Wind Tunnel Test Method Research Articles

Requirements for partial turbulence simulations using nondimensional turbulence energy contributions

Quantifying turbulence effects is crucial for understanding building aerodynamics and for ensuring accurate wind tunnel test methods. This is especially important in wind tunnel methods that require post-experiment adjustments because approximate wind fields are used, such as the Partial Turbulence Simulation (PTS) approach. Understanding and analyzing these effects enables load adjustments since the PTS method only requires matching the high frequency portions of the upstream spectra of the longitudinal velocity component in model and full-scale. However, the limits for which the PTS method is applicable are unclear in terms of the allowable range of wind field characteristics that can be used in the wind tunnel simulation. To address this, the paper utilizes two nondimensional parameters, one representing the small-scale turbulence energy, ES, and the other the large-scale turbulence energy, EL, to elaborate the aerodynamic effects of turbulence intensity and integral length scales in the upstream wind. The results show that the maximum allowable mismatch ratio of integral length scales and of Jensen numbers between model and full-scale simulations depend on the target small-scale turbulence energy and the maximum allowable deviation of small-scale energy. By quantifying the effects of ES and EL on area-averaged pressure coefficients, the allowable limits are identified for wind tunnel test parameters that lead to negligible differences in the resultant pressure coefficient statistics in regions of separated-reattaching flow on the roof of a low-rise building.

Surrogate modeling for aerodynamic static instability of central-slotted box decks using machine learning approaches

Studies on aerodynamic controls of central-slotted box decks primarily focused on mitigating vortex-induced vibrations (VIV), as this type of deck typically performs well against flutter instability. However, as the span length increases, the critical wind speed of aerodynamic static instability ( U cr) might be lower than flutter critical wind speed. Thus, U cr will determine the overall aerodynamic performance of such bridges. Investigating this instability through wind tunnel testing methods and numerical simulation can be expensive and time-consuming. In this paper, surrogate models using machine learning approaches, specifically artificial neural network (ANN) and extreme gradient boosting (XGBoost), were developed and optimized for fast and reliable prediction for U cr based on wind tunnel tests and simulation data. The results demonstrated that the built surrogate models can predict U cr accurately. The parametric study results showed that the height ratio of wind fairing apex ( a/b), wind angle of attack ( α), and length of the main span ( L) have the most influence on the U cr compared with other parameters. Finally, based on the developed ANN surrogate model and the artificial bee colony (ABC) optimization algorithm, an optimized section was proposed to enhance the section’s performance against aerodynamic static instability.

Fast Prediction of Airfoil Aerodynamic Characteristics Based on a Combined Autoencoder

Aircraft airfoils are classified into two main categories: symmetrical and asymmetrical. Both types of airfoils have a significant impact on the flight performance and safety of the aircraft. The fast prediction of the aerodynamic coefficients and pressure distributions of airfoils is crucial for the design of aircraft. The traditional wind tunnel test and CFD methods have the disadvantages of high test cost and high time consumption. To solve these problems, a combined autoencoder (CAE) network is proposed in this paper, which can achieve the fast prediction of airfoil aerodynamic coefficients and pressure distributions. The network consists of an airfoil shape autoencoder (AE) network and a multilayer perceptron (MLP) network. Firstly, an autoencoder network reflecting the characteristics of the airfoil shape is established, and the effects of different latent variables on the performance of the autoencoder network are investigated. Then, the latent variables obtained from the autoencoder are concatenated with the inflow conditions such as the Reynolds number and the angle of attack to be used as inputs to the MLP network, and the aerodynamic coefficients of different airfoils in different inflow conditions are predicted. The effects of various latent variable inputs, as well as the direct input of the airfoil shape into the MLP network, on the prediction performance of aerodynamic coefficients are compared and analyzed. The optimal aerodynamic coefficient prediction network is then obtained. Finally, the CAE network is also applied to predict the pressure distributions of different airfoils in different inflow conditions and the effects of different latent variables and input conditions on the prediction performance of the pressure distributions are analyzed and compared with the advantages and disadvantages of the CAE network and the conditional variational autoencoder (CVAE) network. The results demonstrate that the proposed method is capable of accurately predicting aerodynamic characteristics in a shorter time, offering a valuable reference for the fast and efficient design of aircraft airfoils.

Experimental Study on Wind Load and Wind-Induced Interference Effect of Three High-Rise Buildings

Wind loads of high-rise buildings are a key parameter in architectural design. The magnitude and distribution characteristics of wind loads are of great importance for the safety and economy of structural design. The wind loads of high-rise buildings are quite different from those of monomer buildings. The wind-induced interference effect could significantly increase the local wind pressure of buildings, causing potential safety hazards for the main structure and enclosure structure. For the three common high-rise buildings, we adopted the wind tunnel test method to measure the surface pressure of each building. The corresponding Re number was 8.2×106. This paper studied the shape coefficients, fluctuating wind pressure coefficients and base bending moment coefficient of each building with different wind direction angles and different spacing ratios, and the maximum value of each parameter and the corresponding working condition were statistically analyzed. The results showed that, under any wind direction angle, the fluctuating wind pressure coefficients on all sides of the building were affected by the spacing ratio, and the fluctuation range was large. When the wind angle was 180º, the fluctuating wind pressure coefficients on the sides of Building 1 were most affected by the slope ratio. At this wind angle, the maximum value was 0.43 at a slope ratio of 5.0, which was 65% different from the minimum. Partition shape coefficients of some sides and top surfaces changed significantly with the spacing ratio. When the spacing ratio was 5.0, the base bending moment coefficients in the downwind and crosswind directions reached their maximum values, and the wind direction angles where the maximum values of the base bending moment coefficients in the downwind direction were 40º and 50º, respectively, and the wind direction angle where the maximum value of the base bending moment coefficients in the crosswind direction was 10º. Due to the influence of the wind angle and the building spacing ratio, the wind loads on the facades of the pyramidal group of buildings varied greatly, and the wind-induced interference effect was evident. The wind load between the building facades in the three buildings was different, and the wind disturbance effect was evident. Therefore, the most unfavorable stress state and interference state of the structure should be comprehensively considered in the wind resistance design of the three buildings. The building spacing ratio should preferably be set to 3.0, and wind angles of 10º, 40º, and 50º should be avoided whenever possible.

A novel fabrication method of the three-dimensional forced vibration system for high-rise buildings

The forced vibration wind tunnel test is widely used to estimate the aeroelastic effect of high-rise buildings due to its ease of fabrication and reliable identification of the aeroelastic parameters. However, most traditional forced vibration systems (FVSs) can only realize one-dimensional (1D) or two-dimensional (2D) vibrations at most, and the structural model can only simulate linear or constant mode shapes. The present study proposes a novel three-dimensional (3D i.e., two translational and one torsional vibrations) FVS that can drive the model to vibrate in 3D while maintaining more realistic mode shapes. Employing the proposed 3D FVS, the amplitude, frequency, and phase angle of the model's 3D vibrations can be adjusted independently. Then, the resultant motions of the model are measured by three laser sensors to examine the performance of the system. Results show that the proposed system performs well, providing stable vibration amplitude, frequency, and phase angle in all the three directions. Finally, making use of the 3D FVS, the significant differences between the results of 3D forced vibration and 1D forced vibration are uncovered, in terms of power spectrum density (PSD) of wind forces on the model and the associated aerodynamic stiffness and damping ratios. The proposed system, therefore, provides an alternative of wind tunnel test methods for determining the aeroelastic properties of high-rise buildings.

Experimental Study on the Effect of the Blade Tip Distance on the Power and the Wake Recovery with Small Multi-Rotor Wind Turbines

In order to investigate the output power and wake velocity of small multi-rotor wind turbines compared to single-rotor wind turbines, which operate in the same swept area at various blade tip distances, this paper used the wind tunnel test method to examine single-rotor wind turbines with diameter D of 0.4 m and 0.34 m corresponding to the triple-rotor wind turbines and double-rotor wind turbines with a single rotor diameter D of 0.24 m, respectively. The experimental results indicated that, without rotation speed control, the triple-rotor wind turbine produced more power than the single-rotor wind turbine with an equivalent swept area and that the output power tended to rise initially and then fall as the distance between each rotor increased. Moreover, the power increase reached a maximum of 8.4% at the 0.4D blade tip distance. In terms of wake measurement, triple-rotor wind turbines had smaller wake losses and faster recovery rates than single-rotor wind turbines. The smaller the blade tip distance, the earlier the wake merged and fused and the faster the recovery rate. In designing small multi-rotor wind turbines, the above discussion can serve as a guide.

Measurements of the unsteady lift force on a 5:1 rectangular cylinder based on active-passive hybrid wind tunnel tests

Active-passive hybrid wind tunnel test method was conducted to investigate the unsteady lift force on a 5:1 rectangular cylinder. Active and passive control wind tunnels are adopted to generate streamwise and grid-generated turbulences. Thus, a hybrid theoretical framework was proposed to obtain the u- and w-related aerodynamic admittances (u- and w-AAF) and investigate the effects of streamwise and vertical fluctuating winds on the unsteady behaviour of the lift force on a 5:1 rectangular cylinder at AoAs. The findings revealed that vertical wind fluctuations in the low-frequency domain dominated the lift force at low frequencies. In contrast, the streamwise component of turbulence substantially affects the energy distribution of the lift force in the high-frequency region. Notably, the contribution of streamwise wind fluctuations to unsteady lift becomes more pronounced as the AoA increases within a given range. When the AoA is further increased, the impact returns predominantly to the vertical wind fluctuations.

Aerodynamic characterisation of delta wing unmanned aerial vehicle using non-gradient-based estimator

AbstractAerodynamic characterisation from flight testing is an integral subroutine for evaluating a new flight vehicle’s aerodynamic performance, stability and controllability. The estimation of aerodynamic parameters from flight test data has extensively been explored, in the past, using estimation methods such as the equation error method, output error method and filter error method. However, in the current era, non-gradient-based estimation techniques are gaining attention from researchers due to their inherent data-driven optimisation capability to find the global best solution. In this paper, a novel non-gradient-based estimation method is proposed for the aerodynamic characterisation of unmanned aerial vehicles from flight data, which relies on the maximum likelihood method augmented with particle swarm optimisation. Flight data sets of a wing-alone unmanned aerial vehicle are used to demonstrate the capabilities of the proposed method in estimating aerodynamic derivatives. Estimates from the proposed method are corroborated with the wind tunnel test and output error method results. It has been observed that simulated flight vehicle responses using estimated parameters are in good agreement with measured data in most of the manoeuvers considered. Confidence in the estimates of linear and nonlinear aerodynamic parameters is well established with the lower limit of Cramer-Rao bounds, which are minimal. The proposed method also demonstrates good predictability of the quasi-steady stall aerodynamic model by estimating stall characteristic parameters such as aerofoil static stall characteristics parameter, hysteresis time constant and breakpoint. The overall performance of the proposed estimation method is on par with the output error method and is validated with the proof-of-match exercise.

Influence of geometric parameters of leading edge horn-ice on stall characteristics of airfoil

The irregular characteristics and geometric randomness of horn-type ice are significant while the behaviors of separation are complex. The mechanism and factor leading to the essential change of stall performance are still not clear. According to actual requirements of airworthiness certification of a large passenger aircraft, a family of horn-type ice shapes with different parameters are constructed based on typical supercritical airfoil and icing environment. By combining with wind tunnel test and numerical simulation methods, the parameter sensitivity of airfoil stall characteristics to the change of ice height and angle is systematically analyzed and the essential influence mechanism of the ice shape parameters leading to the change of separation bubble development under stall process is summarized, which provides a theoretical basis for ice airworthiness certification of large passenger aircraft.

Drift Potential Characteristics of a Flat Fan Nozzle: A Numerical and Experimental Study

This study explores the drift potential characteristics of a flat fan nozzle. The atomization and drift characteristics of fan-shaped pressure nozzles were studied at a spraying height of 0.6 m and a lateral wind speed of 0–6 m/s through a combination of computational fluid dynamics (CFD) analyses and wind tunnel experiments. The nozzle Lu 120-03 had a spraying pressure of 0.3 MPa. The results show that as the wind speed varies from 0 m/s to 6 m/s, the spray droplet spectrum also changes, and the droplet volume medium diameter increases. The cumulative droplet ratio and droplet spectral width of M oscillate within certain ranges. The amount of spray drift increases at higher wind speeds. The concentration of droplet deposition on the bottom of the wind tunnel gradually spreads downward in the wind direction. The determination coefficient R2 of the straight-line fitting of the drift characteristics is 0.982, which is highly consistent with the CFD simulation results. A CFD simulation-assisted wind tunnel test method, which is more convenient and repeatable than traditional field tests, is proposed to analyze the droplet spectrum and drift of Lechler series nozzles. The program can accurately simulate the actual drift and provide theoretical and data support for the optimization of atomization and drift characteristics of several types of flat fan nozzles under different spraying pressures and crosswinds in practical applications.

Experimental research on weathercock interference characteristics of weathercock airspeed tube

Pitot tube is one of the most important airborne devices on the aircraft. The airspeed tube can not only provide the pilot with the airspeed of the aircraft, but also the rate of climb of the aircraft. In this paper, the wind tunnel test method is used to test the weathercock type airspeed tube used on a domestic supersonic tailless layout aircraft and it obtains the airspeed tube's angle of attack and sideslip angle weathercock interference characteristics and total static pressure aerodynamic characteristics. In this process, we find that the sideslip angle begins to offset with the angle of attack increasing and the offset is about -1° when the airspeed exceeds 1.5 Ma. Subsequently, CFD calculations are used to compare and supplement the wind vane characteristics obtained from the wind tunnel test. It is found that the pressure data collected by the airspeed tube has a certain error due to the interference characteristics of the wind vane. Finally, the pressure error is corrected by BP neural network prediction model. It provides a reference to calibrating air-data-sensors for researchers.

Unsteady Aerodynamic Simulation Test Based on Ampere Force and Electromagnetic Field

Unsteady aerodynamic force refers to the aerodynamic force that the magnitude and direction of the load borne by the aircraft will change with time during flight. Usually, the simulation of unsteady aerodynamic force is completed by wind tunnel test. This paper introduces a new load simulation method based on electromagnetic field and Ampere force. Compared with the traditional wind tunnel test method, electromagnetic field load test will greatly reduce the test cost and make it possible to repeat multiple tests. In order to verify whether the test method is feasible and effective, this paper introduces a number of verification tests, including static load test and dynamic quasi modal test. By comparing the ground test results with those based on ABAQUS simulation, the reliability of the test method is verified. In this test technology, electromagnetic technology is used to study the force of structure, which is of great significance for multi physical field test and aircraft design test.

Aerodynamic Characteristics of Express Freight Train on Bridges Based on Wind Tunnel Tests

The express freight trains are being developed rapidly in China, and they have the characteristics of smaller axle weight and higher velocity compared with the normal freight trains. The running safety of the trains on the bridge is significantly affected by the strong crosswind, which may cause overturning accidents in severe cases. The wind tunnel tests of the express freight train–bridge scale models are conducted in this study to investigate the aerodynamic characteristics of the vehicles when they run on the box girder bridge and the double-deck steel truss bridge. The uniform flow and the atmospheric boundary layer (ABL) flow are constructed respectively to compare the differences of the aerodynamic characteristics under different flow fields. The test results show that the distribution of pressure coefficients on the car body is related to the type of test flow field and bridge, and it is also greatly affected by the running position on the bridge as well as the location of the vehicle in the train. The magnitude of the side force coefficients and the rolling moment coefficients of the vehicle on the steel truss bridge are less than those on the box girder bridge. The influence of the flow field type on the side force coefficients of the middle vehicle is slightly larger than that of the tail vehicle, but it has a low correlation with the type of bridge. When the vehicle is on the windward track of the bridge, the values of power spectral density (PSD) of the side force are larger than those on the leeward track. The results provide data support for the running safety research of the express freight trains and reference for the railway vehicle wind tunnel test method.

Effects of Curved Wind Barrier on the Aerodynamic Characteristics of a Train–Bridge System and Its Static Wind Load

Wind barriers are important measures that guarantee the running safety of high-speed trains under crosswind conditions, however, they can change the aerodynamic coefficients of a train–bridge system and the distribution of the flow field around a train and bridge, and studies have often ignored the static wind load characteristics of wind barriers. In this paper, the effects of height and porosity on the curved and vertical fence-type wind barriers on the aerodynamic characteristics of a train–bridge system are investigated by using numerical simulation and wind tunnel test methods. The static wind loads of the two types of wind barriers are analyzed by comparing the drag coefficients and the surface wind pressure distributions. The results show that, compared with the vertical wind barrier, the curved wind barrier can reduce the drag force and moment of a train while reducing the impact of the aerodynamic forces on a bridge. The static wind load of the curved wind barrier is less than that of the vertical wind barrier, when a train is on the windward side of a bridge, the drag coefficient of the curved wind barrier is only about 35% of that of the vertical wind barrier.

Influence Mechanism of a Bridge Wind Barrier on the Stability of a Van-Body Truck under Crosswind

Understanding the crosswind stability of cars under strong wind loads and research on wind resistance methods is important for improving the safety performance of wind-induced driving on bridges. Taking van-body trucks as the research object, numerical calculation methods and wind tunnel test methods are used to conduct the wind-induced driving safety analyses of van trucks on a cross-sea bridge. The influence of the structural parameters of the barrier-type wind barrier on the aerodynamic characteristics and straight-line driving stability of the trucks on the bridge is studied and analyzed quantitatively. The results show that the decrease in the porosity of the wind barrier can effectively reduce the average wind speed of the bridge deck, and increasing the height of the wind barrier can effectively reduce the wind speed and increase the occlusion height of the bridge deck. The lateral acceleration, yaw rate, and lateral displacement of trucks decrease with the decrease in the porosity of the wind barrier and decrease with the increase in the height of the wind barrier. The research conclusions can not only provide data support for wind-induced driving safety analysis and the wind-resistant design of bridges but also provide a new method to balance the requirements of bridge wind-induced driving safety and bridge wind-induced structure safety.

Parametric Study for Directional Stability of Tumbling Plates by Wind Tunnel Testing

The tumbling phenomenon is considered to be an important phenomenon for aircraft flight safety because of the possibility of falling objects from the aircraft reaching far away or for knowing the behavior of falling roof tiles blown off by strong winds. Therefore, many tests to measure the force act on the tumbling plate in wind tunnel have been conducted. The authors have been studying the directional stability of the tumbling plate [9], which has a great effect on the reach of falling objects, and have proposed a non-contact measurement method wind tunnel test method from the viewpoint of dynamic balance which can acquire the force without force sensors [12] Here, we call “towing wind tunnel test method”. In this paper, for the evaluation of the directional stability of the tumbling plate, we parametrically changed the planar configuration of the tumbling flat plate and measured the acting force in wind tunnel using this towing wind tunnel test method. As a result, the relationship between the shape of the tumbling plate and the conditions for directional instability was clarified.

Proposal of a method to measure aerodynamic forces without using force sensors in wind tunnel testing of tumbling plates

A new wind tunnel test method is proposed to measure the aerodynamic forces act on the tumbling plate and the tension of the tow string in the wind tunnel not by using force sensors but by measuring the tow position. The tumbling phenomenon is considered to be an important phenomenon for aircraft flight safety because of the possibility of falling objects from aircrafts reaching far away or for knowing the behavior of falling roof tiles blown off by strong winds. Therefore, many tests to measure the force act on the tumbling plate in wind tunnel have been conducted. However, since the rotation of the test piece is accompanied by difficulties ex. support interference, movement restrictions, etc. However, according to present method, the aerodynamic forces act on the tumbling plate in wind tunnel can be measured optically in a non-contact manner, and an expensive force sensor is not required. Furthermore, it is also effective under conditions such as low wind velocity, in which the aerodynamic forces are buried in the measurement accuracy of the force sensors. This paper explains this wind tunnel test method from the viewpoint of dynamic balance and reports the results of verification wind tunnel test in which the effectiveness of this method was confirmed.

Research on Model Validation and Uncertainty Quantification of Airfoil Flow

Numerical simulations and wind tunnel tests are both basic methods for aerodynamic research and application. They are the modeling and simulation of real world system. There are various uncertainties in the implementation process. In Computational Fluid Dynamics (CFD), the main sources of uncertainty are the model form, model parameters and numerical solution methods. In wind tunnel tests, there are many uncertainties sources, such as geometric model, test environment, test devices and instrumentation, test methods, data recording and processing, etc. This paper takes NACA0012 airfoil as an example. Bayesian model averaging method (BMA) and grid convergence study are used to analyse model form and numerical solution uncertainty in CFD. For the geometric configuration uncertainty in wind tunnel test, regression analysis and bootstrap method are used to carry out data fusion. Finally, model validation research is conducted.

Wake-induced vibrations of iced pin joint hangers of suspension bridges based on wind tunnel test and new method of transiting test

The wind-induced vibration of suspension bridge hangers may be due to hanger icing. This study presents a new test method named transiting test method, combining with the section model wind tunnel test, to investigate the wake-induced vibrations of iced pin joint hangers under limited conditions. Results reveal that according to wind tunnel test and DenHartog galloping theory, the attack angle of 3° is the angle at which the wake galloping of iced pin joint hangers is most likely to occur. The driving wind field is stable in the transiting test and exhibits relatively minimal interference from the external factors under limited conditions. The predominant frequencies of vehicular vibration in the transiting test exhibit no marked relation with the fundamental frequency of the model, thereby demonstrating transiting test can satisfy the requirements of wind-resistant research on iced pin joint hangers. The wake galloping-reduced wind speed of iced pin joint hangers with D-shaped ice and a 30 mm icing thickness is 165, and the leeward iced hanger is vulnerable to endurance failure. The wake galloping critical wind speed of pin joint hangers with icing is lower than that without icing. The findings have important implications for the wind-resistance of suspension bridges with pin joint hangers.

Trajectory and attitude deviations for internal store separation due to unsteady and quasi-steady test method

The deviations of trajectory and attitude angle for internal store separation are evaluated by two wind tunnel test methods. One is the Freedrop Test (FDT), which is known as unsteady and time-dependent method of scaled model. The other is the Captive Trajectory System (CTS) test, which is usually regarded as a quasi-steady and time-averaged test technology. The result shows that there is a streamwise adverse pressure gradient on the cavity resulting in a nose-up pitching moment coefficient (>0) acting on the store model. When the initial pitch angular velocity is 0, the store exits the shear-layer with a nose-up pitch attitude causing the store to climb back towards and collide with the aircraft. However, the store passes through the shear-layer into the freestream with a nose-down pitch, which causes a successful separation event when the initial pitch angular velocity < 0. The pitch angle obtained by unsteady test method is different from that by quasi-steady test method. The time-dependent test includes the aerodynamic force induced by pitch angular velocity whereas the time-averaged method (CTS) cannot reflect the effect of unsteady aerodynamic force. The deviation of vertical displacement is not obvious for FDT and CTS test since the store has an initial vertical velocity, which is dominant for the vertical displacement. This means that the highly unsteady flow can create unpredictability in aerodynamic pitching moment of the store, which can lead to the deviation of pitch angle for internal store separation.