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Investigation of multi-level wind flow characteristics and pedestrian comfort in a tropical city
Abstract
An accurate CFD modelling of wind flow around a city is important for a large variety of application. CFD simulations are heavily influenced by the large number of computational parameters defined in the model. This article presents a thorough and broad sensitivity study of the impact of computational parameters on the numerical outcome for wind flow pattern of a tropical city. In this current study, a series of 3D steady state RANS simulations are conducted in full scale for a region in the city with CFD software OpenFOAM. As CFD simulations are influenced by the computational parameters including turbulence models, for accurate wind flow modelling different turbulent models are tested. The numerical outcomes are compared with on-site measured data which are obtained from anemometers placed at different locations and heights within the downtown of the tropical city for a 2-year period. The impact of a variety of computational parameters is considered which include the mesh resolution and different turbulence models. The test for turbulence models shows that SST k-ω returns the most accurate result among other examined models compared to experimental data. A pedestrian comfort map is then derived based on extended land beaufort scale table and velocity field data from CFD. The result is consistent with long-term observations. In addition, vertical profile of the wind speed near every corner of some interested buildings is investigated for the potential installation of micro wind turbines
... Local and national governments are promoting the Smart Cities concept. Dhunny, Siew and Jones [12] point out that it is an increasingly popular concept and that there is a need to further encourage its adoption. The EU is promoting the development of Smart Cities through various programs and projects. ...
... On the other hand, a notable concern can be observed because the automation and digitization of services in cities generate unemployment, affecting individual economic status [14]. Despite these obstacles, experts affirm that the smart city is the ideal solution to manage the challenges that arise with drastic urbanization and population growth [12]. Among these challenges, and under the principles of the EC, we find waste management, air pollution, traffic congestion, adverse effects on human health, the scarcity of resources and materials, and the aging of infrastructure [15] [16]. ...
... Note that there is currently no recognized definition of pedestrian level height. Existing literature defines pedestrian level height variably as 1.5 m (Shi et al., 2015;Adamek et al., 2017;Shui et al., 2018), 1.75 m (Dhunny et al., 2018;Kaseb et al., 2020;Norouziasas et al., 2022), or 2 m (Gromke & Blocken, 2015;Zou et al., 2021;Baş et al., 2024). Considering the recent trend in research to set the pedestrian level height at 2 m, this study adopted wind field values at 2 m to represent pedestrian-level wind. ...
Addressing climate change issues is one of the most important tasks within the United Nations Sustainable Development Goals. Accurate and efficient simulation of wind fields within cities is essential for climate adaptation. Traditional simplified geometric model-based wind flow simulation can lead to significant errors, affecting the ability to develop effective urban climate strategies. This study addresses this limitation by introducing a novel workflow that leverages drone photogrammetry, deep learning, and geometric complexity quantification to create highly detailed 3D models of in-use building clusters within cities. These models are subsequently used for computational fluid dynamics simulations to accurately predict urban wind fields. The proposed method was validated on three real-world building clusters. Compared to traditional footprint extrusion models, the proposed method demonstrates an average error reduction of 29.2% in large eddy simulation cases and 17.6% in steady Reynolds-averaged Navier-Stokes equations cases. Meanwhile, the proposed model improved computational efficiency by an average of 33.7% in large eddy simulations compared to the flashy oblique photography model. The proposed method provides a balanced model of accuracy and efficiency for urban flow simulations. It has the potential to be incorporated into computational fluid dynamics best practice guidelines, thereby promoting the development of climate-resilient cities.
... Within academic literature, the standard practice has often been to simulate 12 wind directions for pedestrian wind comfort assessments, following the guidelines suggested by [9]. Studies by Blocken et al. [40], Blocken and Carmeliet [41], Blocken and Persoon [2],Blocken et al. [3], Janssen et al. [42], Blocken et al. [43], Dhunny et al. [44] have adhered to this convention. However, the findings in this study indicate that this standard leads to misclassifications in pedestrian wind comfort maps for approximately 5%-10% of the assessed area, compared to assessments using enough wind directions for a 'converged' result. ...
... The spatial resolution of mesoscale meteorological simulation results cannot reflect the fine impact of the overall layout of buildings on the urban internal wind field on the overall planning scale of the city [30]. Computational fluid dynamics (CFD) simulation can show the refined wind field inside the block, but its simulation range is small, and the high-resolution wind field simulation at the whole urban scale cannot be completed quickly due to the large computation requirement [31,32]. The long evaluation cycle, high cost, and low universality of wind tunnel experiments make them unsuitable for urban-scale ventilation evaluations [33,34]. ...
Urban ventilation corridors (UVCs) have the potential to effectively mitigate urban heat islands and air pollution. Shanghai, a densely populated city located in eastern China, is among the hottest cities in the country and requires urgent measures in order to enhance its ventilation system. This study introduces a novel approach that integrates land surface temperature retrieval, PM2.5 concentration retrieval, and wind field simulation to design UVCs at the city level. Through remote sensing data inversion of land surface temperature (LST) and PM2.5 concentration, the study identifies the action spaces and compensation spaces for UVCs. The Weather Research and Forecasting (WRF) model, coupled with the multilayer urban scheme Building Effect Parameterization (BEP) model, is employed to numerically simulate and analyze the wind field. Based on the identification of thirty high-temperature zones and high PM2.5 concentration zones as action spaces, and twenty-two low-temperature zones and low PM2.5 concentration zones as compensation spaces in Shanghai, the study constructs seven first-class ventilation corridors and nine secondary ventilation corridors according to local circulation patterns. Unlike previous UVC research, this study assesses the cleanliness of cold air, which is a common oversight in UVC planning. Ignoring the assessment of cold air cleanliness can result in less effective UVCs in improving urban air quality and even exacerbate air pollution in the central city. Therefore, this study serves as a crucial contribution by rectifying this significant deficiency. It not only provides a fresh perspective and methodology for urban-scale ventilation corridor planning but also contributes to enhancing the urban microclimate by mitigating the effects of urban heat islands and reducing air pollution, ultimately creating a livable and comfortable environment for urban residents.
... Simulation approaches obtaining steady-state PLW flow fields, such as SRANS and some data-driven models, provide wind amplification factors for the translation of meteorology data to the building site. Broad applications of the steady-state simulations have proven that their tradeoffs between data fidelity and computation efficiency are acceptable (Dhunny et al., 2018;Ricci et al., 2022;Tsichritzis & Nikolopoulou, 2019). More discussions on PLW comfort assessment with SRANS can be found in the reviews by Blocken and Carmeliet (2004) and Blocken et al. (2016). ...
Pressing problems in urban ventilation and thermal comfort affecting pedestrians related to current urban development and densification are increasingly dealt with from the perspective of climate change adaptation strategies. In recent research efforts, the prime objective is to accurately assess pedestrian-level wind (PLW) environments by using different simulation approaches that have reasonable computational time. This review aims to provide insights into the most recent PLW studies that use both established and data-driven simulation approaches during the last 5 years, covering 215 articles using computational fluid dynamics (CFD) and typical data-driven models. We observe that steady-state Reynolds-averaged Navier-Stokes (SRANS) simulations are still the most dominantly used approach. Due to the model uncertainty embedded in the SRANS approach, a sensitivity test is recommended as a remedial measure for using SRANS. Another noted thriving trend is conducting unsteady-state simulations using high-efficiency methods. Specifically, both the massively parallelized large-eddy simulation (LES) and hybrid LES-RANS offer high computational efficiency and accuracy. While data-driven models are in general believed to be more computationally efficient in predicting PLW dynamics, they in fact still call for substantial computational resources and efforts if the time for development, training and validation of a data-driven model is taken into account. The synthesized understanding of these modeling approaches is expected to facilitate the choosing of proper simulation approaches for PLW environment studies, to ultimately serving urban planning and building designs with respect to pedestrian comfort and urban ventilation assessment.
... The setup of the simulations only differs in the wind direction applied at the inlet, which is evenly distributed in the horizontal plane within the set. Wisse et al. (2002) argue that 12 wind directions are enough for the analysis of pedestrian wind comfort; 12 wind directions with 30°i ncrements are used in most published journal papers, including Blocken and Persoon, 2009;Blocken et al., 2012;Dhunny et al., 2018). Hågbo et al. (2021) instead used the eight wind directions. ...
The construction of a building inevitably changes the microclimate in its vicinity. Many city authorities request comprehensive wind studies before granting a building permit, which can be obtained through Computational Fluid Dynamics (CFD) simulations. Investigating the wind conditions for 12 wind directions has previously been considered sufficient in most literature and the industry. However, the effect of changing the number of simulated wind directions is still not well understood. This article investigates the influence of the number of simulated wind directions on pedestrian wind comfort maps. A neighborhood in Niigata city, Japan, was chosen as a case study. Simulations are performed in OpenFOAM using a Reynolds-averaged Navier-Stokes model and the realizable k-ϵ turbulence model. The inlet profiles form a homogeneous atmospheric boundary layer with neutral stratified conditions and a logarithmic velocity profile. The pedestrian wind comfort maps are converging toward a final map as more wind directions are included. The area of the maps classified with the same comfort as using 64 wind directions is 79% using 4 wind directions, 92% using 8 wind directions, 96% using 16 wind directions, and 99% using 32 wind directions. A greater understanding of the influence of the number of simulated wind directions included may enable more efficient pedestrian wind comfort studies that recognize the associated uncertainties.
... A building comprises multiple design parameters that enhance the overall building utility [29]. Hence, parametric studies aid in investigating the impact of building design on natural ventilation in and around buildings at various levels, ranging from urban context [25,[30][31][32], site planning [33][34][35][36][37], pedestrian comfort [38][39][40], building features (e.g., balconies, atrium and windcatcher) [9,[41][42][43][44][45] and indoor natural ventilation [45][46][47][48]. Sensitivity analysis (SA) helps to identify the contribution of a specific design parameter on the performance of the building while quantifying the uncertainties [29]. ...
Double-loaded affordable apartments, which are commonly seen in tropical developing countries, suffer from poor cross-ventilation, particularly on the leeward side of the buildings. This study aims to parametrically evaluate closed-vertical void configurations to improve the ventilation performance of the double-loaded apartment building using the validated CFD models. The configurations include the aspect ratio of the void, pilotis size and fin size with various wind directions. The results showed that the most influential parameter for enabling natural ventilation by augmenting pressure coefficient differences on the windward and leeward sides of the building was the fin size, followed by wind direction and aspect ratio. Wind direction influenced the windward side more than the leeward side, whereas aspect ratio influenced the leeward side over the windward side. It was concluded that the mass flow rates on both sides of the building could be maximised by optimally combining the void's fin size and aspect ratio under the specific prevailing wind directions. These findings would help create sustainable design guidelines for improving natural ventilation by incorporating a closed-vertical void in the mid-rise apartment buildings in the tropics.
... Zhang et al. [24] presented results on the effect of different aspect ratios on the pedestrian comfort near lift-up buildings. Kang et al. [25] established a new computational fluid dynamics model for the case of trees with applications of the pedestrian level wind comfort in urban areas, and issue of multi-level wind flow characteristics in the tropical areas were addressed by Dhunny et al. [26]. ...
Considering the cubic nature of the most frequent geometries among the urban elements and their configurations, the manipulation of the free stream wind flow around the enormous objects, as well as within relatively narrow corridors, such as street canyons is significant in many regards. One of its instances could be mentioned as pedestrian comfort. In this case study, the implementation of an Oblique Streamlining Membrane (OSM) has been studied on a sub-branch of a low rise, but bulky, building, over which a roof-top outdoor food court area has been primarily designed. The OSM serves as the streamlining mechanism, preventing the roof-top area from the intense fluctuations of the wind flow after the flow is separated from the inlet corner side of the building in question. The optimization of sub-geometries and the proof of the concept for the OSM flow controlling mechanism were the subject of the current manuscript, for which a 3D numerical Reynolds Average Navier-Stokes (RANS) scheme has been used. An unstructured computational grid has been applied around the 3D geometry of the entire building and its sub-branching details, which is in contrast with most studies on full-scale geometries, tending to have simplifications on the body to reach a more generalized set of results. All cases have been numerically tested with and without the presence of the OSM. This comparison has been the grounds for proving the effectivity of the said flow controlling mechanism to eliminate high gradient fluctuations of the separated flow off the roof corners. This has led to pedestrian/resident comfort on the roof-top food court area located on top of the building.
... But some time, this way can be too expensive (Reinhold, 1982). CFD simulations allow to assess parameters and suggest studies (Blocken, 2018), including Natural ventilation of buildings (Tong et al. 2019), dispersion of pollution (Dhunny et al. 2018), heat transfer (Allegrini and Carmeliet, 2018) and so forth. One study showed that the results stem from Fluent software are reliable as well as wind tunnel experiment for balcony and air flow (Montazeri and Blocken, 2013). ...
Natural ventilation is application of natural drift power of wind. Wind can enter and exit buildings through the openings on facades. Hence, Form of facades can impact the air flow behaviour and consequently natural ventilation because they can change the pressure distribution on facades. Moreover, difference between wind-induced pressure on windward and leeward facades is the most important factor affecting natural ventilation. So, it is worthy to focus on facade details in order to enhance natural ventilation. Particularly, geometrical details of facades such as protrusions and indentations e.g. balconies can be considered effective elements on average pressure distribution on both windward and leeward facades, changing pressure difference between these facades. This difference can drive the air flow towards interior spaces significantly. Although this basic rule has been used by different researchers in order to increase natural ventilation buildings, the most research has been studied buildings with flat facades. Therefore, the goal of this research is investigating effects of balcony types on the naturally-ventilated buildings. Three types of balcony are simulated and changes in wind pressure caused on facades are analysed. All these simulations are carried out for normally (perpendicular) and obliquely incident wind. This study is performed with Ansys Fluent 18 for all simulations. The results showed that balcony types can affect the pressure distribution on the opposing facades of buildings, leading to the more or less pressure difference between these two facades. These results show that protrusion (protrusive balcony) can cause more complicated pattern of the wind pressure on facades than the others. Also, re-entrant balcony causes the more pressure difference between the opposing surfaces and enhances wind-driven ventilation in buildings more considerably than the protrusive one.
... In conjunction with wind tunnel experiments and field measurements [7][8][9][10][11][12], CFD has proven to be among the most successful tools for simulating and for gaining an understanding of the continuously changing mechanisms within an urban boundary layer. This approach has also been applied to understand the external flow environment of cities to aid design processes [13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Developers now rely on CFD to explore optimum designs to maximize the saleable areas of their properties while maintaining good ventilation performance. ...
Computational fluid dynamics (CFD) is a mature method in wind engineering studies, but many air ventilation assessment (AVA) reports prepared by consulting firms in Hong Kong still suffer from the use of inappropriate techniques and computational settings in the CFD modeling stage. The main reason behind this is the lack of informative guidelines relating to CFD model settings in the AVA Technical Circular issued by local authorities. Other aspects of AVA that require improvement include terrain modeling techniques and understanding the sensitivity of modeled topographical size to the wind environment.
This paper revisits and summarizes important aspects of current best-practice guidelines for robust CFD simulations. The study compares two conventional approaches to terrain treatment through a series of sensitivity tests. The first approach uses terrain features to cover the entire ground of the computational domain, whereas the second imitates wind tunnel experiments in which the domain includes an inclined buffer area. One drawback of the first approach was found to be the occurrence of numerical divergence when the terrain size is small; meanwhile, in the latter approach, the inclination angle of the buffer area must not exceed 30° to achieve robust results.
The final stage of the study validates the results of CFD simulations based on the two approaches with experimental data from a dense city. The approach that mimics wind tunnel experiments with a buffer zone was found to achieve better correlations, and smaller normalized mean square errors with respect to the experimental data and is thus considered superior.
... Ng et al. (2011) sampled and calculated the heights of buildings in Hong Kong and further divided the urban canopy layer (0-60 m) into podium layer (0-15 m) and building layer (15-60 m). The methods used in urban wind environment studies include wind tunnel model (Brunet et al., 1994;Gromke, 2018), computational fluid dynamics (CFD) simulation ( Dhunny et al., 2018;Wang et al., 2018), and urban morphological parameters. Compared with others, urban morphological parameters, which are widely used, can accurately describe the aerodynamic characteristics of cities and explain most urban climate phenomena and processes with a lower cost. ...
Due to rapid urbanization, China's urban morphology has undergone tremendous changes, resulting in an increased urban heat island (UHI) effect and negative impact of thermal environment, especially in summer. Studying the scale effect between urban wind and thermal environment can provide the best scale for the wind environment planning on mitigating UHI effect. Taking Dalian as an example, using multi-source data, a nonlinear correlation analysis was used to analyze the correlation between the frontal area index (FAI) and land 77uuyyhsurface temperature (LST) under different grids. The results show that first, FAI is sensitive to grid-size changes. When the grid size increases from 25 × 25 m to 150 × 150 m with a step size of 25 m, in July, the numbers of grids with FAI > 1 are 19,992, 1538, 153, 20, 4, and 0 (0%) accounting for 2.106%, 0.645%, 0.081%, 0.019%, 0.006%, and 0% of the total, respectively. In September, the numbers of grids with FAI > 1 are 17,633, 1643, 164, 22, 8, and 0, accounting for 1.849%, 0.689%, 0.155%, 0.037%, 0.021%, and 0% of the total, respectively. When the grid size is greater than or equal to 150 × 150 m, there is no grid with FAI > 1. Second, the most effective grid size to study the relationship between FAI and LST is 25 m. When the grid size increases from 25 m to 300 m with a step size of 25 m, the correlation between FAI and LST shows a significant decrease. When the grid size is 25 m, the correlation is the strongest.
... A review of Port Louis policy guidelines, and academic and professional practice literature by the authors revealed that no prior occupancy cadastre mapping of Port Louis existed, and this knowledge had been little noted [7]. The only and most relevant authoritative research involved an investigation of multi-level wind flow characteristics and pedestrian comfort in Port Louis [22]. ...
The Smart City Scheme, as part of the Smart Mauritius initiative, adopted by the Government of Mauritius in 2014, heavily incentivised the emergence of new smart cities in greenfields. The resulting migration of business and residents from existing cities to new cities affected the liveability standard of existing cities and encouraged property speculation. This shift reduced home pricing affordability further from the grasp of young professionals. With the Mauritian Landlord and Tenant Act of 1999 discouraging investment in Mauritian city centres, property developers were additionally encouraged to invest in housing projects in these emerging Smart Cities. As part of the Smart Urban Regeneration strategy of Port Louis that sought to reduce competition between new and existing cities, the provision of housing was seen as paramount to enabling the Smart Cities concept as promoted by the Government. The findings of this paper, which explores the urban footprint of Port Louis through field survey, provides insights, as to the components of the city, that can assist policy-makers and developers to better shape projects that are more responsive to the Smart Urban Regeneration plan.
... 6a-e) (e.g. Murakami and Mochida 1989;Murakami 1990a;Gadilhe et al. 1993;Takakura et al. 1993;Bottema 1993;Stathopoulous and Baskaran 1996;Murakami 1997;Westbury et al. 2002;Richards et al. 2002;Hirsh et al. 2002;Blocken et al. 2004Yoshie et al. 2007;Mochida and Lun 2008;Tominaga et al. 2008a;Blocken and Carmeliet 2008;Blocken and Persoon 2009;Janssen et al. 2013;Montazeri et al. 2013;An et al. 2013;Yuan and Ng 2014;Iqbal and Chan 2016;Yasa 2016;Allegrini and Kubilay 2017;Ricci et al. 2017b;Du et al. 2018;Liu et al. 2017;Dhunny et al. 2018), urban thermal environment ( Fig. 6f) (e.g. Ashie and Kono 2011;Toparlar et al. 2015Toparlar et al. , 2017Toparlar et al. , 2018Montazeri et al. 2017;Yang et al. 2017;Kang et al. 2017;Gao et al. 2018;Allegrini and Carmeliet 2018), urban ventilation and/or pollutant dispersion ( Fig. 6g) (e.g. ...
Large Eddy Simulation (LES) undeniably has the potential to provide more accurate and more reliable results than simulations based on the Reynolds-averaged Navier-Stokes (RANS) approach. However, LES entails a higher simulation complexity and a much higher computational cost. In spite of some claims made in the past decades that LES would render RANS obsolete, RANS remains widely used in both research and engineering practice. This paper attempts to answer the questions why this is the case and whether this is justified, from the viewpoint of building simulation, both for outdoor and indoor applications. First, the governing equations and a brief overview of the history of LES and RANS are presented. Next, relevant highlights from some previous position papers on LES versus RANS are provided. Given their importance, the availability or unavailability of best practice guidelines is outlined. Subsequently, why RANS is still frequently used and whether this is justified or not is illustrated by examples for five application areas in building simulation: pedestrian-level wind comfort, near-field pollutant dispersion, urban thermal environment, natural ventilation of buildings and indoor airflow. It is shown that the answers vary depending on the application area but also depending on other—less obvious—parameters such as the building configuration under study. Finally, a discussion and conclusions including perspectives on the future of LES and RANS in building simulation are provided.
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.
In the computational fluid dynamics simulation workflow, the geometry preparation step is often regarded as a tedious, time-consuming task. Many practitioners consider it one of the main bottlenecks in the simulation process. The more complex the geometry, the longer the necessary work, meaning this issue is amplified for urban flow simulations that cover large areas with complex building geometries. To address the issue of geometry preparation, we propose a workflow for automatically reconstructing simulation-ready 3D city models. The workflow combines 2D geographical datasets (e.g., cadastral data, topographic datasets) and aerial point cloud-based elevation data to reconstruct terrain, buildings, and imprint surface layers like water, low vegetation, and roads. Imprinted surface layers serve as different roughness surfaces for modeling the atmospheric boundary layer. Furthermore, the workflow is capable of automatically defining the influence region and domain size according to best practice guidelines. The resulting geometry aims to be error-free: without gaps, self-intersections, and non-manifold edges. The workflow was implemented into an open-source framework using modern, robust, and state-of-the-art libraries with the intent to be used for further developments. Our approach limits the geometry generation step to the order of hours (including input data retrieval and preparation), producing geometries that can be directly used for computational grid generation without additional preparation. The reconstruction done by the algorithm can last from a few seconds to a few minutes, depending on the size of the input data. We obtained and prepared the input data for our verification study in about 2 hours, while the reconstruction process lasted 1 minute. The unstructured computational meshes we created in an automatic mesh generator show satisfactory quality indicators and the subsequent numerical simulation exhibits good convergence behavior with the grid convergence index of observed variables less than 5%.
High resolution urban wind field simulations are limited in small simulation domain, short simulation period, or stable boundary conditions due to the high computational requirements. To address these limitations, non-intrusive reduced order models (NIROMs) are developed in this study and first realized the prediction of high-resolution 3D wind field in a city-scale area (~150 km²) during a long simulation period (4 weeks). Within the NIROM, 3D convolutional autoencoder and eXtreme Gradient Boost regression models (XGBoost) are adopted. The urban airflow can be predicted rapidly by the XGBoost-decoder models with the input of boundary conditions via boundary conditions - latent variable - full-order wind fields. By comparing NIROM simulations to large-eddy simulations, we find that the NIROM with portable model size is capable for capturing the main spatial distribution characteristics of urban airflow. Moreover, the relationship between wind speed and building distribution indicates that the sparse layout with taller buildings can yield a 2-fold increase in the near-ground wind speed compared to the dense layout with lower buildings, which also benefits pedestrian thermal comfort and pollutant dissipation. Furthermore, this study can assist the optimization of urban ventilation and air quality in urban planning.
Geometry modeling is a common approach in pollutant dispersion studies. Block typology is a key element for representing geometries closer to real city environments. However, urban pollutant modeling studies and urban planning processes have different approaches regarding block typology and applied metrics. Therefore, the objective of this work is to compare urban block typologies and urban metrics used in literature studies with those found in real cities. The methodology combined a literature review with an empirical analysis of sample areas in selected cities. The results showed that more than 50% of the studies applied idealized building arrays. Nonetheless, the idealized array tends to underestimate real densities, often misrepresenting urban planning indices. On the other hand, derived geometry reduces modeling complexity and increases the applicability of studies in urban planning. Based on our findings, we suggest an urban block parameterization derived from real urban areas (representative of the densest cities in Asia, Europe, and America). This study selects five block typologies derived from actual cities (single block, detached buildings, courtyard, inner courtyards, and row buildings) with estimated values of the floor area ratio (FAR) and surface coverage (SC) that, when combined, provide a more precise representation of density.
Background:
While injuries experienced during hurricanes and other tropical cyclones have been relatively well- characterized through traditional surveillance, less is known about tropical cyclones' impacts on non-injury morbidity, which can be triggered through pathways that include psychosocial stress or interruption in medical treatment.
Methods:
We investigated daily emergency Medicare hospitalizations (1999-2010) in 180 United States counties, drawing on an existing cohort of high-population counties. We classified counties as exposed to tropical cyclones when storm-associated peak sustained winds were ≥ 21 m/s at the county center; secondary analyses considered other wind thresholds and hazards. We matched storm-exposed days to unexposed days by county and seasonality. We estimated change in tropical cyclone-associated hospitalizations over a storm period from 2 days before to 7 days after the storm's closest approach, compared to unexposed days, using generalized linear mixed-effect models.
Results:
For 1999-2010, 175 study counties had at least one tropical cyclone exposure. Cardiovascular hospitalizations decreased on the storm day, then increased following the storm, while respiratory hospitalizations were elevated throughout the storm period. Over the 10-day storm period, cardiovascular hospitalizations increased 3% (95% confidence interval [CI]: 2%, 5%) and respiratory hospitalizations increased 16% (95% CI: 13%, 20%) compared to matched unexposed periods. Relative risks varied across tropical cyclone exposures, with strongest association for the most restrictive wind-based exposure metric.
Conclusions:
In this study, tropical cyclone exposures were associated with a short-term increase in cardiorespiratory hospitalization risk among the elderly, based on a multi-year/multi-site investigation of US Medicare beneficiaries ≥ 65 years.
This work is aimed to suggest a numerical approach able to select the most useful building orientation with respect to the local wind in complex urban areas. It is showed a mesoscale-microscale numerical approach able to predict local flow patterns for building designers. The city of Ancona was selected to analyse wind patterns over complex orography in presence of buildings. The analysed area is characterized by a densely built hilly promontory flanked by a poorly urbanized valley. Two buildings were chosen to carry out energy analyses. At first, the MM5 weather prediction model is used to assess the wind patterns and the wind occurrence distribution. The 2010 year was simulated and compared with real data from a met-mast. After, computational fluid dynamic (CFD) analyses are conducted with and without the surrounding buildings to appreciate speed and inflow effects. CFD results showed great changes in the examined building area. The final step was the energy simulation, by means of EnergyPlus, of two multistoried buildings equipped with a double skin façade; results show a great impact on the energy consumption by comparing a wrong orientation with respect to the best solution derived from the mesoscale-microscale approach.
Air pollutants emitted within high-density urbanized areas have negative impacts on human health and quality of life and raise public concern. With the aim of creating a liveable environment and mitigating potential environmental problems, environmental scientists, architects and town planners have been working together to discover optimum building layouts and guidance principles for building morphology. These efforts have been consolidated via model simulations. Targeting an optimal design strategy, an improved SST k−ω model was first validated against wind and pollutant concentration data from a wind tunnel experiment at Tokyo Polytechnic University. The turbulence model was then applied to a variety of idealized city morphologies with different building permeabilities and building-height profiles. To confirm the findings from these idealized cases, further simulations were performed on two real conceptual cities. To facilitate pollutant dispersion within urbanized areas, at least 20% of the building permeability should be maintained, together with variations in building-height profiles. The innovative “Dragon Hole” design was also found to aid in pollutant dispersion. The study findings show that the pollutant concentration within the source canyon would be reduced by at least 40% for the idealized cases and by approximately 80% for the conceptual real case through incorporation of the abovementioned design features. Moreover, the recommendations resulting from this research are consistent with the requirements documented in the Sustainable Building Design Guidelines.
THE PAPER PRESENTS A NEW MODEL OF TURBULENCE IN WHICH THE LOCAL TURBULENT VISCOSITY IS DETERMINED FROM THE SOLUTION OF TRANSPORT EQUATIONS FOR THE TURBULENCE KINETIC ENERGY AND THE ENERGY DISSIPATION RATE.THE MAJOR COMPONENT OF THIS WORK HAS BEEN THE PROVISION OF A SUITABLE FORM OF THE MODEL FOR REGIONS WHERE THE TURBULENCE REYNOLDS NUMBER IS LOW.THE MODEL HAS BEEN APPLIED TO THE PREDICTION OF WALL BOUNDARY-LAYER FLOWS IN WHICH STREAMWISE ACCELERATIONS ARE SO SEVERE THAT THE BOUNDARY LAYER REVERTS PARTIALLY TOWARDS LAMINAR.IN ALL CASES, THE PREDICTED HYDRODYNAMIC AND HEAT-TRANSFER DEVELOPMENT OF THE BOUNDARY LAYERS IS IN CLOSE AGREEMENT WITH THE MEASURED BEHAVIOUR.(A)
Among renewable energy sources, the electrical generation from micro-wind turbines has not yet disclosed its huge potential especially in urban settings. Increasing the spread of micro-wind turbines not only promotes the decentralized generation of energy, but also helps tackle fuel poverty and to achieve reductions in the emission of greenhouse gases (GHGs).
This work proposes an innovative methodology to exploit wind flow fields, calculated by means of computational fluid dynamic (CFD) codes in urban environments, within the geographical information system (GIS) platform. In this way, the platform of users is amplified, even non-specialist users, that can utilize wind data to evaluate the potential production of electricity using micro-wind turbines. A pilot study was conducted for assessing the applicability of the approach in a Sicilian city. The results of this case study show the energy yield produced from a building-mounted wind turbine (BUWT). The developed methodology permits to enrich the information usually stored in the GIS platform allowing to supply useful information about suitable sites where micro-wind energy plants can be installed and to assess the production of renewable energy in the urban settings.
Although trees are numerous in urban areas, their dynamic effects on the wind flow are usually approximated or neglected altogether in many wind engineering studies, especially those based on numerical modeling. This study investigates the effect of the inclusion of trees in numerical simulations of wind flow in urban area. Three approaches are used to include the dynamic effect of trees: the basic approach (tree effects are neglected), the implicit approach (tree effects are included in the surface parameterizations), and the explicit approach (trees are represented by porous media). Several test cases have been adopted in order to cover a wide range of urban complexities, wind directions, foliage densities, and tree planting configurations. The results show that there are significant effects of trees when the explicit approach is used compared to the basic and the implicit approaches. Thus tree effects need to be considered using an explicit approach to simulate wind flow in urban area. Also, many parameters such as wind direction, foliage density, and urban configuration are believed to influence the intensity of trees effects. This study emphasizes the importance to explicitly consider the effects of trees in numerical model investigations for the wind flow in urban areas.
The European program HORIZON2020 aims to have 20% of electricity produced by renewable sources. The building sector represents 40% of the European Union energy consumption. Reducing energy consumption in buildings is therefore a priority for energy efficiency. The present investigation explores the most adequate roof shapes compatible with the placement of different types of small wind energy generators on high-rise buildings for urban wind energy exploitation. The wind flow around traditional state-of-the-art roof shapes is considered. In addition, the influence of the roof edge on the wind flow on high-rise buildings is analyzed. These geometries are investigated, both qualitatively and quantitatively, and the turbulence intensity threshold for horizontal axis wind turbines is considered. The most adequate shapes for wind energy exploitation are identified, studying vertical profiles of velocity, turbulent kinetic energy and turbulence intensity. Curved shapes
are the most interesting building roof shapes from the wind energy exploitation point of view, leading to the highest speed-up and the lowest turbulence intensity.
The analysis of the wind flow around buildings has a great interest from the point of view of the wind
energy assessment, pollutant dispersion control, natural ventilation and pedestrians wind comfort and
safety. Since LES turbulence models are computationally time consuming when applied to real geome-
tries, RANS models are still widely used. However, RANS models are very sensitive to the chosen tur-
bulence parametrisation and the results can vary according to the application. In this investigation, the
simulation of the wind flow around an isolated building is performed using various types of RANS tur-
bulence models in the open source code OpenFOAM, and the results are compared with benchmark
experimental data. In order to confirm the numerical accuracy of the simulations, a grid dependency
analysis is performed and the convergence index and rate are calculated. Hit rates are calculated for all
the cases and the models that successfully pass a validation criterion are analysed at different regions of
the building roof, and the most accurate RANS models for the modelling of the flow at each region are
identified. The characteristics of the wind flow at each region are also analysed from the point of view of
the wind energy generation, and the most adequate wind turbine model for the wind energy exploitation
at each region of the building roof is chosen.
The increasing interest among architects and planners in designing environmentally friendly buildings has led to a desire to explore and integrate renewable sources of energy. Roof mounted wind turbines is a technology that presents a high potential for integration within the built environment. However, there is a state of uncertainty regarding the feasibility of these wind turbines. This paper argues that part of this uncertainty is attributed to uninformed decisions about positioning and locating urban wind turbines. This is underpinned by lack of consideration to the accelerating effect of different roof shapes, buildings' heights and surrounding urban configurations. This paper aims to present the results of Computational Fluid Dynamics (CFD) simulations for the purpose of identifying the effect of different roof shapes on the energy yield and positioning of roof mounted wind turbines covering different buildings' heights within different urban configurations under different wind directions. Results from this investigation suggest that an increase in energy yield could be achieved which can reach 56.1% more electricity in the case of a vaulted roof if an informed wind assessment above buildings' roofs is carried out.
This report describes the use of some computer programs written by one of the authors (DP) in predicting mean and peak wind pressures on arched-roof buildings. The research was carried out because there is a lack of good wind-tunnel and full-scale data on arched-roof buildings. The programs have been validated by comparing the results with wind-tunnel and full-scale data associated with the Texas Tech building.
The generality of the energy-dissipation model of turbulent heat and
momentum transport, developed by Jones and Launder (1972, 1973), is
tested by applying the model to predict the swirling flows generated by
a rotating disk in a quiescent atmosphere. It is found that this
turbulence model can predict accurately the flow, heat transfer, and
mass transfer near a rotating disk. This is significant for the problem
of predicting convective heat transfer rates in turbine disks.
The Venturi-effect refers to the increase in fluid speed due to a decrease of the flow section in confined flows. The wind speed conditions in converging and diverging passages between perpendicular buildings are studied with Computational Fluid Dynamics (CFD) to investigate the extent to which the so-called Venturi-effect is present in the passages. Model validation is performed by comparing the numerical results with wind tunnel measurements. The validated model is employed for a detailed investigation of the wind speed and the flow rate in the passages for a wide range of passage widths. The simulations show an increase in wind speed near ground-level but a decrease of horizontal wind speed in the upper part of the converging passages. The reason is the wind-blocking effect, which causes a large part of the oncoming wind to flow over and around the buildings, rather than being forced through the passage. Due to this effect, the flow rates through the converging passages are consistently lower than the free-field flow rate, implying that the term Venturi-effect is less applicable for such building configurations. CE Database Subject Headings: Buildings; Computer aided simulation; Validation; Wind speed; Boundary layer flow; Fluid Dynamics; Turbulence; Acceleration; Pedestrians
This paper is devoted to the study of flow within a small building arrangement and pollutant dispersion in street canyons
starting from the simplest case of dispersion from a simple traffic source. Flow results from the commercial computational
fluid dynamics (CFD) code FLUENT are validated against wind tunnel data (CEDVAL). Dispersion results from FLUENT are analysed
using the well-validated atmos pheric dispersion model ADMS-Urban. The k − ε turbulence model and the advection-diffusion (AD) method are used for the CFD simulations. Sensitivity of dispersion results
to wind direction within street canyons of aspect ratio equal to 1 is investigated. The analysis shows that the CFD model
well reproduces the wind tunnel flow measurements and compares adequately with ADMS-Urban dispersion predictions for a simple
traffic source by using a slightly modified k − ε model. It is found that a Schmidt number of 0.4 is the most appropriate number for the simulation of a simple traffic source
and in street canyons except for the case when the wind direction is perpendicular to the street canyon axis. For this last
case a Schmidt number equal to 0.04 gives the best agreement with ADMS-Urban. Overall the modified k − ε turbulence model may be accurate for the simulation of pollutant dispersion in street canyons provided that an appropriate
choice for coefficients in the turbulence model and the Schmidt number in the diffusion model are made.
With rapid development in computer hardware and numerical algorithms, computational fluid dynamics (CFD) techniques are widely utilized to study the wind field and pollutant transport in urban street canyons. The recent advancements and achievements in street-canyon pollution research using mathematical modelling approaches are reviewed in this paper. The standard, renormalized-group (RNG), and realizable k–ε turbulence closure schemes are the most commonly used Reynolds-averaged Navier–Stokes (RANS) models in street-canyon flow research, including the studies on the effects of street-canyon aspect ratio, building configuration, ambient wind direction, inflow turbulence intensities, vehicle-induced turbulence, and thermal stratifications. Another approach to turbulence simulation inside street canyons is large-eddy simulation (LES) which can handle a broad range of turbulent motions in a transient manner. These two approaches have their merits and the choice between them will be a compromise between accuracy and cost. Several guidelines on this choice as well as some comments on the 2D and 3D CFD simulations are given.The outputs from wind field models can be used with pollutant transport models to calculate the pollutant distribution inside street canyons. The most commonly employed pollutant transport models include Lagrangian, Eulerian, and Lagrangian/Eulerian hybrid models. The advantages and shortcomings of these models are summarized. Several other modelling concerns, such as chemically reactive pollutant dispersion and boundary conditions treatment, are also discussed.
This paper evaluates the exposure of four children to carbon monoxide (CO) in two different classrooms during the time spent in school in a typical school day, using a numerical modelling approach. The study is focused on an area of 550 × 550 m2 centred at a primary school of the city of Aveiro, in central Portugal, which is located close to a road with moderate traffic and has naturally ventilated rooms. Air quality data were measured in the school yard. Traffic emissions were estimated with TREM model, using traffic counts data. Simulations of CO concentrations in the study domain were performed with the computational fluid dynamics model VADIS, considering the influence of buildings and trees over the dispersion. Indoor concentrations were simulated using a mass transfer approach. Results show that the individual exposure of children is spatially dependent, as a consequence of the wind flow and air pollutant dispersion patterns.
In the past 50 years, Computational Wind Engineering (CWE) has undergone a successful transition from an emerging field into an increasingly established field in wind engineering research, practice and education. This paper provides a perspective on the past, present and future of CWE. It addresses three key illustrations of the success of CWE: (1) the establishment of CWE as an individual research and application area in wind engineering with its own successful conference series under the umbrella of the International Association of Wind Engineering (IAWE); (2) the increasing range of topics covered in CWE; and (3) the history of overview and review papers in CWE. The paper also outlines some of the earliest achievements in CWE and the resulting development of best practice guidelines. It provides some views on the complementary relationship between reduced-scale wind-tunnel testing and CFD. It re-iterates some important quotes made by CWE and/or CFD researchers in the past, many of which are still equally valid today and which are provided without additional comments, to let the quotes speak for themselves. Next, as application examples to the foregoing sections, the paper provides a more detailed view on CFD simulation of pedestrian-level wind conditions around buildings, CFD simulation of natural ventilation of buildings and CFD simulation of wind-driven rain on building facades. Finally, a nonexhaustive perspective on the future of CWE is provided.
This paper presents results of CFD simulations of flow around and through a cubic building with symmetric openings on two opposite sides. The case where the incoming wind is perpendicular to the front face of the building, and so parallel to the openings, is considered. An unsteady method, Detached Eddy Simulation, is used to capture the unsteady cross-ventilation.
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.
The unsteady, turbulent flowfield around a cubic model has been simulated by means of large eddy simulation (LES). The resolvable-scale flowfield has been obtained directly by solving the filtered, three-dimensional, time-dependent Navier-Stokes equations. The subgrid-scale motions were simulated by an SGS eddy viscosity model. The computed mean velocity dstributions and various turbulence statistics (i.e. turbulence intensity, velocity spectrum, integral scale, etc.) were compared to those obtained from wind-tunnel experiments to examine the accuracy of LES from the viewpoint of engineering applications. The correspondence between numerical simulation and wind-tunnel experiments is found to be good.
Reactive pollutant dispersion in an urban street canyon with a street aspect ratio of one is numerically investigated using a computational fluid dynamics (CFD) model. The CFD model developed is a Reynolds-averaged Navier–Stokes equations (RANS) model with the renormalization group (RNG) k–ε turbulence model and includes transport equations for NO, NO2, and O3 with simple photochemistry. An area emission source of NO and NO2 is considered in the presence of background O3 and street bottom heating (ΔT=5°C) with an ambient wind perpendicular to the along-canyon direction. A primary vortex is formed in the street canyon and the line connecting the centers of cross-sectional vortices meanders over time and in the canyon space. The cross-canyon-averaged temperature and reactive pollutant concentrations oscillate with a period of about 15min. The averaged temperature is found to be in phase with NO and NO2 concentrations but out of phase with O3 concentration. The photostationary state defect is small in the street canyon except for near the roof level and the upper downwind region of the canyon and its local minimum is observed near the center of the primary vortex. The budget analysis of NO (NO2) concentration shows that the magnitude of the advection or turbulent diffusion term is much larger (larger) than that of the chemical reaction term and that the advection term is largely balanced by the turbulent diffusion term. On the other hand, the budget analysis of O3 concentration shows that the magnitude of the chemical reaction term is comparable to that of the advection or turbulent diffusion term. The inhomogeneous temperature distribution itself affects O3 concentration to some extent due to the temperature-dependent photolysis rate and reaction rate constant.
This study numerically investigates how flow and reactive pollutant dispersion in a street canyon with a canyon aspect ratio of one vary with the street-bottom heating intensity. For this, numerical simulations are performed over a wide range of street-bottom heating intensities (ΔT=0–15 °C in 1 °C intervals) using a Reynolds-averaged Navier–Stokes equations (RANS) model with NO–NO2–O3 photochemistry. The pollutants NO and NO2 are emitted from near the street bottom in the presence of background O3.
A computer program has been developed to compute turbulent flows over three-dimensional rectangular surface-mounted bluff bodies and the results have been applied to wind flows over buildings. The program solves the steady-state Reynolds equation using a κ—ϵ model of turbulence. The resulting differential equations are solved by the use of the SIMPLE algorithm.Four flows have been studied and the computed results compared with full scale and wind tunnel measurements carried out by others. Good agreement has been obtained in most cases.
The current work evaluates the impact of urban trees over the dispersion of carbon monoxide (CO) emitted by road traffic, due to the induced modification of the wind flow characteristics. With this purpose, the standard flow equations with a kε closure for turbulence were extended with the capability to account for the aerodynamic effect of trees over the wind field. Two CFD models were used for testing this numerical approach. Air quality simulations were conducted for two periods of 31h in selected areas of Lisbon and Aveiro, in Portugal, for distinct relative wind directions: approximately 45° and nearly parallel to the main avenue, respectively. The statistical evaluation of modelling performance and uncertainty revealed a significant improvement of results with trees, as shown by the reduction of the NMSE from 0.14 to 0.10 in Lisbon, and from 0.14 to 0.04 in Aveiro, which is independent from the CFD model applied. The consideration of the plant canopy allowed to fulfil the data quality objectives for ambient air quality modelling established by the Directive 2008/50/EC, with an important decrease of the maximum deviation between site measurements and CFD results. In the non-aligned wind situation an average 12% increase of the CO concentrations in the domain was observed as a response to the aerodynamic action of trees over the vertical exchange rates of polluted air with the above roof-level atmosphere; while for the aligned configuration an average 16% decrease was registered due to the enhanced ventilation of the street canyon. These results show that urban air quality can be optimised based on knowledge-based planning of green spaces.
This paper presents a practical numerical method to determine both the spatial and temporal distribution of driving rain on buildings. It is based on an existing numerical simulation technique and uses the building geometry and climatic data at the building site as input. The method is applied to determine the 3D spatial and temporal distribution of wind-driven rain on the facade a low-rise building of complex geometry. Distinct wetting patterns are found. The important causes giving rise to these particular patterns are identified: (1) sweeping of raindrops towards vertical building edges, (2) sweeping of raindrops towards top edges, (3) shelter effect by various roof overhang configurations. The comparison of the numerical results with full-scale measurements in both space and time for a number of on site recorded rain events shows the numerical method to yield accurate results.
The International Association for Wind Engineering (IAWE) was born in 1975, at the 4th International Conference on Wind Engineering (ICWE), London, UK, in a pioneering stage of wind engineering. It operated, mostly informally, until 1999, when the IAWE Steering Committee Meeting at the 10th ICWE, Copenhagen, Denmark, decided to open a wide debate and study new tools to make the IAWE coherent with the impressive development in wind engineering. Following this decision, new IAWE by-laws were compiled and a renewed organisation was proposed to and accepted by the Steering Committee Meeting at the 11th ICWE, Lubbock, TX, 2003. This decision promoted several actions aimed at offering the international wind engineering community a more operative and efficient service and support. In particular, an Executive Board was constituted to drive the Association and its activities between two subsequent ICWEs; a Secretariat was established to administer the IAWE and to represent a reference point for the wind engineering community; several associations and societies were accepted into IAWE membership, and a wide network of links and cooperations was created among member organisations, supporting members and other individual contacts spread to all parts of the world; the official IAWE web site—www.iawe.org—was created; renewed liaisons were made operative with international organisations working in wind engineering and similar fields; IAWE Awards were instituted in the broad field of wind engineering; a better sequence of dates and venues of the most important wind engineering conferences was planned. This paper provides a general framework and some critical remarks on the progress and the prospects of the IAWE.
Until recently, urban air quality modelling has been based on operational models of an integral nature. The use of computational fluid dynamics (CFD) models to address the same problems is increasing rapidly. Operational models e.g. OSPM, AERMOD, ADMS-Urban have undergone many comprehensive formal evaluations as to their “fitness for purpose” while CFD models do not have such an evaluation record in the urban air quality context. This paper looks at the application of both approaches to common problems. In particular, pollutant dispersion from point and line sources in the simplest neutral atmospheric boundary layer and line sources placed within different regular building geometries is studied with the CFD code FLUENT and the atmospheric dispersion model ADMS-Urban. Both the effect of street canyons of different aspect ratios and various obstacle array configurations consisting of cubical buildings are investigated. The standard k–ε turbulence model and the advection–diffusion (AD) method (in contrast to the Lagrangian particle tracking method) are used for the CFD simulations. Results from the two approaches are compared. Overall CFD simulations with the appropriate choice of coefficients produce similar concentration fields to those predicted by the integral approach. However, some quantitative differences are observed. These differences can be explained by investigating the role of the Schmidt number in the CFD simulations. A further interpretation of the differences between the two approaches is given by quantifying the exchange velocities linked to the mass fluxes between the in-canopy and above-canopy layers.
The construction of a building inevitably changes the microclimate in its vicinity. In particular near high-rise buildings, high wind velocities are often introduced at pedestrian level that can be experienced as uncomfortable or even dangerous. Therefore, the design of a building should not only focus on the building envelope and on providing good indoor environment, but should also include the effect of the design on the outdoor environment. The outdoor environment of a building, in particular related to wind, has received relatively little attention in the Building Physics community. The present paper addresses Building Physicists and focuses on the outdoor wind environment for pedestrians. First, a litera-ture review on pedestrian wind studies is provided. The relation between wind effects, wind comfort, wind danger and wind climate is outlined. A brief review on wind tunnel and numerical modeling of building aerodynamics and pedestrian wind is given. The typical wind flow pattern around buildings and the related wind environment at pedestrian level are discussed. Second, these problems are illustrated by means of four practical examples, where the unfavorable pedestrian wind environment has been, is or should be a matter of serious concern for the building designers and the building owner.
A numerical study of the wind speed conditions in passages between parallel buildings has been conducted for a wide range of passage widths with the commercial Computational Fluid Dynamics (CFD) code Fluent 6.1.22. CFD validation has been performed by comparison of the numerical results with the corresponding wind tunnel measurements. The study shows that accurate CFD simulation of a horizontally homogeneous atmospheric boundary layer (ABL) flow and of the subsequent building-related flow might be seriously compromised by the use of the wall-function roughness modifications present in many commercial CFD codes. In addition, the simulation results indicate that, at least for the cases studied here, the increase of wind speed in passages is only pronounced at the pedestrian level and that the flow rate through the passage is at most only 8% higher than the free-field flow rate, indicating that the so-called Venturi-effect is rather weak.
Natural ventilation of buildings refers to the replacement of indoor air with outdoor air due to pressure differences caused by wind and/or buoyancy. It is often expressed in terms of the air change rate per hour (ACH). The pressure differences created by the wind depend – among others – on the wind speed, the wind direction, the configuration of surrounding buildings and the surrounding topography. Computational Fluid Dynamics (CFD) has been used extensively in natural ventilation research. However, most CFD studies were performed for only a limited number of wind directions and/or without considering the urban surroundings. This paper presents isothermal CFD simulations of coupled urban wind flow and indoor natural ventilation to assess the influence of wind direction and urban surroundings on the ACH of a large semi-enclosed stadium. Simulations are performed for eight wind directions and for a computational model with and without the surrounding buildings. CFD solution verification is conducted by performing a grid-sensitivity analysis. CFD validation is performed with on-site wind velocity measurements. The simulated differences in ACH between wind directions can go up to 75% (without surrounding buildings) and 152% (with surrounding buildings). Furthermore, comparing the simulations with and without surrounding buildings showed that neglecting the surroundings can lead to overestimations of the ACH with up to 96%.
In an attempt to test a computer simulation of wind flow around a block-shaped building against corresponding flows observed in a boundary-layer wind-tunnel, numerical solutions to the steady-state Navier-Stokes equations are compared with the three time-averaged components of velocity on a 200-point grid surrounding the block in the tunnel. A comparison of the pressure fields is also made. Over a large part of the flow the comparisons are encouraging, but the wake region presents unresolved problems.
It is well known that applications of the standard k−ε model to flowfields around bluff-shaped bodies, often yield serious errors such as overestimation of turbulence kinetic energy k in the impinging region. Murakami, Mochida and Kondo have proposed a new k−ε model which resolves these problems by modifying the expression for eddy viscosity approximation. This paper examines the applicability of this new k−ε model (MMK model) to flowfields around three types of bluff bodies, i.e. a 2D square rib, a cube and a low-rise building model with 1 : 1 : 0.5 shape. The first half of the paper investigates the accuracy of the MMK model in reproducing turbulence characteristics around a bluff body. Results of the MMK model are compared precisely with those of the standard k−ε model, a revised k−ε model proposed by Launder and Kato (LK model) and wind tunnel tests for flow fields around a 2D square rib and a cube. The MMK model is also applied to predicting surface pressures on a low-rise building model with 1 : 1 : 0.5 shape with various wind angles including an oblique one. The accuracy and applicability of the MMK model to wind engineering problems are then discussed by comparing its results with those of the standard k−ε model and of the wind tunnel tests.
Mean wind environmental conditions around buildings necessary for the assessment of pedestrian comfort, dispersion of pollutants, as well as snow and dust transport have been evaluated numerically. Modified Navier-Stokes equations and k-ε turbulence models used in the simulation are discretized by the control volume method. The SIMPLE algorithm is applied to fulfill the condition of continuity. A non-uniform staggered grid arrangement containing 235,000 nodes is utilized for the three-dimensional numerical modelling. A typical Montreal location near the downtown campus of Concordia University has been selected as a test case for the computation. Validation of the computed results has been carried out by using data from experiments conducted in the boundary layer wind-tunnel of the Centre for Building Studies at Concordia University. Computed and measured data indicate that the most significant features of the wind environmental conditions around buildings can be predicted with reasonable accuracy. The advantages and drawbacks of computer simulation are discussed in the paper.
This paper compares computational fluid dynamics (CFD) results using various revised k–ε models and large eddy simulation (LES) applied to flow around a high-rise building model with 1:1:2 shape placed within the surface boundary layer. The first part of the paper examines the accuracy of various revised k–ε models, i.e. LK model, MMK model and Durbin's revised k–ε model, by comparing their results with experimental data. Among the computations using various revised k–ε models compared here, Durbin's revised k–ε model shows the best agreement with the experiment. The reason for the good performance of Durbin's model is discussed on the basis of ‘Realizability’ of predicted results. The second part of the paper describes the computations based on LES with and without inflow turbulence applied to the same flowfield. The results are compared with those of the experiments and Durbin's k–ε model in order to clarify the effect of velocity fluctuations on prediction accuracy of time-averaged velocity fields around the building. Special attention is paid to prediction accuracy for reproducing flow behind a building. The LES results with inflow turbulence show generally good agreement with experimental results in terms of the distributions of velocity and turbulence energy in this region. This improvement is mainly due to the fact that the periodic velocity fluctuation behind the building is well reproduced in LES.
Low wind scenarios are associated with the worst air pollution episodes in urban street canyons. Under these conditions, operational dispersion models often over-predict pollutant concentration. Traffic-producing turbulence (TPT) becomes dominant in mixing and diluting traffic-related pollutants under low wind speed conditions. Determining the TPT effect on the flow and dispersion patterns within urban street canyons is crucial for the development of detailed operational dispersion models for assessing urban air quality. Several spatially averaged TPT formulations have been recently proposed in the literature. However, only a few attempts have been made so far to incorporate different TPT schemes into operational dispersion models and evaluate their performance using measurements.In this paper, several TPT schemes presented in literature were evaluated. Two TPT schemes were implemented in the well-validated Windows version of the Danish Operational Street Pollution Model (WinOSPM). Both formulations were evaluated using six independent datasets of roadside CO concentrations collected in European cities. Statistical and sensitivity analyses were undertaken to test the performance of the different formulations. The results showed that the overall model performance was significantly sensitive to the TPT schemes adopted. The model performance improved when a detailed characterisation of the TPT, depending on the density of road traffic, was used.
The use of computational methods to predict wind-generated pressure distributions around buildings is investigated. These pressure distributions were needed for the prediction of natural ventilation in the buildings. For the example considered, the accuracy of the predicted pressure distribution was found to be acceptable.
High pollution levels have been often observed in urban street canyons due to the increased traffic emissions and reduced natural ventilation. Microscale dispersion models with different levels of complexity may be used to assess urban air quality and support decision-making for pollution control strategies and traffic planning. Mathematical models calculate pollutant concentrations by solving either analytically a simplified set of parametric equations or numerically a set of differential equations that describe in detail wind flow and pollutant dispersion. Street canyon models, which might also include simplified photochemistry and particle deposition–resuspension algorithms, are often nested within larger-scale urban dispersion codes. Reduced-scale physical models in wind tunnels may also be used for investigating atmospheric processes within urban canyons and validating mathematical models.A range of monitoring techniques is used to measure pollutant concentrations in urban streets. Point measurement methods (continuous monitoring, passive and active pre-concentration sampling, grab sampling) are available for gaseous pollutants. A number of sampling techniques (mainly based on filtration and impaction) can be used to obtain mass concentration, size distribution and chemical composition of particles. A combination of different sampling/monitoring techniques is often adopted in experimental studies. Relatively simple mathematical models have usually been used in association with field measurements to obtain and interpret time series of pollutant concentrations at a limited number of receptor locations in street canyons. On the other hand, advanced numerical codes have often been applied in combination with wind tunnel and/or field data to simulate small-scale dispersion within the urban canopy.
A computing technique for low-speed fluid dynamics has been developed for the calculation of three-dimensional flows in the vicinity of one or more block-type structures. The full time-dependent Navier-Stokes equations are solved with a finite-difference scheme based on the Marker-and-Cell method. Effects of thermal buoyancy are included in a Boussinesq approximation. Marker particles that convect with the flow can be used to generate streaklines for flow visualization, or they can diffuse while convecting to represent the dispersion by turbulence of particulate matter. The vast amount of data resulting from these calculations has been rendered more intelligible by perspective-view and stereo-view plots of selected velocity and marker-particle distributions.
Wind-driven rain (WDR) or driving rain is rain that is given a horizontal velocity component by the wind. WDR research is of importance in a number of research areas including earth sciences, meteorology and building science. Research methods and results are exchangeable between these domains but no exchanges could yet be noted. This paper presents the state-of-the-art of WDR research in building science. WDR is the most important moisture source affecting the performance of building facades. Hygrothermal and durability analysis of facades requires the quantification of the WDR loads. Research efforts can be classified according to the quantification methods used. Three categories are distinguished: (1) experimental methods, (2) semi-empirical methods and (3) numerical methods. The principles of each method are described and the state-of-the-art is outlined. It has been the intent of the present paper to bring together the reports, papers and books—published and unpublished—dealing with WDR research in building science to provide a database of information for researchers interested in and/or working in WDR research, independent of their field of expertise.
This paper presented an overview of the tools used to predict ventilation performance in buildings. The tools reviewed were analytical models, empirical models, small-scale experimental models, full-scale experimental models, multizone network models, zonal models, and Computational Fluid Dynamics (CFD) models. This review found that the analytical and empirical models had made minimal contributions to the research literature in the past year. The small- and full-scale experimental models were mainly used to generate data to validate numerical models. The multizone models were improving, and they were the main tool for predicting ventilation performance in an entire building. The zonal models had limited applications and could be replaced by the coarse-grid fluid dynamics models. The CFD models were most popular and contributed to 70 percent of the literature found in this review. Considerable efforts were still made to seek more reliable and accurate models. It has been a trend to improve their performance by coupling CFD with other building simulation models. The applications of CFD models were mainly for studying indoor air quality, natural ventilation, and stratified ventilation as they were difficult to be predicted by other models.
This paper firstly considers the history of wind engineering in five rather arbitrary time periods—the “traditional” period (up to 1750), the “empirical” period (1750–1900), the “establishment” period (1900–1960), the period of growth (1960–1980), and the modern period (1980 onwards). In particular it considers the development of the discipline in terms of the socio-economic and intellectual contexts of the time. This leads to a description of the current state of the discipline and a forward look at possible developments, again taking into consideration the likely socio-economic and intellectual changes in the next few decades.
A computer simulation of wind flow around a block-shaped building has been attempted by using 3-D turbulent flow conditions. The Control Volume Method is used for numerical discretisation. The SIMPLE algorithm inter alia fulfils the continuity condition. Results have been compared with previous computational attempts and also with data obtained in boundary layer wind tunnel tests. The inclusion of modifications in the standard k-ϵ model improves the prediction of pressures on the building envelope.
A new k-[epsilon] eddy viscosity model, which consists of a new model dissipation rate equation and a new realizable eddy viscosity formulation, is proposed in this paper. The new model dissipation rate equation is based on the dynamic equation of the mean-square vorticity fluctuation at large turbulent Reynolds number. The new eddy viscosity formulation is based on the realizability constraints; the positivity of normal Reynolds stresses and the Schwarz' inequality for turbulent shear stresses. We find that the present model with a set of unified model coefficients can perform well for a variety of flows. The flows that are examined include: (i) rotating homogeneous shear flows; (ii) boundary-free shear flows including a mixing layer, planar and round jets; (iii) a channel flow, and flat plate boundary layers with and without a pressure gradient; and (iv) backward facing step separated flows. The model predictions are compared with available experimental data. The results from the standard k-[epsilon]
The invariance theory in continuum mechanics is applied to analyze Reynolds stresses in high Reynolds number turbulent flows. The analysis leads to a turbulent constitutive relation that relates the Reynolds stresses to the mean velocity gradients in a more general form in which the classical isotropic eddy viscosity model is just the linear approximation of the general form. On the basis of realizability analysis, a set of model coefficients are obtained which are functions of the time scale ratios of the turbulence to the mean strain rate and the mean rotation rate. The coefficients will ensure the positivity of each component of the mean rotation rate. These coefficients will ensure the positivity of each component of the turbulent kinetic energy - realizability that most existing turbulence models fail to satisfy. Separated flows over backward-facing step configurations are taken as applications. The calculations are performed with a conservative finite-volume method. Grid-independent and numerical diffusion-free solutions are obtained by using differencing schemes of second-order accuracy on sufficiently fine grids. The calculated results are compared in detail with the experimental data for both mean and turbulent quantities. The comparison shows that the present proposal significantly improves the predictive capability of K-epsilon based two equation models. In addition, the proposed model is able to simulate rotational homogeneous shear flows with large rotation rates which all conventional eddy viscosity models fail to simulate.
A previous investigation into methods of exposure reduction for the pedestrian in the urban commuter environment highlighted the impact of a low boundary wall on the dispersion of air pollutants from adjacent traffic sources. The impact of low boundary walls on the dispersion of air pollutants in street canyons has been brought forward in this investigation to examine them, in more generic terms, with a view to highlighting exposure reduction strategies for pedestrians. 3D Computational Fluid Dynamics (CFD) models were used to examine this effect for varying wind speeds and directions in different street canyon geometries. The results of this investigation show that a low boundary wall located at the central median of the street canyon creates a significant reduction in pedestrian exposure on the footpath. Reductions of up to 40% were found for perpendicular wind directions and up to 75% for parallel wind directions, relative to the same canyon with no wall. The magnitude of the exposure reduction was also found to vary according to street canyon geometry and wind speed.
There have been many studies concerning dispersion of gaseous pollutants from vehicles within street canyons; fewer address the dispersion of particulate matter, particularly particle number concentrations separated into the nucleation (10-30 nm or N10-30) or accumulation (30-300 nm or N30-300) modes either separately or together (N10-300). This study aimed to determine the effect of wind direction and speed on particle dispersion in the above size ranges. Particle number distributions (PNDs) and concentrations (PNCs) were measured in the 5-2738 nm range continuously (and in real-time) for 17 days between 7th and 23rd March 2007 in a regular (aspect ratio approximately unity) street canyon in Cambridge (UK), using a newly developed fast-response differential mobility spectrometer (sampling frequency 0.5 Hz), at 1.60 m above the road level. The PNCs in each size range, during all wind directions, were better described by a proposed two regime model (traffic-dependent and wind-dependent mixing) than by simply assuming that the PNC was inversely proportional to the wind speed or by fitting the data with a best-fit single power law. The critical cut-off wind speed (Ur,crit) for each size range of particles, distinguishing the boundary between these mixing regimes was also investigated. In the traffic-dependent PNC region (UrUr<Ur,critUr,crit), concentrations in each size range were approximately constant and independent of wind speed and direction. In the wind speed dependent PNC region (UrUr>Ur,critUr,crit), concentrations were inversely proportional to Ur irrespective of any particle size range and wind directions. The wind speed demarcating the two regimes (Ur,critUr,crit) was 1.23+/-0.55 m s(-1) for N10-300, (1.47+/-0.72 m s(-1)) for N10-30 but smaller (0.78+/-0.29 m s(-1)) for N30-300.
Effect of natural ventilation and wind directions on the thermal performance of a building ceiling
- A Abdel
- N M Guirguis
- M A Hassan
Abdel, A., Guirguis, N.M., Hassan, M.A., 2007. Effect of natural ventilation and wind directions on the thermal performance of a building ceiling. In: Proceedings:
Buildings simulations 2007.
CFD simulation and full-scale experimental validation of the wind flow in an urban area: Campus of University of Mauritius
- A Z Dhunny
- F Toja-Silva
- C Peralta
- M R Lollchund
- S Rughooputh
Dhunny, A.Z., Toja-Silva, F., Peralta, C., Lollchund, M.R., Rughooputh, S., 2016. CFD simulation and full-scale experimental validation of the wind flow in an urban
area: Campus of University of Mauritius. Wind. Eng. J. 1-12.
Wind Resource Assessment Handbook Fundamentals for Conducting a Successful Monitoring Program
- I Scientific
- Aws
Scientific, I. AWS, 1997. Wind Resource Assessment Handbook Fundamentals for Conducting a Successful Monitoring Program.