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Prediction of wind environment and thermal comfort at pedestrian level in urban area
Abstract
This paper reviews the recent developments in CWE research for predicting the pedestrian level wind and thermal environments in urban areas, primarily achieved by the researchers in the field of environmental engineering in Japan. First the progress in turbulence models in the last decade and in their applications to the problems related to wind climate is briefly reviewed, and the results of Architectural Institute of Japan (AIJ) collaborative project in cross comparisons of CFD results of wind environments are presented. Next, recent achievements in the field of modeling canopy flows for reproducing the aerodynamic and thermal effects of trees, buildings and automobiles are outlined. Examples of numerical results obtained using tree and vehicle canopy models are shown to demonstrate the significant effects of stationary and non-stationary subgrid scale flow obstacles on turbulent flowfield within street canyons.
... In addition to aesthetic considerations, structural characteristics such as size, shape and density, surface complexity, and crown transparency are among the most important factors that determine their ecological features and benefits (Gómez-Baggethun & Barton, 2013). Urban trees are not only important for pedestrian comfort, providing aesthetic benefits, rain protection, shade, and wind mitigation Mochida & Lun, 2008), but can also help save energy on a larger scale through air purification, cooling (Rahman, 2017), wind buffering, and shading (Speak et al., 2020;Meili et al., 2021). Potential noise reduction (Fang & Ling, 2003;Zhao et al., 2021), temperature control (Akbari et al., 2001;Akbari & Konopacki, 2005;Gillner et al., 2015), water flow regulation and water runoff mitigation (Villarreal & Bengtsson, 2005;Pataki et al., 2011;Steele et al., 2014), wind flows Mochida & Lun, 2008), air purification (Nowak & Crane, 2002;Escobedo & Nowak, 2009), and habitat functionality (Tews et al., 2004) are also directly related to the structure of tree (Bayer et al., 2018). ...
... Urban trees are not only important for pedestrian comfort, providing aesthetic benefits, rain protection, shade, and wind mitigation Mochida & Lun, 2008), but can also help save energy on a larger scale through air purification, cooling (Rahman, 2017), wind buffering, and shading (Speak et al., 2020;Meili et al., 2021). Potential noise reduction (Fang & Ling, 2003;Zhao et al., 2021), temperature control (Akbari et al., 2001;Akbari & Konopacki, 2005;Gillner et al., 2015), water flow regulation and water runoff mitigation (Villarreal & Bengtsson, 2005;Pataki et al., 2011;Steele et al., 2014), wind flows Mochida & Lun, 2008), air purification (Nowak & Crane, 2002;Escobedo & Nowak, 2009), and habitat functionality (Tews et al., 2004) are also directly related to the structure of tree (Bayer et al., 2018). Urban biodiversity is being recognised as an increasingly important issue. ...
... Overall, vegetation in cities plays an important role in redistributing wind flows, contributing to a more comfortable and healthy urban environment. This allows cities to reduce the heat load, reduce the risk of extreme weather events, and improve the quality of life of their residents (Mochida & Lun, 2008). ...
Many European countries have extensively practiced the cultivation of black locust. This species is characterised by rapid growth, the application possibility for degraded land reclamation and other useful properties, but its adventiveness and invasive status require more thorough research. The aim of the research was to assess the viability of a population of black locust (Robinia pseudoacacia) in urban environment by determining its vital status and measuring height of the plants and diameter of their trunks as the main morphometric indicators. The research was conducted in the recreational area of the Oles Honchar Dnipro National University Botanical Garden. There were recorded 178 plants of R. pseudoacacia. Tree heights were measured by a Suunto PM-5 mechanical height meter in three-time repetition for each plant, and the average value was calculated based on these data. The trunk diameter was measured at the small fork as a distance between two parallel tangents. The vital status of the trees was determined by the 5-point scale of V. A. Alekseev. The height of the vast majority of the studied trees varied 25 to 30 m. The height of one species representative reached 32 m. The trunk diameter of the most trees in the territory ranged 30 to 40 cm. Plants with a trunk diameter of between 40 cm and 50 cm were the next largest group. A 101 cm trunk diameter was found in just one tree. Most plants in the research area had a vitality score of 2 – good state. Accordingly, these were the plants that had the largest trunks of examined trees. The fewest number of plants was in a very bad state and had a score of 5. The good and satisfactory vital conditions were observed in plants whose trunks were the tallest and had the largest diameter, and whose morphometric indices slightly varied (the height-diameter trunk correlation was reliable). Plants in depressed and poor vital state were characterised by significant variability in the morphometric parameters (the correlation between height and trunk diameter was not reliable). The ecological condition of the black locust population in the area was assessed, and it was concluded that its morphometric parameters cannot be used as indicators of plant vitality.
... Unfortunately, the two-equation "k-ε" turbulence model, a typical turbulence modeling approach in RANS models, is not capable of resolving all complex features of the flow field around bluff bodies. This model typically over-predicts the size of the reattachment length behind the building and under-predicts the velocity magnitudes in wake regions (Mochida & Lun, 2008). It is well known that prediction of surface pressures is less accurate due to overproduction of turbulent kinetic energy in an impingement region (Kato & Launder, 1993). ...
... In this study, the GCI was described as GCI [fine]=FS|ε|/(rp-1), where FS =1.25 represents the safety factor when comparing three grids, ε is the relative error between coarse and fine grid solutions, and p=2 is the order of the discretization method based on second-order discretization of all terms in space, where p = 2 is for the systems of interest (Hefny & Oooka, 2009). The results for the ZEQ simulations showed that GCI (Kato & Launder, 1993;Mochida & Lun, 2008) = 3.05%, and GCI (Mochida & Lun, 2008;Murakami, 1998) = 8.48%. It was observed that a small value of GCI index occurred when comparing medium and fine grid results. ...
... In this study, the GCI was described as GCI [fine]=FS|ε|/(rp-1), where FS =1.25 represents the safety factor when comparing three grids, ε is the relative error between coarse and fine grid solutions, and p=2 is the order of the discretization method based on second-order discretization of all terms in space, where p = 2 is for the systems of interest (Hefny & Oooka, 2009). The results for the ZEQ simulations showed that GCI (Kato & Launder, 1993;Mochida & Lun, 2008) = 3.05%, and GCI (Mochida & Lun, 2008;Murakami, 1998) = 8.48%. It was observed that a small value of GCI index occurred when comparing medium and fine grid results. ...
btaining accurate numerical simulations of airflows for actual building clusters is time consuming due to a vast variety of characteristic flow patterns, combined with a wide spectrum of spatial and temporal scales. In order to provide a faster, yet reliable and simple modeling approach for simulation of outdoor airflow around multiple buildings, the presentstudy evaluated a performance of the modified zero-equation turbulence model (ZEQ). A comprehensive set of velocity field measurements in the wind tunnel experiment was conducted, and the results were used to calibrate the ZEQ model. Additional measured data are used for the validation of different turbulence modeling approaches. The performance of the modified and improved zero-equation turbulence model was compared to the revised “Kato-Launder” version of the “k-ε” model (MMK), and Large Eddy Simulations(LES) using the standard Smagorinsky Subgrid-scale model (SMG). The validation revealed a satisfactory performance of the calibrated ZEQ turbulence model in predicting streamwise mean velocity profiles, and demonstrated its comparative competitiveness with the two other turbulence modeling approaches. A less than satisfactory agreement between numerical results and measured data was identified in the prediction of vertical and lateral velocity components regardless of the turbulence modeling approach. Overall, the calibrated ZEQ turbulence model provided results that were comparable to MMK and SMG and required substantially smaller computational resources. An additional outcome of the present study is a recommendation for future research to improve performance of the calibrates ZEQ turbulence model using more advanced experimental techniques and implementation of macroscopic morphological parameters to account for realistic representation of the buildings settings in urban areas.
... At the current air temperatures, Girne Street is the research area with the lowest air temperature. As Mochida and Lun (2008) [43], Park et al. (2012) [44], and Qaid and Ossen (2014) [45] also emphasized in their studies, trees on urban roads, which act as wind tunnels, have a cooling effect. It is thought that the 1-2 • C temperature change in Girne Street compared to the other study areas is due to this effect and the shade effect of the buildings. ...
... At the current air temperatures, Girne Street is the research area with the lowest air temperature. As Mochida and Lun (2008) [43], Park et al. (2012) [44], and Qaid and Ossen (2014) [45] also emphasized in their studies, trees on urban roads, which act as wind tunnels, have a cooling effect. It is thought that the 1-2 • C temperature change in Girne Street compared to the other study areas is due to this effect and the shade effect of the buildings. ...
Today, rapid urbanization and increasing human activities have affected the climate at macro and micro scales in cities and caused unfavorable conditions in terms of human thermal comfort, especially in outdoor spaces. In this context, new solutions need to be researched, developed,tested, and updated to improve thermal comfort in cities. Using ENVI-met 5.1 software, this study investigated the effects of different NBS combinations on the urban microclimate and human bioclimatic comfort in Izmir (Turkey). The current situation, the scenarios where some nature-based solutions (NBS) are applied within the scope of the European Union’s HORIZON 2020 “URBAN
GreenUP” project, and two other scenarios planned within the scope of the study were evaluated.The findings of the study showed that both the NBS scenarios created within the scope of the EU project and the NBS scenarios with large deciduous trees had the most positive impacts on improving thermal comfort conditions in all three study zones and achieved temperature reductions of up to
2.5 ◦C in urban temperatures. In terms of thermal comfort, the most significant differences were calculated between the minimum PMV values and were close to 1 ◦C. In addition, the simulation results showed positive changes in psychological stress levels.
... CFD has become a commonly used numerical simulation method and analytical tool for studying the wind environment in urban planning and design [5,24,49,50,53]. It is increasingly being used to assess the pedestrian-level wind environment and comfort in urban areas [53][54][55] and to investigate turbulent flow conditions in different street canyon models [36,49,56], as well as to evaluate the influences of building layout and land use patterns on ventilation in order to find optimal planning solutions for mitigating UHIs [57][58][59][60][61]. For example, Yuan and Ng (2012) found that building blocks with limited open spaces, uniform building heights, and large podium structures have led to lower permeability for urban air ventilation at the pedestrian level [57]. ...
... The wind velocity is 2.25 m/s, and the wind direction is southerly. Regarding the selection of turbulence models, the Large-Eddy Simulation (LES) model and RAND/URANS models were compared based on the related literature [54,74,75] and modeling tested in this study. Considering factors such as the geometry of the model, the accuracy of results, and the computing resources and costs, this study finally employed the LES turbulent model, and the time step used in the LES model was 0.01 s. ...
Under the trend in climate change, global warming, and the increasingly serious urban heat island effect, promoting urban wind corridor planning to reduce urban temperature and mitigate the effect of urban heat islands has received widespread attention in many cities. With emerging awareness of the need to explicitly incorporate climate considerations into urban planning and design, integrating current spatial analysis and simulation tools to enhance urban wind corridor planning to obtain the best urban ventilation effect has become an increasingly important research topic in green city development. However, how to systematically carry out urban wind corridor planning by employing related technology and simulation tools is a topic that needs to be explored urgently in both theory and practice. Taking Zhumadian City in China as an example, this study proposes a method and planning approach that uses remote sensing (RS), geographic information system (GIS), and computational fluid dynamics (CFD) in an integrated way to understand urban landscape and to conduct urban wind corridor planning. The research results reveal that the urban form of Zhumadian City favors the development of urban wind corridors, and that the railway lines and some major roads in the city have the potential to be developed as the city’s main wind corridors. However, there are still ventilation barriers resulting from the existing land use model and building layout patterns that need to be adjusted. In terms of local-level analysis, the CFD simulation analysis also reveals that some common building layout patterns may result in environments with poor ventilation. Finally, based on the results of our empirical analysis and local planning environment, specific suggestions are provided on how to develop appropriate strategies for urban wind corridor planning and adjustments related to land use planning and building layout patterns in order to mitigate the impact of the urban heat island effect.
... In a study completed in Japan, CFD applications in the pedestrian level wind environment were examined in detail, and Blocken (2014) reviewed CFD studies in wind engineering in the last 50 years [27,28]. Also many studies have been carried out with CFD on both indoor comfort and energy performances and outdoor pedestrian level comfort, building facade pressure, speed values and design-comfort performance values [29][30][31][32][33][34][35][36]. In these studies, it is seen that CFD significantly reduces the costs of studies while allowing a more comprehensive and in-depth analysis of subjects that are objectively difficult to investigate experimentally [35][36][37][38]. ...
... Also many studies have been carried out with CFD on both indoor comfort and energy performances and outdoor pedestrian level comfort, building facade pressure, speed values and design-comfort performance values [29][30][31][32][33][34][35][36]. In these studies, it is seen that CFD significantly reduces the costs of studies while allowing a more comprehensive and in-depth analysis of subjects that are objectively difficult to investigate experimentally [35][36][37][38]. When the comparing with wind tunnel testing and on-site monitoring technique, CFD simulation has some advantages such as whole flow wind data and low costs. ...
In urban design, the shape and form of the building and the layout of the buildings on the topography significantly influence the microclimatic comfort quality at the pedestrian level or in the public spaces all around the buildings by directing the winds to the streets and the designed open spaces. In this study, The Arabahmet region, one of the oldest historical settlements and cultural heritage of the Turkish Republic of Northern Cyprus, is located within the capital city of Nicosia, Cyprus, and the continuation of the Arabahmet doctrine under the control of the United Nations, which is now between the territories of Southern part of Cyprus and the Turkish Republic of Northern Cyprus (TRNC). This region has been a witness to many urban and periodical experiences over a wide period of time, covering many ages. This settlement is one of the settlement areas in which the Ottoman Empire and Republican periods, especially the Byzantine empire, and rarely seen the chance to see the official and civic influences on a city together. The overall aim of the study is to reveal the general potentials of the historic land of the Arabahmet region, which is about to become a depressed region due to different reasons, in many parameters, especially the physical comfort criteria.
... This also implies that computer modeling appears to be the prevalent method for establishing problem concepts and solutions for structures in the twenty-first century. [9,10] noted that as wind modeling improved as well as with computer speed and capacity, the approach was growing in popularity not only for its adaptability and informative results but also for its affordable labor and equipment expenses. A domain including both stationary objects (such as buildings) and non-stationary barriers (such as moving autos, trees, etc.) could be modeled using CFD.) [11]. ...
... Second class: It represents 13 % of the city [21]. It consists of (7) blocks (8,9,25,26,27,28,29), and the number of sections is (2469), number of populations is (988) persons. Third class: it represents 58.7% of the city as shown in figure 1(a-b) . ...
This paper evaluates an architectural design using an Energy Consumption consideration of Natural Ventilation in a hot dry climate (Khartoum State), at dwellings design applied. Method was used analysis of Autodesk IEVS software natural ventilation and energy consumption simulation. It resulted that to cooling, by natural ventilation in dwelling design used to get indoor temperature at the comfortable level during the summer. The Best-Case Situation of natural ventilation with consider of energy saving Based on the CFD simulation analysis, the performance of internal air velocity is approximately 0.7m/s. The wind velocity starts to slow down towards the rear of the apartment spaces. Approximately 95% of the internal areas have average air velocity between 0.43 m/s to 0.9 m/s. Internal Air flow pattern single floor house plan at Khartoum (Alazhari City); showing the internal air velocity of 0.7m/s near the window opening positions with the wind directions in the details and pressure of the air as worst-case situation, with velocity and temperature of the air with average 22o as a best-case situation. during a year. Architectural design process in the urban area of Alazhari City for dwelling towards to saving energy was applied and determined into an urban planning neighbourhood at Khartoum.
... The CFD simulations were performed to analyze the interactions between individual buildings and wind as well as the performance of the wind conditions in the HRCs before and after a building layout optimization. CFD simulations are a low-cost, efficient method for analyzing wind conditions with an accuracy that has been extensively validated [29][30][31][32]. The quantitative methods used in this study involved field monitoring and computational fluid dynamics (CFD) simulations. ...
... The CFD simulations were performed to analyze the interactions between individual buildings and wind as well as the performance of the wind conditions in the HRCs before and after a building layout optimization. CFD simulations are a low-cost, efficient method for analyzing wind conditions with an accuracy that has been extensively validated [29][30][31][32]. ...
In recent years, residents in high-rise residential complexes (HRCs) in China have been placing an increasing demand on the living quality in HRCs. Particularly, the outdoor wind conditions are garnering more attention; however, few studies on the wind conditions within HRCs with densely arranged buildings and high plot ratios have been reported. Therefore, this study investigated the relation between the buildings’ layouts in HRCs and their wind conditions and it proposes optimization strategies to enhance body comfort in their outdoor environments. The research methods in this work involved field surveys, computational fluid dynamics (CFD) simulations, and field monitoring. The field surveys were used to determine the types of activities undertaken by the residents in the selected HRCs and their perceptions of the wind conditions within the HRCs. Field monitoring was primarily conducted to measure the present wind conditions in the HRCs. The CFD simulations were performed to analyze the interactions between individual buildings and the wind as well as the performance of the wind conditions in the HRCs before and after a building layout optimization. The simulation results and monitoring data showed that the present wind conditions in the HRCs were uncomfortable due to high wind speeds (exceeding 5 m/s) and large windless areas. To achieve a comfortable outdoor wind environment, future HRCs should adopt a point-to-point building layout and the buildings should be oriented south. Moreover, the ratios of the height to width (Hb/Wb) for individual buildings should be kept at approximately 1.33. For existing HRCs, landscape walls, trees, and moveable windbreak panels can be used to reduce the wind speeds, especially in open exit/entrance areas and windward areas.
... Advancing our understanding and ability to model turbulent flows is critical for accurate weather forecasting (Skamarock et al., 2008) and climate projection (Mochida and Lun, 2008;Toparlar et al., 2015), to improve urban sustainability and resilience (Chen et al., 2012;Casola, 2019;Krayenhoff et al., 2020;and Kameyama et al., 2020), and to design more performant and reliable engineering systems (Cheikh and Momen 2020;Chung et al., 2021). Historically, scientific discoveries in the field of turbulence have been achieved through computational methods (Scotti et al., 1993;Moser et al., 1999;Bou-Zeid et al., 2005;Chung and Pullin, 2009;and Lee and Moser, 2015), experimental techniques (Champagne et al., 1967;Raupach et al., 1980;Gong and Ibbetson, 1989;Prasad, 2000;Elsinga et al., 2006;Elsinga and Marusic, 2010;and Westerweel et al., 2013), and field observations (Menzies and Hardesty, 1989;Gal-Chen et al., 1992;and Rotach et al., 2005). ...
Obtaining accurate and dense three-dimensional estimates of turbulent wall-bounded flows is notoriously challenging, and this limitation negatively impacts geophysical and engineering applications, such as weather forecasting, climate predictions, air quality monitoring, and flow control. This study introduces a physics-informed variational autoencoder model that reconstructs realizable three-dimensional turbulent velocity fields from two-dimensional planar measurements thereof. Physics knowledge is introduced as soft and hard constraints in the loss term and network architecture, respectively, to enhance model robustness and leverage inductive biases alongside observational ones. The performance of the proposed framework is examined in a turbulent open-channel flow application at friction Reynolds number Reτ=250. The model excels in precisely reconstructing the dynamic flow patterns at any given time and location, including turbulent coherent structures, while also providing accurate time- and spatially-averaged flow statistics. The model outperforms state-of-the-art classical approaches for flow reconstruction such as the linear stochastic estimation method. Physical constraints provide a modest but discernible improvement in the prediction of small-scale flow structures and maintain better consistency with the fundamental equations governing the system when compared to a purely data-driven approach.
... The physical structure of cities controls and modifies the exchange of momentum, heat, water, and air pollutants between the land surface and the atmosphere (Belcher, 2005). Accurately predicting these exchanges is crucial across a wide range of applications, including local weather forecasting (Skamarock et al., 2008), climate projections (Murakami et al., 1999;Mochida and Lun, 2008;and Toparlar et al., 2015), air-quality monitoring (Lee et al., 1997;Vardoulakis et al., 2003;Li et al., 2006;and Boppana et al., 2010), and urban climate studies (Chen et al., 2012;Krayenhoff et al., 2020), to name but a few. The intricate interplay between turbulent airflow and urban geometry governs these complex processes. ...
Surrogate modeling is a viable solution for applications involving repetitive evaluations of expensive computational fluid dynamics models, such as uncertainty quantification and inverse problems. This study proposes a multi-layer perceptron (MLP) based machine-learning surrogate for canopy flow statistics accommodating any approaching mean-wind angle. The training and testing of the surrogate model are based on results from large-eddy simulations of open-channel flow over and within surface-mounted cubes (fixed geometry) under neutral ambient stratification. The training dataset comprises flow statistics from various approaching mean-wind angles, and the surrogate is asked to “connect between the dots,” i.e., to predict flow statistics for unseen values of the approaching mean-wind angle. The MLP performance is compared against a more traditional spline-based interpolation approach for a range of training data. In terms of relative mean absolute errors on individual flow statistics, the proposed MLP surrogate consistently outperforms the spline interpolation, especially when the number of training samples is reduced. The MLP model accurately captures mean profiles and three-dimensional flow variability, offering robust predictions, even when trained with as few as four approaching wind angles. The model is 10 4 × faster than large-eddy simulations, thus proving effective for multi-query tasks in the context of urban canopy flow modeling.
... In recent years, CFD simulations have become an important method for studying the microclimate in architecture due to advancements in computer technology [20][21][22][23][24][25][26]. CFD methods allow for full-scale modeling of individual buildings or urban streets, with easily controllable boundary conditions. ...
CFD offers advantages over wind tunnel experiments in the prediction and optimization of building wind environment; however, the computational costs associated with optimizing architectural wind environment remain a challenge. In this study, an approach that combines deep learning techniques with CFD simulations is proposed for the prediction and optimization of the architectural wind environment efficiently. A dataset of wind field is constructed using CFD simulation, considering various wind directions, wind speeds, and building spacing. Subsequently, a U-net deep learning model is trained as a surrogate model to rapidly predict the architectural wind field under different conditions. The results indicate that the model can accurately predict the wind field in buildings. The prediction time of building wind field is only 1/900 of that of CFD simulations, making it a viable surrogate model for wind environment optimization. Furthermore, considering all the building layouts and inflow conditions examined in this study, the maximum and minimum uniform wind speed area ratios Auni are 0.84 and 0.13, respectively. Under a single inflow speed, the maximum improvement in the Auni is 0.4, with an improvement rate of 48%. The results demonstrate the effectiveness of the proposed method as an efficient approach for optimizing architectural wind environment.
... Rapid urbanization has led to a proliferation of high-rise buildings in densely populated urban areas, posing a significant challenge to achieving acceptable wind conditions [1][2][3][4][5]. The decline in wind speed not only compromises ventilation and air quality [6][7][8][9][10], but also undermines the cooling effect of wind flow, increasing the risk of urban heat islands [11][12][13]. ...
... In this context, it is relevant to address the choice of RANS over alternative simulation methods. While transient simulations like Large Eddy Simulations (LES) offer more precise predictions of wake regions than steady RANS simulations, it should be acknowledged that RANS has generally proven effective for calculating mean values at ground level [35][36][37]. LES methods capture the wind's dynamic and instantaneous behavior more effectively but require substantially higher computational resources. Hence, the selection of RANS for this study aligns with our focus on achieving a balance between computational efficiency and the accuracy necessary for evaluating pedestrian-level wind comfort. ...
... The evaluation standard of wind environment is based on the current Chinese specification "Assessment standard for green building" (GB/T50378-2019) [29] and relevant studies on the correlation between the wind environment and human comfort [30,31], which establish 5 m/s as the outdoor wind environment evaluation threshold and 0~1.0 m/s as the range of indoor wind speed comfort value. ...
The building wind environment in coastal areas is highly complex and variable, particularly during winter when strong winds prevail. Understanding the influence of winter winds on human comfort and addressing health issues caused by wind noise in human settlements are very valuable research topics. This study focuses on developing strategies to optimize the wind environment in dormitory buildings located in the southern coastal area, where prolonged periods of strong winds have a significant impact. Specifically, we investigated the current wind in the teacher–student dormitory at Jinjiang Campus of Fuzhou University through questionnaire surveys and field measurements. Additionally, computational fluid dynamics (CFD) simulations were employed to evaluate different dormitory layouts. The research results indicate that it is preferable to position the dormitory areas downwind of large-scale buildings, adopt a staggered layout instead of a regular determinant layout to mitigate the narrow tube effect, avoid designing large-scale squares in the center of the dormitory areas, and enclose the dormitory groups with low-level corridors. These findings provide valuable guidance for the optimizing of winter windproof designs of university buildings located in the same climatic zone along the southeast coast.
... In recent years, computational fluid dynamics (CFD) has become an important tool for wind field assessment to simulate complex flow field phenomena (Blocken 2015), which is used to assist in architectural and urban design in the UK, Japan, and the US (Tang et al. 2012), and is now also actively used in urban construction in China (Fu et al. 2019). Urban planning based on the CFD model is an effective means of urban spatial layout and control, and open space , and building configuration (such as height, width, layout and density) have been shown to affect the influence of ground wind, such as pedestrian-level wind fields around buildings 1.5-2 m above the ground, affecting the thermal comfort of walking and standing pedestrians (Mochida & Lun 2008). Provide designers with accurate parameters to help them scientifically plan cities and residential areas (Zeng et al. 2019),reduce the impact of new designs on the surrounding environment and energy use (Yuan & Ng 2014;Sun et al. 2021), and provide technical support to combat the heat island effect, haze, and other problems. ...
Traditional villages contain human beings adapting to the natural environment and spontaneously forming a living environment in the process of their evolution. However, with the frequent occurrence of harsh weather in recent years, the livability of traditional villages is also facing challenges. In order to improve the climatic adaptability of traditional villages, scholars have proposed many methods, but there is a lack of research on the spatial microclimate adaptation of traditional villages based on the perspective of spatial accessibility. This paper selects typical traditional villages in the Taihu Lake Basin, analyzes spatial accessibility and CFD numerical simulation comfort by spatial syntax from the two levels of village and iconic nodes, and discusses the correlation between spatial accessibility and climate comfort. Also, the study concludes the following: (1) The overall integration degree of Mingyuewan Village is not high, and the overall accessibility is poor. (2) The correlation between wind environment and spatial accessibility is weak. The thermal environment is associated with spatial accessibility. Comfort is strongly correlated with the degree of spatial accessibility. This paper proposes to consider the lake surface to dominate the seasonal wind, reserve windward outlets, and add green plants and shade facilities in green public open spaces.
HIGHLIGHTS
A typical waterfront traditional village was selected.;
The scientific method uses spatial syntax combined with CFD simulation.;
The article discusses the correlation between spatial accessibility and climate adaptation.;
The waterfront and layout have proven to provide good thermal comfort for traditional villages.;
Climate adaptability of traditional villages is crucial for urban renewal.;
... For the purpose of the conducted considerations, the author of the study analyzed how London-type smog is formed, as this is the type of smog we most often deal with in Poland, including Krakow. The shortcomings of the methodology in the field of urban ventilation embedded in the planning and management of the city mean that wind is one of the main criteria in the formation of smog, or its absence, which is clearly emphasized by research [7,[24][25][26][27][34][35][36][37][38][39][40][41][42][43]. Air pollution translates into increased pathogenicity, mortality, and thus burdening the state health care system, also economic losses [2,3,6,17,21,22,[44][45][46][47]. ...
The purpose of this publication is to analyze air pollution on the example of the city of Krakow, as well as to consider the possibility of using geodata for environmental protection. In addition to case study analysis as the leading research method, the article also uses the observation, analysis, and statistical methods. The article presents the concept of using GIS spatial analyzes and spatial planning as an element of the Green New Deal in the process of ventilating the city of Krakow.
When developing a project related to city ventilation, it is extremely important to have the most accurate data on the strength, direction of the wind, type of pollution, and the number of emitters. Spatial analyzes are also able to indicate the main ventilation corridors of the city. These include, above all, areas located on the Vistula River, but also the widest city streets. Such results make it possible to more consciously manage space.
... The implementation of CFD also reduces the effect of new designed projects on the surrounding environment and decreases future energy use. General research using CFD has studied ventilation in a building or a city, pedestrian wind fields, contaminant diffusion, the urban heat island effect, and wind energy (Amorim, Rodrigues, Tavares, Valente, & Borrego, 2013;Chu, Hsu, & Hsieh, 2017;Mochida & Lun, 2008). ...
... Pedestrian-level wind environment (PLWE) is an important concept that directly impacts human safety and comfort (Blocken and Carmeliet, 2004;Stathopoulos, 2006). Previous studies of PLWE have entailed analyses of strong mean wind speed regions (Janssen et al., 2013;Mochida and Lun, 2008;Yoshie et al., 2007), and gust wind speeds (calculated using the mean wind speed and amplification factors) (Murakami et al., 1986;Vita et al., 2020;Yoshie et al., 2014). However, these previous studies of PLWE were centered around the use of mean wind speed and empirical or semi-empirical parameters to estimate the strong winds. ...
Low-occurrence strong wind speed Weibull distribution Gram-charlier series Pedestrian-level wind environment Probability density function Computational fluid dynamics A B S T R A C T Understanding low-occurrence strong wind speed (LOSWS) distributions at the pedestrian level is important. However, the robustness of the statistical methods for estimating LOSWSs under different conditions remains uncertain. In this study, the performances of the Weibull distribution method and Gram-Charlier series (GCS) method were compared. Their accuracies for isolated building and building array cases were analyzed. It was found that the constant peak factor (PF) of the Gaussian distribution showed acceptable accuracy only when the exceedance probability q = 10%. For q = 0.1%, the PF of the three-parameter Weibull distribution (3W) was more accurate than that of GCS-3rd. For fitting probability density functions, GCS-6th exhibited better flexibility than the two-parameter Weibull distribution (2W) and 3W. However, large leading terms leaded to oscillations at several points in GCS-6th. Regarding the estimation accuracy of LOSWSs, the 2W and 3W methods are superior to the GCS methods when the available orders of statistics are equal. Although the GCS methods showed higher accuracy than the 3W method in some regions, the oscillations at specific points in the GCS methods may lead to lower accuracy on average. The present findings can serve as an illuminating reference for further applications of these statistical methods.
... This implies that computer modeling is the dominant method for creating problem concepts and solutions for structures in the 21st century. Mochida and Lun (2008) and Ai and Mak (2017) highlighted that as wind modeling and computer technology has advanced, the use of natural ventilation has become increasingly popular. This is due to its adaptability, informative results, and costeffectiveness in terms of labor and equipment. ...
Introduction: Sudan is taking proactive steps towards environmental sustainability, including initiatives to improve energy efficiency and reduce costs in a hot, dry climate. This article assesses the contribution of natural ventilation to heat transfer and temperature conditioning in urban areas in Khartoum, Sudan. Methods: The research methodology used a combination of building modeling with computational fluid dynamics (CFD) integrated with IESV Autodesk software to model natural ventilation and simulate energy consumption by incorporating natural ventilation into home design. Results: The best-case scenario for natural ventilation resulted in a 71.1% yearly energy savings. The design point of internal air speed was approximately 0.7 m/s, the point at which 95% of the indoor areas had an average air speed between 0.43 m/s and 0.9 m/s. The worst-case scenario occurred in the east/west direction, when 80% of the interior had an airflow between 0.05 m/s and 0.01 m/s; near open windows, the airflow was approximately 0.1 m/s. Discussion: This study was the first research in Khartoum on the design of clean and energy-saving sustainable architecture. The architectural design process for energy-efficient living in the urban region of Al-Azhari City was implemented and defined in a city quarter in Khartoum. The results showed that natural ventilation can maintain a comfortable indoor temperature in summer and significantly reduce energy costs. The findings may have implications for the design of sustainable buildings in other hot, dry climates.
... Further, PA engaged in outdoor natural settings is related to increased emotional wellbeing and reduced tension, anger, and depression compared to activity indoors or outdoors in built spaces (34)(35)(36). As the urban outdoor environment creates complex and dynamic ambient conditions, microclimate factors such as temperature, humidity, and wind velocity have been investigated as determinants of pedestrian thermal comfort (37,38). Air pollution exposure has also been revealed in recent studies as a major risk factor affecting the health and safety of pedestrians (30,39). ...
Background
Despite the growing research on environment-physical activity (PA) relationships, field experimental studies are limited. Such studies offer opportunities to focus on real-world environmental exposure and related PA and health outcomes, allowing researchers to better isolate the causal effect of exposures/interventions. Focusing on the street/pedestrian environment as a routine setting for people's daily activities, this research aims to develop and test a field experiment protocol that integrates instantaneous assessments of the environment, PA, and health outcomes. The protocol involves the use of state-of-the-art environmental monitoring and biosensing techniques and focuses on physically active road users (pedestrians and bicyclists) who are more directly exposed to their surrounding environment than others such as drivers.
Methods/Design
An interdisciplinary research team first identified the target measurement domains for the health outcomes (e.g., stress, thermal comfort, PA) and the street-level environmental exposures (e.g., land use, greenery, infrastructure conditions, air quality, weather) guided by the previous literature which was primarily observational. Portable or wearable measurement instruments (e.g., GPS, accelerometer, biosensor, mini camera, smartphone app, weather station, air quality sensor) were identified, pilot tested, and selected for the identified measures. We ensured that these measures are readily linkable using the time stamp and include eye-level exposures as they impact the users' experiences more directly yet missing in most prior studies relying on secondary, aerial-level measures. A 50-min experimental route was then determined to include typical everyday environments in park and mixed-use settings and to engage participants in three common modes of transportation (walking, bicycling, and driving). Finally, a detailed staff protocol was developed, pilot-tested, and used in a 36-participant within-subject field experiment in College Station, TX. The experiment was successfully executed, showing its potential to support future field experiments that can provide more accurate real-time, real-environment, and multi-dimensional information.
Discussion
Our study demonstrates the feasibility of capturing the multifold health benefits/harms related to walking and bicycling in varying urban environments by combining field experiments with environmental, behavioral, and physiological sensing. Our study protocol and reflections can be helpful for a broad spectrum of research addressing the complex and multi-level pathways between the environment, behavior, and health outcomes.
... Apart from just measuring wind against urban structures, we would need to take into account more realistic settings where the presence of vehicles and trees canopy cannot be ignored (Mochida and Lun, 2008). We would also need to take into account pollutants, especially from transport (Tsou et al., 2001b), momentum and heat concentrations (Baik et al., 2003). ...
... The representation of traffic movement in the CFD model is crucial to capture their effects on wind flow insides the street canyon (Cai et al., 2020b;Kondo and Tomizuka, 2009). Besides the dynamic mesh updating technology to simulate the characteristics of moving vehicles adopted by our research team (Cai et al., 2020b;Li et al., 2017;Shi et al., 2020;Wang et al., 2019), the aerodynamic effects of the inclusion of traffic movement can be also modeled by an explicit method in the literature (Mochida and Lun, 2006). This method to model traffic movement is defined as a "vehicle canopy model" (Mochida and Lun, 2008). ...
Pollutant distribution remains poorly understood when traffic tidal flows (TTFs) happen. By conducting computational fluid dynamic (CFD) simulations, the research efforts first focus on how different-side traffic-produced flow and turbulence (TPFT) affect in-canyon airflow and corresponding pollutant dispersion. Second, the composite effects of non-uniform traffic emission and TPFT are investigated. Finally, the influences of TTFs while varying different street canyon geometry and approaching wind condition is explored.
The results demonstrate that the turbulent diffusion terms enhanced by the traffic movement contribute to the pollutant dispersion around traffic lanes. Besides, both-side TPFTs push leeward pollutants towards traffic flow “downstream” due to the unidirectional advection terms along the traffic direction. Simultaneously considering the non-uniform traffic emission and TPFT, either leeward- or windward-congested TTFs has a higher concentration at the pedestrian level close to the congested traffic lane. Besides, the TTF with windward congestion has a higher volume-average concentration of the whole street canyon. With varying building separation, street canyon aspect ratio, and incoming wind direction, the TTFs still result in a larger pollutant accumulation above the pedestrian level, which is nearby the congested traffic flow.
... The most critical parts of UAV urban operations entail flight in very close proximity to buildings and may include entering buildings through windows or air vents or landing on their rooftops (see Figure 1). Whilst the flow field around buildings has been extensively studied from a fixed reference frame (e.g., by wind engineers for the purposes of structural loadings [27,28], dispersion of pollutants [29,30], pedestrian wind comfort [31,32], etc.), there appear to be very few studies from the reference frame of the moving aircraft and at the relevant frequencies [33]. We therefore examine this relative flow field with an overall aim to reveal the characteristics of a "severe" gust for UAVs in close proximity to buildings. ...
There is a growing desire to operate Uncrewed Air Vehicles (UAVs) in urban environments for parcel delivery, and passenger-carrying air taxis for Advanced Air Mobility (AAM). The turbulent flows and gusts around buildings and other urban infrastructure can affect the steadiness and stability of such air vehicles by generating a highly transient relative flow field. Our aim is to review existing gust models, then consider gust encounters in the vicinity of buildings as experienced by flight trajectories over the roof of a nominally cuboid building in a suburban atmospheric boundary layer. Simplified models of fixed- and rotary-wing aircraft are used to illustrate the changes in lift and thrust experienced by flight around the building. The analysis showed that fixed-wing aircraft experienced a substantial increase in angle of attack over a relatively short period of time (<1 s) as they fly through the shear layer at a representative forward velocity, which can be well above typical stall angles. Due to the slow flight speeds required for landing and take-off, significant control authority of rotor systems is required to ensure safe operation due to the high disturbance effects caused by localized gusts from buildings and protruding structures. Currently there appears to be negligible certification or regulation for AAM systems to ensure safe operations when traversing building flow fields under windy conditions and it is hoped that the insights provided in this paper will assist with future certification and regulation.
... Pressure coefficients for high-rise buildings have been studied to provide a clear picture of pressure differences [38][39]. while some studies concentrated on the impact of wind on pedestrians [40][41][42][43]56]. Some previous studies used Autodesk Flow Design for simulating the aerodynamics around buildings [2,44,45]. ...
Wind Tall buildings CFD Drag coefficient A B S T R A C T The streamlined exterior shapes of tall buildings are important to reduce the effect of the wind. Therefore, an examination of different techniques for the exterior design of tall buildings is required. This study aims to analyses some tall buildings to select the most streamlined design in order to reduce high wind risks. The benchmark used in the current study is a building with a height of 120 m and a triangular cross-section with a side length of 20 m. A square cross-section twisted building design is used as a modified model in tall buildings of about 120 m. The rotation angle of the building is 45° for each twisted path. Six configurations of this type of building are tested with different radiuses of fillet on their edges, which are 0, 1, 2, 3, 4, and 5 m respectively. All geometries of the buildings are created by SolidWorks, while mesh and simulations are achieved using ANSYS Fluent. A great agreement is obtained between the current results and the previous related study for the benchmark. Using twisted buildings with a fillet of 5 m can lead to a reduction of the drag coefficient of about 27.5% relative to the benchmark. Wind in a horizontal direction can be reduced by using twisted geometry. But in terms of separation, using a fillet with a large radius can lead to avoiding early separation of air.
... Computational fluid dynamic (CFD) simulations and wind tunnel experiments are popular methods to study and evaluate the outdoor wind environment [11,12], and they are widely used in architectural design. As a simple and fast method, a CFD simulation can obtain abundant data at a low cost [13][14][15][16][17]. However, it is greatly influenced by the turbulence models adopted and the user's experience. ...
One of the key issues in architectural design and regional planning is to create a safe and comfortable outdoor building environment, which calls for more studies. Wind tunnel experiments and computational fluid dynamic (CFD) simulations are the primary methods for the current studies. The airflow and boundary conditions are controllable for the wind tunnel experiment, and the data is reliable. In most wind tunnel platforms, spires and roughness elements are applied to create the gradient wind of the atmospheric boundary layer, leading to the oversized, high construction cost, and complex operation. In this paper, in order to explore a simple method for measuring and studying the outdoor building wind environment using wind tunnels, a compact wind tunnel platform adopting grids with unequal spacing was designed and tested, based on the theoretical model of the atmospheric boundary layer. A comparison between the test results and the theoretical values indicated that this new wind tunnel platform could achieve a gradient wind field and is accessible in applying low-speed wind tunnels to the measurement and research of the building wind environment. The application case in a high-rise building of the central business district (CBD) region in Beijing, was presented in this paper. Compared with another analytical method, the CFD simulation, the compact wind tunnel revealed its applicability that could be used for predicting and evaluating the outdoor wind environment around the building. This compact wind tunnel is more flexible and convenient than the traditional ones, with a smaller size, easier construction and operation, and lower costs. Therefore, we suggest more applications of this compact wind tunnel platform in future experimental studies of outdoor wind environments.
... It refers to the wind speed at 1.5-2 m above the ground around buildings, which influences pedestrians' comfort. The configuration of a building, such as its height, width, arrangement and density, has been shown to have a significant impact on the surface wind speed [16,17]. The wind environment is the wind field formed by natural winds under the influence of terrain conditions, architectural layout, greenery and water [18]. ...
As a theory in ancient China, Feng Shui is used in terrain exploring to find ideal living environments. In this study, 62 traditional villages documented on China’s and Jiangxi’s protection lists in Jinxi County, Jiangxi Province were divided into four categories according to their landscape patterns and were simulated by CFD (computational fluid dynamics) with PHOENICS and quantitatively analyzed based on their wind and thermal environments. The results showed that hills greatly improve the wind environment of villages when they are in the windward direction. Concerning thermal environments, water and vegetation effectively reduced the summer temperatures in villages, while hills kept villages warm in winter. This paper verified the positive effect of elements such as mountains, water and forests on the improvement of wind and thermal environments of villages and the rationality of the site election principle of Bei Shan Mian Shui, also known as back mountain facing water, which is upheld by Feng Shui. This paper explored the philosophy of traditional village location selection, demonstrating the ecological wisdom of ancient Chinese people in creating a good living environment, and provides a new direction for current sustainable development planning.
... However, most studies were limited to the viewpoint that atmospheric conditions was an important factor that influence thermal properties within rivers, they were not directly interested in the impact of river on surrounding climate. In recent years, due to various considerations of unban thermal environment, complex types of underlying surface and largescale urban construction, the numerical simulation methods take advantage of its flow analysis on optimal design comparing to other solutions (Akashi et al. 2008). Many reasearchers in china have used CFD to predict thermal envrionment by different purposes (Zhao et al. 2002), (Chen et al. 2007), however, few were involved in the relationships among water bodies, building distribution of waterfront and unban thermal climate. ...
Wind flow studies using wind tunnels can be very costly due to their nature and implementation. An alternative method involves using numerical methods, specifically CFD (Computational Fluid Dynamics), which offers significant time and cost savings, along with quicker and more flexible results for meaningful research outcomes. To conduct this research effectively, two software tools were required: Sketch Up for modeling the various urban morphologies, and the Fluent module of Ansys for simulations, which is recognized by the scientific community. The objective of this study was to provide an evaluation of airflow behavior in three samples of different morphologies within the old city of Constantine, namely: the traditional vernacular fabric (Zone A), the hybrid fabric (Zone B), and the colonial fabric (Zone C), based on a series of CFD simulations. The study aimed to assess the various effects of wind flow and velocity through the different typologies of the old city and identify the resulting aerodynamic effects that impact pedestrian comfort.
Wind environment is closely related to people's lives and has a great influence on the comfort and safety of the environment. This research examines the influence of trees on wind environment in pedestrian-level. By integrating the theories of CFD simulation method and trees benefits, six canopy morphologies (Spheroid, Cone, Inverted Cone, Cylinder, Ellipsoid, Cuboid) models are proposed and validated. The PHOENICS is used for numerical simulation (144 scenarios), and the data are analyzed using Photoshop and linear regression model. It is found that the influence of trees on wind is linearly correlated with the varying crown width, trunk height and plant spacing. The influence of tree on wind velocity can be expressed by IF wind (the wind reducing ability) and AZ (the area of downwind deceleration zones). The framework and the numerical simulation in this paper are intended to support and guide future studies of wind comfort and wind safety of trees in pedestrian-level, and to contribute to improved wind environmental quality in urban areas through reasonable tree planting.
An innovative experimental method, called aeroelastic real-time hybrid simulation (aeroRTHS), is proposed to study the aerodynamic vibrations of a building model in a boundary layer wind tunnel (BLWT). The aeroRTHS method aims to capture the dynamic interactions between an aeroelastic structure and the applied wind load to accurately characterize complicated, unstable phenomena such as vortex-induced vibration, and in doing so, to broaden the application of real-time hybrid simulation (RTHS) from seismic applications to wind engineering. The aeroRTHS tests were conducted in the BLWT at the University of Florida Natural Hazards Engineering Research Infrastructure Equipment Facility (UF NHERI EF). A 1-m-tall rigid physical model with an aspect ratio (height/width) of 7.3 was mounted on a modified single-axis shake table converting translational motions to corresponding rotations at the base of the model allowing the model to behave in the wind tunnel as an aeroelastic structure. A total of 128 pressure sensors located on the cross-wind sides of the physical building model measured wind pressures which then were converted to equivalent forces and ultimately resolved into a single equivalent force at the top of the physical building model based on the moment equilibrium at its base. The results from a series of aeroRTHS tests in the BLWT are reported herein to constitute a proof-of-concept study that validates the aeroRTHS method and demonstrates the aeroelastic effects on a flexible and slender structure.
The numerical simulation of urban wind environments faces difficulties in capturing the turbulent characteristics due to the large computational domain. Traditional Reynolds-averaged methods (RANS) can effectively capture the average wind characteristics of urban areas. However, due to the significant dissipation and attenuation of turbulent energy in the downstream direction, this method fails to provide accurate turbulent characteristics after time-averaging processing. Therefore, in order to obtain a higher-precision turbulent wind field distribution within urban areas, this paper proposed a new numerical method named an equilibrium atmospheric boundary layer model (EABL) by modifying the control equation of the shear stress transport k–ω model. During the process, the equilibrium atmospheric boundary layer was achieved successfully, and the attenuation problem of the turbulent kinetic energy and dissipation rate during the computational fluid dynamics numerical simulation was resolved. Simultaneously, a wind tunnel experiment and six turbulence models [standard k–ε, realizable k–ε, renormalization group k–ε, large eddy simulation—narrowband synthesis random flow generator (LES-NSRFG) and LES vortex method and EABL] were employed to simulate the wind field characteristics in an actual residential area. The simulation results demonstrate that, relative to traditional RANS models, the EABL model enhances the simulation accuracy of turbulence characteristics by over two times. Furthermore, compared to LES models, the EABL model can reduce computational time by threefold.
Human beings by nature are social beings. Therefore, the provision of public spaces for social activity is an integral part of urban design. It is known that public spaces have positive impacts on the health and well-being of people. However, the modern-day decline in the use of urban public spaces is due to comfortable thermal environments being created indoors through technologies and advanced design principles. In this context, this study examines the effect of microclimatic conditions on the behavior of people in outdoor urban public spaces, in order to identify design methods to create more conducive environments. This research employs a case study method: a plaza and waterfront in the city of Kandy as an urban public space. Data collection involved physical observations, activity mapping, a photographic survey, a thermal sensation questionnaire, 3D modelling, and simulations of the thermal environment. Data was subject to triangulation for establishing validity, to generate a better understanding and to show that tropical climate shade is not the only solution. Air temperature and solar radiation greatly affect the use of urban public spaces and people adapt to environmental conditions by experience. Wind, shade, vegetation cover, and surrounding urban geometry also contribute to thermal perception. It was inferred that there was no one primary factor but rather the culmination of all factors in different ratios that causes the environmental temperature to morph and change, affecting the thermal comfort of a space. This study provides a design-based recommendation in order to achieve an optimum level of thermal comfort and provide design efficacy for urban public spaces.
The use of computational fluid dynamics (CFD) in the wind engineering (WE) is generally defined as computational wind engineering (CWE). Since its foundation in 2004, the use of OpenFOAM in CWE has been increasing progressively and covers nowadays a wide range of topics, from wind environment to wind structural engineering. This paper was drafted in response to the invitation from the organizers of the 18th OpenFOAM workshop held in Genoa (Italy) on 11–14 July 2023, when a technical session on Civil Engineering and Wind Engineering was organized. In this paper the author briefly reviews the history of WE and surveys the evolution, methods, and future challenges of OpenFOAM in the CWE. Topics are here regrouped into three main research areas and discussed from a physical, engineering and purely computational perspective. The study does not cover the Wind Energy and related topics, since this can be considered nowadays as a stand-alone subfield of the WE. This review confirms that OpenFOAM is a versatile tool widely used for WE applications that often require new models to be developed ad hoc by CFD users. It can be coupled easily with numerical weather prediction models for mesoscale-microscale wind and thermal studies, with building energy simulation models to determine the energy demand, with finite element method for structural engineering design. OpenFOAM represents an extraordinary opportunity for all CFD users worldwide to share codes and case studies, to explore the potential of new functionalities and strengthen the network within the CFD community.
The urban ambient environment is directly responsible for the health conditions of millions
of people. Comfortable living space is a significant aspect that urban policymakers need to address
for sustainable planning. There is still a notable lack of studies that link the spatial profile of urban
climate with city-specific built-up settings while assessing the vulnerability of the city population.
Geospatial approaches can be beneficial in evaluating patterns of thermal discomfort and strategizing
its mitigation. This study attempts to provide a thorough remote sensing framework to analyze the
summer magnitude of thermal discomfort for a city in a tropical hot and humid climate. Spatial
profiles of dry bulb temperature, wet bulb temperature and relative humidity were prepared for
this purpose. A simultaneous assessment of various discomfort indices indicated the presence of
moderate to strong heat stress to a vast extent within the study area. The central business district
(CBD) of the city indicated a ‘danger’ level of heat disorder for outdoor exposure cases. Nearly
0.69 million people were vulnerable to a moderate threat from humid heat stress, and around
0.21 million citizens faced strong heat stress. Combing city morphology in the study showed that
mid-rise buildings had the maximum contribution in terms of thermal discomfort. City areas with
built-up cover of more than 68%, along with building height between 5.8 m and 9.3 m, created the
worst outdoor discomfort situations. Better land management prospects were also investigated
through a multicriteria approach using morphological settlement zones, wind direction, pavement
watering, building regulations and future landscaping plans. East–west-aligned road segments of a
total 38.44 km length were delineated for water spray cooling and greener pavements. This study is
likely to provide solutions for enhancing ambient urban health.
Bu çalışma, Trabzon ili Ortahisar ve Akçaabat ilçeleri kent merkezi ve çevresinin arazi yüzey değişimlerinin kentsel ısı adasına (KIA) etkisini değerlendiren bir araştırmayı içermektedir. Araştırma, aylık ortalama sıcaklık, aylık ortalama minimum sıcaklık, günlük maksimum sıcaklığın 30 °C ve üzeri olduğu gün sayısı ve aylık ortalama rüzgâr hızı gibi tüm değişkenler üzerinden gerçekleştirilmiştir. Çalışmada, 2000-2018 yılları arasında Akçaabat ve Ortahisar ilçelerinde arazi kullanım değişimleri incelenmiştir. Trabzon kent merkezi ve Akçaabat ilçesinin neredeyse birleştiği ve kentsel dokunun sürekli hale geldiği tespit edilmiştir. Seçilen meteoroloji istasyonlarının çevresi, 2000-2018 yılları arasındaki arazi kullanım değişikliklerinden etkilenmiştir. Bu etki genellikle yapay yüzeylerin artmasına bağlı olarak doğal alanların azalması şeklinde kendini göstermiştir. Araştırma sonuçlarına göre, çalışma alanında bulunan Trabzon Bölge, Trabzon Limanı Ana Mendirek ve Trabzon Havaalanı istasyonları ile Akçaabat İstasyonu, KIA etkisinin belirgin olduğu bölgeler olarak ortaya çıkmıştır. Özellikle Ağustos ayında bu istasyonlar arasında 0.64°C'ye varan sıcaklık farkları gözlenmiştir. Bu durum, kentsel arazi kullanımının KIA oluşumundaki etkisini göstermektedir. Trabzon'daki kentsel arazi kullanım değişiklikleri, kent iklimi üzerinde belirgin etkilere yol açmıştır. Trabzon kentinin KIA sorunu ile karşı karşıya olduğu görülmüştür.
In hot and humid regions of China, people experience great discomfort. Good ventilation improves human comfort by facilitating the discharge of heat in a region. None of the previous studies considered which scale is appropriate for the outdoor ventilation of building arrays, and the ventilation performance differs with the array size. Moreover, the building density has an upper limit in Chinese cities, and many studies overestimate this density. Based on these considerations, the neighborhood block is proposed to represent the scale of building arrays with the combination of the urban planning scale and climatic scale. Using this scale, the building density and representative building array configurations for hot and humid regions of China were determined. The outdoor ventilation of these building arrays at the pedestrian height was then studied via computational fluid dynamics simulations. The results show that, in the neighborhood block, an increase in the building height and length is beneficial for the mean velocity, whereas an increase in the building distance is not, and a staggered layout has a negative effect on ventilation. Furthermore, the semi-enclosed layouts are no better than the enclosed layouts in terms of ventilation and sunlight. Some contributions contradict the existing studies because of the selection of different array scales and densities, which prove their significance.
Understanding low-occurrence strong wind speed (LOSWS) distributions at the pedestrian level is important. However, the robustness of the statistical methods for estimating LOSWSs under different conditions remains uncertain. In this study, the performances of the Weibull distribution method and Gram–Charlier series (GCS) method were compared. Their accuracies for isolated building and building array cases were analyzed. It was found that the constant peak factor (PF) of the Gaussian distribution showed acceptable accuracy only when the exceedance probability q = 10%. For q = 0.1%, the PF of the three-parameter Weibull distribution (3W) was more accurate than that of GCS-3rd. For fitting probability density functions, GCS-6th exhibited better flexibility than the two-parameter Weibull distribution (2W) and 3W. However, large leading terms leaded to oscillations at several points in GCS-6th. Regarding the estimation accuracy of LOSWSs, the 2W and 3W methods are superior to the GCS methods when the available orders of statistics are equal. Although the GCS methods showed higher accuracy than the 3W method in some regions, the oscillations at specific points in the GCS methods may lead to lower accuracy on average. The present findings can serve as an illuminating reference for further applications of these statistical methods.
Wind shear has a negative impact on aircraft safety, particularly during takeoff and landing processes. The buildings inside or around the airport can induce wind shear by disturbing the airflow along the glide path. This paper investigates the building-induced wind shear along the glide path of aircraft by utilizing two coherent Doppler lidar systems deployed at Beijing Capital International Airport. A well-designed coordinated scanning strategy of lidar was used to measure the building-induced wind shear along the glide path and the wind field influenced by buildings. With a correlation coefficient of 0.97 for wind speed and 0.99 for wind direction, the wind field estimated by lidar was well validated by those from sonic anemometers. In addition, the lidar-observed wind shear events are verified by pilot reports. The results show that building wakes bring the velocity deficit and turbulence increase along the glide paths. It is susceptible to wind shear due to the rapidly changing wind speeds when the aircraft flies through these wake regions. The relative frequencies of wind shear events reached above 70 and 50 at 36L and 01, respectively, in the wind direction range of 270°∼300° with a wind speed greater than 12 m/s. The statistical analysis of lidar-observed wind shear reveals that the wind shear frequently occurs within the height of 40 ∼ 80 m and the distance of 763 ∼ 1526 m at both 36L and 01.
Urban water bodies reduce urban heat through evaporation and transfer of sensible heat. However, today's highly intense urban construction patterns cause poor urban air mobility and excessive residual heat accumulation, and weaken water bodies' regulating effects. This study examines the relationship between urban morphology and water bodies' microclimatic regulation during summer in the water-network city, Wuhan, using remote sensing data and the weather research and forecasting (WRF). This study found (1) on the waterfront, the key impact indicators for microclimate in the waterfront are building density (BD) and floor area ratio (FAR), both of which can lead to higher temperatures and lower humidity, (2) BD significantly warmed the waterfront on the large lakes, while FAR impacted the urban main windway areas, (3) urban development with high FAR significantly suppressed the water's cooling ability in the downtown and main windway areas, with the cooling intensity decreased by 28.7% and 20.6%, respectively, and the cooling distance decreased by 13.5% and 15%. These findings provide insights for the practice of climate adaptive planning and design on the water network-related urban areas of Wuhan and other places with similar environments.
Nowadays, it is considered that urban areas consume the bulk of vital natural and energy resources that raise concerns of environmental deterioration on different scales. Now, worldwide energy assessments indicate that improving the energy efficiency and sustainability of buildings, and urban communities could free-up enormous amounts of current energy expenses. Those energy fluxes and change of airflow that resulted from urban morphology can lead to phenomenon such as the urban heat island and convective rainfall initiation. In this research it initiates-Urban Fluid Mechanics (UFM) by using Computational Fluid Dynamics (CFD) tools that delve into fundamental fluid flow problems of immediate utility for the development of resorts at Qarun lake in Egypt through a comparative study between different urban patterns through three main processes. Firstly, it starts by using of results from a mesoscale model to indicate the best place for building a wind turbine farm and to generate data for the microscale model of the urban canopy. Secondly, using qualitative modeling method for urban analysis that can evaluate the airflow conditions of the urban canopy in different seasons. Thirdly, making a comparative study between different urban patterns by changing a certain parameter. As a result from these three processes that qualitative simulation process will be of use for building and urban scale performance predictions as well as for the future simulation of pedestrian comfort. In this paper, it describes in detail one such approach, along with some sample results demonstrating the capabilities of this tool in Planning and urban design decisions, and raises questions as How Architects, Planners, Urban designers get advantages through using CFD method and its tools?, How can that method indicate the best places for renewable energy resources? and How can such ways of comparative studies can but a certain criteria for urban design in a certain zone?
This paper describes wind tunnel experiments on turbulent flows over a two-dimensional ridge and a circular hill, both having cosine-squared cross-section and maximum slope of about 32°. The experiments were made in the adiabatic atmospheric boundary layers. Mean flow and turbulence were measured using split-fiber probes designed for measuring flows with a high turbulence and separation. The experimental emphases are on differences in the flow pattern between two- and three-dimensional hills; roughness effects; and turbulence structures in the near-wake region. Principle results are: (1) the cavity zones behind circular hills are smaller
than two-dimensional ridge, because of the convergence of flow in the three-dimensional wake. (2) The increased roughness on the hill surface causes a earlier separation, resulting in a larger recirculation. (3) A strong mixing layer forms just downwind of the top of each hill, corresponding to the flow separation on the lee slope of the hill. (4) The lateral velocity variances behind the circular hills show second local maxima in the wall layer, which are generated by a cross-wind motion and can not be observed in the 2D cases. (5) The increase of turbulence in the incident flow reduces turbulence levels in the near-wake region.
Numerical flow computations around an aeroelastic 3D square cylinder immersed in the turbulent boundary layer are shown. Present computational code can be characterized by three numerical aspects which are 1) the method of artificial compressibility is adopted for the incompressible flow computations, 2) the domain decomposition technique is used to get better grid point distributions, and 3) to achieve the conservation law both in time and space when the flow is computed a with moving and transformed grid, the time derivatives of metrics are evaluated using the time-and-space volume. To provide time-dependant inflow boundary conditions satisfying prescribed time-averaged velocity profiles, a convenient way for generating inflow turbulence is proposed. The square cylinder is modeled as a 4-lumped-mass system and it vibrates with two-degree of freedom of heaving motion. Those blocks which surround the cylinder are deformed according to the cylinder's motion. Vigorous oscillations occur as the vortex shedding frequency approaches cylinder's natural frequencies.
The guideline for CFD prediction of wind environment around buildings was proposed by Working Group of the Architectural Institute of Japan (AIJ). It is described based on the results of benchmark tests which have been conducted for investigating the influence of many kinds of computational conditions for various flowfields. This paper delineates the guideline proposed by our group. 1 INTRODUCTION As computer facilities and Computational Fluid Dynamics (CFD) software have been improved in recent years, the prediction and the assessment of wind environment around buildings using CFD have become practical at design stages. Therefore, a guideline which summarizes important points of using CFD technique for appropriate prediction of wind environment is needed. Although there have been the recommendations with similar objectives proposed by COST group [1], those are mainly based on the results published elsewhere. On the other hand, the guideline proposed by AIJ is based on the results of benchmark tests which have been conducted to investigate the influence of many kinds of computational conditions for various flowfields by our own [2-6]. This paper briefly summarizes the guideline and the full version of the guideline will be available in the final paper. This guideline is mainly based on using high Reynolds (Re) number RANS (Reynolds Averaged Navier-Stokes equations) models. In order to obtain more accurate result, it is desirable to use a Large Eddy Simulation (LES) and a low Re number type model. However, it is difficult to use those models for practical analysis because many computational cases and a huge number of grids are required for the prediction and analysis of wind environment under severe time restrictions. If it is necessary to use a highly accurate model like LES or low Re number type model, it is recommended to use it after the calculations and analysis which have been done by high Re number type RANS models following this guideline.
This study extends the previous researches of tree canopy models conducted by the present authors to reproduce the effects generated from various small obstacles, including moving objects such as automobiles, in actual urban space. Four test cases of computations were carried out by using the new developed 'Vehicle Canopy Model'. In the cases without automobiles, k values were largely underpredicted, but the prediction accuracy of k values was greatly improved in the case with moving automobiles.
The dynamic mixed subgrid‐scale model of Zang et al. [Phys. Fluids A 5, 3186 (1993)] (DMM1) is modified with respect to the incorporation of the similarity model in order to remove a mathematical inconsistency. Compared to DMM1, the magnitude of the dynamic model coefficient of the modified model (DMM2) is increased considerably, while it is still significantly smaller than as occurs in the dynamic subgrid‐scale eddy‐viscosity model of Germano [J. Fluid Mech. 238, 325 (1992)] (DSM). Large eddy simulations (LES) for the weakly compressible mixing layer are conducted using these three models and results are compared with direct numerical simulation (DNS) data. LES based on DMM1 gives a significant improvement over LES using DSM, while even better agreement is achieved with DMM2.
The canopy model for reproducing the aerodynamic effects of trees based on k-ε model was optimized for the CFD prediction of wind environment at pedestrian level. After reviewing the previous researches on modeling canopy flows, two types of canopy models were selected. In addition, the model coefficients adopted in the extra term added to the transport equation of turbulence energy dissipation rate, ε were optimized by comparing numerical results with field measurements.
Over a decade ago, the author (Ferziger, 1983) wrote a review of the then state-of-the-art in direct numerical simulation (DNS) and large eddy simulation (LES). Shortly thereafter, a second review was written by Rogallo and Moin (1984). In those relatively early days of turbulent flow simulation, it was possible to write comprehensive reviews of what had been accomplished. Since then, the widespread availability of supercomputers has led to an explosion in this field so, although the subject is undoubtedly overdue for another review, it is not clear that the task can be accomplished in anything less than a monograph. The author therefore apologizes in advance for omissions (there must be many) and for any bias toward the accomplishments of people on the west coast of North America. In the earlier review, the author listed six approaches to the prediction of turbulent flow behavior. The list included: correlations, integral methods, single-point Reynolds-averaged closures, two-point closures, large eddy simulation and direct numerical simulation. Even then the distinction between these methods was not always clear; if anything, it is less clear today. It was possible in the earlier review to give a relatively complete overview of what had been accomplished with simulation methods. Since then, simulation techniques have been applied to an ever expanding range of flows so a thorough review of simulation results is no longer possible in the space available here. Simulation techniques have become well established as a means of studying turbulent flows and the results of simulations are best presented in combination with experimental data for the same flow. There is also a danger that the success of simulation methods will lead to attempts to apply them too soon to flows which the models and techniques are not ready to handle. To some extent, this is already happening. Direct numerical simulation (DNS) is a method in which all of the scales of motion of a turbulent flow are computed. A DNS must include everything from the large energy-containing or integral scales to the dissipative scales; the latter is usually taken to be the viscous or Kolmogoroff scales.
Three-dimensional numerical simulations for air flow around a surface-mounted cube are carried out using the standard κ-ε model and Large Eddy Simulation (LES) with similar boundary con- ditions. The results of LES agree fairly well with the experimental results. The shortcomings of the κ-ε model are examined precisely using both the experimental data from the wind tunnel tests and the numerical data given by LES. The inaccuracies are concerned with the expression for evaluating the turbulence production under Eddy Viscosity Model and the unsuccessful reproduction of Karman's vortex street.
In the previous paper, we proposed a model for simulating the budgets of heat, water vapor, and carbon dioxide within three-dimensional vegetation. And we applied the model to a single tree and investigated the detail of heat balance within the foliage. Then we investigated the effect of the environmental factors on the heat budget within the foliage, by varying the environmental factors. In this paper, we examined the validity of our model. We compared the results from the model with the measured data. Our model accurately estimated the measured data.
The flowfield around a high-rise building model placed within the surface boundary-layer was analyzed using various revised k-ε models. The accuracy of these models was examined by comparing their results with the experimental data. Among the computations using various revised k-ε models compared here, the result with the Durbin's revised k-ε model showed the best agreement with the experiment. The reason for the good perfomance of Durbin's model was discussed based on 'Realizability' of predicted results.
Outdoor thermal environment in summer become worse due to a change of land cover and an increase of artificial heat release according to the urban development. In this paper, the authors have developed a new method for predicting the human comfort in outdoor thermal space with the aid of CFD (Computational Fluid Dynamics). Furthermore, the effect of greening on outdoor wind and thermal environment was analyzed. Spatial distribution of SET (Standard Effective Temperature) was calculated in order to assess the pedestrian level comfort using the data given from the CFD predictions. Two cases of predictions were carried out. In easel, green area ratio of ground surface was assumed 10%, while the green area ratio of ground surface was changed to 100% in case2. By comparing the SET* distributions in both cases, effects of greening were thus clarified.
A turbulent vortex-shedding flow past a two-dimensional(2D) square cylinder at Re=2.2×10^4 is analyzed by Large Eddy Simulation(LES) using two types of dynamic Subgrid-scale(SGS) models, i.e., the Smagorinsky type and mixed type. Results given from the two dynamic SGS models are compared with those from the standard Smagorinsky model and the experiments conducted by Lyn et al. Two types of dynamic SGS model improve the accuracy of the predictions remarkably. In particular, the mixed type provides more accurate results than those given by the Smagorinsky type dynamic model.
In the conventional expression of experimental stomatal conductance, the assumption of separation of variables should be admitted without any validation of it. In this paper, we adopt the neural network for making the experimental expression. It becomes clear that the neural network has the capability in expressing the experimental data with excellent accuracy than in the conventional method.
The Ross'es model is one of the most excellent ones that estimate a radiation field within a plant community. It is, however, expressed by an integro-differential equation for radiance. A five-dimensional computing domain is necessary to solve a three-dimensional radiation field such as a tree-radiation. So, it is difficult to exactly compute the Ross'es equation, even if we use any super computer. In this report, we discuss the Diffusion Approximation, which seems most adequate to approximately calculate the Ross'es equation for two- and three-dimensional radiation fields. We extend the Diffusi on A pproximation of gas-transfer-equation to the Ross'es equation.
A three - dimensional turbulent flowfield around a cube placed in a surface boundary layer is predicted using Algebraic Stress Model (ASM) and Differential Stress Model (DSM). The results from these models are compared with those of wind tunnel tests conducted by the authors, and Large Eddy Simulation (LES). The overestimation of turbulent energy values around the frontal corner occurred in the k-e model are corrected by ASM. But ASM cannot reproduce anisotropic properties of each component of normal stresses in the area above the frontal corner while these discrepancies do not appear in the results of DSM. The differences between the results from two models are derived from the expression of convection and diffusion terms of transport equation of <u_i'u_j'>. Algebraic approximation in the case of ASM is examined precisely by the numerical data given by LES.
A turbulent vortex-shedding flow past a two-dimensional (2D) square cylinder at Re=2.2×10^4 was simulated by Large Eddy Simulation (LES) using the dynamic Subgrid-scale (SGS) model. Here, the dynamic SGS model was incorporated into the second-order finite volume method. Results from the dynamic SGS model were compared with those from the standard Smagorinsky SGS model and the experiments conducted by Lyn. The dynamic SGS model improved the accuracy of the predictions remarkably. The mean velocity distribution given by the dynamic SGS model showed very close agreement with the experiment in the wake region, while the standard Smagorinsky model somewhat underestimated the size of the reverse flow region behind the cylinder.
The purpose of this study is to predict the influence of trees on airflow around buildings by using CFD. In order to analyze the air-flow around and through trees, the modeling of the aerodynamic effect of trees is required. Many plant canopy turbulence models have been developed in the past study of dendrology and agricultural meteorology. Almost all the models, however, were examined under horizontally homogeneous conditions. Using one- or two-dimensional computational domains, they have been developed for plant fields (e.g. corn fields, coniferous forests). In this study, airflow caused by an individual tree is estimated through three-dimensional calculations on these above models. The calculated airflow, compared with results of the wind-tunnel experiment, shows usefulness and limitations of the models, allowing for improvement of the model for analysis of airflow around an individual tree.
A series of large-eddy simulations of flow past a square cylinder at Re = 21400 have been conducted by seven groups of researchers. A comparative report is presented of the time-average results with a view to establishing any clear advantage of particular subgrid scale modelling approaches, wall treatments, and numerical methods.
Models for subgrid-scale turbulence are analyzed. The analysis indicates that there is enough information in the resolved scales to allow some of the characteristics of the complete flow field to be determined. The kinetic energy of the small-scale motions can be decomposed into two parts. One is due to energy transfer from the large scales and is correlated with them; the other is uncorrelated. This leads to a two-component eddy-viscosity model. The ″production equals dissipation″ argument does not hold for the small scales in the decay of turbulence. The two-component model can be reduced to the single-component models used previously, but it shows some of the flaws in arguments made earlier. The exchange between the large and small scales takes place mainly between the smallest scales of the former and the largest scales of the latter. This argument is the basis of a new model which preliminary tests show to be superior to the J. Smagorinsky model. Refs.
Predictions of the pedestrian level wind speeds for the downtown area of Auckland that have been obtained by wind tunnel and computational fluid dynamic (CFD) modelling are presented. The wind tunnel method involves the observation of erosion patterns as the wind speed is progressively increased. The computational solutions are mean flow calculations, which were obtained by using the finite volume code PHOENICS and the κ-ε turbulence model. The results for a variety of wind directions are compared, and it is observed that while the patterns are similar there are noticeable differences. A possible explanation for these differences arises because the tunnel prediction technique is sensitivity to gust wind speeds while the CFD method predicts mean wind speeds. It is shown that in many cases the computational model indicates high mean wind speeds near the corner of a building while the erosion patterns are consistent with eddies being shed from the edge of the building and swept downstream.
The accurate prediction of the wind energy distribution over terrains is important for making an appropriate selection of a suitable site for installing wind power plant. In this study, two-dimensional numerical simulations of flow over two common types of topographic features, i.e. a cliff and a hill, are presented. Three types of turbulence models, namely standard k–ε and its revised linear form (Durbin model) as well as a revised nonlinear form (Shih model) are employed in this work. The performance of these models in predicting flow over these features is investigated. The accuracy of the prediction by using a z0 type wall function to reproduce the effect of surface roughness on flowfield from these turbulence models is also examined.
Recent developments in advancing Detached-Eddy Simulation (DES) for predic-tion of complex turbulent flows at high Reynolds numbers will be presented. In natural appli-cations of the technique, attached boundary layers are modeled using Reynolds-averaged Navier-Stokes (RANS) methods. The method becomes an LES in regions away from the wall provided the grid density is sufficient. DES has been applied to a wide range of massively separated flows with predictions typically superior to those obtained using RANS models and at much lower cost than possible using LES. The developing experience base is encouraging expansion of the method beyond the originally intended regime of massive separations and an overview of the challenges and recent successes in DES research will be presented. These include devel-opment of a new version of the method that modifies the DES length scale to overcome errors that can arise from the interface between the RANS and LES regions.
In this paper, the influences of the boundary layer modeling and the turbulence model parameters on the numerical simulation research for wind engineering were investigated through detail comparison between the numerical results and that of the wind tunnel test data. The applicability of suggested model parameters and inflow turbulence boundary conditions being construct equilibrium boundary layer in SST k ω − model had been validated successfully. The research work of this paper would be helpful to realize the importance of these usually ignored problems as well as to improve the accuracy of numerical simulation for CWE. KEY WORDS: Computational wind engineering, RANS, SST k ω − model, analysis of parameters, equilibrium atmosphere boundary layer 1. INTRODUCTION Some important numerical factors which would affect the calculation results heavily still have not been emphasized in the numerical simulation research for CWE, such as the numerical simulation of the equilibrium boundary layer, and the applicability of the model parameters of the turbulence models employed.
The article presents some recent efforts in the authors' group toward accommodat-ing Reynolds-averaged Navier-Stokes (RANS) modeling to computing complex high-Reynolds and high Rayleigh number industrial and environmental flows. Considered are some recent de-velopments both in the second-moment and in the eddy-viscosity framework. The treatment of the wall boundary conditions, which has long been the stumbling block in the RANS computa-tional fluid dynamics (CFD), is discussed with focus on some new concepts for robust integration up to the wall (ItW), generalized wall functions (GWF), and a compound wall treatment (CWT) that combines the both concepts. Arguing that LES will not for long be applicable for large-scale industrial computations, we consider the potential of Transient RANS for flows subjected to strong forcing, as well as combing RANS with LES. Several noted controversial issues in hybrid RANS/LES are discussed, supported with some illustrations. Various concepts and improvements are illustrated in several examples of wind-and buoyancy driven environmental flows.
Recently, the prediction of wind environment around a building using Computational Fluid Dynamics (CFD) technique comes to be carried out at the practical design stage. However, there have been very few studies which examined the accuracy of CFD prediction of flow around a high-rise building including the velocity distribution at pedestrian level. The working group for CFD prediction of wind environment around building, which consists of researchers from several universities and private companies, was organized in the Architectural Institute of Japan (AIJ) considering such a background. At the first stage of the project, the working group planned to carry out the cross comparison of CFD results of flow around a high rise building by various numerical methods, in order to clarify the major factors which affect prediction accuracy. This paper presents the results of this comparison.
When predicting unsteady flow and pressure fields around a structure in a turbulent boundary layer by Large Eddy Simulation (LES), velocity fluctuations of turbulence (inflow turbulence), which reproduce statistical characteristics of the turbulent boundary layer, must be given at the inflow boundary. However, research has just started on development of a method for generating inflow turbulence that satisfies the prescribed turbulence statistics, and many issues still remain to be resolved. In our previous study, we proposed a method for generating inflow turbulence and confirmed its applicability by LES of an isotropic turbulence. In this study, the generation method was applied to a turbulent boundary layer developed over a flat plate, and the reproducibility of turbulence statistics predicted by LES computation was examined. Statistical characteristics of a turbulent boundary layer developed over a flat plate were investigated by a wind tunnel test for modeling the cross-spectral density matrix for use as targets of inflow turbulence generation for LES computation. Furthermore, we investigated how the degree of correspondence of the cross-spectral density matrix of the generated inflow turbulence with the target cross-spectral density matrix estimated by the wind tunnel test influenced the LES results for the turbulent boundary layer. The results of this study confirmed that the reproduction of cross-spectra of the normal components of the inflow turbulence generation is very important in reproducing power spectra, spatial correlation and turbulence statistics of wind velocity in LES.
Accurate turbulence modeling is an essential prerequisite for the use of Computational Fluid Dynamics (CFD) in Wind Engineering. At present the most popular turbulence model for general engineering flow problems is the model. Models such as this are based on the isotropic eddy viscosity concept and have well documented shortcomings (Murakami et al. 1993) for flows encountered in Wind Engineering. This paper presents an objective assessment of several available alternative models. The CFD results for the flow around a full-scale (6 m) three-dimensional surface mounted cube in an atmospheric boundary layer are compared with recently obtained data. Cube orientations normal and skewed at to the incident wind have been analysed at Reynolds at Reynolds number of greater than . In addition to turbulence modeling other aspects of the CFD procedure are analysed and their effects are discussed.
At present the most popular turbulence models used for engineering solutions to flow problems are the k-epsilon and Reynolds stress models. The shortcoming of these models based on the isotropic eddy viscosity concept and Reynolds averaging in flow fields of the type found in the field of Wind Engineering are well documented. In view of these shortcomings this paper presents the implementation of a non-linear model and its evaluation for flow around a building. Tests were undertaken using the classical bluff body shape, a surface mounted cube, with orientations both normal and skewed at 45 degrees to the incident wind. Full-scale investigations have been undertaken at the Silsoe Research Institute with a 6 m surface mounted cube and a fetch of roughness height equal to 0.01 m. All tests were originally undertaken for a number of turbulence models including the standard, RNG and MMK k-epsilon models and the differential stress model. The sensitivity of the CFD results to a number of solver parameters was tested. The accuracy of the turbulence model used was deduced by comparison to the full-scale predicted roof and wake recirculation zone lengths. Mean values of the predicted pressure coefficients were used to further validate the turbulence models. Preliminary comparisons have also been made with available published experimental and large eddy simulation data. Initial investigations suggested that a suitable turbulence model should be able to model the anisotropy of turbulent flow such as the Reynolds stress model whilst maintaining the ease of use and computational stability of the two equations models. Therefore development work concentrated on non-linear quadratic and cubic expansions of the Boussinesq eddy viscosity assumption. Comparisons of these with models based on an isotropic assumption are presented along with comparisons with measured data.
One major drawback of the eddy viscosity subgrid‐scale stress models used in large‐eddy simulations is their inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in transitional regimes. In the present work a new eddy viscosity model is presented which alleviates many of these drawbacks. The model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model is based on an algebraic identity between the subgrid‐scale stresses at two different filtered levels and the resolved turbulent stresses. The subgrid‐scale stresses obtained using the proposed model vanish in laminar flow and at a solid boundary, and have the correct asymptotic behavior in the near‐wall region of a turbulent boundary layer. The results of large‐eddy simulations of transitional and turbulent channel flow that use the proposed model are in good agreement with the direct simulation data.
A turbulent boundary layer at high Reynolds number generated by a rough surface was calculated by large eddy simulation (hereafter abbreviated as LES). The inflow wind fluctuations conditioned by the experimental data were generated artificially. The velocities at the inlet boundary were interpolated in Fourier space as stochastic processes in a conditional random field so as to realize the equivalent statistical quantities of experimental results. The calculated turbulent field just behind the roughness elements was compared with the experimental data and examined. The calculated result shows rather good agreement regarding the mean wind field and the turbulent energy spectra in the low frequency. Otherwise the energy of the high-frequency wind fluctuation decreased and the wind fluctuations were less correlated in the calculated results.
A computational fluid dynamics (CFD) technique is applied to the prediction of snowdrift around a nine-storey apartment building. A modified version of the Launder–Kato-type k–ε model (LK model) is used. In the first part of the paper, results of a preliminary study for a flowfield around a cube placed in a channel flow are presented. Here, results obtained by using the modified LK model are compared with those of measurements and the standard k–ε model. The latter part describes the numerical prediction of snowdrift around a nine-storey apartment building which is presently under construction in Nagaoka City, Niigata Prefecture. Special emphasis is given to snowdrift into the elevator hall.
Turbulent diffusion of gaseous contaminant near a cubic-shaped building model is predicted by LES using a Dynamic Mixed SGS (DM) model with the aid of the composite grid technique. The results obtained using a composite grid show better agreement with experiment than does the case using a single grid. Some discrepancies from the experimental results are observed in the results of the standard Smagorinsky model with a composite grid. These discrepancies are improved remarkably by using the DM model.
Velocity and pressure fields around a low-rise experimental building located at Texas Tech University are predicted using Large Eddy Simulation ( LES ). The distributions of mean and rms surface pressure coefficients predicted by LES are compared with those of field and wind tunnel measurements. The results of LES correspond very well with the measured data.
A two-equation turbulence for canopy flows is formulated and explored. The turbulence model is based on the κ-ϵ model, which is extended by including terms due to the drag caused by the canopy. Drag terms are also added to the mean momentum equations. The closed set of equations is solved using the general equation solver PHOENICS. PHOENICS is based on a finite volume technique and solves the equations in a fully implicit manner.The applications of the model include a one-dimensional comparison with a laboratory experiment, the two-dimensional boundary layer development over a canopy and a three-dimensional analysis of secondary flow patterns generated by a canopy. Although the results are evaluated in a rather qualitative way, it is concluded that the results obtained are encouraging and motivate further and more detailed studies of the model.
The paper summarizes current strategies for computing heat transfer coefficients in complex turbulent flows based on numerical solution of the averaged equations for momentum and enthalpy and corresponding equations for averaged properties of the turbulent flow field. It argues that, for accuracy and width of applicability, a fine-grid low-Reynolds-number treatment should be employed near the wall in place of wall functions, despite the attractive simplicity of the latter approach. Several examples are provided that bring out the benefit from adopting second-moment closures, in which attention is focused on the turbulent stresses and heat fluxes themselves rather than on effective viscosities and thermal diffusivities. Directions for future research are briefly discussed, an important contribution to this effort being the direct numerical simulation of the near-wall dynamic and thermal turbulence field.