Wind Incidence Angle Research Articles

Wind-induced mean interference effects between two closed spaced buildings

The mean interference effects between two rectangular buildings located in close proximity in a geometrical configuration of ‘L’ and ‘T’ plan shape are studied through wind tunnel test on 1:300 scale rigid models. The mean surface pressure distributions on all the walls of two buildings located in close proximity as well as in an isolated position are measured over an extended range of wind directions. The mean responses of pair of buildings namely, block-1 and block-2 subjected to interference effects are evaluated using experimentally obtained wind loads and, subsequently compared it, with the responses of a similar building in an isolated position. Effectiveness of upstream building location and wind orientation in changing the mean wind pressure distributions and responses of upstream and downstream building are also assessed. At wind incidence angle of 0°, presence of upstream block-1 reduces the mean along-wind displacement of block-2 of ‘L’ and ‘T’ shape arrangements up to 25% and 71% respectively as compared to that of corresponding block in an isolated position. However, the presence of upstream block-1 increases the maximum mean torque on block-2 of ‘L’ and ‘T’ shape arrangement up to 28%, and up to 88% respectively as compared to maximum mean torque developed on a similar block in an isolated position.

Wind-Driven Natural Ventilation in an Areaway-Attached Basement with a Single-Sided Opening for Residential Purposes

This paper discusses the sustainability of the areaway-attached basement concept with the attentions focused on wind-driven single-sided natural ventilation. First, numerical simulations were performed on an areaway-attached basement with a single-sided opening. Two CFD approaches: Reynolds averaged Navier-Stokes (RANS) and large-eddy simulation (LES) were used and compared with the previous experimental results of effective ventilation rate. A good agreement between the measurement and LES model was found and RANS model tends to underestimate the ventilation rates. Furthermore, Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement was investigated for different wind incidence angles to examine the influences of wind direction on ventilation performances.

Wind tunnel simulation of the three-dimensional airflow patterns behind cuboid obstacles at different angles of wind incidence, and their significance for the formation of sand shadows

Sand shadows commonly form downwind of obstacles in arid and semi-arid regions. Understanding their dynamics requires insights into the airflow patterns behind the obstacles under different wind regimes. Here, we studied models of cuboid obstacles to characterize the three-dimensional responses of airflow behind obstacles with different shape ratios to variations in the incident flow in a wind-tunnel simulation. Wind velocity was measured using particle image velocimetry (PIV). The flow patterns behind cuboid obstacles were complicated by changes in the incidence angle of the approaching flow and in the obstacle's shape ratio. The flows separated both horizontally and vertically, creating reverse-flow cells downwind of the obstacles. The horizontal cells were characterized by two asymmetrical, opposing reverse vortices at flow incidence angles greater than 60 to 65°, whereas the vertical cells formed a single vortex at all angles. The cells shifted position in response to changes in the incidence angle and shape ratio, reflecting the interaction between outer and reverse flows. The parameters of the horizontal and vertical reverse cells depended on the shape ratios and incidence angles but not on the wind velocity. The sizes of the horizontal and vertical reverse cells were correlated, reflecting their interactions. The low-velocity “shadow” behind the obstacle caused sand deposition and determined the sand shadow's evolution. Field experiments will be required to relate these airflow patterns to sand shadow development.

Mean interference effects between two buildings: effects of close proximity

AbstractThis paper presents the mean interference effects between a pair of buildings located in close proximity in a geometrical configuration of L‐ and T‐plan shapes. Experiments are carried out in a closed‐circuit wind tunnel on models of a 1:300 scale to measure the mean pressure distributions on two building models located in close proximity and on models in isolated position over an extended range of wind directions. The mean responses of buildings, namely block 1 and block 2 of L‐ and T‐shaped arrangements subjected to interference effects, are evaluated using the experimentally obtained wind loads and compared it with the responses of a similar building in isolation. Significant changes are observed in the responses of block 1 and block 2 of L‐ and T‐shaped arrangements as compared to a similar building in an isolated position. The interference levels are found to be dependent strongly on the angle of attack and the arrangement of the buildings with respect to each other. At wind incidence angle 0°, the presence of block 1 reduces the mean along the wind displacement of block 2 of the L‐ and T‐shaped arrangements up to 21% and 37%, respectively, as compared to a similar block in an isolated position. Copyright © 2009 John Wiley & Sons, Ltd.

Experimental study of wind-induced pressures on buildings of various geometries

This paper presents the experimental investigation of wind pressure distributions on models of typical plan shape buildings over an extended range of wind incidence angles of 0° to 180° at an interval of 15°. Two L-shaped and two T-shaped models of same plan area and height but having the different dimensions were tested in a closed circuit wind tunnel under boundary layer flow. The models were made from Perspex sheets at a geometrical scale of 1:300. Fluctuating values of wind pressures are measured at pressure points on all the sides of the models and mean, maximum, minimum and r.m.s. values of pressure coefficients were evaluated from pressure records. It is observed that plan shape and dimensions of models significantly affects the wind pressure distributions on different faces of the models. The location and magnitude of the measured peak pressure coefficient vary considerably with wind direction. The influence of shifting the upstream block from edge of the downstream block to center of it, which transforms the L-shape into T-shape model, is also noticeable on the pressure coefficient distribution.

Influence of an upstream building on the wind-induced mean suction on the flat roof of a low-rise building

The effect of an upstream building on the suction forces on the flat roof of a low-rise building placed in the wake of the former is analyzed. The analysis has been performed by wind tunnel testing of a flat roof, low-rise building model equipped with pressure taps on the roof and different block-type buildings (only configurations where the upstream building is as high or higher than the downstream one are considered in this paper). The influence of the distance between both buildings on the wind loads on the downstream building roof is analyzed, as well as the height of the upstream one and the wind angle of incidence. Experimental results reveal that the wind load increases as the relative height of the upstream building increases, the wind load being highest for intermediate distances between buildings, when a passage between them is formed.

Wind-induced loading and dynamic responses of a row of tall buildings under strong interference

This paper studies wind-induced interference effects on a row of five square-plan tall buildings arranged in close proximity. Mean and fluctuating wind loads are measured on each building member and wind-induced dynamic responses of the building are estimated with the high-frequency force-balance technique. The modifications of building responses from interference over a practical range of reduced velocities are represented by an envelope interference factor. Wind tunnel experiments and response analysis are carried out under all possible angles of wind incidence, at four different building separation distances, and for two arrangement patterns of buildings in the row, that is the parallel and diamond patterns. It is found that building interference leads to amplified dynamic responses in many cases but reduction in responses also occurs at some wind incidence. For a building row of the parallel pattern, five distinct wind incidence sectors of different levels and mechanisms of interference effect can be identified. The largest values of envelope interference factors can reach 2.4 for the torsional responses. When the row of tall buildings is arranged in the diamond pattern, increase in wind excitation occurs at many wind angles due to a “wind catchment” effect. The interference factors have larger peak values, reaching 2.1 in the sway directions and above 4 in torsion. However, all large amplifications of building responses do not occur in the situations of peak resonant dynamic responses of the single isolated building. Thus, the design values of peak dynamic responses of a tall building are not significantly magnified when placed in a row.

Design Wind Loads on Reinforced Concrete Chimney – An Experimental Case Study

The present paper is aimed at providing a better understanding of the effect of interference and influence of strakes for wind load on Thermal Power Station (TPS) chimneys. Measurements of across and along vibration have been made on scale model of Panipat power station chimney, India. The aeroelastic model of the chimney has been tested in a simulated atmospheric boundary layer of height 1.0 m in the Boundary Layer Wind Tunnel at IIT Roorkee, India.The chimney model has been fabricated with FRP (fiber-reinforced plastic) at a geometric scale of 1:150 representing a chimney with height of 100 m in prototype. The wind tunnel tests for the present study have been carried out with the objective of obtaining the maximum along-wind and across-wind response of the chimney and this has been expressed in terms of bending moments. In particular, the interference effect between other nearby structures of the TPS has been investigated. Based on dimensional analysis measured values of chimney model have been converted into prototype values.In the present study, particular attention has been given to bending moment due to across-wind vibration, because it has been found that across-wind vibration is more predominant for the case of interference at a 45o angle of wind incidence. Bending moment due to across-wind vibration for interference is found to be approximately double compared to that of stand-alone condition.To control across wind vibration, strakes have been mounted over the top one-third height of the chimney. It is found that there is a significant decrease in the magnitude of across as well as resultant bending moment in presence of strakes.

Wind-induced ventilation performances and airflow characteristics in an areaway-attached basement with a single-sided opening

In the present study, we performed both wind tunnel experiments and numerical simulations on a scale model with the focus on wind-driven natural ventilation in an areaway-attached basement with a single-sided opening. In the experiments, the mean value of the effective ventilation rate, purging flow rate ( PFR) was measured for nine wind incidence angels based on the homogeneous emission rate method. The experimental results were used to validate two numerical approaches: Reynolds averaged Navier–Stokes (RANS) modeling and large-eddy simulation (LES). The influences of inflow turbulent fluctuations for LES modeling were also examined. The comparisons between the experiment and the numerical simulation indicate that LES can provide more accurate results than RANS and the inflow turbulent fluctuations should be taken into account for LES modeling. Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement were further studied for different wind incidence angles to investigate the influence of wind direction on ventilation performance in the areaway space. Furthermore, the relationships between the effective ventilation rate and the kinetic energy in the basement space were analyzed for three wind directions: 0°, 90° and 180°. A close correlation was found between the mean values, whereas the corresponding time variations showed large discrepancies. Finally, we compared the effective ventilation rate obtained using the homogeneous emission rate method and the airflow rates through the opening using two integration procedures. The effective ventilation rates were found lower than the airflow rates through the opening.

Comparison Between Large-Eddy Simulation and Reynolds-Averaged Navier–Stokes Computations for the MUST Field Experiment. Part II: Effects of Incident Wind Angle Deviation on the Mean Flow and Plume Dispersion

Large-eddy simulations (LES) and Reynolds-averaged Navier-Stokes (RANS) computations of pollutant dispersion are reported for the Mock Urban Setting Test (MUST) field experiment flow. In particular we address the effects of incident wind angle deviation on the mean velocity and on the mean concentration fields. Both computational fluid dynamical methods are assessed by comparing the simulation results with experimental field data. The comparative analysis proposes to relate the plume deflection with the flow channelling effects. The results show that the plume deflection angle varies with the altitude. As the ground is approached the plume is shown to be almost aligned with the street canyon direction and independent of the incident wind directions considered. At higher altitudes well above the obstacles, the plume direction is aligned with the mean wind direction as in dispersion over flat terrain. The near-ground plume deflection is the consequence of a strong channelling effect in the region near the ground. The mean concentration profiles predicted by LES and RANS are both in good qualitative agreement with experimental data but exhibit discrepancies that can be partly explained by the influence of small incident wind angle deviation effects. Compared to RANS, LES predicts a higher channelling and thus a higher deflection of the plume. Results on the fluctuating intensity of the concentration obtained from LES show a satisfactory agreement with experiments. This information is not available from RANS for which only the mean concentration modelling is considered.

Aerodynamic flow simulation of wind turbine: Downwind versus upwind configuration

Large scale wind turbines and wind farms continue to grow mounting 94.1 GW of the electrical grid capacity in 2007 and expected to reach 160.0 GW in 2010. Wind energy plays a vital role in the quest for renewable and sustainable energy as well as in reducing carbon emission. Early generation wind turbines (windmills) were used mainly for water pumping and seed grinding, whereas today they generate 1/5 of the current Denmark’s electricity and will double its grid capacity reaching 12.5% in 2010. Wind energy is plentiful (72 TW estimated to be commercially viable) and clean while its intensive capital cost still impede widespread deployment. However, there are technological challenges, i.e. high fatigue load, noise emission, and meeting stringent reliability and safety standards. Newer inventions, e.g., downstream wind turbines and flapping rotor blades, are sought to enhance their performance, i.e. lower turning moments and cut-in speed and to absorb portion of the cost due to the absent of yaw mechanisms. In this work, numerical analysis of the downstream wind turbine blade is conducted. In particular, the interaction between the tower and the rotor passage is investigated. Circular cross sectional tower and aerofoil shapes are considered in a staggered configuration and under cross-stream motion. The resulting blade static pressure and aerodynamic forces are computed at different incident wind angles and wind speeds. The computed forces are compared to the conventional upstream wind turbine. Steady state and transient, incompressible, viscous Navier–Stokes and turbulent flow analysis are employed. The k-epsilon model is utilized as the turbulence closure. The passage of the rotor blade is governed by ALE and is represented numerically as a sliding mesh against the upstream fixed tower domain.

Evaluation of a fast response pressure solver for flow around an isolated cube

This work describes and evaluates a pressure solver that has been incorporated into a fast response three-dimensional building-resolving diagnostic wind modeling system. The solver computes the three-dimensional pressure field around buildings and on exterior walls in terms of a coefficient of pressure by solving a simplified pressure Poisson equation (that neglects turbulence stresses in the Navier-Stokes) for incompressible flow. The input to the solver is the three-dimensional mean wind field obtained from a fast response empirical-diagnostic urban wind model. The present study is an evaluation of the pressure solver using wind-tunnel data for flow normal to and at a 45° angle to an isolated cubical building. Results for the normal incident wind angle case indicate that the model satisfactorily reproduces the general spatial patterns and the magnitude of the pressure difference around much of the cube. Details of the flow field that are not satisfactorily predicted include the spatial distribution of pressure on the roof and the lower half of the front side of the building and the magnitude along the sidewalls where pressures are over predicted. The results for the 45° case show reasonable agreement between the model and experiments on the front and the back walls, but over predict pressures on the leading edge of the rooftop. Regions with poor pressure predictions appear to be a result of unsatisfactory mean wind modeling.

Turbulence effects on the discharge coefficient and mean flow rate of wind-driven cross-ventilation

This experimental study uses a wind tunnel and scale model to investigate turbulence effects on the discharge coefficient and mean flow rate of wind-driven cross-ventilation. The approaching flows include low turbulence smooth flow and grid-generated turbulent flow. Two different cross-ventilation configurations are considered in this study: (1) two opposite walls, each with one opening, and (2) two adjacent walls, each with one opening. The discharge coefficients of different flow conditions are determined by a fan technique. It is found that the discharge coefficient is a function of Reynolds number, wind incidence angle and direction of air flow (inhale or exhale), but independent of external turbulence intensity and wall porosity. However, because the leeward pressure is affected by external turbulence, the internal pressure and inlet velocity are dependent on external turbulence when the openings are on the opposite walls. The experimental results also verify that internal pressure and mean air flow rate can be predicted once the external pressure distribution and opening areas are known, regardless of whether the openings are on opposite walls or on adjacent walls.

Evaluation of the Flow Distortion around the Campbell Scientific CSAT3 Sonic Anemometer Relative to Incident Wind Direction

Abstract In June 2002, a high-frequency air–sea momentum system was deployed in the surf zone for 3 days as part of an experiment to quantify air–sea momentum transfer when the wind and wave direction were at angles. The system obtained measurements in the nearshore via a high-resolution Campbell Scientific CSAT3 3D sonic anemometer and five high-frequency saltwater wave staffs. An advantage of the air–sea momentum system is that direct measurements of the atmospheric turbulent fluctuations can be obtained and applied to the calculation of momentum transfer at the air–sea interface. The Campbell Scientific CSAT3 sonic anemometer was postcalibrated under turbulent wind conditions to determine incident wind direction measurements influenced by the geometry of the instrument. Measurement results are compared to a pre-established benchmark, constant tow speed; and the mean wind speed, incident wind direction, and spectral density characteristics are evaluated to resolve specific instrument orientations in which the measurements are corrupted by the head and probe supports of the sonic anemometer. Calibration testing of the sonic anemometer determined that the mean wind speeds are reduced by 16% over a 40° range for incident wind angles of 160°–200° relative to the head of the anemometer. Tilting the anemometer is found to decrease mean wind speed reduction influenced by the geometry of the anemometer. Variations in the measured wind directions were found to be greater than 1° for incident wind angles between 160° and 200° for 0° and 10° of tilt. Spectral characteristics were highly repeatable for all wind angles except for incident wind angles of 180° for 0° and 10° of tilt.

Sediment Catcher to Trap Coarse Organic Matter and Soil Particles Transported by Wind

Wind can erode fertile topsoil and reduce soil fertility. Evaluating the effect of wind erosion on soil fertility is crucial to achieve sustainable agriculture in areas suffering from desertification caused by wind erosion. To estimate soil loss and associated soil nutrient loss by wind erosion, flux of coarse organic matter (COM) (defined here as free organic debris larger than 200 µm) and soil particles (defined as the other soil components) must be measured separately. This is because their modes of transport are different, and COM plays a prominent role in soil nutrient dynamics in some semiarid zones where COM accounts for a large percentage of the total soil carbon. Because the Big Spring Number Eight (BSNE) sampler can trap both COM and soil particles 0.05 m above the surface, we designed a sediment catcher, the Aeolian Materials Sampler (AMS), to trap these components below 0.05 m. This device can be manufactured easily at low cost. AMS performance was tested by wind tunnel experiments over a range of wind velocities typically observed in erosive storms and with six incident wind angles because the AMS is a buried-type sampler that is unable to rotate toward the wind. The trapping efficiency of the AMS for COM and soil particles was not 100%, but it can be calibrated easily using wind data. Therefore, we can estimate the mass flux of COM and soil particles and evaluate the effect of wind erosion on soil fertility using the AMS with the BSNE sampler.

A probability density function of liftoff velocities in mixed-size wind sand flux

With the discrete element method (DEM), employing the diameter distribution of natural sands sampled from the Tengger Desert, a mixed-size sand bed was produced and the particle-bed collision was simulated in the mixed-size wind sand movement. In the simulation, the shear wind velocity, particle diameter, incident velocity and incident angle of the impact sand particle were given the same values as the experimental results. After the particle-bed collision, we collected all the initial velocities of rising sand particles, including the liftoff angular velocities, liftoff linear velocities and their horizontal and vertical components. By the statistical analysis on the velocity sample for each velocity component, its probability density functions were obtained, and they are the functions of the shear wind velocity. The liftoff velocities and their horizontal and vertical components are distributed as an exponential density function, while the angular velocities are distributed as a normal density function.

Interference effects on wind loading of a row of closely spaced tall buildings

Interference effects on a row of square-plan tall buildings arranged in close proximity are investigated with wind tunnel experiments. Wind forces and moments on each building in the row are measured with the base balance under different wind incidence angles and different separation distances between buildings. As a result of sheltering, inner buildings inside the row are found to experience much reduced wind load components acting along direction of the row ( x) at most wind angles, as compared to the isolated building situation. However, these load components may exhibit phenomena of upwind-acting force and even negative drag force. Increase in x-direction wind loads is observed on the upwind edge building when wind blows at an oblique angle to the row. Other interference effects on y-direction wind loads and torsion are described. Pressure measurements on building walls and numerical computation of wind flow are carried out at some flow cases to explore the interference mechanisms. At wind angle around 30° to the row, wind is visualized to flow through the narrow building gaps at high speeds, resulting in highly negative pressure on associated building walls. This negative pressure and the single-wake behavior of flow over the row of buildings provide explanations for the observed interference effects. Interference on fluctuating wind loads is also investigated. Across-wind load fluctuations are much smaller than the isolated building case with the disappearance of vortex shedding peak in the load spectra. Buildings in a row thus do not exhibit resonant across-wind response at reduced velocities around 10 as an isolated square-plan tall building.

Natural cross-ventilation in buildings: Building-scale experiments, numerical simulation and thermal comfort evaluation

The constantly increasing energy consumption due to the use of mechanical ventilation contributes to atmospheric pollution and global warming. An alternative method to overcome this problem is natural ventilation. The proper design of natural ventilation must be based on detailed understanding of airflow within enclosed spaces, governed by pressure differences due to wind and buoyancy forces. In the present study, natural cross-ventilation with openings at non-symmetrical locations is examined experimentally in a test chamber and numerically using advanced computational fluid dynamics techniques. The experimental part consisted of temperature and velocity measurements at strategically selected locations in the chamber, during noon and afternoon hours of typical summer days. External weather conditions were recorded by a weather station at the chamber's site. The computational part of the study consisted of the steady-state application of three Reynolds-Averaged Navier-Stokes (RANS) models modified to account for both wind and buoyancy effects: the standard k– ɛ, the RNG k– ɛ and the so-called “realizable” k– ɛ models. Two computational domains were used, corresponding to each recorded wind incidence angle. It is concluded that all turbulence models applied agree relatively well with the experimental measurements. The indoor thermal environment was also studied using two thermal comfort models found in literature for the estimation of thermal comfort under high-temperature experimental conditions.

Experimental study on possible vortex shedding in a suspension bridge - Part II - Results when under typhoon Babs and York

Statistical analysis on the measured responses of a suspension bridge deck (Law, et al. 2007) show that vibration response at the first torsional mode of the structure has a significant increase at and beyond the critical wind speed for vortex shedding as noted in the wind tunnel tests on a sectional model. This paper further analyzes the measured responses of the structure when under typhoon conditions for any possible vortex shedding events. Parameters related to the lifting force in such a possible event and the vibration amplitudes are estimated with a single-degree-of-freedom model of the system. The spatial correlation of vortex shedding along the bridge span is also investigated. Possible vortex shedding events are found at both the first torsional and second vertical modes with the root-mean-square amplitudes comparable to those predicted from wind tunnel tests. Small negative stiffness due to wind effects is observed in isolated events that last for a short duration, but the aerodynamic damping exhibits either positive or negative values when the vertical angle of wind incidence is beyond <TEX>${\pm}10^{\circ}$</TEX>. Vibration of the bridge deck is highly correlated in the events at least in the middle one-third of the main span.

Experiments on 2D rectangular prisms at high Reynolds numbers in a pressurised wind tunnel

Experiments on rectangular prisms with fineness ratio (width-to-depth ratio) of 2, 3 and 4 are reported in this paper. The tests were performed in the 2D test section of a pressurised wind tunnel in smooth and turbulent flow for Reynolds numbers ranging from 0.15 × 10 6 to 4 × 10 6 , for Mach numbers not exceeding 0.30. Steady and unsteady measurements of surface pressures on a chord-wise strip as well as overall lift, drag and pitching moment on the model were carried out. Flow fluctuations in the wake were also captured with a hot-film probe. The experiments helped define the influences of Reynolds number, after-body length, angle of wind incidence and approaching flow turbulence on the aerodynamics of rectangular prisms. The influence of the edge treatment of the rectangular prisms, i.e. square edges versus small or large chamfer, was also studied at high Reynolds numbers. The paper presents a detailed description of the experiments and an overview of the effects of Reynolds number, Mach number and flow turbulence observed in the study.