Pedestrian-level Wind Conditions Research Articles

A study on urban block design strategies for improving pedestrian-level wind conditions: CFD-based optimization and generative adversarial networks

Urban block layout design presents a critical and challenging task for urban planners, as block layout directly influences the physical structure of the urban area, the interaction between people and their environment, and the microclimate in urban areas. Thus, developing appropriate design strategies plays a decisive role in this process. This research uses the generative adversarial networks (GAN) technique to explore block layout design strategies. The GAN technique can effectively generate real and diverse urban blocks based on learning existing morphological properties. Therefore, it can be a powerful approach to urban block layout research. Genetic algorithms not only help to identify the ideal design solution but also enable the summary of key design strategies by numerous evolutionary periods. The study presents a CFD-based optimization framework that utilizes a genetic algorithm and 3D block models generated by the GAN technique to improve the urban wind conditions at the block scale. By comparing solutions, the study successfully optimized three objectives by 68.36%, 51.74%, and 41.83%. Ridge regression models examined the relationship between objective functions and urban morphological indices. The maximum R2 value of the ridge regression models reached 0.801, indicating that the models can effectively predict wind conditions by morphological indicators. Design strategies for wind-friendly blocks were developed by regression models and validated by case studies. The design strategies suggest that architects should prioritize the building layout, the building height at boundary areas, and the building shape, as these factors significantly affect the urban outdoor wind conditions.

Effect of the angle of attack on the flow around two non-identical-height square buildings in tandem arrangement

The paper investigates the flow around two non-identical height buildings, each with the same square cross-section, arranged in tandem using a particle image velocimetry technique. Fixed gap spacing between objects G=1.5D (where D is the side building’s length) and fixed Reynolds number Re=17000 were considered in the study. The key goal of the research was examining the effect of the angle of attack α in the range from 0° to 30° on the flow structure. Considerable attention was paid to assessing the ventilation performance for the investigated flow configurations. Also, the pedestrian-level wind conditions were evaluated for all the considered values of the angle α. When α grows up, the flow is more prone to enter the gap space and elevates locally the velocity in that region. When the flow leaves the gap on the other side, it mixes with the side shear layer and both generate the recirculation area next to the downstream buildings. As α increases, the highest values of the turbulence kinetic energy are seen outside the gap space. The strength of the downwash and upwash effects on the symmetry plane becomes reduced with growing α. No clear dependency between the Strouhal number and the angle α was observed. The contribution of α to the ventilation process in the gap is different at different heights. A conversion from the weak to tolerable wind condition takes place in the gap when α increases.

A CFD study on the Irwin probe flows

Irwin probes are surface sensors commonly used to determine the shear stress in near-wall regions, by calibration of related pressure signals. These devices have been widely used in wind tunnel studies dealing with pedestrian-level wind conditions. In this work, three-dimensional Computational Fluid Dynamics (CFD) simulations are performed to characterize the complex flow field and pressure distribution developed around and within the Irwin probe, at three distinct low-Reynolds number regimes. The emergence of coherent flow structures past the sensor is categorised and preventive spacing intervals, necessary to mitigate mutual interference, is numerically evaluated. The computations corroborate the original spacing recommendations by Irwin. For typical operation conditions, long streamwise tip vortices are observed in the wake of a single sensor. In addition, the predictions suggest the existence of a low-Reynolds number threshold, below which such structures are supressed, resulting in diminished interference effects. Numerical results also suggest a nearly uniform axial pressure distribution and place in evidence very interesting flow field characteristics.

Flow field around two tandem non-identical-height square buildings via LES

Although the study of flow around buildings has a rich background, the development of construction material, the congestion of buildings, the urban ventilation and consideration of pedestrian wind condition make the necessity of further insightful flow-physic studies. This study numerically investigates the gap and wake flows associated with two inline non-identical-height (aspect ratios of 4 and 7 for the up- and downstream) buildings at a Reynolds number of 2.2 × 104 and gap spacing (G*) of 1, 3, and 5 through the large eddy simulation technique. It is found that an increase of G* mostly affects the flow pattern in the gap, so that the slender-body, alternate reattachment and semi-stable gap flow at the G* of 1 (or 3) turns into the co-shedding flow at the G* of 5. The pressure coefficients (C¯p) on the cylinders' faces show that an increase of G* from 1 to 3 increases/decreases the C¯p on the side (and top) faces of upstream/downstream cylinders, respectively. Further increasing G* from 3 to 5, however, drops the C¯p on the side and top faces of both cylinders. On the other hand, the flow regime produces a profound effect on the pedestrian level so that the strong wind condition appears in the small gap, and a very weak wind condition in the vortex cores. Hence a minimum gap of 3 is recommended for better pedestrian level wind conditions. Besides, increasing gap from 1 to 5 reduces the shielding effect of the interfering building markedly.

Application of artificial intelligence to urban wind energy

Optimal implementation of urban wind energy contributes towards the development of sustainable cities. This paper focuses on generating an adequate database to use with artificial intelligence (AI) tools to improve the generation of urban wind energy. The paper presents wind tunnel results for square, rectangular, U-shaped, T-shaped, L-shaped buildings and some measurement points in various city configurations. Moreover, the effect of building shapes on turbine street level locations was elaborated using validated CFD literature results on pedestrian level wind conditions. Using these results and literature review from the past decade, a decisional flow chart approach was developed, allowing a preliminary assessment of the modification of upstream wind velocities due to urban parametric conditions. Expert and artificial neural network (ANN) systems were built and tested on city configurations with their results compared with those from wind tunnel measurements. The ANN system shows better predictive values than the expert system, with up to 99% success rate. AI programs with the decisional flow chart approach may be used for the identification and assessment of potential turbine locations to maximize the production of urban wind energy.

Classification and pedestrian-level wind environment assessment among Tianjin's residential area based on numerical simulation

In this study, Tianjin's 36 practical residential areas were classified into four main categories and nine subcategories of layout modes based on actual planning methods. The wind conditions of each layout mode were evaluated with ENVI-met software and compared using three wind environment factors: wind speed, calm wind area ratio and wind speed dispersion. Further, correlations between spatial morphological factors and wind environment factors were established. Results indicate that the classification method of layout modes used in this study can fully reflect spatial differences between real residential areas. From comparison of the three wind environment factors, the mid-rise enclosed mode was found to exhibit the worst wind environment due to its low wind speed while the mid-rise parallel and mid high-rise modes are recommended as the most suitable for Tianjin's climate. The wind environment of high-rise layout modes are not as favourable as the wind environments of the mid-rise and mid high-rise modes. Frontal area density and average building height are shown to be key spatial morphological factors which affect the pedestrian-level wind environment. They can be used in residential planning practices to improve the wind condition. This research presents an opportunity to assist urban planners and researchers in developing a comprehensive understanding of pedestrian-level wind conditions in different residential layout modes.

A framework for pedestrian-level wind conditions improvement in urban areas: CFD simulation and optimization

Given the complexity of urban wind flow, acceptable wind conditions can hardly be achieved in all regions within an urban area. In some regions, high wind speeds can lead to wind discomfort and danger, while some regions suffer from poor outdoor urban ventilation. In order to evaluate and improve urban wind conditions, the combined impacts of wind flow and morphological and aerodynamic characteristics of the urban area should be taken into account. In this perspective, performing extensive and time-consuming parametric analyses is required – which is very difficult – even impossible. This paper, therefore, presents an evolutionary-based framework to optimize building heights and plan area densities to improve wind conditions in complex real urban areas. The framework consists of four steps: (i) urban area identification, (ii) optimization algorithms, (iii) CFD simulations, and (iv) evaluation. The optimization consists of Genetic Algorithm and Particle Swarm Optimization. The framework is applied to a real urban area in the city of Tehran, Iran. The focus is on minimizing low-wind-speed regions. In total, 920 possible combinations of building height variations and plan area densities are assessed. 3D steady Reynolds-averaged Navier-Stokes (RANS) simulations are performed based on a detailed validation study and grid-sensitivity analysis. The results show that the use of this framework can effectively reduce computational time and significantly improve the wind conditions in the entire urban area. Urban planners, architects, and building engineers can benefit from this framework in the early stages of design for better wind conditions in complex real urban areas.

Numerical simulation of pedestrian level wind conditions: effect of building shape and orientation

Pedestrian level wind comfort, natural ventilation and pollutant dispersion are strongly influenced by building shape and orientation. In the recent years, the trend of building shape is not restricted to basic square and rectangular cross-section, and various unconventional shapes are also considered. Considering this fact, the present study is focused on the investigation of different building shape with major and minor modifications on the pedestrian level wind environment and aims to evaluate the effect of different building shapes on the extent of different wind conditions surrounding the building systematically. An investigation was performed using a computational fluid dynamics (CFD) approach based on realizable $$k - \varepsilon$$ model and the standard $$k - \varepsilon$$ turbulence model with revised closure coefficients for different orientation ( $$\theta = 0^\circ$$ , $$22.5^\circ$$ and $$45^\circ$$ ) and shape of buildings. Further, wind tunnel experiment was conducted to validate the CFD results. The results of CFD simulations obtained using realizable $$k - \varepsilon$$ model fairly match with experimental values for high wind speed conditions, whereas the standard $$k - \varepsilon$$ with LK modification and revised closure coefficients performs better for the low wind speed regions. It was observed that the wind conditions at the pedestrian level are influenced mostly by corner modification and projected width at 1/3rd height of the building from the ground.

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.

Wind tunnel study on the pedestrian-level wind comfort in residential areas of Harbin

Pedestrian-level wind conditions in residential areas are closely related to the quality of urban residents' daily life. In this paper, seven representative building layouts of urban residential areas were summarized from actual residential areas of Harbin, and wind tunnel experiments were carried out to study the pedestrian-level wind comfort in these residential areas. The assessments of pedestrian wind comfort are performed by combining the wind tunnel results and long-term local wind statistics. The results show that the hybrid-type and the enclosed-type layouts can provide better pedestrian wind comfort than parallel-type layouts, and the building heights of residential areas need to be controlled in cities of severe cold regions.

Numerical simulation of pedestrian level wind flow around buildings: Effect of corner modification and orientation

Environmental wind conditions at the pedestrian level are strongly influenced by building shape and orientation. The present study investigates the effect of corner modified buildings on the pedestrian level wind conditions, by using a computational fluid dynamics (CFD) approach with a realizable k−ε model and the standard k−ε model (SKE) with LK modification and revised closure coefficients. This study systematically explores the extent of different wind conditions surrounding buildings at the pedestrian level. Wind tunnel experiments were conducted to validate the CFD results. The results of CFD simulations obtained using a realizable k−ε model fairly matches with experimental values for strong wind conditions, whereas the modified SKE model performs better for simulating the flow in low wind speed regions. The area-averaged amplification factor is evaluated for different wind speed conditions and compared for different cases. Its value for high wind speeds reduces nearly 3% for circular modified buildings, and for low wind speeds its value increases significantly. Further, the wake length behind the corner modified building reduces significantly, and for circular corner modified building it reduces nearly 32%.

Pedestrian-level wind conditions in the space underneath lift-up buildings

Lift-up buildings are advantageous in improving the wind circulation in a congested and compact city. However, the wind conditions in the void underneath a lift-up building, also known as the lift-up area, are vital for wind comfort of occupants of lift-up buildings. This study tested 28 lift-up buildings in a boundary layer wind tunnel to assess the influence of key design parameters; height and width of the main structure, and height, width, depth, and the shape of the central core on the wind conditions in the lift-up area. The results of the analyses show a significant influence of building height on the magnitude of wind speeds in the lift-up area while the width of the central core controls the area with low wind speeds. Tall buildings with short lift-up cores have small areas with acceptable pedestrian wind comfort, which can be increased by adopting corner modifications for the central core. The area of acceptable pedestrian wind comfort increases in oblique wind directions as the areas of high (>3.5 m s−1) and low (<1.5 m s−1) wind speeds are decreased. Finally, a non-linear second-order multivariable regression model is developed to predict pedestrian wind comfort in the lift-up area.

Assessment of pedestrian-level wind conditions in severe cold regions of China

Pedestrian-level wind environment in urban areas has a significant impact on the quality of urban dwellers' daily life. For pedestrian-level wind studies in severe cold regions, the cooling effect of wind and related thermal discomfort in winter is quite significant. However, thermal effects of wind are not considered in most wind comfort studies and wind comfort generally only refers to the mechanical effects of wind on people. Therefore, particular consideration is given to the chilling effect of wind on exposed skin and risk of frostbite in winter, and a wind chill criterion based on the wind chill temperature is proposed in this study. The pedestrian-level wind conditions in seven representative residential areas summarized from cities in severe cold regions of China are assessed based on the wind mechanical comfort criterion of NEN 8100 and the wind chill criterion. CFD simulations are performed to provide the pedestrian-level aerodynamic information, and the simulation results are validated by wind tunnel experiments. The assessment results show that the wind mechanical comfort or wind chill criterion need to be combined when assessing the wind conditions in severe cold regions. From the perspective of wind mechanical comfort and wind chill, the multi-storey residential areas with hybrid-type and the enclosed-type layout are recommended in severe cold regions. Moreover, a strict control of building height in residential areas is important to improve the pedestrian-level wind mechanical comfort, but not very helpful to reduce the occurrence of frostbite in winter.

Microclimatic comfort measurements evaluation of building physics: The effect of building form and building settled area, on pedestrian level comfort around buildings

Wind discomfort and the dangers that the wind may lead can be harmful in terms of comfort conditions of both indoor and outdoor environment of the building/buildings to be constructed or just completed. The extent of discomfort to pedestrian varies from inducing slightly unpleasant feeling to producing a falling down hazard. Typically, the cause of frequent occurrences of strong wind at pedestrian area is primary related to the configuration of building structures and/or topography in the vicinity of the pedestrian area. Depending on the characteristics of the wind including magnitude, uniformity, ambient temperature, and so on, the level of disturbance to users of pedestrian areas can be different. In this context, the regions where Necmettin Erbakan University temporary education buildings are located have a fairly intensive topography in terms of wind. Therefore, detailed analysis of the inside regions and the surrounding areas of education buildings in particular are performed in terms of microclimatic comfort and indoor energy recovery. Especially, the topography where university campus temporary educational buildings are located has very high wind climate conditions compared to the city of Konya climate conditions. In this study, pedestrian-level wind conditions around N.E.U. campus buildings and in urban areas and the topography of campus settlements were analyzed through on-site measurement with Delta OHM microclimatic instruments. The purpose of this study is to investigate the pedestrian-level comfort conditions around the project buildings suggested by concept architects together with microclimatic measurements of comfort conditions, in the light of current topographic and climatic conditions presented by the head architect. However, presentation of these topographic and microclimatic measurements around currently completed temporary classrooms of the university campus have not yet been completed. The topography of the university campus, which is at an altitude higher than that of Konya centrum, is exposed to an extremely high wind velocity. The pedestrian-level comfort conditions are measured using Delta OHM instrument. The study also aims to compare pedestrian-level comfort conditions at locations of various buildings. In addition, outdoor comfort survey was also conducted in the campus area. However, measurement results of the microclimatic measurement device, DeltaOHM, are evaluated in this study. It can be observed from the results that pedestrian-level comfort of current campus settlements around the buildings reach very discomforting levels. Since the university’s topography varies between very high and very low temperature levels and wind velocity values, climatic comfort problems are observed in the area. Some reasons for the discomfort problems observed in current settlement are; incorrect use of climatic parameters, incorrect directions of buildings, thermal effects due incorrect selection of materials used in constructions of buildings. In order to achieve thermal comfort, more studies are required on pedestrian-level comfort, use of passive design techniques such as correct direction of buildings and correct selection of materials utilized in the buildings based on their thermal effects. This would help university campus buildings consume less energy and maximize people’s satisfaction.

Computational evaluation of building physics—The effect of building form and settled area, microclimate on pedestrian level comfort around buildings

Wind discomfort and the dangers that the wind may lead can be harmful in terms of comfort conditions of both indoor and outdoor environment of the building/buildings to be constructed or just completed. The wind effects on a site can be divided in two as: mechanical wind effects and thermal wind effects. This study is specifically about mechanical wind stress and pedestrian wind comfort. Typically, the cause of frequent occurrences of strong wind at pedestrian area is primary related to the configuration of building structures and/or topography in the vicinity of the pedestrian area. Depending on the characteristics of the wind including magnitude, uniformity, ambient temperature, etc., the level of disturbance to users of pedestrian areas can be different. In this context, the regions where Necmettin Erbakan University (N.E.U.) temporary education buildings are located have a fairly intensive topography in terms of wind. Therefore, detailed analyses of the inside regions and the surrounding areas of education buildings in particular are performed in terms of microclimatic comfort and indoor energy recovery. Especially, the topography where the university campus temporary educational buildings are located has very high wind climate conditions comparing to the city of Konya, Turkey, climate conditions. In this study pedestrian level wind conditions around N.E.U. campus buildings and in urban areas and campus buildings settlements topography are analyzed by CFD FloEFD. The aim of the study is to analyze causes of wind nuisance in campus site area and around temporary education buildings, and compare and evaluate remedial measures. The results show that current campus settlement, around the buildings and amphi classes are seen to reach very discomforting levels in terms of in classroom comfort. Draft architectural campus temporary education buildings projects proposed by the author can improve on existing wind conditions where possible, and as a minimum, can not significantly degrade wind conditions especially when considering the safety criteria.

Large eddy simulation of flow around an inclined finite square cylinder

The flow field around a rigid finite square cylinder inclined away from the vertical direction was numerically investigated via large eddy simulations. The cylinder under investigation had a height-to-width ratio of 18 and the inclination angle, defined as the angle between the cylinder orientation and the vertical direction, varied from forward inclination to backward inclination. Pressure measurements and flow visualizations were taken in a wind tunnel to validate the numerical simulations. The forward inclination is found to enhance the downwash, which is initially observed behind the free end of the vertical cylinder, and amplify it to a downward axial flow. Conversely, the backward inclination promotes upwash, which originates behind the base of the vertical cylinder, to be an upward axial flow. On the other hand, the vertical cylinder produces two pairs of counter-rotating streamwise vortices (quadrupole wake) in its wake, but only one pair of vortices (dipole wake) is observed to form behind both the forward and backward inclined cylinders. Moreover, only a free-end vortex pair is exhibited behind the forward inclined cylinder whereas a base vortex pair exists behind the backward inclined cylinder. They are considered to generate the downward and upward axial flow respectively. It is anticipated that the presence of the axial flow significantly influence both the pedestrian-level wind conditions and the aerodynamic characteristics of the cylinder.

Further experiments on Irwin's surface wind sensor

The simple surface wind sensor proposed by Irwin measures wind speeds through pressure differences. It has been applied in several wind-tunnel laboratories for the study of pedestrian-level wind conditions. However, some characteristics related to sensor performance for wind-tunnel measurements have not been fully investigated. Discussed in this paper are: calibration of the sensor for measuring mean and rms wind speeds, the effect of sensor height on measurement errors, the interference between nearby sensors, and the response of sensors to turbulent wind conditions. Data presented here supplement Irwin's original results on the surface wind sensor and provide additional insight in the performance of the sensor.

Determination of the pedestrian wind environment in the city of Ottawa using wind tunnel and field measurements

The objective of this study was to determine the pedestrian-level wind conditions throughout the central area of the City of Ottawa, Canada. A 1:400 scale model, 7.3m in diameter, of the central area was tested in the NRCC 9×9m wind tunnel. Windspeeds were measured simultaneously at 615 pedestrian-level locations, and above three selected model buildings, for 16 directions of the approaching winds. Fullscale wind measurements were made for 7000 hours at the city airport and simultaneously above the same three buildings over a period of 15 months and for 217 hours with a mobile anemometer unit that measured the windspeed at a height of 2m. Special techniques used radio and telephone links to transmit wind data from both fixed and mobile remote sites. The objective was achieved by combining the modelscale and fullscale wind measurements with the long-term wind statistics from the airport. From these measurements we can now predict the mean and gust windspeeds which will occur with weekly, monthly, seasonal and per annum probabilities at each of the 615 locations, for each of the 16 wind directions.