key: cord-353325-41ke6vor authors: Mittal, Hemant; Sharma, Ashutosh; Gairola, Ajay title: A review on the study of urban wind at the pedestrian level around buildings date: 2018-07-31 journal: Journal of Building Engineering DOI: 10.1016/j.jobe.2018.03.006 sha: doc_id: 353325 cord_uid: 41ke6vor Abstract Urbanization is leading towards the change of local wind climate in the vicinity of tall buildings, which influences the pedestrian level wind environment to an uncomfortable or even dangerous level. Therefore nowadays, building design should not be limited only for the consideration of wind load and indoor environment, but outdoor wind environment should also be considered. This study presents a review of the methods for the assessment of pedestrian level wind climate, different wind comfort criterion and various techniques to evaluate the wind speed at the pedestrian level. In later sections, brief review for the influence of different parameters related to building design and configuration on pedestrian level wind is presented. After analyzing previous literature it is suggested that there is a strong need for the homogenization of different wind comfort criterion, as it may lead to different consequences for the architects. Among various wind tunnel measurement techniques, use of Irwin probe is simple and accurate compared to hot-wire anemometry and it can be installed at numerous locations for simultaneous measurement of pedestrian level wind speed. For numerical simulation, Reynolds Averaged Navier Stokes based technique has been used by various researchers, although this technique is not accurate as much as large eddy simulation and detached eddy simulation. But this technique is cost effective and requires less computing resources. The socio-economic growth of a nation is majorly driven by urbanization, as it accommodates the increased demand for business and residential space. As an evidence of the current scenario, many cities of developed and developing nation like Japan, Hong-Kong, China, Malaysia, and India are moving towards the construction of cohesive skyline structures or mega tall buildings. On contrary to these advancements, mega tall buildings in the urban area affect the surrounding wind flow pattern and pedestrian level wind (PLW) comfort. Presence of tall building in the urban area tends to deflect the upper-level high-speed wind to the ground, which creates conditions that could be unpleasant or even dangerous to pedestrians. There are many such incidents which are reported due to strong winds. But nowadays modern megacities are packed with the high density of high rise buildings, which influences the air movement. The reduced air movement at pedestrian level causes weak natural ventilation and allow the pollutants to be accumulated at ground level which increases air pollution. Such wind conditions are persistent in Hong Kong, Tokyo and New Delhi [1] . Many causalities have been reported due to the accumulation of air-borne SARS virus (Severe Acute Respiratory Syndrome) because of low wind speed zone at a building site in Hong Kong [2] . So it is inevitable to assess wind condition for pedestrian level comfort in the view of low wind speed as well as strong winds near buildings corners. Many urban authorities have made it is essential to study the pedestrian level wind environment for large urban projects during initial design stage [3] [4] [5] [6] . Initially, studies related to PLW speed measurement had been conducted with on-site field measurement. As it is not viable to conduct full-scale testing for the initial design of a building project site, so wind tunnel measurements on the scaled model make it feasible to investigate the effect of changes in building design at the initial stage of the urban project. During early days, wind tunnel measurement for PLWs was conducted with hot wire or film anemometry at limited measurement points [7] [8] [9] [10] . Later on, Irwin [11] devised a simple omni-direction probe for PLW speed measurement. In which pressure difference between tubes at scaled pedestrian height and surface of the tunnel is calibrated with the corresponding velocity. Recently the use of Irwin probes has been paced up due to the availability of high precision simultaneous pressure measuring sensor. Further, the use of sand erosion technique for such studies is limited as it provides qualitative information over the whole area under investigation [12] . There are other measuring techniques which have been used to evaluate PLW speed such as laser Doppler anemometry (LDA), particle image velocimetry PIV, Infrared thermography and thermistor anemometry. Computational fluid dynamics (CFD) technique is also becoming a viable tool for PLW studies with the advent of high-performance computational resources. Till now steady Reynolds averaged Navier-Stokes (RANS) modelling approach was used successfully which requires less computing cost and time. But this technique is less accurate for predicting the flow in low wind speed region (deviation up to 5 times) as compared to other high-cost techniques such as LES and DES. The present study comprehensively reviews the urban wind at the pedestrian level around buildings. The content of this paper is organized as follows: the second section presents the method for the assessment of PLW climate with different wind comfort criteria. The third section describes the different techniques to evaluate the pedestrian level winds. The fourth section reviews effect of the various parameter related to building design on PLW for generic building configuration. The last section presents different studies related to the actual urban environment, which comprises the effect of building design parameters and general guidelines for the urban planning in response to pedestrian comfort. The procedure for the assessment of favourable wind climate to pedestrians is comprised of (1) Statistical meteorological data of nearby weather station; (2) Aerodynamic information of the area and (3) Mechanical wind comfort criteria [13] . The aerodynamic information helps to compute the statistical data at particular building site obtained from the weather station. Then transformed data at this location is compared to wind comfort criterion. This procedure is schematically depicted in Fig. 1 . Meteorological data from weather station consist of hourly mean wind speed (U ms , measured at 10 m height) and wind direction in open terrain ( = y m 0.03 meteo 0, ). This wind speed data obtained from weather station is analyzed statistically using Weibull distribution function [14] [15] [16] to calculate the probability of exceedance of threshold wind speed as following Eq. (1). Where > P U ( )represents the exceedance probability of the wind speed; U is the mean wind velocity magnitude at building site; c is the dispersion parameter and k is the shape parameter. These constants are obtained by fitting Eq. (1) to the meteorological data. Then statistical information has to be transformed to the area of interest by the means of aerodynamic information using amplification factor R (Eq. (2)). This amplification factor consists of design related contribution and terrain related contribution (Eq. (3)) [16] . The design related contribution comprises of modification of statistical wind climate information due to local building design. These modification can be obtained by either wind tunnel measurement or using CFD simulation. The whole research community in this area is devoted to evaluate the design related modification. The terrain related modification accounts for the differences in terrain roughness between the weather station and area of interest [17] and can be obtained using Eq. (4) and Eq. (5). Where U 0 is the reference wind speed at certain distance upstream of area of interest or without the presence of building or at the inlet of computational domain; u* site and u * meteo are the friction velocity at building site and meteorological station respectively; y site 0, and y meteo 0, are the aerodynamic surface roughness length at building site and meteorological station respectively. The dependency of the probability of exceedance and amplification factor R is given by Eq. (6) [16] . In wind comfort assessment, besides the wind speed, the frequency of its occurrence also matters. Therefore the criteria for wind comfort involves threshold wind speed above which pedestrian will feel discomfort and its frequency of occurrence. A wide variety of wind comfort criterion, based on threshold mean wind speed and the probability of exceedance has been proposed earlier [14, 15, [18] [19] [20] [21] [22] [23] . Details of different wind comfort criterion are shown in Fig. 2 , in which threshold mean wind speed (m/s) for different activities and its corresponding exceedance probability (%) is presented. Most of the criterion is based on the same probability of exceedance and different threshold wind speed for different pedestrian activities. While NEN 8100 [23] considers same threshold mean wind speed and different exceedance probability. The comparison of different wind comfort criterion for different activities is shown in Fig. 2 , in which typical wind climate for Indian city (Palam Airport, New Delhi) is represented. It can be identified that, based on comparison with mentioned wind comfort criteria except by Melbourne, (1978) [14] , this place is vulnerable to high wind speed, which causes danger to pedestrians. Since most of these criterion reports different threshold mean wind speed and exceedance probability, so it is difficult for developers, architects and planners to choose a general guideline on comfort criterion. With regard to this, various comparative assessments of wind comfort criteria have been proposed. Based on discussion with developers and building managers, Soligo et al. [20] converted the different wind comfort criteria on the same scale of frequency of occurrence (20%) or for a particular activity. Janssen et al. [24] also focused on the standardization of different wind comfort criterion. However, all of the above-discussed criteria did not consider pedestrian discomfort due to weak wind conditions for the densely-built urban areas. Du et al. [25] proposed the wind comfort criteria for the urban areas of poor wind conditions such as Hong Kong, where the wind comfort becomes worst in hot and humid season. In this criterion overall mean velocity ratio (OMVR) is used as threshold parameter (Table 1) , which represents the integration of direction values of mean velocity ratio ( = MVR U U / P r ), Where U P is wind velocity at pedestrian level and U r is wind velocity measured at 200 m height. To obtain design related contribution for the assessment of pedestrian level wind environment, generally field measurement on the real urban environment, wind tunnel testing on the scaled model of the urban area and CFD simulation are employed. But to make changes in the early design stage, it is not possible to conduct field measurement for urban developmental projects. The following sections describe the details of each method and comparison based on the accuracy of each method. This technique is regarded as a robust method to evaluate wind speed at limited points and was used successfully by several researchers [26] [27] [28] [29] [30] . Generally, a portable three cup-anemometer with wind vane system is used for this purpose. This instrument has very low onsetspeed of 0.1 m/s and light in weight [28] . The output of this instrument is in the form of one electrical pulse per revolution of the rotor and this pulse rate is calibrated against the wind speed. A comparison of this technique with others is provided in the later section. In wind tunnel, the PLW measurements are conducted by using hotwire/film anemometry (HWA, HFA), Irwin probes, thermistor anemometer, sand erosion, laser Doppler anemometry (LDA), infrared thermography, and particle image velocimetry (PIV). Each of the mentioned technique is based on different working principle and unique experimental setup. Since it is beyond the scope of this paper to discuss the working principle of each technique, only their application and capability is discussed in Table 2 . To simulate PLW environment, CFD methods are gaining much popularity among researchers and industrialists recently owing to the development of the computer hardware and software. One of the major advantages of CFD over wind tunnel testing is that it gives detailed flow field data of associated parameters over the entire computational domain. In addition, similarity law requirements associated with wind tunnel testing is not a limitation of CFD simulation. Most of the studies, to simulate wind environment are based on the use of different RANS turbulence models e.g. Std. − k ε, Realizable − k ε and RNG − k ε model with default values of model closure coefficients in CFD tools. However, the major issue for the acceptance of CFD results is related to the accuracy, which suffers badly in predicting the flow on leeward side of building. Therefore CFD simulation results require verification and validation [40] . Zahid Iqbal et al. [2] mentioned that the simulation results for PLW speed obtained by std. − k ε are also affected for different model closure coefficients. Table 1 Wind comfort criteria based on overall mean velocity ratio (OMVR) representing weak wind conditions by [25] . Threshold Velocity (Jun-Aug) Threshold Velocity (Dec-Feb) Exceedance Probability (%) Activity Remark The accuracy of CFD simulation largely depends on the selection of turbulence model. The capability of each turbulence model and their accuracy is discussed in Table 3 . To evaluate PLW environment on existing project site, it is suitable to conduct field measurements. But to assess the effect of changes in the initial design of developmental projects, wind tunnel measurements are preferred. Comparison of these techniques is generally associated with practical difficulties such as variability inherent to the atmospheric phenomena, obstructions due to automobiles etc. Isyumov and Davenport [26] obtained full-scale and wind tunnel measurement for mean wind speed at a site project in Toronto, Canada. They reported the agreement between full-scale and wind tunnel measurement within 10% for windy locations. Dye [28] compared the same in a sheltered urban area and found that wind tunnel test generally underpredicts the mean speed of 20% at most severe locations. While Visser et al. [30] reported the comparison of these two techniques to be dependent on the duration of full-scale data measurement, as the wind speed data of longer period will agree well with the model test. The use of CFD technique provides entire flow field data, whereas field measurement can be performed for few location only. However, it is a challenging task to simulate wind environment using CFD techniques accurately. Blocken et al. [6] compared the results of CFD simulation at a university campus. The simulation was performed using a realizable − k ε model with standard wall function and field measurement was performed with 3D ultrasonic anemometers. The authors clearly indicate that the short term measurement for few hours cannot serve as a validation data because the data suffers from intrinsic variability of meteorological conditions. Large deviation of 25% between measured and simulated mean wind speed was reported at the locations where the gradient of wind speed is high. In addition, the comparison of the wind speed in the regions of high gradients can yield large deviation by a small shift in location. The CFD technique has attracted wide acceptability and strong support due to the establishment of several best practice guidelines [75] . Wind tunnel testing is often used to benchmark CFD models and simulation results. The use of RANS was found to provide quite accurate results for wind speed ratio, however, it significantly underestimates wind speed in the regions of lower wind speed ratios [6] . A possible [33, 34] . HFA [7, 9, 13, 26, [35] [36] [37] [38] Pros: less susceptible to fouling and fragility, easy to clean, shorter sensing length, The agreement between wind tunnel and fullscale measurement is within 10% [26] . Cons: Intrusive technique, only suitable for moderate turbulence intensity, insensitive to direction changes. LDA [37, 39] Pros: Non-intrusive point-wise technique, allows measurement of high-turbulence intensity and calibration is not required. [40] Cons: This technique is costlier than HFA and HWA. Infrared thermography [10, 32, 37] Pros: Non-intrusive Area technique, RMS, peak and spectrum value can be measured [37] Cons: Due to convection wind flow gets disturbed, sturdy and non-standard experimental set-up. No perfect correlation is obtained for temperature drop and wind speed [10] PIV [41, 42] Pros: Non-intrusive area technique, high spatial resolution and directional sensitivity. Cons: Very expensive, sometimes dangerous, laser light shielding and reflection from buildings, not suitable for the cluster of buildings. Erosion Technique [12, 34, [42] [43] [44] [45] Pros: Area technique, results are comparable to HWA for high wind speed [12] . For high turbulent flow, this technique agrees well with PIV measurements of mean wind speed [42] . Cons: It is non-quantitative technique and difficult to ensure the repeatability. [3, [46] [47] [48] [49] [50] Pros: Allows measurements at numerous locations. No re-alignment for different wind direction. Simple in design and easy to operate [11] . Cons: Less accurate for high turbulence intensity, it cannot accurately measure wind speed below 1.5 m/s [47] . Thermistor Anemometer [51] Pros: Small sensor size, susceptible to wind direction. The simple circuitry and low cost of thermistors make it economically feasible to operate the probes in large numbers. Cons: Only suitable for mean velocity measurements, fragile, require alignment for change in wind direction; nonlinear calibration of velocity. Use of different CFD technique by various authors and their pros. and cons. Std. − k ε [2, 44, [52] [53] [54] [55] [56] [57] [58] Pros: Computationally efficient and economically viable. Agreement with wind tunnel measurement of wind speed is within 10% for regions with high wind speed ratio ( [59] Cons: Underestimates wind speed notably five times or more for low wind speed regions [59] . It cannot reproduce the reverse flow on the roof [60] and overpredicts turbulent kinetic energy in separated flows around windward corners of buildings [55] . Realizable − k ε [6, 17, 50, [61] [62] [63] [64] Pros: Sensitive to flow separation, reattachment and recirculation. For high wind speed region accuracy further improves as compared to std. − k ε model [17] . Cons: Less accurate compared to std. − k ε model for low wind speed region due to underestimation of TKE in the wake region [17] RNG − k ε [65] [66] [67] [68] Pros: For high wind speed region, accuracy improves as compared to std. − k ε model. [59] Cons: Less accurate compared to std. − k ε model for low wind speed region due to underestimation of TKE in the wake region [59] . LES [69] [70] [71] [72] Pros: Superiority of this method over steady RANS is clearly reported [60] . It can reproduce turbulence intensity and gustiness. Cons: Computationally very expensive as it requires more time and sensitive to many parameters such as sub-grid scale model, mesh resolution and time step size [73] . DES [67] Pros: Capable of producing similar results as LES with less computing time and lower mesh size. [74] Cons: Sensitive to parameters such as sub-grid scale model, mesh resolution and time step size and sampling time. [74] reason for high wind speed ratio is characterized by lower turbulence intensities and lower wind direction fluctuation, therefore better modelled by the statistically RANS approach. Richards et al. [44] adopted erosion technique to investigate the PLW environment downtown area of Auckland and compared erosion contour with CFD simulation using std. − k ε model. The authors observed the difference at the location of highest wind contours. Using CFD simulation, this location was immediately around the corner of the buildings, whereas the wind tunnel shows that the earliest erosion emanates from the corner and sweeps across the buildings. In past decade, various parametric studies related to the evaluation of pedestrian level wind environment around generic building configuration have been conducted, which considered the effect of building height, shape and pattern of a group of buildings. These studies are listed in Table 4 . In this section brief discussion about the effect of parameters related to the design of building configuration on pedestrian level flow is presented. As the height of building increases, the maximum wind speed ratio increases due to strong downwash effect, as taller building catches the more upper-level wind and directs it to pedestrian level. Hence it poses high wind speed conditions but improves near-field air ventilation conditions as shown in Fig. 3.(a) [35, 47, 51] . Whereas turbulence intensity is not influenced by height variation of building significantly [35] . Wider buildings increases the sheltering effect to the incoming wind, which enlarges the extent of low wind speed zone in the downstream side of the building. Changes in cross-section of the building, such as tapering, rounding, and corner cut improve the wind environment around the building corners, as it reduces the extent of high wind speed zone near building corners due to less deviation of separated flow in comparison to the square building as shown in Fig. 3(b) [8, 35] . But root mean square value of wind speed distribution remains unaffected due to corner modification [8] . Circular and polygon shaped cross-section of the building also tends to have better wind climate in terms of reduced high wind speed zone as compared to the square-shaped building due to reduced downwash [35] . Till now this modification is investigated in detail by Xu et al. [51] for various building models and it was proposed that the change of building width at one-third height from the ground, majorly influences the PLW environment. Whereas the use of permeable floor at midheight of the building reduces the extent of high wind speed zone. However, it does not lower the maximum wind speed ratio [39] , as this permeable floor provides a way for upper-level wind to pass through the building before reaching it to ground level. This design consists elevated main structure of the building from the ground by the central core and has a potential solution to improve wind conditions near the building. This design modification increases area averaged high wind speed ratio but decreases area averaged low wind speed zone on the leeward side of the building because of weak downwash [1, 3] . To illustrate the effect of this building design, numerical simulation using CFD software Ansys/Fluent 17.0 was conducted. The governing equations of the flow are 3D steady-state Reynolds-averaged Navier-Stokes with standard − k ε turbulence model. Numerical Simulation has been conducted using best practice guidelines [75] for pedestrian level wind flow. All the details related to CFD simulation is not included as it is beyond the scope of this paper. The result of this simulation is presented in Fig. 4 , which represent the contours of mean wind speed at pedestrian height for lift-up and conventional square buildings. The qualitative results of the present simulation are similar to the experimental study by Tse et al. [1] which shows high wind speed near the lift up area and further lower values of low wind speed as compared to conventional building design. Which helps in improving ventilation near the building In addition to this lift up area can be used for other purposes as the recreational area, parking, or shelter for pedestrians. Besides this, use of lift up building design is limited due to unacceptable or high wind speed zone near the lift-up area [76] . This unacceptable wind condition arises due to flow through openings of positive and negative pressure faces of the building. Podium structure creates a sheltering effect at pedestrian level wind flow near the building and results in undesirable low wind speed zone at pedestrian level [47] , as podium structure enhances the spatial extent of low wind speed zone near upstream and downstream of the building. In general podium structure is not recommended where the conditions for natural ventilation are required. Besides this, it is believed that podium structure is used to protect pedestrians from high wind speed. The orientation of two buildings such as side by side, parallel, angular (converging, diverging and perpendicular) creates an adverse effect on PLW speed differently as shown in Fig. 5 . When wind flow is perpendicular to the row of buildings, the windiest condition occurs in the upstream corners due to flow channelling and suppressed horseshoe vortices [31] . As the separation between the buildings increases, channelling effect gets minimized and flow tends to be independent of the further increase in separation. For the converging arrangement, the windiest condition occurs for narrowest passage and decreases further for higher passage width with its location moving further away in the downstream direction as shown in Fig. 6(a) . Whereas for diverging arrangement wind speed ratio is often more adverse than converging passage as it does not provide shelter to the wind [38] and its value decreases for higher passage width as shown in Fig. 6(b) . In urban design, different arrangements of building govern the microclimate of the urban area differently. But orientation and shape of buildings majorly helps to improve PLW climate. Several studies [2, 53, 56] propose the configuration with square central space with prevailing wind direction towards the windward opened side face offer better PLW environment. As this configuration can effectively contain the air flow movements. In the lower part of the hilly regions (below 500 m), wind profile gets twisted with large angles i.e. varying wind direction along the height, therefore wind-structure interaction in these conditions is different from interaction with the conventional profile. To investigate the effect of twisted wind flow on pedestrian level, Tse et al. [77] simulated such kind of twisted wind profile in boundary layer wind tunnel. The authors concluded that the spatial extent of low wind speed zone increases with the scattered type of flow conditions. The extent of low wind speed zone further increases with the increase of wind twist angle. The flow features around two parallel buildings were observed to be asymmetric. This section describes the general flow conditions around the actual complex urban area, the effect of various parameters affecting the PLW speeds. In addition, the methodology to assess the pedestrian comfort is discussed and lastly, the key factors for the design of urban development projects in response to pedestrian comfort are discussed. When high rise building is located upstream of the low-rise building, the wind tends to flow over low rise building. The presence of tall building at downstream position intercepts high-speed winds and redirects to ground level [70] . The wind conditions within space between tall buildings are accelerated due to so-called venturi effect, which results in high wind movement especially at pedestrian level [57] . Use of podium structure deflects the high wind to the upper level, thereby protects the pedestrian due to high-speed winds [47] . These are the common flow condition, which arises due to different building configurations in an urban area and can be depicted in Fig. 7 . The wind flow over the ground surface is mostly affected by roughness element and building configuration, e.g. width, height, the arrangement of buildings and its density. It is considered that an increase in building density reduces the wind velocity in an urban area due to increased friction near the ground [80] . Stathopoulos & Wu [46] investigated the effect of spatial density of street blocks and the relative height of buildings. The authors concluded that the wind speed along streets decreases with blockage ratio (R B describe the percentage of oncoming air flow captured by building block) and proposed a simplified relation for wind speed up ratio as given in Eq. (7) . They also concluded that, the maximum wind speed ratio increases with the height difference between reference and surrounding buildings. In addition to this Wu & Kriksic [4] reported that, the narrow streets and uniform building height results in low wind speed. Most of the studies related to PLW environment tackle the problem based on discrete point analysis [17, 24, 81] . In this method, wind speed is evaluated at discrete locations. Then this wind speed is compared to the suitable wind comfort criteria. But obviously, pedestrian wind environment varies spatially in an urban area. So this type of discrete analysis is not efficient to address the real needs of urban planner in design [66] . In order to improve assessment method, Shi et al. [66] proposed that the practical pedestrian wind comfort for urban planning design must be space-based. The authors defined two parameters to analyze the pedestrian wind, the spatially averaged wind V avg (Eq. (8)) and the maximum wind speed V max in a plane. In above equation a i is the proportion of i-th wind direction; V j is the wind speed in j-th mesh grid; n is the total number of mesh grid in the plane. The above calculated wind speed should be within the specified limit defined in comfort criteria. To achieve better outdoor pedestrian comfort, there are following considerations which needs to be incorporated while designing urban area. (1) For hot and humid climate, the streets should be aligned parallel to the prevailing wind direction to remove accumulated pollution and improved air movements [4] . (2) In low wind speed and high-temperature areas, use of lift up building design [3] and a cluster of buildings with central square space [2, 56] promote the ground level natural ventilation. (3) For cold climate regions, corner modified buildings [8, 35] and a large stepped podium [47] around the building are convenient to reduce the high wind speeds at the pedestrian level. (4) Modification in building width at one-third level from the ground influences the PLW environment mostly [51] . (5) The positioning of taller buildings should be on the downside of a street to catch more winds at the pedestrian level [4] . Moreover, the addition of recreation spaces and wide streets, removing the obstacles to the flow throughout the urban area improves the pedestrian comfort level. (6) For decision making in response to pedestrian comfort, suitable wind comfort criterion, improved terrain mapping and accurate design related modifications are required. The construction of high rise building in the vicinity of urban area alters the wind climate significantly. Eventually, it becomes necessary to evaluate the wind environment at the initial design phase of urban projects so that suitable modification could be suggested to improve wind climate for pedestrians. While designing urban area, either it is considered to minimize high wind speed zone to reduce mechanical forces on pedestrians or to improve natural outdoor air ventilation. The present study reviews the different wind comfort criterion for pedestrians and measurement techniques to evaluate these wind speeds. Further, the effect of various parameters related to building design is analyzed and at last, evaluation of urban wind at pedestrian level and urban design consideration are discussed. The findings from this review study are summarized as follows. (1) Wind climate statistics obtained from nearby weather station are obligatory for selecting the building shape, orientation and alignment of streets in urban planning and these wind statistics are compared with suitable wind comfort criterion. (2) The probability of exceedance of threshold wind velocity at the particular site requires terrain and design related modifications. To obtain terrain related modification accurately, improved roughness mapping is required. Otherwise, it may lead to wrong decisions in urban planning. (3) To obtain design related modifications, Irwin probes provide relatively accurate results and can be facilitated at numerous locations for simultaneous measurement of mean wind speed and turbulence intensity. (4) To simulate PLW environment, steady RANS method is the best choice economically, however, LES and DES provide more accurate results. Further to improve the accuracy of steady RANS using std. − k ε model, the effect of different model closure coefficient needs to be investigated in detail. (5) Several parameters related to building design e.g. height & width of buildings have an adverse effect on PLW environment, however, building depth does not affect PLW environment significantly. Moreover, studies based on different grouping of buildings suggest that configuration with square central space provides better PLW environment. In addition, uses of lift up buildings podium, corner modified buildings offer a positive design approach. Adopting "lift-up" building design to improve the surrounding pedestrian-level wind environment Pedestrian level wind environment assessment around group of high-rise cross-shaped buildings: effect of building shape, separation and orientation Evaluation of pedestrian wind comfort near "lift-up" buildings with different aspect ratios and central core modifications Designing for pedestrian comfort in response to local climate Sensitivity of inflow boundary conditions on downstream wind and turbulence profiles through building obstacles using a CFD approach CFD simulation for pedestrian wind comfort and wind safety in urban areas: general decision framework and case study for the Eindhoven University campus Wind environmental conditions in passages between buildings Effects of the corner shape of high-rise buildings on the pedestrian-level wind environment with consideration for mean and fluctuating wind speeds The effect of architectural detailing on pedestrian level wind speeds A visual technique for the evaluation of the pedestrian-level wind environment around buildings by using infrared thermography A simple omnidirectional sensor for wind-tunnel studies of pedestrian-level winds Enhanced scour tests to evaluate pedestrian level winds Studies of the pedestrian level wind at the boundary layer wind tunnel laboratory of the university of Western Ontario Criteria for environmental wind conditions Study on acceptable criteria for assessing wind environment at ground level based on residents' diaries Pedestrian wind environment around buildings: literature review and practical examples Pedestrian wind conditions at outdoor platforms in a highrise apartment building: generic sub-configuration validation, wind comfort assessment and uncertainty issues, Wind Struct The effects of wind on people; New criteria based on wind tunnel experiments Wind Tunbnel Investigations A comprehensive assessment of pedestrian comfort including thermal effects Pedestrian level wind criteria using the equivalent average Accuracy of assessment of wind speed in the built environment Design for wind comfort in The Netherlands: procedures, criteria and open research issues Pedestrian wind comfort around buildings: comparison of wind comfort criteria based on whole-flow field data for a complex case study New criteria for assessing low wind environment at pedestrian level in Hong Kong Devenport, the ground level wind environment in built-up area Study of wind environmental problems caused around buildings in Japan Comparison of full-scale and wind-tunnel model measurements of ground winds around a tower building Environmental wind characteristics around the base of a tall building-A comparison between model test an dfull scale experiment Wind comfort predictions by wind tunnel tests: comparison with full-scale data Evaluation of pedestrian-level wind environment around a row of tall buildings using a quartile-level wind speed descripter Application of infrared thermography and a knowledge-based system to the evaluation of the pedestrian-level wind environment around buildings Numerical study on the existence of the venturi effect in passages between perpendicular buildings Pedestrian level wind studies at the Wright brothers facility Wind environmental conditions around tall buildings with chamfered corners Comparison, of pedestrian wind acceptability criteria Application of infrared thermography for pedestrian wind evaluation Wind Environmental Conditions in Passages between Two Long Narrow Perpendicular Buildings Wind environment around the base of a tall building with a permeable intermediate floor Pedestrian-level wind conditions around buildings: review of wind-tunnel and CFD techniques and their accuracy for wind comfort assessment The influence of angular configuration of two buildings on the local wind climate Sand erosion technique applied to wind resource assessment Visual techniques for the determination of wind environment Pedestrian level wind speeds in downtown Auckland, Wind Struct Study of pedestrin level wind environment in the vicinity of tall buildings Generic models for pedestrian-level winds in built-up regions Wind tunnel study of pedestrian level wind environment around tall buildings: effects of building dimensions, separation and podium Wind tunnel studies of a pedestrian-level wind environment in a street canyon between a high-rise building with a podium and low-level attached houses Effects of twisted wind flows on wind conditions in passages between buildings Pedestrian-level wind environment on outdoor platforms of a thousand-meter-scale megatall building: sub-configuration experiment and wind comfort assessment Characteristics of pedestrian-level wind around super-tall buildings with various configurations Using a CFD approach for the study of street-level winds in a built-up area Prediction of wind environment in different grouping patterns of housing blocks A decision support tool for evaluating the air quality and wind comfort induced by different opening configurations for buildings in canyons Natural ventilation assessment in typical open and semi-open urban environments under various wind directions Numerical studies of the outdoor wind environment and thermal comfort at pedestrian level in housing blocks with different building layout patterns and trees arrangement CFD evaluation of wind speed conditions in passages between parallel buildings-effect of wall-function roughness modifications for the atmospheric boundary layer flow Revisiting the "Venturi effect" in passage ventilation between two non-parallel buildings Cooperative project for CFD prediction of pedestrian wind environment in the Architectural Institute of Japan Comparison of various revised kε models and LES applied to flow around a high-rise building model with 1:1:2 shape placed within the surface boundary layer CFD evaluation of new second-skin facade concept for wind comfort on building balconies: case study for the Park Tower in Antwerp Use of Cfd Simulations To Improve the Pedestrian Wind Comfort Around a High-Rise Building in a Complex Urban Area Air ventilation impacts of the "wall effect" resulting from the alignment of high-rise buildings Modification of pedestrian wind comfort in the Silvertop Tower passages by an automatic control system Numerical simulation of the wind field around different building arrangements Assessment of pedestrian wind environment in urban planning design Detached eddy simulation of pedestrian-level wind and gust around an elevated building Prediction of building interference effects on pedestrian level comfort Pedestrian Level Wind Assessment through City Development: a Study of the Financial District in Toronto Analysis of airflow over building arrays for assessment of urban wind environment Evaluation of pedestrian winds in urban area by numerical approach Large-eddy Simulation of flow and dispersion around an isolated building: analysis of influencing factors CFD simulation of the wind environment around an isolated high-rise building: an evaluation of SRANS, LES and DES models AIJ guidelines for practical applications of CFD to pedestrian wind environment around buildings environment around building: a knowledge-Based approach Simulation of twisted wind flows in a boundary layer wind tunnel for pedestrian-level wind tunnel tests Pedestrian-level wind environment around isolated buildings under the influence of twisted wind flows Effects of lift-up design on pedestrian level wind comfort in different building configurations under three wind directions Wind tunnel tests on the relationship between building density and pedestrian-level wind velocity: development of guidelines for realizing acceptable wind environment in residential neighborhoods CFD simulation of wind flow over natural complex terrain: case study with validation by field measurements for Ria de Ferrol This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The authors thank the anonymous reviewers for their valuable comments and suggestions on the manuscript.