Approaching Wind Direction Research Articles

Pressure distribution on rectangular buildings with changes in aspect ratio and wind direction

This study aims to enhance the understanding of the surface pressure distribution around rectangular bodies, by considering aspects such as the suction pressure at the leading edge on the top and side faces when the body aspect ratio and wind direction are changed. We carried out wind tunnel measurements and numerical simulations of flow around a series of rectangular bodies (a cube and two rectangular bodies) that were placed in a deep turbulent boundary layer. Based on a modern numerical platform, the Navier–Stokes equations with the typical two-equation model (i.e., the standard k-e model) were solved, and the results were compared with the wind tunnel measurement data. Regarding the turbulence model, the results of the k-e model are in overall agreement with the experimental results, including the existing data. However, because of the blockage effects in the computational domain, the pressure recovery region is underpredicted compared to the experimental data. In addition, the k-e model sometimes will fail to capture the exact flow features. The primary emphasis in this study is on the flow characteristics around rectangular bodies with various aspect ratios and approaching wind directions. The aspect ratio and wind direction influence the type of wake that is generated and ultimately the structural loading and pressure, and in particular, the structural excitation. The results show that the surface pressure variation is highly dependent upon the approaching wind direction, especially on the top and side faces of the cube. In addition, the transverse width has a substantial effect on the variations in surface pressure around the bodies, while the longitudinal length has less influence compared to the transverse width.

Wind tunnel study of wind structure at a mountainous bridge location

Wind tunnel tests of a 1/2200-scale mountainous terrain model have been carried out to investigate local wind characteristics at a bridge location in southeast Tibet, China. Flows at five key locations on the bridge at deck level were measured for 26 directions. It was observed that wind characteristics (including mean wind velocity and overall turbulence intensity) vary significantly depending on the approaching wind direction and measurement position. The wind inclination angle measured in the study fluctuated between $-18^{\circ}$ and $+16^{\circ}$ and the ratio of mean wind velocity to reference wind velocity was small when the wind inclination angles were large, especially for positive wind inclination angles. The design standard wind speed and the minimum critical wind speed for flutter rely on the wind inclination angle and should be determined from the results of such tests. The variation of wind speed with wind inclination angles should be of the asymmetry step type. The turbulence characteristics of the wind were found to be similar to real atmospheric flows.

Ventilation Processes in a Three-Dimensional Street Canyon

The ventilation processes in three different street canyons of variable roof geometry were investigated in a wind tunnel using a ground-level line source. All three street canyons were part of an urban-type array formed by courtyard-type buildings with pitched roofs. A constant roof height was used in the first case, while a variable roof height along the leeward or windward walls was simulated in the two other cases. All street-canyon models were exposed to a neutrally stratified flow with two approaching wind directions, perpendicular and oblique. The complexity of the flow and dispersion within the canyons of variable roof height was demonstrated for both wind directions. The relative pollutant removals and spatially-averaged concentrations within the canyons revealed that the model with constant roof height has higher re-emissions than models with variable roof heights. The nomenclature for the ventilation processes according to quadrant analysis of the pollutant flux was introduced. The venting of polluted air (positive fluctuations of both concentration and velocity) from the canyon increased when the wind direction changed from perpendicular to oblique, irrespective of the studied canyon model. Strong correlations ( $$>$$ 0.5) between coherent structures and ventilation processes were found at roof level, irrespective of the canyon model and wind direction. This supports the idea that sweep and ejection events of momentum bring clean air in and detrain the polluted air from the street canyon, respectively.

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

The pedestrian-level wind environment quality in street canyons formed by high-rise buildings and other low-level buildings could be affected by multiple factors, such as the height and geometry of the surrounding buildings, street width, wind direction, and wind speed. This study conducted wind tunnel experiments to determine the characteristics of the pedestrian-level wind environment in street canyons under different conditions, including different street widths, podium heights, and approaching wind directions. The experimental results revealed that the effects of the street canyon width on the pedestrian-level wind in a street canyon can be categorized into three different flow regimes. A higher podium creates stronger wind speeds of the flow within the street canyon, and different approaching wind directions change the high-wind-speed zone within the street canyon accordingly.

Impact of trees on pollutant dispersion in street canyons: A numerical study of the annual average effects in Antwerp, Belgium

Effects of vegetation on pollutant dispersion receive increased attention in attempts to reduce air pollutant concentration levels in the urban environment. In this study, we examine the influence of vegetation on the concentrations of traffic pollutants in urban street canyons using numerical simulations with the CFD code OpenFOAM. This CFD approach is validated against literature wind tunnel data of traffic pollutant dispersion in street canyons. The impact of trees is simulated for a variety of vegetation types and the full range of approaching wind directions at 15° interval. All these results are combined using meteo statistics, including effects of seasonal leaf loss, to determine the annual average effect of trees in street canyons. This analysis is performed for two pollutants, elemental carbon (EC) and PM10, using background concentrations and emission strengths for the city of Antwerp, Belgium. The results show that due to the presence of trees the annual average pollutant concentrations increase with about 8% (range of 1% to 13%) for EC and with about 1.4% (range of 0.2 to 2.6%) for PM10. The study indicates that this annual effect is considerably smaller than earlier estimates which are generally based on a specific set of governing conditions (1 wind direction, full leafed trees and peak hour traffic emissions).

Analysis of fluctuating characteristics of wind-induced airflow through a single opening using LES modeling and the tracer gas technique

The turbulent nature of wind significantly complicates the airflow-exchange process at single openings that function as both inlets and outlets simultaneously. For such flow problems, describing the ventilation rate using a constant value is insufficient if the fluctuating intensity is too large. This paper uses a large eddy simulation (LES) model combined with the tracer gas concentration decay method to investigate fluctuating ventilation characteristics through a single opening under various approaching wind directions. The numerical method is validated against a field measurement of single-sided ventilation rates. Results show that wind direction (which characterizes the external airflow pattern) greatly influences the airflow exchange at a single opening. The ventilation rate is relatively steady for a windward opening and shows more unsteadiness for a lateral and a leeward opening. The airflow-exchange process is mainly driven by the mean flow at the windward opening and is dominated by the turbulent flow at the lateral opening. The findings from this study imply that the turbulence-induced component of single-sided ventilation rates should always be considered, especially for non-windward openings.

Natural ventilation characteristics of one-sided wind catchers: experimental and analytical evaluation

Wind tunnel experiments, flow visualization tests as well as analytical modeling are conducted to investigate the influence of wind speed and its direction on the ventilation capacity of one-sided wind-catcher models. These are wind-catchers with flat, inclined and curved roofs which are in common use in central part of Iran for passive cooling. Induced airflow rate and pressure coefficients over all the internal surfaces of the wind-catchers’ channels are measured. Using measured pressure coefficients and analytical modeling, natural ventilation efficiencies of wind-catchers are calculated and compared with the experimental measurements. It is seen that for all wind directions, the semi-analytical prediction of ventilation efficiencies has a good agreement with the experimental results.Based on the measured quantities, it is shown that the flow pattern, the internal pressure field and induced airflow rate inside the wind-catchers are strongly influenced by the geometry of wind-catcher's roof and the approaching wind direction. Measured airflow rate inside the wind-catcher revealed that for zero air incident angle, the one with curved roof is capable of capturing higher airflow while for high values of air incident angles, the inclined roof wind-catcher is more suitable and less sensitive to changing the outdoor wind direction.

Wind load transfer mechanisms on a low wood building using full-scale load data

The wind-induced response of low-rise wood buildings has been evaluated by monitoring a specially instrumented test building exposed to real wind action. The field facilities included a state-of-the-art data acquisition system which collected wind, pressure and force data. In addition to the field monitoring, a 1:200 scaled model of the test building was tested in the wind tunnel and the envelope wind pressures were estimated for various terrain exposures. The wind-induced pressures obtained from both the full-scale and wind tunnel experiments were incorporated in the finite element model of the test building and its response was numerically derived.Vast amounts of experimental data were generated during the long-term monitoring of the test building. These data were used to successfully verify the simulation approaches in terms of both wind-induced pressures and structural forces. Some limited discrepancies were observed in the peak pressure coefficients for locations close to the roof ridge and corners. The field acquired force data revealed that the majority of the wind uplift force is supported by the two side walls. Moreover, it was experimentally verified that the wind-induced load was attenuated as it was transferred through the buildings' structural system. This attenuation was estimated to be at least 17%, as far as the total foundation uplift force is concerned, and reached the 28% for certain approaching wind directions.

Pollutant Concentrations in Street Canyons of Different Aspect Ratio with Avenues of Trees for Various Wind Directions

This study summarizes the effects of avenues of trees in urban street canyons on traffic pollutant dispersion. We describe various wind-tunnel experiments with different tree-avenue models in combination with variations in street-canyon aspect ratio W/H (with W the street-canyon width and H the building height) and approaching wind direction. Compared to tree-free street canyons, in general, higher pollutant concentrations are found. Avenues of trees do not suppress canyon vortices, although the air ventilation in canyons is hindered significantly. For a perpendicular wind direction, increases in wall-average and wall-maximum concentrations at the leeward canyon wall and decreases in wall-average concentrations at the windward wall are found. For oblique and perpendicular wind directions, increases at both canyon walls are obtained. The strongest effects of avenues of trees on traffic pollutant dispersion are observed for oblique wind directions for which also the largest concentrations at the canyon walls are found. Thus, the prevailing assumption that attributes the most harmful dispersion conditions to a perpendicular wind direction does not hold for street canyons with avenues of trees. Furthermore, following dimensional analysis, an estimate of the normalized wall-maximum traffic pollutant concentration in street canyons with avenues of trees is derived.

Comparison of Numerical and Experimental Results for the Evaluation of the Depollution Effectiveness of Photocatalytic Coverings in Street Canyons

Towards the aim of improving the air quality in the urban environment via the application of innovative TiO2 based photocatalytic coverings, a field campaign took place within the frame of the EU PICADA project (http://www.picada-project.com) to asses the expected depollution efficiency of such materials under realistic conditions. Furthermore, extensive numerical modeling was performed via the application of the RANS CFD code for microscale applications MIMO, in an effort to asses the sensitivity of the developing flow field and the corresponding dispersion mechanism and hence of the depollution efficiency of the PICADA products on a wide range of factors, with most notably the length of the street canyon, the thermal exchange between the heated street canyon walls and the air and the approaching wind direction. For the needs of the PICADA project a new, simple module had to be implemented into MIMO to be able to model the removal of NOx from a street canyon whose walls have been treated with a photocatalytic product. The model simulations results presented in this paper, show that MIMO is indeed capable of predicting the effectiveness of the photocatalytic products in question. At the same time, they reveal a strong dependence of the developing flow and concentration fields inside the field site street canyon configuration on most of the aforementioned factors with most notably the direction of the approaching wind.

Wind-tunnel and field investigation of the effect of local wind direction on speed-up over hills

Measurements of flow past simulated sinusoidal hills were taken in an atmospheric boundary layer wind tunnel (ABLWT) that modeled typical full-scale complex terrain for many wind turbine locations in the Altamont Pass, California, USA. Velocity profiles and speed-up factors for several model hills were determined. All hills modeled had the same height and sinusoidal cross-section, and length-to-width aspect ratios of infinity, four and one. Each of the three models was tested with approach wind directions from 0° to 90°, in 15° increments. It was observed that speed-up can vary significantly depending on the approaching wind direction. The effect of wind direction on speed-up was also investigated using field data from a site in the Altamont Pass. Average speed-up factor was found to vary significantly at the site in time, and as a function of atmospheric stability.

Wind tunnel simulation studies on dispersion at urban street canyons and intersections—a review

Increased traffic emissions and reduced natural ventilation cause build up of high pollution levels in urban street canyons/intersections. Natural ventilation in urban streets canyons/intersections is restricted because the bulk of flow does not enter inside and pollutants are trapped in the lower region. Wind vortices, low-pressure zones and channeling effects may cause build up of pollutants under adverse meteorological conditions within urban street canyons. The review provides a comprehensive literature on wind tunnel simulation studies in urban street canyons/intersections including the effects of building configurations, canyon geometries, traffic induced turbulence and variable approaching wind directions on flow fields and exhaust dispersion.

Effects of the homogeneous traffic on vertical dispersion parameter in the near field of roadways – A wind tunnel study

The vertical dispersion parameter of Pasquill–Gifford needs some modification in the close vicinity of urban roadways by considering the influence of traffic-induced turbulence. Wind tunnel simulation experiments have been carried out with controlled traffic parameters to evaluate traffic-induced effect on vertical dispersion parameter (σz) in the near field of roadways. The aerodynamic similarities in atmospheric flow, vehicles size and speeds have been considered with appropriate similarity criteria. The tracer gas experiments have been performed to evaluate σz in the near field of the roadways for variable traffic volumes and two approaching wind directions (i.e. 90○ and 60○). The results showed that the value of σz increased monotonically with increase in traffic volumes and becomes nearly constant at a particular downwind distance. It has also been found that the σz was considerably affected by approaching wind directions. Further, the comparison of experimental σz values for both approaching wind directions with those of Chock (1978) and Rao and Keenan (1980), showed an agreement within ±15%.

Heterogeneous Traffic Induced Effects on Vertical Dispersion Parameter in the Near Field of Roadways - a Wind Tunnel Study

The varying traffic parameters such as traffic volume, speed, shape and size, and terrain roughness conditions play a vital role on dispersion of pollutants in the near field of roadways. Simulation experiments were carried out in the Environmental Wind Tunnel (EWT) to evaluate the traffic induced effects on vertical dispersion parameter (σ z ) for heterogeneous traffic conditions in the near field of roadways for evaluating the effect of variations in traffic volume, terrain roughness condition and approaching wind direction. The model vehicle movement system was fabricated and made operational in the EWT, which allowed the variation in traffic volume, speed and wind road inclination. Sixty-six hydrocarbon tracer experiments were performed to evaluate σ z in the near field of roadways for variable traffic volume, three terrain roughness conditions and two approaching wind directions (i.e., 90° and 60°). The values of σ z for heterogeneous traffic conditions were found to be higher for low roughness conditions in comparison to other two higher roughness conditions for various traffic volumes and approaching wind directions.

Wind tunnel measurements of concentration fluctuations in an urban street canyon

A wind tunnel study was performed to examine some turbulent characteristics and statistical properties of the concentration field developing from the steady release of a tracer gas at street level in a canyon amidst urban roughness. The experiment was conducted with the approaching wind direction perpendicular to the street axis and, with a street width to building height aspect ratio equal to one. Concentration time series were recorded at 70 points within the test street cross-section and above. Mean concentrations, variances and related turbulent quantities, as well as other statistical quantities including quantiles were computed. Concentration spectra and autocorrelation functions were also examined. The emphasis is put here on the results concerning mean concentrations and the variance of concentration fluctuations. The main objective of this paper is to put forward potential benefits of the experimental approach taken in this study. Through a simple and already widely studied configuration it is aimed to show how, for modelling purposes, this approach can help improving our understanding of the mechanisms of dipersion of pollution from car exhausts in built-up areas and, with further measurements, how it could assist in drawing specifications for siting monitoring networks.

風洞実験およびCFDを併用した通風時の開口条件や主風向が異なる場合における建物内外の気流性状に関する研究

Air flow characteristics of cross-ventilation in and around 5 types of building models were examined in this paper. The examination cases of cross-ventilation were changed by the conditions of the openings and the angles of the approaching wind. Both methods of wind tunnel experiment and numerical simulation were employed. The air flow characteristics were discussed from the following 5 viewpoints: ventilation rate, main air flow path, wind pressure coefficient distribution, air velocity distribution and coefficient of pressure loss. The following findings were obtained: 1) The difference of wind pressure coefficient among models is within 0.2, even though the conditions of the openings were different and overall flow exhibits no substantial change around the building when the angle of approaching wind was 0°. The air flow passing through the windward opening ran downward. The coefficients of pressure loss of windward and leeward openings were not different. 2) The ventilation rate in 0〜45° angles of approaching wind was decreased in small amount and pressure coefficient was decreased with the increase of the angle of approaching wind by every 22.5°. The air flow keeping approaching wind direction ran straight after entering the windward opening.

A numerical study of wind flow around the TTU building and the roof corner vortex

Comprehensive studies on wind flow around the TTU (Texas Tech University) building were conducted in both field test and wind-tunnel modeling. The results are very useful benchmark database for computational wind engineering studies. Therefore, a number of numerical studies have been carried out since then to explore a deeper insight into the physical nature of the flow characteristics. However, the previous numerical studies have not reported much about the results on the roof corner vortex, which is believed to be very important in engineering applications. This paper presents a recent numerical study of wind flow around the TTU building using an advanced CFD method with large eddy simulation approach. The main focus of this paper is the roof corner vortex. Two approaching wind directions (215° and 225°) to the building were investigated with three mesh systems. The three-dimensional roof corner vortex pattern is successfully simulated. The mean values are generally in good agreement with the wind tunnel modeling and field test, but the rms values are not comparable since the numerical results only include the resolvable part due to the large-scale eddies while the small-scale eddies are modeled by SGS model and not included in the comparison. However, as the mesh system is made finer, the rms values are closer to the measured data since more smaller scale eddies are directly resolved.

Optical porosity and windspeed reduction by coniferous windbreaks in Southern Ontario

Relative windspeed reduction was measured behind nine relatively narrow, homogeneous windbreaks in southern Ontario, Canada to assess whether any characteristics of the windspeed reduction curve could be predicted from optical porosity. The latter was determined for each windbreak using high contrast black and white photographic silhouettes on a computer digitizing system. Minimum windspeeds behind the windbreaks ranged from 29 to 71% of open windspeed; these minima were located 2 to 6 multiples of windbreak height away from the windbreak. Optical porosities of the bottom half of the windbreak ranged from 0 to 31%. Multiple regression of the shelter parameters (location and value of minimum relative windspeed) on the independent variables (optical porosity, open windspeed, surface roughness, approaching wind direction relative to the windbreak, average tree diameter and average tree spacing) showed that the minimum relative windspeed could be predicted from the optical porosity of the bottom half of the windbreak. The results suggest that optical porosity can be used to predict minimum relative windspeeds and may therefore be useful as a guide in the field evaluation of windbreaks.