Wind Discomfort Research Articles

City configurations to optimise pedestrian level ventilation and wind comfort

Mediterranean coastal cities encounter two conflicting urban environmental challenges. First, strong winds that pose a risk of pedestrian wind discomfort on coastal streets, and second, weak winds that lead to inadequate outdoor ventilation in inner urban fragments. This study aims to optimise pedestrian level ventilation and wind comfort in Izmir, a compact coastal city in the Mediterranean climate. Three hypothetical city configurations were created based on four morphological parameters: street layout, urban street canyon form, tower layout, and tower height variation. Computational fluid dynamics simulations of the city configurations were performed and validated by wind tunnel experiments. The weak, comfortable, and strong winds were determined and mapped at the pedestrian level to assess each city configuration's performance. The results show that using the strategy of a shifted coastal street layout with adding towers on second-row blocks results in a 20 % reduction of the maximum wind velocity ratio on coastal streets compared to a grid street layout without towers. Moreover, positioning step-up towers on step-up city blocks and shifted towers on step-down city blocks can increase pedestrian-level ventilation efficiency by up to 73 %. The research methodology and findings can be transferred to other climates and urban environments and guide urban designers.

A proposal of urban coastal pattern for improving pedestrian wind comfort in coastal cities

High-speed wind flow in urban areas poses a risk of pedestrian wind discomfort. Coastal cities, particularly, are at risk of wind discomfort as they are exposed to strong sea breezes. To improve the wind climate in coastal cities, we redesigned a standard coastal urban fabric by placing a new building at its center. Then we investigated the effect of critical variables, the central building’s location ( x/L ratio) and dimensions ( height, width, length) on wind conditions with a parametric design approach based on the computational fluid dynamics (CFD) method validated by experimental data. We found that an optimum combination of x/L ratio and central building height ( H) can reduce the corner and double corner effect between two parallel buildings by up to 45% and minimize the risk of wind discomfort. The findings can be applied to newly-designed coastal settlements where wind shelter is required and can help urban policymakers and designers.

Wind adaptive urban seafront buildings design for improving urban ventilation and pedestrian wind comfort in Mediterranean climate

Coastal cities in the Mediterranean region have cool sea breezes that can reduce the effects of global warming, urban heat islands (UHI), and air pollution. However, in many coastal cities, impermeable urban seafront buildings prevent cool sea breezes from penetrating the city while at the same time posing a risk of pedestrian wind discomfort. This study aims to design wind-adaptive urban seafront buildings that improve urban ventilation and pedestrian wind comfort in Izmir, a high-density Mediterranean city, using the parametric design and computational fluid dynamics (CFD) method. Alternative seafront buildings consisting of two-rows and shifted configurations were designed using the two proposed urban geometric indicators. The authors found that the denser and more compact seafront building configuration can prevent the risk of wind discomfort and achieves the highest ventilation efficiency (82%). The findings apply to similar coastal urban environments and help urban policymakers and designers.

Improving pedestrian micro-climate in urban canyons: City Center of Alexandria, Egypt

Due to the accelerated pace of urbanization, the study of the local urban microclimate has acquired significance. A detailed and accurate prediction of outdoor ventilation and thermal comfort is required for a healthy environment, particularly in densely built areas, due to the complex interaction of physical phenomena across different length and time scales. Engineering approaches are critical for solving the issues of wind discomfort. These approaches can however not be applied independently of the architectural context. An interdisciplinary approach can bridge the gap between architectural design and engineering wind-comfort solutions in a coastal city of developing countries with a temperate climate. The current study aims to evaluate the effect of urbanization on an asymmetrical historical canyon in the city center of Alexandria, Egypt. Challenges and limitations are imposed regarding applying retrofitting techniques to improve pedestrian comfort without changing the historical features of these areas.This paper provides a Computational Fluid Dynamics (CFD) simulation of a residential district in the modern city of Alexandria which contains the library of Alexandria and the two oldest paved roads in the world which still in use until today. The 3D steady Reynolds-averaged Navier-Stokes (RANS) equations and the standard k-ε model are used to calculate the aerodynamic flow field. These computational settings were validated with previously published wind-tunnel results. The indices of thermal comfort were calculated using a Predicted Mean Vote (PMV) model utilizing Custom Field Functions (CFF). On-site measurements of air velocity, temperature, and humidity were conducted to validate the thermo-flow characteristics with the numerical simulation and they were in a good agreement.To reach the comfort level which contributes to a pedestrian-friendly environment, it brings a range of measures that covers qualitative design guidelines on street and building level to mitigate wind discomfort and excessive solar access in urban canyons. One of these measures presents (CFD) simulations for comparing the model of the modern city with a visualized model of the ancient city of Alexandria at the end of Cleopatra's reign. This comparison aims to give a close vision on how urbanization has influenced the aerodynamics and thermal comfort in this region. The current study helps urban planners and architects to enhance the current situation for better urban microclimate at the pedestrian level, without setting up new developments during hot summer days.

Pedestrian Wind Distribution Within an Urban University City Campus using Wind Tunnel Test

There is a necessity to further explore the pedestrian wind studies in Malaysia as in concerning the impact and risk of hazard wind towards community due to the occurrence of strong wind events. The gradually increase of high-rise buildings in an urban city might lead to artificial strong wind, causing wind discomfort or infrastructure damages, In this study, the research framework is demonstrated and the wind distribution within Universiti Teknologi Malaysia Kuala Lumpur (UTMKL) city campus is revealed by conducting wind tunnel test. The results showed that the high wind speeds are spotted near high buildings (MJIIT, Menara Razak, and Residensi Tower of UTMKL) where U(z)/U(zref) ranging from 0.60-0.90. Factors that are causing the wind amplification near tall buildings are downdraft wind at windward of building, wakes at corners, and leeward of building, as well as the venturi effect occurred between two tall buildings. The layout of the buildings also shall be one of the factors that affecting the wind distribution, as there is a case where a group of buildings served as a shelter and refrained the wind to flow through some areas. This preliminary result is also aligned with the storm event that happened. Thus, for the sake of the safety and comfort of the pedestrians, incorporating the wind tunnel data in the future master planning in this city campus should be considered to reduce the wind nuisance issues

A Study on Developing Ventilation in Restaurants in Re-purposed Row Houses

The building ventilation of seventy-seven row houses in eight districts in Chiang Mai province of Thailand was surveyed and investigated. A typical row house re-purposed as a restaurant refers to a 3.5 m high space with two stoves in the front of the building and a closed rear area to serve as storage. As a base-case, restaurants had an average capacity of 24 customers in the dining area. Measurements of internal air quality of a selected restaurant were conducted in the summer season of 2015 and 2017, and the results revealed average air temperatures of 36°C and 33°C, relative humidity values of 46% and 33%, and air speed values of 0.28 m s-1 and 0.10 m s-1, respectively. The Computerised Fluid Dynamics (CFD) and the Center for the Built Environment (CBE) thermal comfort tool were used to simulate the efficiency of current and proposed ventilation techniques and also analyse thermal comfort conditions for each scenario. Low-cost cooling techniques of air speed and humidity adjustment were chosen to improve thermal conductions. By applying the combined techniques, the overall temperature was reduced by 2°C and the thermal comfort levels were improved from the ‘hot’ to the ‘warm’ zone. Some conditions in the second restaurant are in the expanded ‘adaptive thermal comfort zone’. Although most results appear to exceed the ‘adaptive thermal comfort zone’, conditions could not be further ameliorated since 1.5 m s-1 was the maximum air speed that could be employed in the dining area to avoid wind discomfort. Limited investment in ventilation improvement was the main challenge since air-conditioners and multiple fans were not affordable and were also insufficient for the re-adaptation option. Feasibility study of ventilation improvement technique is limited in this study.

Design for improving pedestrian wind comfort: a case study on a courtyard around a tall building

ABSTRACTWind has an important impact on pedestrian comfort around buildings. Wind around tall buildings may cause significant problems at the pedestrian level and requires analysis. Wind comfort analyses are conducted via computational fluid dynamics (CFD) simulations and wind-tunnel studies. Engineering solutions are crucial in addressing wind discomfort issues. However, such solutions should not be applied independently of the architectural context. A multidisciplinary approach can bridge the gap between architectural design and engineering wind-comfort solutions. Adopting such an approach, this paper presents a design strategy to mitigate wind discomfort in a courtyard around a tall building. The CFD simulation results indicate that the proposed design provides the required wind comfort levels according to the NEN 8100 standard. In addition, using CFD simulations in combination with the standard is demonstrated to be an efficient method for improving pedestrian wind comfort. This outcome can help guide future research on wind comfort and thus contributes to improving the environmental quality of urban areas.

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.

CFD simulation of train aerodynamics: Train-induced wind conditions at an underground railroad passenger platform

The Dutch railways plan to increase the amount of trains and their running velocities to avoid overcrowded trains during rush hours. This can cause pedestrian wind discomfort or danger at the platforms as trains will be allowed to pass small railway stations at high speeds up to 140km/h. A number of these railway stations lie underground, where wind gusts caused by trains are amplified by space confinement. The purpose of this study is to evaluate the effect of passing passenger trains and freight trains on the wind conditions induced on a passenger platform inside an underground tunnel by means of Large-Eddy simulations (LES). First, the computational model, which includes stationary (tunnel and platform) and moving (train) subdomains, is validated by available experimental data for a train running through a tunnel. Next, case studies are performed for a passenger train and a freight train, where the dimensions of the tunnel and the platform are chosen from the Dutch design requirements for railroad tunnels and platforms. The results of the study show that passengers standing on a platform can experience strong wind effects when passenger trains or freight trains are passing at speeds of 140 and 100km/h, respectively. These effects might give rise to wind discomfort or even wind danger, and should be taken into account in the design of railway tunnels and platforms and in safety regulations.

Assessing Wind Comfort in Urban Planning

There are increasing concerns regarding the quality of urban public spaces. Wind is one important environmental factor that influences pedestrians' comfort and safety. In modern cities there are increasing numbers of high constructions and complex forms which can involve problems of significant wind discomfort around these buildings. Architects and town planners need guidelines and simple design tools to take account of wind in their projects. This paper reports the progress made in using computational fluid dynamics (CFD) simulations for assessing wind comfort in urban planning. Fluent software was validated for wind studies in urban environments by comparing CFD simulation results with published wind-tunnel tests. This validation shows that mean wind velocities around buildings can be simulated numerically with a very high degree of accuracy. On the basis of the results of a large number of CFD simulations, a methodology and simple graphical tools were developed to quantify critical wind speeds around buildings. In practice these should help architects and town planners when designing our built environment. Moreover, this study shows how numerical modelling is now a high-performance tool for developing useful guidelines and simple design tools for urban planners.

A method for optimisation of wind discomfort criteria

Wind discomfort criteria are compared and optimised using a U/ U pot framework; U pot is the 10 m wind speed at an ideal meteorological site. A new estimate of turbulence intensity is proposed for the conversion of criteria to a U/ U pot ratio. Using this estimate, differences between existing criteria turn out to be much larger than remarked upon in the past. The criteria are also checked against empirical evidence. For the test case of Amsterdam, the maximum recommended value of U/ U pot varies between 0.3 (for sitting) and 0.7 (safety only). Optimum thresholds are proposed as well.

Urban climatological studies in the Reykjavı́k subarctic environment, Iceland

The distribution of air temperature and wind speed was investigated in Reykjavı́k, the capital of Iceland, during the period from November 1991 to September 1992. The obtained data reveal that the climate in Reykjavı́k is mainly affected by the subarctic radiation budget, frequent cyclones penetrating into the investigation area and the closeness to the ocean. Nevertheless, Reykjavı́k shows a weak heat island effect, which converts to a `cold island’ by day in mid summer. The anthropogenic heat release amounts to ca. 35 W m −2. The study also indicates that the bioclimate and human comfort in Reykjavı́k is determined more by a high wind discomfort than by severe winter temperatures or high air pollution typical for high-latitude cities.

Wind climate and smoke control in covered shopping malls

The paper presents results of a wind tunnel study concerning pedestrian comfort in a covered shopping mall having permanently open entrances at both ends. Using surface flow pictures and flow visualization studies, the critical areas concerning wind discomfort have been determined. Local wind speeds and wind speed fluctuations have been measured for those critical areas using hot film anemometry. Various configurations have been considered. While at present the threshold wind speed will be surpassed in large areas of the shopping street by about 25 % of the time, the proposed roof will eliviate the situation considerably. Further possibilities for improvement have been determined and will be described.