Pedestrian Wind Comfort Research Articles

Machine Learning for Pedestrian-Level Wind Comfort Analysis

(1) Background: Artificial intelligence (AI) and machine learning (ML) techniques are being more widely employed in the field of wind engineering. Nevertheless, there is a scarcity of research on the comfort of pedestrians in terms of wind conditions with respect to building design, particularly in historic sites. (2) Objectives: This research aims to evaluate ML- and computational fluid dynamics (CFD)-based pedestrian wind comfort (PWC) analysis outputs using a novel method that relies on the sophisticated handling of image data. The goal is to propose a novel assessment method to enhance the efficiency of AI models over different urban scenarios. (3) Methodology: The stages include the analysis of climate data, CFD analysis with OpenFOAM, ML analysis using Autodesk Forma, and comparisons of the CFD and ML results using a novel image similarity assessment method based on the SSIM, MSE, and PSNR metrics. (4) Conclusions: This study effectively demonstrates the considerable potential of utilizing ML as a supplementary tool for evaluating PWC. It maintains a high degree of accuracy and precision, allowing for rapid and effective assessments. The methodology for precise comparison of two visual outputs in the absence of numerical data allows for more objective and pertinent comparisons, as it eliminates any potential distortions. (5) Recommendations: Additional research can explore the integration of ML models with climate data and different case studies, thus expanding the scope of wind comfort studies.

Rapid pedestrian‐level wind field prediction for early‐stage design using Pareto‐optimized convolutional neural networks

AbstractTraditional computational fluid dynamics (CFD) methods used for wind field prediction can be time‐consuming, limiting architectural creativity in the early‐stage design process. Deep learning models have the potential to significantly speed up wind field prediction. This work introduces a convolutional neural network (CNN) approach based on the U‐Net architecture, to rapidly predict wind in simplified urban environments, representative of early‐stage design. The process of generating a wind field prediction at pedestrian level is reformulated from a 3D CFD simulation into a 2D image‐to‐image translation task, using the projected building heights as input. Testing on standard consumer hardware shows that our model can efficiently predict wind velocities in urban settings in less than 1 ms. Further tests on different configurations of the model, combined with a Pareto front analysis, helped identify the trade‐off between accuracy and computational efficiency. The fastest configuration is close to seven times faster, while having a relative loss, which is 1.8 times higher than the most accurate configuration. This CNN‐based approach provides a fast and efficient method for pedestrian wind comfort (PWC) analysis, potentially aiding in more efficient urban design processes.

Application of a comprehensive atmospheric boundary layer model to a realistic urban-scale wind simulation

Atmospheric Boundary Layer (ABL) is the region below the stratosphere that is significantly affected by Earth’s surface. In this article, an improved ABL model has been tested and validated with field measurements, while simultaneously highlighting the consequences of using an incorrectly formulated ABL model when performing pedestrian wind comfort and safety analysis using Computational Fluid Dynamics (CFD) in a full-scale, realistic setting. The improved ABL model was successfully validated on wind tunnel scale test cases previously, and this article provides evidence that the validation can be extended to realistic, urban-scale test cases as well. Steady, incompressible, Reynolds Averaged Navier–Stokes (RANS) simulations were performed and the results obtained from the incorrect ABL model are compared with those from an improved, consistent ABL model, and the main differences between the two formulations are pointed out in terms of wind velocities and turbulent kinetic energies at the pedestrian height level, and wind comfort maps. The analyses show that using an incorrectly formulated ABL model results in an over-prediction of near-ground velocities due to an artificial wind acceleration, a significant under-prediction of turbulent kinetic energy values, and consequently resulting in a significantly worse pedestrian wind comfort map that differs up to 3 comfort classes in some regions.

Sensitivity of urban morphology and the number of CFD simulated wind directions on pedestrian wind comfort and safety assessments

Pedestrian wind comfort and safety are critical in urban design, especially as cities densify and climate change impacts intensify. While Computational Fluid Dynamics (CFD) simulations are increasingly used in these assessments, a universally agreed-upon number of wind directions for accurate results has yet to be established. This study addresses this gap by exploring the influence of urban morphology, characterized by different degrees of urbanization and building layouts, on the required number of wind directions for accurate assessments. Extensive CFD simulations were conducted in five geometrically diverse locations: Bryne, Oslo, London, Singapore, and New York. Pedestrian wind comfort maps were generated, and velocity amplification factor (VAF) dynamics were analyzed. The results suggest that urban complexity does not significantly affect the required number of wind directions for reliable assessments. The study provides practical guidance for selecting the number of wind directions based on the study’s focus: a minimum of 8 for basic assessments, 24 for high-accuracy assessments, and at least 36 for safety-focused assessments. This research significantly contributes to urban planning and design, empowering stakeholders with valuable insights for shaping resilient and comfortable urban environments.

INFLUENCE OF DIFFERENT WIND ANGLES ON PEDESTRIAN WIND COMFORT IN 3D SPACE

Abstract. Wind can impact pedestrian comfort. This comfort can be observed by integrating a 3D city model into the study area. However, little research has been done on the influence of different wind angles on pedestrian wind comfort and rarely on implementing 3D city models in the wind environment. Therefore, this study aims to fill the gap in using 3D city models to examine the effect of wind flow angles on pedestrian wind comfort. The Computational Fluid Dynamics (CFD) wind simulation environment presented in this study was constructed through the applied steady Reynolds-Average Navier-Stokes (RANS) with K-epsilon (k-ε) turbulence model. It is integrated with the standalone building model with a roof overhang structure represented in LoD2.3 of the CityGML standard. Three wind angles have been introduced to allow for variation in the analysis of pedestrian wind comfort: 0°, 15°, and 30° wind angles. Through the observation of multiple locations, which are directed beneath the roof overhang structure, the highest wind velocity is recorded in 0° wind angles compared to 15° and 30° wind angles. Thus, from these recorded values, pedestrian wind comfort is based on the Beaufort wind scale (BWS). The computed average recorded values show that 3.24 m/s corresponds to a wind angle of 0°, 2.761 m/s for 15°, and 2.415 m/s for 30°, which shows that all these values fall in BWS Scale 2. Thus, these areas experience a light breeze. However, the lowest value from a 30-degree environment presents the most reposeful surrounding.

Investigating the influence of 3D building models on pedestrian wind comfort through wind computational fluid dynamics analysis

Wind flow plays a crucial role in determining pedestrian comfortability in the surrounding environment. However, the shape and detailing of buildings, as well as the angle of the wind, can manipulate the wind flow patterns and velocity. Different urbanized areas have different building shapes and detailing, which can lead to diverse wind flow patterns and velocities, affecting pedestrian wind comfort (PWC). This study utilized wind Computational Fluid Dynamics (CFD) technique to investigate the influence of building models on wind velocity and its impact on PWC. The CFD simulation integrated with a 3D urbanized building model provided wind velocity values throughout the study area, which were used to analyze wind comfort at 1.75m elevation based on Beaufort wind force criteria. The study found that diverse effects due to different building detailing were observed, leading to multiple flow patterns and changes in wind velocity. The downstream building recorded a lower velocity value than the upstream building mainly because of wind flow separation from the building frontal. Wind comfort levels were represented using the Beaufort wind force scale (BWS), and all values fell in level 2 and 3, indicating good wind comfort level because of the BWS ≤ 3. This study highlights the significance of building models in determining wind flow patterns and velocity, which ultimately impacts PWC. Despite the study area involving multiple buildings with different shapes and detailing, the wind comfort levels were found to be suitable for pedestrians.

Systematization of spatial functional layouts and pedestrian wind comfort assessment for an ultra-thin triangular free form shell structure

This paper aims to study various spatial functional layouts and test how these different design approaches affect pedestrian comfort under shell structures. The considered shell shape was developed aiming an efficient distribution of loads allowing prefabrication with ultra-thin concrete elements. As shell structures can define semi-exterior spaces and assume open locations within some urban contexts, the study of how different design strategies for the underlying space affect user's comfort is of upmost importance.Several wind tunnel tests were performed on a triangular thin shell scale model with a few different spatial user's area layouts allowing to understand to which extent some design decisions compromise pedestrian wind comfort. The experimental campaign follows an iterative process leading to conclusions that can guide future projects and contribute to a multidisciplinary and transversal understanding of these innovative structures.

Modeling the effects of urban form on ventilation patterns and traffic-related PM2.5 pollution in a central business area of Bangkok

Traffic-related PM exposure is a significant concern in several cities. This study used ENVI-met simulation to perform the airflow and PM2.5 dispersions in Bangkok's central business district during summer. The impact of urban forms and traffic pollution on airflow and PM2.5 distributions was assessed using correlation analysis. Results showed that during summer, road traffic contributed to urban PM2.5 concentrations. Sky view factor and road area significantly affected wind speeds and PM2.5 concentrations, and these two parameters positively correlated. High wind speeds and PM2.5 concentrations were found in the urban main road, while those levels in the areas far from the road dropped by 50% due to building obstacles. Large open spaces (high sky view factor) could improve wind speeds in inner-city areas by 63%. Based on wind and PM2.5 performance classification, this study introduced new performance-based zoning, including five subzones with design recommendations. Urban planners and architects can use this information to improve pedestrian wind comfort and control air pollution dispersion from road traffic.

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

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

Shape optimization during design for improving outdoor wind comfort and solar radiation in cities

This paper delivers an idea of weather-based optimization as a sustainable design strategy addressing the changing climate. An environment-driven design technique is introduced and tested at the urban and architectural scale. Utilizing the interplay between the architectural intention and weather influences (specifically solar radiation and wind effects), the optimal design solution for the urban configuration and architectural shape emerges. An exploratory case study near the amphitheater in Kosice, Slovakia, demonstrates the proposed approach. Through the real-time iterative analysis of the environmental performance of multiple design variants, an urban concept of offices/apartment blocks, reacting to the local wind and sun situation, is formed. The wind flow situation and comfort are investigated in a design loop, blending the newly developed AI-driven simulation prediction models of InFraRed11InFraRed: AI-based real-time analysis of wind, sun, and thermal comfort in the streets developed by the CIL of the AIT in Vienna, Austria. and the sun hours analysis in Ladybug with the Galapagos optimization within Grasshopper. The final step of this method is the design and subsequent wind and sun analysis of fluid-shaped lamellae in three variants acting as wind catchers/shading systems. Improved pedestrian wind comfort for outdoor sitting (more than 30% increase in areas suitable for short and prolonged sitting) and optimum sunlight hours (25% gain in sunlight during winter solstice) is achieved using the proposed technique.

Pedestrian Wind Comfort Assessment Using Computational Fluid Dynamics Simulations With Varying Number of 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.

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

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

Mean Wind Velocity Distribution at Near-ground Level Obtained Through Field Measurements

Mean wind velocity profiles enable researchers to conduct efficient and accurate analyses of a wide variety of urban microclimatic problems, such as pollution dispersion, heat island effect and pedestrian wind comfort. However, due to the heterogeneity in the complex urban context, the wind profile at near-ground level within the real urban context remains insufficiently investigated. The present study aims to measure the near-ground level mean wind profiles in an industrial park. To this practical end, a sonic anemometer was equipped to a height adjustable bar on a mobile measurement platform. Through adjusting the sonic anemometer’s height, the mean wind velocities at different heights of the near-ground level were measured. Results indicate that the mean wind velocities’ variation along the near-ground heights measured at the site exposed to open and flat upwind areas can be reasonably captured by the power-law profile, while the other two conventional profiles, i.e. the log-law and the exponential profiles, show different levels of inaccuracy.

Comparing the Role of High-Rise Building Form in Improving Pedestrian Wind Comfort Andreducing Wind Velocity by CFD Simulation

Comparing the Role of High-Rise Building Form in Improving Pedestrian Wind Comfort Andreducing Wind Velocity by CFD Simulation

THE IMPACT OF LEVEL OF DETAIL IN 3D CITY MODELS FOR CFD-BASED WIND FLOW SIMULATIONS

Abstract. Climate change and urbanization rates are transforming urban environments, making the use of 3D city models in computational fluid dynamics (CFD) a fundamental ingredient to evaluate urban layouts before construction. However, current geometries used in CFD simulations tend to be built by CFD experts to test specific cases, most of the times oversimplifying their designs due to lack of information or in order to reduce complexity. In this work we explore what are the effects of oversimplifying geometries by comparing wind simulations of different level of detail geometries. We use semantic 3D city models automatically built and adjust them to their suitable use in CFD. For the first test, we explore wind simulations within a troublesome section of the TUDelft campus, the passage next to the EWI building (the tallest building in our domain), where the use of 3D city model variants show how differences in geometry and surface properties affect local wind conditions. Finally we analyze what these differences in velocity magnitude could mean for practitioners in terms of pedestrian wind comfort.

Aerodynamic characteristics of tall buildings with porous double-skin façades: State of the art and future perspectives

Double-skin facades (DSFs) have been increasingly implemented on tall buildings with the goal of improving building energy efficiency, natural ventilation and visual appearance. It is commonly known that wind and earthquakes represent major environmental load types impacting tall buildings. However, at this point, the aerodynamic characteristics of tall buildings equipped with porous facades are still relatively unknown, although it may be expected that the addition of porous outer skins will substantially affect the overall building aerodynamics. The scope of the present study is therefore to carefully review all the relevant parameters playing an important role in the aerodynamic characteristics of tall buildings with porous facades. Fluid flow and turbulence through porous surfaces were reviewed first with an emphasis on the wake and pressure drop behind perforated plates to analyze the phenomena of fundamental fluid mechanics relevant for porous surfaces. As the inflow characteristics predominantly dictate the aerodynamic characteristics of tall buildings, it is therefore useful to review major wind types, including the atmospheric boundary layer (ABL) and strong local winds, which have previously proved to cause major structural damage and failure. In order to be able to properly assess the aerodynamic loading of tall buildings with porous facades, it is necessary to understand the aerodynamic features of tall buildings with smooth surfaces. For this reason, the aerodynamic performance of smooth tall buildings was reviewed, as were the design features commonly adopted to mitigate adverse wind effects. The existing and rather sparse current knowledge of the aerodynamic characteristics of porous DSFs of high- and low-rise buildings is outlined. Based on the provided information, it is clear that a substantial amount of knowledge still needs to be acquired in the future in regard to various aerodynamic features of tall buildings with porous DSFs, particularly concerning wind loads, building energy efficiency, pedestrian wind comfort, renewable energy aspects, air pollution dispersion and dilution. It is expected that the optimal approach to advancing this topic is in combining field measurements, laboratory experiments and computational modeling.

Validation of a CFD model for the evaluation of urban microclimate at high latitudes: A case study in Trondheim, Norway

The urban microclimate is a rapidly evolving field of research gaining increasing interest from public authorities and researchers. However, studies at high-latitude cities are scarce and researchers primarily focus on summerly overheating. This study focuses on the validation process of a CFD model that applies the 3D URANS approach with the realisable k-ε turbulence model at a highly complex urban area in Trondheim, Norway (63.4° N) during autumn. The CFD model features a polyhedral grid of the urban environment, including geometrically explicitly modelled buildings and trees in the area of interest. Furthermore, solar radiation, longwave radiation exchange, heat transfer from the buildings, heat storage in the urban surface, and the thermal effects of evapotranspiration from trees and grass surfaces are considered. The CFD model is validated with experimental results from a network of five mobile and one reference weather stations in the study area, providing hourly-averaged measurements for wind speed, wind direction (only reference weather station) and air temperature for two 48-h periods from September 27–28 and October 19–20. The results show that the CFD model is well able to reproduce the measured conditions at the area of interest with a mean R2 of 0.60, 0.63, and 0.96 for wind speed, wind direction and air temperature, respectively, at the reference weather station. It will be used in future studies, including the analysis of the impact of urban microclimate on buildings’ energy performance, outdoor thermal and pedestrian wind comfort.

Lattice Boltzmann Method-Based Simulations of Pollutant Dispersion and Urban Physics

Mesocale atmospheric flows that develop in the boundary layer or microscale flows that develop in urban areas are challenging to predict, especially due to multiscale interactions, multiphysical couplings, land and urban surface thermal and geometrical properties and turbulence. However, these different flows can indirectly and directly affect the exposure of people to deteriorated air quality or thermal environment, as well as the structural and energy loads of buildings. Therefore, the ability to accurately predict the different interacting physical processes determining these flows is of primary importance. To this end, alternative approaches based on the lattice Boltzmann method (LBM) wall model large eddy simulations (WMLESs) appear particularly interesting as they provide a suitable framework to develop efficient numerical methods for the prediction of complex large or smaller scale atmospheric flows. In particular, this article summarizes recent developments and studies performed using the hybrid recursive regularized collision model for the simulation of complex or/and coupled turbulent flows. Different applications to the prediction of meteorological humid flows, urban pollutant dispersion, pedestrian wind comfort and pressure distribution on urban buildings including uncertainty quantification are especially reviewed. For these different applications, the accuracy of the developed approach was assessed by comparison with experimental and/or numerical reference data, showing a state of the art performance. Ongoing developments focus now on the validation and prediction of indoor environmental conditions including thermal mixing and pollutant dispersion in different types of rooms equipped with heat, ventilation and air conditioning systems.

Influence of geometry acquisition method on pedestrian wind simulations

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 by Computational Fluid Dynamics (CFD) simulations. When performing wind simulations, the quality of the geometry model is essential. Still, no available studies examine different geometry inputs' impact on the wind flow through an urban environment. This study investigates the influence of the building geometry acquisition method on the simulated wind field in an urban area, focusing on the application of pedestrian wind comfort. A suburban area in the west coast of Norway was chosen as a case study. Four building model types were produced and used in the simulations for comparison. The simulations using a building model produced from data stored in the national general feature catalog (FKB) in Norway showed minor differences to the simulations using more detailed and accurate models based on remote sensing measurements. Prominent variations were seen using a model based on the extrusion of the building footprint. A greater understanding of the geometry acquisition method's influence may enable more efficient pedestrian wind comfort studies that recognize the uncertainty of different geometric model use in urban wind simulations.

A robust metamodel-based optimization design method for improving pedestrian wind comfort in an infill development project

Constructing a new building inevitably modifies the microclimate in its vicinity. We propose a metamodel-based optimization method to devise near optimal designs that minimize building’s adverse impacts on nearby pedestrians’ wind comfort in hot and cold seasons. Four design parameters, i.e., building width, building depth, building height, and building orientation, are considered for a greatly simplified building design task. Specifically, computational fluid dynamics (CFD) analyses are performed to calculate the mean wind velocity, while all CFD experiment samples are determined through the Box-Behnken design of experiment method. Based on 54 CFD experiments, the relationships between building design variables and the summer and winter mean wind velocities within a specified assessment area are learned using the response surface methodology. Finally, a genetic algorithm with the desirability function as the objective function is applied to identify near optimal design options under the robustness control (i.e., family error rate λ) for response surface models. The framework is applied to an infill development project to highlight its suitability in a real application. The experiment results show that as λ gradually decreases from 1 to 0.05, the overall desirability index dwindles from 0.33 to 0.22, consequently generating a more conservative optimal design decision.