Wind Nuisance Research Articles

Efficient Quality Diversity Optimization of 3D Buildings through 2D Pre-optimization.

Quality diversity algorithms can be used to efficiently create a diverse set of solutions to inform engineers' intuition. But quality diversity is not efficient in very expensive problems, needing 100.000s of evaluations. Even with the assistance of surrogate models, quality diversity needs 100s or even 1000s of evaluations, which can make it use infeasible. In this study we try to tackle this problem by using a pre-optimization strategy on a lower-dimensional optimization problem and then map the solutions to a higher-dimensional case. For a use case to design buildings that minimize wind nuisance, we show that we can predict flow features around 3D buildings from 2D flow features around building footprints. For a diverse set of building designs, by sampling the space of 2D footprints with a quality diversity algorithm, a predictive model can be trained that is more accurate than when trained on a set of footprints that were selected with a space-filling algorithm like the Sobol sequence. Simulating only 16 buildings in 3D, a set of 1024 building designs with low predicted wind nuisance is created. We show that we can produce better machine learning models by producing training data with quality diversity instead of using common sampling techniques. The method can bootstrap generative design in a computationally expensive 3D domain and allow engineers to sweep the design space, understanding wind nuisance in early design phases.

Numerical evaluation of pedestrian-level wind and indoor thermal comfort of a historical monument, Muğla, Turkey

PurposeThe study aims to analyze both thermal and wind comfort conditions of a historical mosque's interior and outdoor spaces for the planning of further conservation decisions.Design/methodology/approachThe method is composed of two steps. First, thermal comfort analyses are conducted via Design-Builder Software. The predicted mean vote (PMV) and predicted percentage of dissatisfied indices were calculated and evaluated using the ASHRAE 55–2010 standard. Thermal comfort conditions are analyzed with the proposed three operations. Second, wind comfort analyses are conducted via computational fluid dynamics (CFD) software. Outdoor thermal comfort conditions are predicted by air temperature, mean radiant temperature, wind speed and relative humidity.FindingsThe (PMV) in the harim was calculated as −1.83 (cool) which corresponds to a predicted percentage of dissatisfaction (PPD) equal to 68.54%. Thermal comfort was provided by daytime and continuous operations; however, intermittent operations did not provide thermal comfort. The wind velocities around the mosque are well below the 5 m/s limit value for standing defined by NEN 8100 wind nuisance standard. Moreover, the limit value of 2.5 m/s for sitting was also satisfied with more than 80% of the semi-enclosed area around the entrance of the mosque. Last comer's hall remains in a slight cold stress range, the rest of the areas have no thermal stress.Originality/valueThis two-stage study creates a base for further improvements to provide comfort conditions in a historical building without interfering with its original features.

CFD simulations of wind flow and mean surface pressure for buildings with balconies: Comparison of RANS and LES

Façade geometrical details can substantially influence the near-façade airflow patterns and pressures. This is especially the case for building balconies as their presence can lead to multiple separation and recirculation areas near the façades and hence large changes in surface pressure distribution. Computational fluid dynamics (CFD) has been widely used to investigate the impact of building balconies, mainly based on the steady Reynolds-averaged Navier-Stokes (RANS) approach. The objective of the present study is to evaluate the performance of steady RANS and large-eddy simulations (LES) in predicting the near-façade airflow patterns and mean surface pressure coefficients (Cp) for a building with balconies for three wind directions θ = 0°, 90°, 180°, where 0° is perpendicular to the façade under study. The evaluation is based on validation with wind-tunnel measurements of Cp. The results show that both RANS and LES can accurately predict Cp on the windward façade for θ = 0° with average absolute deviations of 0.113 and 0.091 from the measured data, respectively. For the other two wind directions, LES is clearly superior. For θ = 90°, the average absolute deviations for RANS and LES are 0.302 and 0.096, while these are 0.161 and 0.038 for θ = 180°. Large differences are found in the computed flow fields on the balcony spaces. Because RANS systematically underestimates the absolute values of both Cp and mean wind speed on the balconies, it is suggested that building design based on RANS might result in excessive ventilation and in too high wind nuisance level.

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

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

Introducing the urban wind island effect

Wind is a key component of the urban climate due to its relevance for ventilation of air pollution and urban heat, wind nuisance, as well as for urban wind energy engineering. These winds are governed by the dynamics of the atmosphere closest to the surface, the atmospheric boundary layer (ABL). Making use of a conceptual bulk model of the ABL, we find that for certain atmospheric conditions the boundary-layer mean wind speed in a city can surprisingly be higher than its rural counterpart, despite the higher roughness of cities. This urban wind island effect (UWI) prevails in the afternoon, and appears to be caused by a combination of differences in ABL growth, surface roughness and the ageostrophic wind, between city and countryside. Enhanced turbulence in the urban area deepens the ABL, and effectively mixes momentum into the ABL from aloft. Furthermore, the oscillation of the wind around the geostrophic equilibrium, caused by the rotation of the Earth, can create episodes where the urban boundary-layer mean wind speed is higher than the rural wind. By altering the surface properties within the bulk model, the sensitivity of the UWI to urban morphology is studied for the 10 urban local climate zones (LCZs). These LCZs classify neighbourhoods in terms of building height, vegetation cover etc, and represent urban morphology regardless of culture or location. The ideal circumstances for the UWI to occur are a deeper initial urban boundary-layer than in the countryside, low-rise buildings (up to 12 m) and a moderate geostrophic wind (∼5 m s−1). The UWI phenomenon challenges the commonly held perception that urban wind is usually reduced due to drag processes. Understanding the UWI can become vital to accurately model urban air pollution, quantify urban wind energy potential or create accurate background conditions for urban computational fluid dynamics models.

The investigation of the function of the central courtyard in moderating the harsh environmental conditions of a hot and dry climate (Case study: City of Yazd, Iran)

As one of the arid areas of Iran, Yazd is always exposed to extreme winds with dust and shifting sands. Therefore, the architectural principles in the residential architecture of the city need be adapted to such environmental conditions in order to minimize the influence of the severe winds on the interior spaces. This study investigates the influence of storms on the interior space of the central courtyards in Yazd, constructed during the Muzaffarid, Safavid and Qajar periods using CFD simulation. Three-dimensional models were prepared via Gambit software and studied in Fluent software. The wind speed entering the computing field was equal to 26.4m/s and the Dutch wind nuisance standard NEN 8100 was applied as the comfort criterion. The results showed a relationship between the extent of the central courtyard and the impact of severe storms on it, since an increase in the area of the courtyard provides enough space for the wind flow and move around it. This feature reaches its climax if the length to height proportion increases, as the wind brings the shifting sands into large courtyards, therefore, the architects tried to provide better conditions by creating microclimates.

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

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

CFD evaluation of new second-skin facade concept for wind comfort on building balconies: Case study for the Park Tower in Antwerp

High wind speed around high-rise buildings can lead to wind discomfort or wind danger at building balconies. This paper presents the evaluation of a new facade concept that is intended to significantly reduce the wind speed and therefore improve wind comfort on the balconies of high-rise buildings. The concept consists of a staggered semi-open second-skin facade in front of the balconies, which partly shields them from the wind. The concept is evaluated for the new 78 m high Park Tower in the urban area of Antwerp, where it will be implemented. 3D steady Reynolds-averaged Navier–Stokes Computational Fluid Dynamics (CFD) simulations are performed for the case with and without this facade concept. The simulations are made with the realizable k–ε turbulence model on a high-resolution grid. Validation is conducted using wind-tunnel measurements of surface pressure distribution on a building model with balconies. Wind comfort for the Park Tower is assessed with the Dutch wind nuisance standard NEN8100 for the case with and without the second-skin facade concept. The analysis shows that this concept is effective in providing a zone with pressure equalisation at the balconies. The related reduction in pressure gradients across the width of the facade strongly decreases the local wind speed. At many positions along the balconies this yields a wind comfort improvement of one or even two classes in the Dutch wind nuisance standard compared to the situation without implementation of this concept.

CFD Simulation for Wind Comfort and Safety in Urban Area: A Case Study of Coventry University Central Campus

Concern towards the quality of public urban areas has increased in recent years. Wind comfort and safety in pedestrian areas has become one important environmental parameter when designing new cities. Hence, architects and town planners need guidelines and simplified design tools to take account of the wind in their projects. The objectives of this study provide more insight in the pedestrian living conditions around the Hub, a newly built structure, part of Coventry University campus and at the same time study the influence of building shapes on the wind distribution. The latter is based on a series of computational fluid dynamics simulations (CFD), used to advise the University's Estates Department of the possibility of wind nuisance around the central campus area. The velocity field was computed using the finite volume method. The simulations were performed for dierent wind speeds and directions. The predicted results showed that the distribution of the velocity field varied and had dierent characteristics with dierent wind directions. Also, it was established that the wind speed amplification factors in diverging passages were generally larger than those in converging passages. The case study incorporated is intended to support and guide future studies of wind comfort and safety with CFD and thus makes a modest contribution in improving wind environmental quality in urban areas.

Pedestrian wind comfort around buildings: Comparison of wind comfort criteria based on whole-flow field data for a complex case study

Assessment of pedestrian wind comfort around buildings requires the combination of wind statistics from a meteorological station, aerodynamic information and a comfort criterion. A wide range of different comfort criteria exist. In the past, several comparison studies of comfort criteria have been made. In the present paper, a different approach is pursued. The goal of this paper is threefold: (1) to provide an illustrative case study based on CFD as a framework for the comparison of different criteria; (2) to compare and evaluate the results by the different criteria as part of a complete wind comfort assessment study; and (3) to stress the importance of standardization of the wind comfort assessment procedure. The case study area is the campus of Eindhoven University of Technology. The 3D steady Reynolds-averaged Navier–Stokes (RANS) equations and the realizable k–ɛ model are used to provide part of the aerodynamic information. The CFD simulations are performed on a high-resolution grid based on grid-sensitivity analysis. Validation is conducted with on-site measurements. Part of the wind comfort assessment procedure is performed with the Dutch wind nuisance standard NEN 8100. The criteria compared in this study are the four complete criteria by Isyumov and Davenport (1975), Lawson (1978), Melbourne (1978) and NEN 8100 (2006). It is shown that the different criteria can lead to very different conclusions about the wind comfort. Because the outcome of wind comfort studies is often decisive in granting building permits, this illustrates the importance of wind comfort standardization, in particular concerning the comfort criterion.

Pedestrian wind comfort around a large football stadium in an urban environment: CFD simulation, validation and application of the new Dutch wind nuisance standard

Three-dimensional steady Reynolds-averaged Navier–Stokes (RANS) Computational Fluid Dynamics (CFD) simulations are used in combination with the new Dutch wind nuisance standard to assess pedestrian wind comfort around a large football stadium in Amsterdam, before and after the addition of new high-rise buildings. The focus of the study is on the elevated circulation deck and the surrounding streets and squares. CFD validation is performed by comparison of the simulated mean wind speed at the deck with full-scale measurements. The important effect of local ground roughness specification on the simulated wind speed values is indicated. Application of the Dutch wind nuisance standard shows that wind comfort at the elevated circulation deck is only slightly influenced by the new buildings. Wind comfort at the surrounding streets and squares however significantly deteriorates. Finally, the results obtained by the Dutch wind nuisance standard are compared to those obtained by a more simplified procedure for the transformation of wind statistics to the building site, as used in earlier studies. The more sophisticated transformation procedure in the Dutch standard was successfully validated based on full-scale measurements in earlier research. Comparison of the Dutch standard results in this study with those of the simplified procedure shows that the latter provides overestimations by up to 25% for the highest discomfort probabilities. This type of large discrepancies can significantly change the outcome of wind comfort studies.

KnoWind: a database-oriented approach to determine the pedestrian level wind environment around buildings

High buildings generally have an adverse effect on the wind conditions in their immediate vicinity, sometimes giving rise to dangerous wind conditions. So far, the whole issue is hardly considered in the design stage since there are no easy tools available for use by designers. To fill this gap, a user-friendly database-oriented computer programme has been developed, called KnoWind, with which the pedestrian level wind environment around buildings can be determined easily, provided that the windclimate of the country considered is available. Complex building configurations must be schematised to their main dimensions. The roughness of the environment of the building under consideration is taken into account, but not adjacent buildings. With remarkable accuracy, the programme can be used to predict the potential wind nuisance and wind danger around buildings in simple and even complex situations, provided that the building under consideration is higher than the surrounding buildings. The user-friendly set-up, the simple input and the fast calculations make the programme suitable as a tool for laymen in the field of wind engineering and for quick scans of potential wind problems.

Building wake effects in complex situations

The recently prepared ‘Handbook on Obstacle Wake Effects related to Wind Turbine Siting’ [1] offers an opportunity, when combined with results of windtunnel tests, to estimate the effect of a newly projected building on the local wind climate at pedestrian level around it. This could be of great importance in order to establish already in the early design stage the possibly negative effects a building might cause, and to gain insight into the necessity and possibility of wind protecting means. This presentation explains the prediction method for wind nuisance for pedestrians and the assumptions behind the method.

A topographical study to investigate wind nuisance

Selected results of a small-scale wind tunnel investigation into the characteristics of the boundary layer influenced by a dominant topography are presented. The investigation has shown that the severe wind conditions experienced in a city centre approached by this boundary layer are due to an unfortunate combination of several factors.