Wind Tunnel Study Research Articles

Wind loads on contemporary Australian housing

Design pressures given in wind loading standards are based on wind tunnel studies conducted during the 1970s to 90s on rectangular hip and gable roofs. However, most contemporary houses have complex hip-roof geometries with a range of plan footprints. Wind tunnel model studies were carried out on representative one- and two-storey houses to determine cladding design and truss hold-down loads. These loads were compared to design loads determined from wind loading standards AS/NZS 1170.2 and AS 4055. AS 4055 gave conservative design loads in most situations, and AS/NZS 1170.2 underestimated the loads near the windward edges and ridge on the roof. AS/NZS 1170.2 does give satisfactory design loads for wall cladding and truss hold down.

Aerodynamic Interference on Finned Slender Body

Aerodynamic interference can occur between high-speed slender bodies when in close proximity. A complex flowfield develops where shock and expansion waves from a generator body impinge upon the adjacent receiver body and modify its aerodynamic characteristics in comparison to the isolated case. The aim of this research is to quantify and understand the multibody interference effects that arise between a finned slender body and a second disturbance generator body. A parametric wind tunnel study was performed in which the effects of the receiver incidence and axial stagger were considered. Computational fluid dynamic simulations showed good agreement with the measurements, and these were used in the interpretation of the experimental results. The overall interference loads for a given multibody configuration were found to be a complex function of the pressure footprints from the compression and expansion waves emanating from the generator body as well as the flow pitch induced by the generator shockwave. These induced interference loads change sign as the shock impingement location moves aft over the receiver and in some cases cause the receiver body to become statically unstable. Overall, the observed interference effects can modify the subsequent body trajectories and may increase the likelihood of a collision.

Wind tunnel and numerical study of a straight-bladed Vertical Axis Wind Turbine in three-dimensional analysis (Part II: For predicting flow field and performance)

A fluctuating inflow around the surface of rotor blade in the spanwise direction presents a more significant challenge in the performance of wind turbine. In this paper, three-dimensional (3D) experimental and computational investigations of a straight-bladed VAWT (Vertical Axis Wind Turbine) are proposed and analyzed with two straight blades. In wind tunnel experiments, LDV (Laser Doppler Velocimeter) system is presented to investigate the influence of spanwise direction on the straight-bladed of NACA0021 symmetric airfoil in unsteady wind condition. In numerical analysis, 3D transient CFD (Computational Fluid Dynamics) models have been performed to simulate the flow field characteristics of VAWT at the same experimental conditions as wind tunnel experiments. From comparing the results of wind tunnel experiments and numerical analysis, it is found that momentum amount is the largest at the blade center height and the smallest at the blade tip. Furthermore, it is well able to predict the experimental results using CFD model based on k– ε Shear Stress Transport turbulence model.

Wind tunnel and numerical study of a straight-bladed vertical axis wind turbine in three-dimensional analysis (Part I: For predicting aerodynamic loads and performance)

This paper presents a straight-bladed VAWT (vertical axis wind turbine) model for the evaluation of aerodynamic forces and inertial contributions to rotor blade deformation. In this paper, a two-bladed VAWT is proposed and analyzed with CFD (computational fluid dynamics) and wind tunnel experiments in three-dimensional (3D) investigation. In wind tunnel experiments, pressure measurement system is presented to measure the pressure acting on a single blade of straight-bladed VAWT in the spanwise direction. In numerical analysis, 3D CFD models have been performed to simulate the aerodynamic forces characteristics of VAWT with k–ε SST (Shear Stress Transport) (k–ε) turbulence model. From comparing the results of the wind tunnel experiments and numerical analysis, it is found that the fluid force decreased with the increase of spanwise positions excluding the position of support structure. Furthermore, according to the result from six-component balance, the waveforms of the power coefficient Cpw have similar characteristics and show smaller values than CFD calculations.

In situ measurements of wind pressures on low slope membrane roofs

Pressure distributions created by wind flow on low slope roofs is an issue addressed by many wind tunnel studies and selective field experimental studies. Building codes and standards specify pressure coefficient data to determine the wind loads for commercial roofing claddings. Field measurements can provide valuable data to validate the current code provisions for wind loads, as well provide supporting data for existing wind uplift test methods for roof claddings. Thus the Special Interest Group on Dynamic Evaluation of Roofing Systems (SIGDERS) selected four locations (Ottawa, Vancouver, Mt. Pleasant and Rialto) across North America and collected wind speed, wind direction and wind pressure data for extended time periods to understand the wind interaction with low slope membrane roofs. This paper presents the data collected from November 2012 to November 2013 from the Ottawa, Ontario site.Based on the National Building Code of Canada׳s (NBCC) zoning procedure, pressure taps were installed to obtain data for the corner, edge and field roof zones. Occurrences of wind speed exceeding 16ms−1 were considered for various wind directions. Peak and mean pressure coefficients were calculated and compared with NBCC (2010)’s specifications. When instantaneous peak pressure coefficients were compared with the NBCC (2010), the measured data exceeded NBCC (2010)’s specifications for some wind directions. Nevertheless, when the pressure coefficients were compared by paring with their respective tributary area, the data concluded that the current NBCC (2010)’s specifications for the roof cladding and components are equally adequate for the wind load design of low slope membrane roofs.

Evaluation of the Aerodynamics of Drag Reduction Technologies for Light-duty Vehicles: a Comprehensive Wind Tunnel Study

Evaluation of the Aerodynamics of Drag Reduction Technologies for Light-duty Vehicles: a Comprehensive Wind Tunnel Study

Effect of a motorcycle helmet on the airborne dust concentration near a rider’s nose and mouth: wind tunnel study and field test

Wind tunnel experiments were performed to investigate how the presence of a driver wearing a motorcycle helmet affects the airborne dust concentration near the driver’s nose and mouth relative to the ambient dust concentration. Data were collected for different grain size fractions of dust ranging from less than 20 μm to approximately 100 μm. The wind tunnel data were also applied to a field experiment with motorcycles and quads. Results show that the presence of a driver wearing a helmet significantly affects dust concentration. For the helmet tested, the concentration at the mouth position was about 50 % lower than the ambient concentration. At the nose position, the concentration depended on the particle size considered. For fine particles (smaller than approximately 30 μm), the dust concentrations at the nose position were lower than the ambient concentrations, similar to the situation near the mouth. For particles larger than 30 μm, which represent most dust released during typical off-road driving on natural surfaces, the dust concentration at the nose position was higher than the ambient concentration. The reason is most probably the chin guard of the helmet, which disturbs the trajectory of the dust particles and brings many particles to a higher elevation as they flow over the chin guard. Most helmets currently on the market have a chin guard and will behave similarly to the one tested in this study. Applying the wind tunnel results to the field experiment showed that the dust concentrations near the nose of the driver were more than 10 % higher than the ambient concentration, but only for particles coarser than 30 μm. For finer particles, they were lower, up to 70 % lower for particles smaller than 20 μm. On the other hand, the dust concentration near the mouth was significantly lower than the ambient concentration, less than half for all particle size classes investigated. This study shows that the effect of wearing a helmet should be taken into consideration when calculating human exposures to airborne dust.

Numerical and experimental analysis of a multi-directional wind tower integrated with vertically-arranged heat transfer devices (VHTD)

The aim of this work was to investigate the performance of a multi-directional wind tower integrated with vertically-arranged heat transfer devices (VHTD) using Computational Fluid Dynamics (CFD) and wind tunnel analysis. An experimental scale model was created using 3D printing. The scale model was tested in a uniform flow closed-loop wind tunnel to validate the CFD data. Numerical results of the supply airflow were compared with experimental data. Good agreement was observed between both methods of analysis. The Grid Convergence Method (GCI) method was used to estimate the uncertainty due to discretisation. Results have indicated that the achieved indoor air speed was reduced by 8–17% following the integration of the VHTD. The integration of VHTD had a positive effect on cooling performance of the wind tower, it reduced the incoming fresh air by up to 12K. The effect of varying the number of VHTD rows (1–3 rows) on the system’s performance were also investigated. Additional simulations were also conducted to investigate the effect of atmospheric boundary layer (ABL) flows on the wind tower ventilation performance and also compare it with the results of uniform flow wind tunnel study.

A wind tunnel study of sand-cemented bodies on wind erosion intensity and sand transport

Wind tunnel experiments were used to test the capacity of sand-cemented bodies (SCB) on mulch beds. The total sand transport rate decreased as the level of SCB coverage increased. At higher SCB coverage (more than 40 %), the sand transport was basically unaffected by further increases in SCB coverage. While at low SCB coverage (less than 10 %), wind velocity played an important role in sand transport. Under the same SCB coverage, the sand transport depends on the increasing SCB size, due to the decrease in SCB density. The wind erosion intensity exponentially decreased with increasing SCB coverage (less than 40 %). The vertical profiles of horizontal mass flux from the SCB mulch–sand surface were also described by an exponential relationship. The vertical sand movement of particles was more sensitive to changes in SCB coverage at 20–40 %, compared with at less than 10 %. When the SCB coverage was more than 40 %, the decay rate of sand transport with height was nearly invariable. In summary, increases in SCB coverage had anti-erosion benefits for the underlying sand surface and could be considered for the development of a new type of sand fixation technology.

Numerical Investigation of Mini Wind Turbines Near Highways

High-speed vehicle motion on the highways produces localized winds whose energy can be harnessed. These local winds have less variability especially if the highway traffic is constant. The idea of extracting energy from highway winds has been conceptualized in many studies before. However, the feasibility of this idea has never been tested using analytical, computation, or experimental methods. In this study, we numerically compute the amount of power that can be extracted from local highway winds due to vehicular motion. A unsteady Reynolds-averaged Navier–Stokes (URANS) method is used for modeling the atmospheric boundary layer (ABL). Realistic computer-aided design (CAD) models of cars and trucks separated by spacing information obtained from the existing standards are used to model the vehicle motion. A vertical axis wind turbine (VAWT) is used for extracting energy from the wind. The entire framework of ABL, vehicles, and turbine is simulated using overset grids and multiple translating and rotating frames of reference. Many vehicle motion scenarios were compared to the case of an isolated wind turbine. The initial results show a significant increase in the power that can be extracted by these turbines. The average extracted power increases about 317% when compared to the case without any vehicular motion. Field measurements or wind tunnel studies are required to provide validation for the computations and to determine if more advanced turbulence modeling methodologies have to be employed for these studies.

Variation of aerodynamic coefficients with air flow parameters on long span bridge deck

Wind load is critical for bridges with high strength to weight ratio and determined experimentally using wind tunnel study that involves huge expenditure and time. In this study, behaviour of bridge deck is analysed by changing air flow parameters considering the structure submerged in turbulent flow using k-e turbulence model with boundary conditions calibrated to simulate neutral equilibrium atmospheric boundary layer. A computational model was considered to determine aerodynamic behaviour of bridge deck for different angle of attack of wind and results were compared with wind tunnel experiments keeping boundary conditions same. The aerodynamic behaviour of different bridge deck cross section are analysed using the computational model for different air flow parameters. The variation of aerodynamic coefficients are found and presented for box girder, plate girder, trapezoidal section and section of Great Belt East Bridge and attempt was made to select the optimum section to minimise the aerodynamic forces.

Effect of shelter porosity on downwind flow characteristics

Previous wind-tunnel studies were focused mainly on lonely standing windbreaks or wind fences with respect to their wind velocity reduction efficiency and effective shelter distance. In presented wind-tunnel study, we investigated the effects of a three different fence porosities (0.5, 0.25 and 0) embodied in a shelter-like building for coal convey by means of two-component Laser Doppler Anemometry (LDA). The turbulent flow characteristics behind the fences were compared with those performed without the fence. For characterization of the fence effectiveness we used following quantities: wind-speed and turbulence kinetic energy reduction, and time fractions of the turbulent coherent structures associated with the sediment transport (sweeps and outward interactions). Results from mentioned quantities revealed that for the case of embodied fence the shelter construction has significant impact on the flow characteristics behind. The fence of the 0.5 porosity has been indicated as the most shelter effective considering the studied quantities.

Numerical Investigations on Intermittency Route to Aeroelastic Flutter

Recent wind tunnel studies have shown that an aeroelastic system, prior to losing stability through flutter, goes through a regime where the response is characterized by intermittent bursts of periodic oscillations. The focus of this study is to investigate the reasons for this intermittent behavior through a numerical model. The studies indicate that the intermittency is observed only when the flow is accompanied by small random fluctuations. A stochastic bifurcation analysis is carried out to gain an understanding for this phenomenological interesting behavior.

Wind tunnel study of axial force variation in guys of flexible mast modelWind models

Measurements of the axial force variation in guys of mast model subjected to wind load of three different wind structures are presented in the paper. The measurements have been carried out in the wind tunnel of Wind Engineering Laboratory at Cracow University of Techn ology. The subjects of the research are two guyed masts of triangular and square shaft cross-sections. Mean values of forces and standard deviations as functions of wind parameters and wind attack angle have been calculated. Significant influence of wind structure on the forces in guys has been confirmed as the result. Additionally there has been noticed possibility of mast vibrations at critical velocities.

Experimental Determination of Wind Flowing around a Building Configuration

This paper deals with a solution of air flow around the group of structures. Boundary layer for urban terrain was simulated in BLWT STU wind tunnel. The series of flow characteristics were investigated with boundary layer for the urban terrain, which was simulated with rough elements and barriers of different heights. Experimental results presented as mean velocity, turbulence intensity, integral length scale of turbulence and power spectral density were compared with [1] and ESDU data. Wind environment studies around idealized building and building configurations were carried out with the major focus on flow caused by strong wind with different directions. In this research, a series of parametric wind tunnel studies was carried out to investigate the effects of building width, height and the building configurations on the wind pressure distribution [2,3 and 4]. In the article, we will discuss this issue for atypical building configuration in the center of Bratislava. We will indicate the high wind speed areas for strong wind conditions and try to find optimal solutions in terms of the planned groups of new buildings. The wind pressure distribution on the structures is an important parameter in terms of wind load calculation.

Wind tunnel studies of gas dispersion over complex terrain

Wind tunnel studies of gas dispersion over complex terrain model were performed in VZLU Prague. The terrain model with a ground-level emission source was mounted in a boundary layer wind tunnel. Flow and concentration field behind the source was measured. The model presented an area of the Liberec city, 9.0 × 2.4 km in full scale. The emission source was mounted at the position of a heating plant in the model centre and concentration field was measured using flame ionisation detectors. The experimental results will be used for validation and verification of a new computational dispersion model intended for use in case of accidents with dangerous gas leakages in selected areas in Czech Republic.

Wind tunnel study on vortex-induced Helmholtz resonance excited by oblique flow

A wind tunnel study examining the vortex-induced internal pressure dynamics of a rigid structure with a single dominant opening in laminar flow is presented. The internal pressures in a rigid structure configured with three different openings and two different internal volumes were measured under four different incoming wind velocities and different wind angles from 0° to 90°. The mechanism of vortex-induced internal pressure dynamics under oblique wind was explored, and the effect of Strouhal number on the vortex-induced internal pressure dynamics was investigated. It was found that vortex shedding is produced across the orifice under grazing flow, and a significant double resonance phenomenon may appear in the internal pressure spectra. Vortex-induced internal pressure resonance may occur in some cases, which leads to a significant increase in internal pressure pulsation. Wind velocity, wind angle, Helmholtz frequency, and the opening width exert a significant influence on the frequency and amplitude of the internal pressure resonance characteristic. Theoretical estimation about Helmholtz frequency and vortex shedding frequency is of good reliability but it is not suitable if the interaction of vortex shedding and Helmholtz resonance is significant enough. The Strouhal number is an important parameter in the evaluation of vortex-induced internal pressure resonance, and the vortex-induced internal pressure resonance is more likely to occur when the Strouhal number, expressed as fHw0/U0 (U0 can be estimated as U sinθ or measured by a cobra probe), lies within the range of 0.2–0.7. The Strouhal number, expressed as fHw0/U, can be used to access the internal pressure resonance characteristic at different wind angles.

Experimental study of the effects of dish antennas on the wind loading of telecommunication towers

A several number of communication lattice tower collapsed in the past years due to strong winds in Cuba, most of them with a high number of dish antennas. Antennas generate a modification on the wind flow around the tower acting as a screen against wind load and transmitting strong efforts to the tower members. Structural design under wind loads of latticed towers is concerned about the approach to take into account the effect of dish antennas and their interference at different positions in the tower. In this paper, an experimental study in a boundary layer wind tunnel was performed to obtain the drag coefficients and the interference factor on a square section latticed tower with dish antennas. The tower was divided into three sections, which were studied with one and two dish antennas. Results show that interference factor can achieve values smaller and greater than the unity for dependent on the wind direction and relative position of dishes on the tower section. Drag coefficients for sections without antennas are in correspondence with codes.

Aerodynamic interference and vortex-induced vibrations on parallel bridges: The Ewijk bridge during different stages of refurbishment

This paper presents the results of sectional wind tunnel studies of the Ewijk bridge, a 270m span cable-stayed bridge crossing over the river Waal in Netherlands, which during its refurbishment was doubled with a close parallel bridge. The aerodynamics of parallel bridges may be complex and unpredictable, therefore specific wind tunnel tests were conducted.The tests were performed with sectional models in a 1:50 scale with the aim of identifying the aerodynamic interference effects between the two decks, in terms of aeroelastic stability, vortex-induced vibrations, and stationary aerodynamic loads. Several configurations were tested, since during various stages of refurbishment, the profile, the eigen-frequencies, the mass, and the relative position of the deck change.Results show that for the considered case, the interference effect is characterized by a significant change in the steady aerodynamic coefficients, vortex-induced vibrations of the upstream box-girder and forcing of the downstream bridge section, and no stability problems.

A wind tunnel study on control methods for cable dry-galloping

The common vibration of cable caused by rain-wind combination has been known as most typical type and a lot kind of its countermeasures has been proposed for suppressing this phenomenon. Recently, stayed-cables were also proved that they could be excited in dry state (without rain), which is called dry-galloping. Recently, its mechanisms have been explained by axial flow, Reynolds number and so on. To clarify the characteristics of this galloping, wind tunnel test of a cable model with various kinds of wind angle was conducted. Then, three types of countermeasure were examined to suppress dry- galloping of bridge cable. The tests confirmed that the occurrence of dry-galloping depends on relative wind attacked angles and onset reduced wind speed. Furthermore, single spiral wire, double spiral wire and circular ring were found to have high effectiveness in mitigating this galloping when those are installed properly.