Wind Tunnel Study Research Articles

A field study to estimate the impact of noise barriers on mitigation of near road air pollution

Air pollution associated with vehicle emissions from roadways has been linked to a variety of adverse health effects. Wind tunnel and tracer studies show that noise barriers mitigate the impact of this pollution up to distances of 30 times the barrier height. Data from these studies have been used to formulate dispersion models that account for this mitigating effect. Before these models can be incorporated into Federal and State regulations, it is necessary to demonstrate their applicability under real-world conditions. This paper describes a comprehensive field study conducted in Riverside, CA, in 2019 to collect the data required to evaluate the performance of these models. Eight vehicles fitted with SF6 tracer release systems were driven in a loop on a 2-km stretch of Interstate 215 that had a 5-m tall noise barrier on the downwind side. The tracer, SF6, was sampled at over 40 locations at distances ranging from 5 to 200 m from the barrier. Meteorological data were measured with several 3-D sonic anemometers located upwind and downwind of the highway. The data set, corresponding to 10 h collected over 4 days, consists of information on emissions, tracer concentrations, and micrometeorological variables that can be used to evaluate barrier effects in dispersion models. An analysis of the data using a dispersion model indicates that current models are likely to overestimate concentrations, or underestimate the mitigation from barriers, at low wind speeds. We suggest an approach to correct this problem.

Wind Tunnel Tests of a Model Small-Scale Horizontal-Axis Wind Turbine Developed From Blade Element Momentum Theory

Abstract The small-scale horizontal-axis wind turbines (SHAWTs) have emerged as the promising alternative energy resource for the off-grid electrical power generation. These turbines primarily operate at low Reynolds number and low tip speed ratio conditions. Under such circumstances, the airfoil selection and blade design of a SHAWT becomes a challenging task. The present work puts forward the necessary steps starting from the aerofoil selection to the blade design and analysis by means of blade element momentum theory (BEMT) for the development of four model turbine rotors composed of E216, SG6043, NACA63415, and NACA0012 airfoils. This analysis shows the superior performance of the model rotor with E216 airfoil in comparison with other three models. However, in the subsequent wind tunnel study with the E216 model, a marginal drop in its performance due to mechanical losses has been observed.

Wind tunnel study of a fish-plan shape modelunder different isolated wind incidences

Wind tunnel study of a fish-plan shape modelunder different isolated wind incidences

A CFD study on the Irwin probe flows

Irwin probes are surface sensors commonly used to determine the shear stress in near-wall regions, by calibration of related pressure signals. These devices have been widely used in wind tunnel studies dealing with pedestrian-level wind conditions. In this work, three-dimensional Computational Fluid Dynamics (CFD) simulations are performed to characterize the complex flow field and pressure distribution developed around and within the Irwin probe, at three distinct low-Reynolds number regimes. The emergence of coherent flow structures past the sensor is categorised and preventive spacing intervals, necessary to mitigate mutual interference, is numerically evaluated. The computations corroborate the original spacing recommendations by Irwin. For typical operation conditions, long streamwise tip vortices are observed in the wake of a single sensor. In addition, the predictions suggest the existence of a low-Reynolds number threshold, below which such structures are supressed, resulting in diminished interference effects. Numerical results also suggest a nearly uniform axial pressure distribution and place in evidence very interesting flow field characteristics.

Wind tunnel study on influences of morphological parameters on drag coefficient of horizontal non-uniform buildings

The implementation of morphometric evaluations of complex buildings in urban areas is essential for urban canopy models. There are two main reasons for this: the impossibility of conducting a micrometeorological evaluation of a building that is still in the design phase and the difficulty of estimating the roughness height of an urban area containing complex buildings using an anemometric method. This study used wind tunnel experiments to investigate the effects of the planar area, frontal area, shape, and layout of buildings on their aerodynamic characteristics. The results indicated that the curves showing the relationships between the buildings drag coefficient, Cd, and the four morphological parameters had similar patterns, with Cd=b·exp(−xca)·xd. The influences on Cd of both the shape and layout parameters showed peaks, as did the planar and frontal densities. A surface roughness model based on the morphometric evaluations of the aerodynamic parameters of non-uniform buildings was developed.

Wind turbine wakes on escarpments: A wind-tunnel study

In this study, the wake behind a wind turbine located on an escarpment is investigated using particle-image velocimetry in a wind tunnel. Five different escarpment models are used, which vary in the windward side shape from forward facing steps (FFS) with different curvatures at the leading-edge to sinusoidal ramp shapes with varying slopes. The difference in the base flow (flow without the turbine) resulting from the change in the geometry of the escarpment leads to significant differences in the average and dynamic characteristics of the turbine wake. The relatively high level of turbulence intensity in the base flow induced by the FFS escarpments leads to a faster wake recovery accompanied by higher turbulence kinetic energy, compared with the ramp-shaped ones. The self-similar behavior of the velocity deficit profiles in the far wake is confirmed for all the cases; unlike turbine wakes over flat terrain, the wake growth rate is found to be larger in the vertical direction than in the lateral direction. Meandering of the wake is observed to be higher on the FFS escarpment with an upward wake trajectory, compared to the ramp-shaped one. Finally, an analytical model is assessed to predict the wake velocity deficit of the turbine.

Comparative Study of Ram Air Turbines based on Wind Tunnel Study for Specific Air Borne Energy Extraction

Ram Air Turbines (RAT) are used for emergency on-board power generation on aircraft and associated systems. Many studies on usage of RATs have shown promising results in terms of using RATs as a source of emergency on-board power generation. Many external podded systems on aircraft utilise RATs for self-sufficient adaptation. These pods generate their own power using RATs for their power requirements instead of depending on the mother aircraft power. Commercial cargo planes use RATs for generating emergency hydraulic power. A RAT was suggested to be used for emergency power, during failure of main alternator on a prototype aircraft. A specific requirement of the RAT was also to produce high drag for aerodynamic braking when deployed and concurrently generate electrical energy. Three models with different solidity were studied in wind tunnel at different wind speeds for suitability of this drag-energy combination. This paper presents the results of the study. Based on the results, a suitable RAT was selected for further analysis and ground trials.

Yaw effects on train aerodynamics on a double-track viaduct: A wind tunnel study

The aerodynamic performance of a scaled high-speed train model mounted on a double-track viaduct was studied through a wind tunnel test. The pressure distribution of different loops and the centerline on the streamlined nose region, as well as the aerodynamic load coefficients of the leading car were explored under yaw effects ranging from Β=-30° to Β=30°. Results showed that Reynolds effects became independent when the wind speed surpassed 40 m/s, the corresponding Re of which equals 6.51 x 105. The pressures recorded along the centerline of train nose for the upstream scenario, was more sensitive to the yaw effects as the largest pressure difference gradually broadened against yaw angles. In addition, the pressure coefficients along the centerline and symmetrical taps of the loops, approximately fit a quadratic relationship with respect to yaw angles. The presence of the tracks and viaduct decks somehow mitigated the intensity of the airflow at downstream side. The experimental test also revealed that, the upstream configuration provided higher mean side force, yawing, and rolling moments up to Β=20° whereas over that angle the force and moments exhibited the opposite performance. 40 m/s, the corresponding Re of which equals 6.51

Comparison of the turbulence in the wakes of an actuator disc and a model wind turbine by higher order statistics: A wind tunnel study

Knowledge of the turbulence in the wakes of wind turbines is important to improve the operation and lifetime of downstream turbines exposed to these wakes. As the investigation of a rotating turbine can be challenging, both experimentally and numerically, static actuator discs can substitute rotating turbines. To investigate the similarity of the turbulence in the wakes and how turbulent inflow alters the result, an experimental wind tunnel study is presented that compares hot-wire measurements in the central wakes of an actuator disc and a model wind turbine (diameter-based Reynolds number Re ≈ 300000). Two turbulent inflows are investigated, an intermittent, i.e. gusty, atmospheric-like inflow generated by an active grid, and a non-intermittent inflow generated by a regular grid. The data is investigated using one-point and higher-order two-point statistics. We find that the wakes of both models have similar properties for all investigated quantities within the far wake. The turbulence in the central wake is independent of the inflow conditions, and both models filter larger scale intermittency in the far wake with regard to the inflow. Also, we find that the turbine generates its own kind of turbulence that dominates the ambient turbulence and has strong features of homogeneous, isotropic turbulence.

Wind tunnel study of wind effects on 90° helical and square tall buildings: A comparative study

Wind effects on a square model and a 90° helical model are investigated by both pressure measurement and aero-elastic model tests in a boundary layer wind tunnel. Based on the pressure measurement results, local wind force coefficients, base moment coefficients, vertical correlation coefficients and power spectral densities for the two models were analyzed and discussed in detail. The aerodynamic damping ratios were calculated by the random decrement technique (RDT) on the basis of the wind-induced acceleration obtained from the aero-elastic tests. Comparisons of wind loads and wind-induced accelerations were made for the square and helical models. The results shown that the aerodynamic damping should not be ignored, especially for across-wind direction. Moreover, the helical model has been proved to yield a better behavior in aerodynamic performance than square model. This study aims to provide useful information for wind-resistant design of helical building.

Permeable Leading Edges for Airfoil and Fan Noise Reduction in Disturbed Inflow

A detailed experimental study on the aerodynamic performance and noise emission of airfoils and fan blades with permeable leading edges under disturbed inflow conditions was performed. The airfoils and fan blades with permeable leading edges were made of an aluminum alloy using a powder bed fusion-based additive manufacturing process. In a first step, a wind-tunnel study was carried out. This consisted of detailed aerodynamic and aeroacoustic measurements on 16 airfoils with different permeable leading-edge designs that were performed for various flow speeds and geometric angles of attack. Based on the results from that study, unskewed fan blades with four different permeable leading-edge designs were manufactured in a second step. With the aim of reducing turbulence interaction noise of axial fans, the fans were examined with regard to their aerodynamic and acoustic properties under grid-generated turbulent inflow conditions. In a third step, a possible transfer of the observed noise emission from airfoils with permeable leading edge to that of fan blades was investigated. It was found that a notable broadband noise reduction can be transferred from airfoil applications to the sound spectra of axial fans. At the same time, the porous modifications can reduce the aerodynamic performance, and hence the fan efficiency.

Wind Tunnel Studies on Hover and Forward Flight Performances of a Coaxial Rigid Rotor

The aerodynamic performance of a reduced-scale coaxial rigid rotor system in hover and steady forward flights was experimentally investigated to gain insights into the effect of interference between upper and lower rotors and the influences of the advance ratio, shaft tilt angle and lift offset. The rotor system featured by 2 m-diameter, four-bladed upper and lower hingeless rotors and was installed in a coaxial rotor test rig. Experiments were conducted in the Φ3.2 m wind tunnel at China Aerodynamics Research and Development Center (CARDC). The rotor system was tested in hover states at collective pitches ranging from 0° to 13° and it was also tested in forward flights at advance ratios up to 0.6, with specific focus on the shaft tilt angle and lift offset sweeps. To ensure that the coaxial rotor was operating in a similar manner to that of the real flight, the torque difference was trimmed to zero in hover flight, whilst the constant lift coefficient was maintained in forward flight. An isolated single-rotor configuration test was also conducted with the same pitch angle setting in the coaxial rotor. The hover test results demonstrate that the figure of merit (FM) value of the lower rotor is lower than that of the upper rotor, and both are lower than that of the isolated single rotor. Moreover, the coaxial rotor configuration can contribute to better hover efficiency under the same blade loading coefficient (CT/σ). In forward flight, the effective lift-to-drag (L/De) ratio of the coaxial rigid rotor does not monotonously change as the advance ratio increases. Increases in the required power and drag in the case with a high advance ratio of 0.6 leads to the decreasing L/De ratio of the rotor. Meanwhile, the L/De ratio of the rotor is relatively high when the rotor shaft is tilted backward. The increasing lift offset tends to result in reduced required rotor power and an increase in the rotor drag. When the effect of the reduced rotor power is greater than that of the increased rotor drag, the L/De ratio increases as the lift offset increases. The L/De ratio can benefit significantly from lift offset at a high advance ratio, but it is much less influenced by lift offset at a low advance ratio. The forward performance efficiency of the upper rotor is poorer than that of the lower rotor, which is significantly different from the case in the hover flight.

Effect of cable surface geometry and ice accretion shapes on the aerodynamic behaviour of inclined stay cables

A wind-tunnel study has been conducted to evaluate changes in the aerodynamic behaviour of stay cables of a bridge due to ice accretion from freezing rain and, due to different cable surface geometries. Numerical simulations were performed to predict the three-dimensional ice shapes resulting from freezing rain for a variation of environmental conditions: wind speed, wind direction, air temperature, velocity of precipitation and duration of precipitation. Stay-cable models were fabricated using laser selective sintering for three different surface geometries (double helical fillet, concentric rings, and double helical strakes) with ice formed under the same environmental conditions. Additional models with the helical fillet geometry were fabricated to evaluate the effect of the air temperature at which ice was formed, the effect of wind direction during the precipitation event and the effect of the duration of the precipitation. The aerodynamic drag and lift forces acting on the models were measured for different wind speeds and cable-wind angles. The overall study evaluated the mean aerodynamic force coefficients of ten models in smooth flow, and two of the models were also tested in turbulent flow. The critical Reynolds number regime for the models of stay cable with ice accretion shapes occurred at a lower Reynolds number (below 100,000) than for the un-iced cables and the drag coefficient was less sensitive to increases in Reynolds numbers than the equivalent un-iced cables. These effects were attributed to the combined role of the ice-shape in determining the separation point combined with the higher surface roughness of the ice. An important observation was that for the three surface geometries and the range of test conditions that were considered, the maximum drag coefficients for ice-accreted models ranged from approximately 1.1 to 1.3, and were up to 50% greater than those observed without ice. The model with helical strakes and ice accretion exhibited the highest drag coefficient and exhibited more variation in lift coefficient with changes in Reynolds number than the other two cable surface geometries. The aerodynamic forces of an ice-accreted model followed similar trends in smooth and turbulent flow, but the drag coefficients were greater in turbulent flow. The presence and shape of the ice appeared to have a more dominant effect on the separation behaviour of the models than the presence of turbulence (for an ice-accreted model). The aerodynamic coefficients did not change greatly between the cases where ice was accreted at −0.5°C and −1.5°C due to the similar ice shape and thickness near the separation locations. The ice shape formed at −5°C was thicker but more localized and resulted in drag and lift coefficients that had greater variation with changes in the cable-wind plane. The effect of ice duration from 10 h to 20 h resulted in a increased variation in mean lift coefficient behaviour due to the asymmetric shape that resulted from the ice accretion parameters.

Wind-Tunnel Studies on Sand Sedimentation Around Wind-Break Walls of Lanxin High-Speed Railway II and Its Prevention

Wind-break walls along Lanxin High-Speed Railway II were studied and approved as effective measures to reduce strong wind damage to the high-speed trains. The results show that sand sedimentation on the leeward sides of wind-break walls along the railway within Gobi Desert could significantly threaten the operation safety of running trains. Different from the current sand sedimentation prevention measures without adequate consideration of the deposition process of airborne sand particles, this study revealed the mechanism of sand sedimentation on the leeward sides of three wind-break walls within different terrains. A series of wind-tunnel experiments were carried out to measure the horizontal velocity, number density, transport flux, and deposition rate of sand particles, and it was found that the horizontal speed of sand particles was first increased and then decreased on the railway track, and the peak speed over the concave subgrade was much smaller than those over convex and flat subgrades. The number density and horizontal sand flux were largest over the concave subgrade, and were the smallest over the convex subgrade. The sand particle deposition rate and distribution were also the largest within the concave subgrade, and some measures were also proposed to prevent sand sedimentation on the leeward sides of wind-break walls.

Wind tunnel study of the effect of planting Haloxylon ammodendron on aeolian sediment transport

Revegetation is a widely used way to minimise aeolian sediment transport in desertified land. An optimal vegetation density and planting pattern reduces the economic investment for revegetation and competition for limited water resources. This study aimed to ascertain the effects of vegetation density and planting pattern on aeolian sediment transport at the regional scale. A series of wind tunnel tests were implemented with artificial shrubs representing Haloxylon ammodendron . These tests were designed with three planting densities (i.e., 600 plants ha −1 , 1200 plants ha −1 , and 1650 plants ha −1 ) and four patterns (uniform distribution, random distribution, two rows/one belt, and one row/one belt pattern). Geostatistical interpolation methods available in ArcGIS were used to analyse the spatial variation of sand heights. Vegetation density and planting pattern and their interaction all significantly affected the aeolian sediment transport but vegetation density had the greatest impact. With increasing density of vegetation, wind erosion rate decreased significantly following quadratic function, and wind erosion still occurred around the artificial shrubs regardless of vegetation density and planting pattern. For wind erosion rate, erosion and deposition area, the uniform distribution pattern had little protective benefit at the three planting densities, whilst the combinations of the random distribution pattern with 600 plants ha −1 , two rows/one belt pattern with 1200 plants ha −1 , and one row/one belt pattern with 1650 plants ha −1 had the best protective benefit in controlling the aeolian sediment transport. • Influence of vegetation density and pattern at a regional scale investigated. • Geostatistical interpolation used to analyse the spatial variation of sand depth. • Density and pattern of artificial shrubs significantly affected sediment transport. • Wind erosion still occurred around shrubs regardless of vegetation density and pattern. • Optimal planting pattern for reducing aeolian transport different in the 3 densities.

Wind-tunnel study of the aerodynamic characteristics and mechanical response of the leaves of Betula platyphylla Sukaczev

It is necessary to examine the aerodynamic behaviour of leaves in wind in order to understand wind-induced tree disasters. The effect of the wind deflection angle on the aerodynamic characteristics of leaves remains relatively unexplored. Thus, the reconfiguration, vibration and wake characteristics of the Betula platyphylla Sukaczev leaves at various wind deflection angles and vegetative Cauchy numbers were investigated in a wind tunnel. Wind deflection angle (θ) is defined as the angle between the wind direction and the normal vector of the lamina, and a vegetative Cauchy number characterises the reconfiguration of an elastic structure under flow and is defined as the ratio of the product of the dynamic pressure and the third power of the slenderness ratio to the elasticity modulus. The results showed that at the different cases with an increase of Cauchy number, all the leaves mainly experience three states, a static bending of the laminas, and an opening and closing vibration of the laminas on left and right sides and a reconfiguration of the leaf. Except for the leaves with θ = 0, the leaves with θ = π/6, π/3 and π/2 also experience torsional motion. Four critical Cauchy numbers were defined corresponding to the four reconfigurations and vibration states. The mean critical Cauchy numbers for the torsional motion of the leaves were at θ = π/6, π/3 and π/2 this decreased with the increasing θ. The reconfigured mean Cauchy numbers of leaves for θ = π/6, π/3 and π/2 were significantly larger than those in θ = 0. Furthermore, compared with the case for θ = 0, the cases with θ = π/6, π/3 and π/2 proved to be disadvantageous for the reduction of vortex-induced vibrations through reconfiguration.

Wind-tunnel studies on the characteristics of indoor/outdoor airflow and pollutant exchange in a building cluster

The diffusion of air pollutants in urban areas is essentially a multiscale problem, which has aroused increasing concerns. Wind-tunnel experiments were employed to explore the characteristics of indoor/outdoor airflow and pollutant exchange in a building cluster. Under two wind directions ( β ​= ​0°,45°), smoke visualization tests were firstly conducted to visualize the diffusion characteristics of air pollutants released from different pollution sources. Then the 3D hot-film anemometer and SF 6 quantitative detector were used to measure the turbulence parameters and pollutant distributions. The smoke visualization tests showed that under β ​= ​0°, the pollutants were mainly concentrated in the middle main street canyons (S-1 and S-2), spread downstream, and were gradually diluted. However, the influence area under β ​= ​45° was wider. The results confirmed that the indoor pollutant concentration along different floors was closely related to that around the outside target building. The window-opening mode had great influence on indoor pollutant concentration, but little influence on the other floors. Additionally, when the pollution source was located in the building leeward wake, regardless of the building height, it could reduce the indoor air quality of the leeward building. This study is helpful to understand the characteristics of flow and dispersion through different urban scales. The configurations of multiscale diffusion models. • Wind-tunnel tests are employed to study indoor/outdoor exchange in a building cluster. • Two wind directions and different window opening modes are considered. • The smoke visualization tests allow the visualization of pollutant diffusion. • Pollutants in the building wake can diffuse vertically to the top leeward rooms. • The characteristics of pollutant diffusion through different urban scales are understood.

Scanning Doppler lidar measurements of drag force on a solitary tree

Abstract

Vis-NIR spectroscopy predicts threshold velocity of wind erosion in calcareous soils

Wind erosion potential can be assessed using the Threshold Friction Velocity (TFV) of the soil, which is not always easy to measure, especially on regional and global scales. To overcome this difficulty, the spectroscopy technique can provide a useful approach in estimating the TFV as an alternative for time-consuming wind tunnel studies in the field. In this study, we evaluated the potential of Vis-NIR spectroscopy in predicting the TFV and some TFV-related soil properties using Partial Least Square Regression (PLSR) and the Support Vector Regression (SVR). We also developed a Point Spectrotransfer Function (PSTF) using Multiple Linear Regression (MLR) to predict the TFV based on diagnostic wavelengths and compared it to the derived Pedotransfer Function (PTF). For this purpose, 300 in-situ wind tunnel tests were performed in the Fars Province, Iran and the spectral reflectance of soil samples were analysed using a spectrophotometer apparatus. The 10 best key wavelengths resulting from the correlation analysis between the TFV and the spectral reflectance were 750, 1342, 1446, 1578, 1746, 1939, 2072, 2162, 2217, and 2338 nm which were mostly located in the short-wavelength infrared (SWIR) area. The derived PSTF performed better than the PTF for the TFV estimation (R2 = 0.94, RMSE = 0.71). Results of the predictive models revealed that machine learning using the SVR had a significantly (P < 0.01) higher prediction accuracy for the TFV estimation (R2 = 0.85, RMSE = 0.45, RPD = 2.50, and RPIQ = 4.06) than the PLSR (R2 = 0.68, RMSE = 1.01, RPD = 1.72, and RPIQ = 2.64). The same results were obtained for the soil moisture, clay and CaCO3 content. This study proved that reflectance spectroscopy coupled with the machine learning algorithm is a promising technique for large-scale assessment of wind erosion.

The NATO generic destroyer – a shared geometry for collaborative research into modelling and simulation of shipboard helicopter launch and recovery

The helicopter-ship dynamic interface is the environment above the landing deck of a ship where a helicopter pilot has to control the aircraft while contending with a moving deck and an unsteady airflow known as the ship airwake. Research into understanding this environment has included modelling the airwake using wind tunnel studies and Computational Fluid Dynamics, and has often used the Simple Frigate Shape (SFS), a generic ship geometry representative of a naval frigate. This paper reviews the contribution that the SFS has made to research into the helicopter-ship dynamic interface, and introduces a new ship geometry for future research. The new ship, developed within a NATO Research Task Group, is the NATO Generic Destroyer (NATO-GD), a concept ship with a simplified geometry that is more representative of a modern helicopter-enabled combat ship with a stealthy superstructure. As well as introducing the NATO-GD as a common platform for research, the paper also introduces a number of ship motion profiles to encourage new research that will include the effect of ship motion on the airwake. It is anticipated that future research on a common ship, with prescribed motion and adopting a common helicopter will lead to improved or new modelling methodologies.