cost with result accuracy to satisfy the requirements of exploratory urban design at the neighborhood scale. Alternatively, current morphological models, algorithms that correlate urban geometries with aerodynamic properties, are inexpensive but can only provide results with low spatial resolution. This study describes the balance between the momentum transfer and drag force in both an averaged sense over an area and a moving air particle to extend conventional frontal area density (λf) to a point-specific index (λf_point). Through correlation with data from wind tunnel experiments, λf_point was determined to be a good index to assess the pedestrian-level wind speed at a test point with multiple input wind directions. Regression equations were developed to map the pedestrian-level wind environment at 1 m × 1 m resolution. This modelling-mapping approach requires less computational time and support technology than CFD simulations. Meanwhile, from a practical point of view, the modelling method provides accurate results at high resolution. Therefore, the modelling results of the urban wind environment can be well integrated into the neighborhood-scale design. Using this approach, urban planners and architects can estimate the neighborhood-scale pedestrian-level wind speed and optimize proposed planning and design at the onset of the procedure.

Air ventilation in cities with dense high-rise developments

Ground-level air condition in inner city areas is becoming increasingly poor as buildings become taller and more closely spaced. This paper explains how wind flow in cities is primarily governed by the amount of air blowing in from outside and how this is modified by buildings, particularly taller ones. Based on experiences in Hong Kong, the paper shows how local topography affects the available wind and how city layouts, the configuration of building complexes and the geometry of individual buildings affect pedestrian-level wind speeds. Mitigation measures to improve air ventilation are proposed.

Reliability of numerical computation of pedestrian-level wind environment around a row of tall buildings

This paper presents numerical results of pedestrian-level wind environment around the base of a row of tall buildings by CFD. Four configurations of building arrangement are computed including a single square tall building. Computed results of pedestrian-level wind flow patterns and wind speeds are compared to previous wind tunnel measurement data to enable an assessment of CFD predictions. The CFD model uses the finite-volume method with RNG k-e model for turbulence closure. It is found that the numerical results can reproduce key features of pedestrian-level wind environment such as corner streams around corners of upwind building, sheltered zones behind buildings and channeled high-speed flow through a building gap. However, there are some differences between CFD results and wind tunnel data in the wind speed distribution and locations of highest wind speeds inside the corner streams. In locations of high ground-level wind speeds, CFD values match wind tunnel data within ?0%.

Pedestrian level wind speeds in downtown Auckland

Predictions of the pedestrian level wind speeds for the downtown area of Auckland that havernbeen obtained by wind tunnel and computational fluid dynamic (CFD) modelling are presented. The windrntunnel method involves the observation of erosion patterns as the wind speed is progressively increased.rnThe computational solutions are mean flow calculations, which were obtained by using the finite volumerncode PHOENICS and the k- e turbulence model. The results for a variety of wind directions are compared, andrnit is observed that while the patterns are similar there are noticeable differences. A possible explanationrnfor these differences arises because the tunnel prediction technique is sensitivity to gust wind speeds whilernthe CFD method predicts mean wind speeds. It is shown that in many cases the computational modelrnindicates high mean wind speeds near the corner of a building while the erosion patterns are consistent withrneddies being shed from the edge of the building and swept downstream.

Wind tunnel tests on the dispersion of vehicular pollutants in an urban area

Abstract Results are presented from an extensive series of wind tunnel tests to investigate the dispersion of a tracer gas emitted from a ground level source on a 1 : 125th scale model of an urban area typical of those found in the UK. Concentrations of a tracer gas, propane in air, were measured at a number of pedestrian level locations around the model using fast-response flame ionisation detectors. These were supplemented by pedestrian level wind speed measurements using hot-film anemometry. Measurements were made for changes in the wind azimuth angle and for changes to the building geometry. General conclusions were drawn about the relationships between building geometry and the pedestrian level atmospheric environment and a number of simple empirical relationships derived between the changes in the measured wind characteristics and the characteristics of tracer concentration. Both mean and fluctuating wind speeds and concentrations were measured in the experiments and subsequently quantified using a novel empirical method that may potentially be of use to both urban planners and wind tunnel engineers.

The effect of architectural detailing on pedestrian level wind speeds

This paper presents results from a wind tunnel study on the effects of architectural detailing on pedestrian level wind speeds around city buildings. Mean and gust speeds were measured in the streets around a range of different building designs placed within a representative city model. The designs included different building shapes, towers with and without podiums, carparking buildings, and the use of fences at street level.