Oblique Wind Directions Research Articles

Enhancing LES efficacy in wind load evaluation of low-rise buildings using synthesized inflow turbulence

In Large-Eddy Simulation (LES), the turbulence inflow can be generated synthetically, where the input value of the maximum turbulence frequency can impact the accuracy. LES efficacy can be influenced by the designated computational domain (CD) size and grid specifications. This study proposes multiple parametric studies that aim to correlate the effective parameters controlling the accuracy of numerical wind load evaluation on a low-rise building without compromising the computational cost. The study includes the efficient selection of turbulence maximum frequency (fmax) that can accurately capture the pressure fluctuation induced on the building facade. Both CD size, which involves the distances from the building to the boundary condition, and CD discretization in terms of grid size scheme and shape, are examined. The error assessment is conducted by comparing wind flow aerodynamics and evaluating the RMSE for the pressure parameters with respect to the wind tunnel test. The findings of this study suggest using fmax which can be resolved by the minimum grid size as an input in the inflow turbulence generated to accurately transport the majority of eddies when a satisfactory wavelength of 4 Δx is utilized. This study shows that computational domain size and discretization can be significant sources of error that can reach 21 %, compromising the reliability of computational wind load predictions. The current code in selecting computational minimum width and length is found to be insufficient. In addition, it is found that there are currently no recommendations for selecting the width computational dimension specifications when examining low-rise buildings oriented in an oblique wind direction. The domain grid specification induced a considerable error of 14 % in the mean pressure across the roof when tetrahedral grid shapes were used. Overall, this study's proposed recommendations can significantly impact the efficacy of computational wind load evaluation for low-rise building geometry.

Scaling effects on peak wind load estimation for low-rise buildings: An experimental and analytical study

Though scaling effects on estimation of peak wind loads are extensively documented in the literature, there is a lack of systematic comparison of such scaling effects across different model scales tested in wind tunnels. Moreover, the limited studies on large-scale physical models accepted the inadequacy of simulating the large turbulent eddies rather than addressing the missing low-frequency turbulence simulation inherent in such large-scale testing. This study provides an in-depth comparison of estimates of peak wind loads obtained using a range of experimental scaled models (1:100 and 1:6 model scales) of the Wind Engineering Research Field Laboratory (WERFL) building while applying a Partial Turbulence Simulation (PTS) methodology to incorporate the effects of turbulence. Large-scale wind tunnel testing of structures provides the advantage of achieving an improved Reynolds number (Re) similarity, more accurate geometric similarity, and enhanced resolution of flow details such as corner vortices, than is possible with the use of smaller model scales. However, as the model scale increases, achieving turbulence similarity becomes challenging due to limitations in simulating the low-frequency turbulent eddies in the wind tunnel. The PTS method has been used in the recent past to account for the low-frequency turbulence effects in the peak wind load estimation. The method is referred to as 1DPTS when considering longitudinal turbulence components only and 2DPTS when considering both longitudinal and lateral turbulence components in the analysis. The computationally intensive 2DPTS can be further simplified by using a weighted average method as described in this paper as “weighted average PTS.” The current study explores the effect of scaling on peak wind load estimation by using the 1DPTS, 2DPTS, and weighted average PTS methods. Results from the multi-scale experimental tests demonstrate that using larger model scales and compensating for the low-frequency turbulence deficit in the post-test analysis significantly improve the agreement with the prototype data owing to the simulation of a higher Reynolds number. Furthermore, comparing the results of the proposed weighted average method with full-scale data reveals its potential as a substitute for the original 2DPTS method, offering enhanced accuracy, particularly at the roof corner for oblique wind directions. While the effects of Re are well known, the findings of this study explore its impact in conjunction with the application of the PTS methods on peak Cp estimation across five different model scales with Re ranging from 3.65 × 104 to 2.43 × 106, the latter being closest to the full-scale (field) Re. The findings provide new insights into how large-scale physical model testing in high Re flows, supported by analytical PTS-based compensation, can enhance the accuracy of peak wind load estimations for critical scenarios including cornering winds that generate conical vortices.

Interference effects on the wind loads and wind-induced responses of parallel-arranged rectangular-planed air-supported membrane structures

In many practical projects, two air-supported membrane structures are parallel-arranged. The interference effects of parallel-arranged rectangular-planed air-supported membrane structures are important in the wind-resistant design. In order to address this issue, the wind pressures on isolated and parallel-arranged structures are obtained through pressure measurement wind tunnel tests. The wind-induced responses are calculated via nonlinear dynamic time–history analysis. Consequently, the interference effects on wind loads and wind-induced responses are analyzed. The results show that the wind suctions of downstream structures are amplified by the interferences of parallel-arranged structures particularly under oblique wind directions. The mean wind loads on the most disturbed zone are amplified up to about 65 %. The interference characteristics of wind-induced displacement are basically similar to mean wind loads. The membrane stresses and cable forces are significantly interfered only in oblique wind directions, which are amplified up to about 15 % in all zones of downstream structures. The strongest interference effects can be observed with a spacing-span ratio of 0.2 when the wind direction is oblique or parallel to the gap between neighboring structures. The interference factors for zones are provided to analyze the interference characteristics. In addition, recommendation values of the overall response interference factors are summarized for design reference. The overall response interference factors for displacement, membrane stress, and cable force should be considered as 1.21, 1.33, and 1.20, respectively.

Interference effect on flow features and aerodynamic mechanism over the roof between two tall buildings

Interference effect of an upwind building on flow features and wind power potential over roof of principal building was investigated through numerical simulations. Flow features were examined at different wind directions and spacing ratios (d/B = 2, 3, 4, 5, and 6), and associated aerodynamic mechanisms were analyzed. Turbulence intensity was less affected by interfering building than mean velocity. d/B exerted a more important impact on mean velocity at θ = 0° and 180° than those at oblique wind directions. The isolated building had large power potential at leeward locations due to strong flow separation at θ = 0° compared with principal building. The largest skew angle βmax fluctuated greatly with roof locations (from −15° to 80°) of isolated building at θ = 0°. In comparison, βmax over principal building changed slightly with roof locations (from −16° to 3°) due to smooth flow separation and reattachment at θ = 0°. Effect of d/B on the largest wind energy and hub height of roof-mounted wind turbines depended on θ. Recommendations for the siting of HAWTs on roofs were finally provided.

Optimum design parameters for a venturi-shaped roof to maximize the performance of building-integrated wind turbines

Venturi-shaped roofs provide advantageous wind conditions for efficiently operating building-integrated wind turbines without losing usable floor area. Despite these advantages, venturi-shaped roofs have been sparsely adopted for buildings due to the lack of understanding of their optimum designs to maximize the performance of building-integrated wind turbines. For the first time in literature, this study investigated four design parameters: support structure, corner modification, tunnel shape, and wind turbine arrangement to estimate the optimum venturi-shaped roof design by conducting Computational Fluid Dynamics (CFD) simulations. The results revealed the advantages of shorter support structures with convex and concave shapes at upwind and downwind ends, creating high wind speeds with low turbulence intensities. Corner modifications to the tunnel's entrance and exit are vital to suppress flow separation at the tunnel's entrance and uniform distributions of wind speed and pressure. This study recommends aerodynamic tunnel shapes that follow a non-uniform rational B-spline (NURBS) to accelerate wind without increasing turbulence intensities. The optimum design parameters performed better in normal and oblique wind directions, confirming their universal applicability. This study proposes integrating all optimum design parameters into a venturi-shaped roof design to alleviate the adverse effects of support structures, which are essential for a stable roof design.

Large-eddy simulations on pollutant reduction effects of road-center hedge and solid barriers in an idealized street canyon

This study conducted large-eddy simulations (LES) on the pollutant reduction effects of hedge and solid barriers in a three-dimensional idealized street canyon with an aspect ratio of 0.5. The wind direction was perpendicular and oblique (45°) to the street. The results were validated with data from wind tunnel experiments. LES accurately predicted the concentration distribution in the barrier-free case and reproduced well the barrier-induced concentration reduction. In the barrier-free case, a large recirculation vortex was observed. However, the central barriers forced the recirculated airflow in the middle of the canyon and newly formed vortices near the leeward walls. The two counter-direction vortices in the hedge and solid barrier cases transported pollutants toward the center of the canyon and enhanced the vertical pollutant removal at the top of the street canyon. The hedge barrier (solid barrier) reduced spatially-averaged concentration by about 59% (45%) near the leeward wall, 64% (20%) near the windward wall, and 45% (17%) in the whole street canyon compared to the barrier-free case. The effects of leaf area density (LAD) and barrier width were further investigated under the perpendicular wind direction. Increasing the LAD or the width of the hedge barrier decreased concentration near the leeward walls but increased canyon-averaged concentration. Increasing the width of the solid barrier decreased the concentration near the leeward walls and the canyon-averaged concentration. In an oblique wind direction, the hedge and solid barriers reduced by about 30% and 60% the spatially-averaged concentration near the building walls compared to the barrier-free case.

Experimental study on the galloping characteristics of single ice-coated transmission lines under oblique flows

Galloping of ice-coated transmission lines is occasionally observed under oblique wind directions. However, most current investigations on the galloping mechanisms are for flow perpendicular to the span of the transmission lines. In order to address this gap, this research studies the galloping characteristics of ice-coated transmission lines under oblique flows based on wind tunnel tests. The wind-induced displacement of an aero-elastic iced-coated transmission line model was measured with a noncontact displacement measurement equipment in a wind tunnel at different wind speeds and directions. The results show that galloping is characterized by elliptical trajectories and negative damping, which is more likely to occur under oblique flows than the direct flow (0°). At 15° wind direction, a galloping in vertical direction was observed at wind speeds above 5 m/s. At 30° wind direction, galloping was observed over the entire range of the tested wind speeds. Moreover, the galloping amplitudes under oblique flows are observed to be larger than that at the direct flows. Consequently, when the wind direction between the major winter monsoon azimuth and the lateral direction of transmission line route is between 15° and 30°, appropriate anti-galloping devices are highly recommended in practice.

Comparison of simulation methods for dynamic internal air distribution in naturally ventilated livestock buildings

Accurate internal air distribution prediction facilitates the analysis of occupant thermal comfort and the control of gaseous contaminants within naturally ventilated livestock buildings (NVLB). However, the dynamic and random change in external wind conditions makes it difficult to predict the air distribution. This study compares three scenarios based on real-time monitored external wind conditions: the quasi-static simulation method with moving average data, the transient simulation method with raw data, the transient simulation method with Kalman filtering, and the continuous fast Fourier transform. The quasi-static simulation was verified for computational efficiency and reliability within different time spans. The simulation results were validated with measurement data in a low-rise stand-alone NVLB surrounding a low-density building complex. The quasi-static simulation results of internal air distribution in oblique wind directions partially agreed with the hourly averaged wind speed measurements and turbulent kinetic energy. Additionally, the quasi-static simulation agrees with the direct transient method for predicting the air distribution within a long-time span. The quasi-static simulation shows promise for the future simulation of internal air distribution in naturally ventilated livestock buildings under dynamic boundary conditions.

Experimental Investigation of Wind Loads on Roof-Mounted Solar Arrays

An experimental study was conducted to investigate the aerodynamic loads on roof-mounted solar arrays. Four different parapet heights of 0 m, 0.9 m, 1.2 m, 1.5 m, and two tilt angles of 5° and 10°, are set to examine their effects on wind pressure coefficients. The statistics (means, standard deviations, skewness, kurtosis, maximum and minimum peaks) of wind pressure coefficients in different wind directions are exhibited and discussed in the current study. The results show that the oblique wind directions are critical for most measured locations, as the extreme of maximum and minimum peak pressure coefficients occur. The parapet can decrease wind loads on solar arrays, as expected. However, as the parapet is within a limited height in practice, it is not quite efficient to decrease wind loads despite the increasing of the parapet height. When the solar arrays are installed on the roof almost horizontally (tilt angle is less than 10°), the statistics of the aerodynamic load change a little with the decreasing of the tilt angle.

Wind tunnel experiment on rectangular-shaped arch-supported membrane structures

This paper highlights the investigation of wind tunnel experiment on rectangular-shaped arch-supported membrane structures. Series of wind tunnel experiments are carried out to record the time history of pressure under different wind directions for both enclosed and open structures. In order to present the comparative analysis, contours and graphs for mean and peak wind pressure coefficients are plotted considering different parameters such as rise-span ratio, wind direction, and boundary wall. Study shows that under oblique wind direction, strong flow separation occurs in the windward arch edge which creates larger suction pressure coefficient on the immediate downside of windward arch. Based on area and intensity of negative pressure coefficient, 45⁰ is the most critical wind direction. Influence of rise-span ratio is noticeable. When rise-span ratio increases from 0.2 to 0.35, pressure coefficient increases significantly, however when rise-span ratio further increases to 0.5, increase in pressure coefficient is marginal. Moreover, in order to ease the engineering design application, roof surface is divided into different zones and assigned with mean and peak wind pressure coefficient.

Aerodynamic shape optimization of large-span coal sheds for wind-induced effect mitigation using surrogate models

Large-span coal sheds commonly used in thermal power plants are particularly vulnerable to wind loads, and the aerodynamic performances are largely affected by their external shapes. The search for the best performing shape through an aerodynamic optimization is still of importance for the mitigation of the design wind loads and responses. This study investigated the possibility of using surrogate models combined with genetic algorithm to carry out the aerodynamic shape optimization of large-span roof structures. The approach is applied to tri-centered coal sheds with closed and open gables, respectively. The shape optimization is numerically performed to minimize the vertical displacement of the shed model while subjecting to one normal and two oblique wind directions, 0°, 30° and 45°. The aerodynamic forces acting on coal sheds immersed in turbulent flow are obtained by the CFD simulation with RSM turbulence model, and the results are validated with wind tunnel tests. Kriging model is used to establish a global mapping between design variables and objective function by conducting a set of CFD and structural static response analyses. Results show that the aerodynamic loads and the optimal geometry are sensitive to the selection of gable types and wind directions. The optimal design presents a reasonable performance improvement compared with the near-optimal and original designs. Several compromised designs are finally provided in order to seek a balance between the effects of wind directionality and construction cost.

Ventilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections.

To gain further insight into the ventilation at urban street intersections, this study conducted 3D simulations of the ventilation at right- and oblique-angled intersections under eight wind directions by using the Reynolds-averaged Navier–Stokes (RANS) -ε turbulence model. The divergent responses of ventilation and pollution concentration for the pedestrian zone (ped), the near-wall zone (nwz), and the canopy layer to the change in intersection typology and wind direction were investigated. The flow characteristics of the intersections, taken as the air flow hub, were explored by employing indices such as the minimum flow ratio (β) between horizontal openings. The results show that oblique wind directions lead to a lower total volumetric flow rate (Qtotal) but a higher β value for right-angled intersections. For T-shaped intersections, a larger cross-sectional area for the outflow helps to increase Qtotal. Oblique-angled intersections, for example, the X-shaped intersection, experience a more significant difference in Qtotal but a steady value of β when the wind direction changes. The vertical air-exchange rate for the intersection was particularly significant when the wind directions were parallel to the street orientation or when there was no opening in the inflow direction. The spatially averaged normalized pollutant concentration and age of air () for the pedestrian zone and the canopy layer showed similar changing trends for most of the cases, while in some cases, only the or changed obviously. These findings reveal the impact mechanism of intersection configuration on urban local ventilation and pollutant diffusion.

The effect of external airflows on ventilation with a rooftop windcatcher

This study aims to investigate how a modern style windcatcher, which is much shorter than the traditional ones, is more sensitive to the exterior flows interacting with the associated building itself. This interaction between the onset flows and building façades can influence the ventilation behaviour inside the building. Therefore, full simultaneous exterior and interior measurements are conducted in the wind tunnel around the envelope of a 1:12 generic building model with a two-sided rooftop windcatcher and a wall window. Wind tunnel flow visualisations are carried out to gain insights into the effect of the exterior building topology on ventilation. It was found that rooftop windcatchers performance is strongly influenced by the flows surrounding the building's façades, especially at the building roof with dominating flow separation, and near the room window. Hence, the windcatcher was most effective at oblique wind directions and with an opened room window. On the other hand, the performance response of two Reynolds-averaged Navier-Stokes (RANS) based turbulence models was presented throughout the results.

Impacts of urban morphology on improving urban wind energy potential for generic high-rise building arrays

Previous findings have indicated better performance attained by modified urban morphologies for wind energy utilization only in single and pair buildings, or medium-dense low-rise building arrays. Hence, the main purpose of this study is to address the research gaps to complete a fundamental understanding of the influences of urban morphology in compact high-rise urban areas on enhancing urban wind energy harvest for sustainable urban development. A comprehensive parametric study is conducted using the computational fluid dynamics tool to analyze the impacts of urban morphologies on the wind energy potential for a 6 × 6 array of generic high-rise buildings, including (i) urban density altered from compact to sparse urban layouts, (ii) building corner shapes of sharp and rounded corners, (iii) urban layouts of in-line and staggered patterns, and (iv) wind directions of 0° and 45°. This investigation implements the three-dimensional steady Reynolds-averaged Navier-Stokes equations with the Reynolds stress model to explore the distributions of wind speed, power density, and turbulence intensity over the building array. The results indicate that decreasing urban plan area density reduces the unacceptable turbulence areas with relatively higher wind power density on the roof. Besides, round corners can produce elevated power densities up to 201% greater than sharp corners beside the building. Even under the oblique wind direction of 45°, the rounded corner still shows better wind energy potentials than the sharp corner. The in-line urban layout demonstrates more significant areas with higher power densities and low turbulence intensities than the staggered urban layout.

Investigation of aerodynamic performance ofpitch-control wind turbine with polygonal towers

Wind turbines are commonly used power generation systems around the world and their application is becoming increasingly widespread. Traditionally, they have been mounted on circular towers, but their recent upsizing has exposed weaknesses of these structures, including problems related to manufacturing and insufficient strength. Thus, the concept of site-assembled modular towers with polygonal cross-sections has been proposed, but their aerodynamic performances have not been properly investigated. In the present study, the aerodynamic performances of a wind turbine with seven polygonal towers were investigated. Wind tunnel tests have shown that the forces on the upper structure (rotor and nacelle) are larger than those on the tower, which makes the effect of cross-sectional shape of tower relatively small. Drag forces decrease with increasing number of sides of the tower, and lift forces on the square helical tower are quite small. For the power spectra, there are peaks in high reduced frequency for oblique wind directions at azimuth angles of 60° and 90°, which were considered to result from vortices that were formed and shed behind the blade in front of the tower.

Clean air in cities: Impact of the layout of buildings in urban areas on pedestrian exposure to ultrafine particles from traffic

Traffic-related pollutant concentrations are typically much higher in near-roadway microenvironments, and pedestrian and resident exposures to air pollutants can be substantially increased by the short periods of time spent on and near roadways. The design of the built environment plays a critical role in the dispersion of pollutants at street level; after normalizing for traffic, differences of a factor of ~5 have been observed between urban neighborhoods with different built environment characteristics. We examined the effects of different built environment designs on the concentrations of street-level ultrafine particles (UFP) at the scale of several blocks using the Quick Urban and Industrial Complex (QUIC) numerical modeling system. The model was capable of reasonably reproducing the complex ensemble mean 3D air flow patterns and pollutant concentrations in urban areas at fine spatial scale. We evaluated the effects of several built environment designs, changing building heights and spacing while holding total built environment volumes constant. We found that ground-level open space reduces street-level pollutant concentrations. Holding volume/surface area constant, tall buildings clustered together with larger open spaces between buildings resulted in substantially lower pollutant concentrations than buildings in rows. Buildings arranged on a ‘checkerboard’ grid with smaller contiguous open spaces, a configuration with some open space on one of the sides of the roadway at all locations, resulted in the lowest average concentrations for almost all wind directions. Rows usually prohibit mixing for perpendicular and oblique wind directions, even when there are large spaces between them, and clustered buildings have some areas where buildings border both sides of the roadways, inhibiting mixing. The model results suggest that pollutant concentrations drop off rapidly with height in the first 10 m or so above the roadways. In addition, the simulated vertical concentration profiles show a moderate elevated peak at the roof levels of the shorter buildings within the area. Model limitations and suggestions both for urban design are both discussed.

Investigation on wind tunnel experiment of oval-shaped arch-supported membrane structures

This paper presents wind pressure distribution characteristics of oval-shaped arch-supported membrane structures based on the wind tunnel experiments. Distribution of mean and fluctuating wind pressure coefficient is presented meticulously using pressure maps. Influence of different factors including rise-span ratio, wind direction, and terrain category, on the distribution of mean, fluctuating and peak wind pressure coefficient is discussed. Both enclosed and open structures are considered. Results show that structure experiences critical suction pressure at immediate downslope of arch axis under oblique wind direction. The significant influence of rise-span ratio and wind direction on the distribution of mean and peak wind pressure coefficient is observed. Variations of wind pressure coefficient, due to change in key parameters, are distinct in windward area but changes are insignificant in leeward area. Relatively larger area of roof of open structure is loaded with positive wind pressure coefficient, as compared to an enclosed roof. Moreover, clustering analysis is performed to divide the roof surface into different zones, then mean and peak wind pressure coefficient are proposed for corresponding zones of roof surface considering different rise-span ratios under different wind directions. The outcomes are expected to be useful to engineers and researchers to understand similar type of structures.

Characteristic Scales for Turbulent Exchange Processes in a Real Urban Canopy

An experimental field campaign is designed to unveil mechanisms responsible for turbulent exchange processes when mechanical and thermal effects are entwined. The focus is an urban street canyon with a mean aspect ratio H/W of 1.65 in the business centre of a mid-size Italian city (H is the mean building height and W is the mean canyon width). The exchange processes can be characterized by time scales and time-scale ratios specific to either mechanical or thermal process. Time scales describe the mixing caused by momentum and heat exchange within different canyon layers, while their rates are surrogates of their efficacy. Given that homogeneous mixing does not always occur within the canyon, several time scales are estimated at different levels, showing that mechanical and thermal processes may both contribute to enhance mixing. By computing mechanical time scales, it is found that the fastest mixing occurs at the canyon rooftop level for perpendicular or oblique wind directions, while slow mixing occurs for parallel directions. Thermal processes are faster than the mechanical ones and are particularly efficient for perpendicular wind directions. By calculating the time-scale ratios, exchange processes are found to facilitate mixing for most wind directions and to regulate the pollutant-concentration variability in the canyon. This variability can be associated with the local-circulation regime, demarcated as thermally driven or inertially driven using a buoyancy parameter, i.e., the ratio between thermal and inertial forcings. Using this approach, a generalization of the results is proposed, enabling the extension of the current investigation to different street-canyon aspect ratios.

Farklı Rüzgar Yönlerinde Yere Monte Bir Güneş Panelinde Aerodinamik Mekanizmalar

Aerodynamics mechanisms on a solar panel were studied using Computational Fluid Dynamics methodology at different wind directions. The wind velocity was chosen as 10 m/s that corresponding turbulent flow. The inclination angle of the panel was fixed as 25°, while the wind directions were varied as 180°, 135°, 45°, and 0°. Governing equations were solved by utilizing a finite volume method with a realizable k-ε turbulence model and standard wall functions. The results showed that the recirculation area occurred for the straight wind directions, but it was not observed for the oblique wind directions. The highest pressure coefficients occurred at the leading edges of the solar panel and they reduced to the trailing edge for all wind directions. The maximum drag and uplift coefficient was obtained at the wind direction of 0° and 180°, respectively.

Characteristics of conical vortices and their effects on wind pressures on flat-roof-mounted solar arrays by LES

Large eddy simulations (LES) are performed to examine the flow characteristics around solar arrays mounted on a flat-roof building for two oblique wind directions, 45° and 135°. The main purpose of this study is to clarify the mechanisms of some special features of wind pressure characteristics acting on solar panels obtained by wind tunnel experiments. Numerical simulation is first conducted for a flat-roof building without solar arrays to validate the accuracy of LES for oblique wind directions. Numerical simulations are then made for a flat-roof building with solar arrays. For 45° wind direction, local separations and reattachments of the downflows of the left-side conical vortex are found to play important roles in large negative pressures near the higher edges of the upper surfaces and positive pressures on some parts of the lower surfaces of solar panels. For 135° wind direction, local vortices generated from the higher edges of the solar panels form local wake regions downwind of the panels and cause downward net pressures on most of the panels. The effects of the gaps on pressures on the upper surfaces of solar arrays are not significant, but those on the lower surfaces are significant because of the flows passing under the panels.