Wind Tunnel Pressure Research Articles

A simplified analytical formula for the coefficient of 3rd-order Hermite moment model and its application

Based on the 3rd-order softened Hermite nonlinear equations, a new simplified formula of the Hermite moment model is proposed. According to the wind tunnel pressure test data of a flat roof, the new and existing simplified formulas are used to calculate the Hermite parameters and peak factors respectively. The calculation accuracies of different simplified formulas are compared and analyzed to verify the applicability of the new simplified formula. The results show that the new simplified formula has higher accuracy for the peak factor calculation of high-order softened time histories, and the relative error is kept within 15%. And the applicability for mild non-Gaussian time histories is relatively better. For low-order softened time histories, the calculation errors of the new simplified formula are relatively large for the Hermite parameters, but the calculation accuracy of the peak factor is kept within the applicable range. Specifically, the calculation errors of the negative peak factors distributed only in the 1st-order softened applicable range are less than 20%, and the calculation errors of the negative peak factors distributed only in the 2nd-order softened applicable range are less than 15%. Finally, the new simplified formula shows good applicability to the extreme value analysis of the high-order and low-order softened wind pressure time histories.

Equivalent static wind load based on displacement mode and load combination for high‐rise buildings

AbstractUnder the action of the fluctuating wind load, the low frequency part produces background response to the structures, while the high frequency part produces resonance response to the structures. In structural design, equivalent static wind load is usually used to equate the fluctuating wind load. Although there are various methods of evaluating the equivalent static wind load, they did not consider the correlation between modal responses or considered them insufficiently. Therefore, in this paper, the correlation between modal response is considered to evaluate the equivalent static wind load, the displacement response is decomposed by proper orthogonal decomposition (POD) method, the correlation between modal displacement is removed, the equivalent static wind load is expressed in the form of displacement mode, and then the correlation between modal response is fully considered in the extreme value combination. This paper combines the equivalent static wind loads in order to make the wind resistance design more reasonable for high‐rise buildings. First, the formulas of equivalent static wind loads expressed by displacement modes of background and resonant response are deduced based on modal decomposition and POD method. Second, the combination formulas of square‐root‐of‐sum‐square (SRSS) and complete‐quadratic‐combination (CQC) rules for the equivalent static wind loads considering the mean wind loads are proposed. Both the linear combination formula of SRSS for the equivalent static wind load and the weighting factor expressions of background and resonance equivalent static wind load are given. Third, the accuracy and validity of the formulas of equivalent static wind load are verified by a wind tunnel pressure test of a high‐rise building. Finally, the simplified combination coefficient formulas for the equivalent static wind loads are proposed, and the combination of the high‐rise building base's fluctuating equivalent static wind loads of along‐wind direction, across‐wind direction, and torsional direction is analyzed.

Estimation of extreme wind pressure coefficients of buildings using POT with automated threshold selection

Extreme wind pressure coefficients of the high-rise buildings are critical for determining wind loads on components and claddings. To address the issue of insufficient samples in the widely used block maximum (BM) method, the peak over threshold (POT) method has been introduced in wind engineering for more effective and accurate estimation of extreme wind pressure coefficients. However, it is quite a challenge to appropriately select the threshold. This study proposes an automated threshold selection procedure using L-moment theory. Monte Carlo simulation is conducted to substantiate the theoretical feasibility of this procedure. Utilizing data from wind-tunnel pressure measurements of a high-rise building model, the study automatically selects thresholds and estimates extreme wind pressure coefficients. Comparative analysis with the BM method demonstrates that thresholds determined through automated threshold selection procedure exhibit stability with minimal deviation from standard extreme values. Furthermore, the developed procedure can effectively adapt to non-Gaussian characteristics of the sample time histories.

A machine learning-augmented aerodynamic database of rectangular cylinders

Rectangular cylinders submerged in a fluid encounter intricate aerodynamic forces, and the forces significantly influence the stability and safety of structures possessing a rectangular cross section. Although aerodynamic characteristics of these cylinders have been extensively studied, a comprehensive database cataloging these characteristics remains absent. This study conducted a large number of wind tunnel pressure testings to establish an aerodynamic database for rectangular cylinders with 2470 distinct configurations, including turbulent intensities ranging from 1% to 20%, side ratios ranging from 0.6 to 5, and wind attack angles ranging from 0° to 90°. The accuracy of the database was validated by data from the literature and wind tunnel force measurement experiments. More importantly, machine learning models were developed and have substantially expanded the experimental data, resulting in a comprehensive, continuous aerodynamic database for rectangular cylinders. By evaluating the model performance and verifying its generalization capability, the accuracy of the machine learning-augmented database is proved. This database is anticipated to serve as a critical reference for academic research and a practical reference for engineering applications.

The wind tunnel test research on the aerodynamic stability of wind turbine airfoils

The issue of nonlinear aerodynamic stability of blades is a significant technological bottleneck in the development of large-scale wind turbines. In order to explore the influencing parameters and mechanisms of the nonlinear aerodynamic stability of large-scale wind turbine blades, the flexible blade was simplified into a two-dimensional rigid blade segment with elastic supports, which formed the pitch single-degree-of-freedom aeroelastic wind tunnel test system. Through wind tunnel vibration and pressure measurement synchronization tests, the torsional vibration characteristics and the flow field development mechanism of the airfoil under different wind speeds and attack angles were studied in detail. The wind tunnel tests revealed two distinct torsional aeroelastic behaviors: the static equilibrium state with negligible amplitude and high vibrational randomness, and the stall flutter state with larger amplitude, which was changed according to sinusoidal law substantially. The stall flutter state was confined within a specific wind speed range, and its stability boundary, which included the critical initiation wind speed and the critical cessation wind speed, all varied linearly with the installation attack angle. The growth rate of the critical cessation wind speed with the installation attack angle was significantly higher than that of the critical initiation wind speed, making the wind speed range for the occurrence of stall flutter also linearly larger. Additionally, the frequency of the stall flutter was significantly higher than the natural frequency of the model, and it exhibited a positive correlation with the critical initiation wind speed. The flow state around the airfoil during stall flutter was primarily distinguished from its static counterpart by the presence of leading-edge vortices. The formation and shedding of these leading-edge vortices would significantly influence the characteristics of stall flutter.

Unsupervised Learning Based Image Registration of Wind Tunnel Pressure Sensitive Paint Image

Unsupervised Learning Based Image Registration of Wind Tunnel Pressure Sensitive Paint Image

Experimental study on the influence of maintenance track position on vortex-induced vibration performance of a box girder suspension bridge

To study the influence of maintenance track on the vortex-induced vibration (VIV) performance of main girder, the VIV response and time history of surface pressure data of a section model were obtained by wind tunnel vibration and pressure measurements for a large-span steel box girder suspension bridge. The VIV performance of the main girder was tested at ±5° attack angles of various maintenance track positions, including 1, 2.5, and 5 m away from the outer edge of the girder bottom plate. The mean values, root variances and amplitude spectra of vortex-induced force and the correlation and contribution coefficients of local aerodynamic force to overall aerodynamic force were analyzed. The results show that when the maintenance track is 1 m away from the outer edge of the bottom plate, the main girder exhibits the worst VIV performance with a maximum amplitude of 0.457 m, far beyond the allowable value of the specification. The VIV performance of the main girder was greatly improved by moving the maintenance track inward. The pressure analysis indicates that the large pressure fluctuation at the front and rear parts of the upper surface is attributed to the strong VIV of the main girder. In this sense, the improved VIV performance is mainly contributed by the weakening of pressure fluctuation in these two areas and the reduced local aerodynamic force. When the distance between the maintenance track and bottom plate is adjusted to 2.5 m, a 3.5 m wind barrier with a ventilation rate of 30% effectively inhibits the VIV of the box girder. The main reason for the suppression is that the elimination of pressure fluctuation on the upper surface of the girder disturbs the correlation between local aerodynamic force and overall aerodynamic force, consequently diminishing the contribution of local aerodynamic force to the vortex-induced force.

Wind pressure distribution variation law and interference effect of heliostats

The heliostat is different from the ordinary low building because of the special shape of the heliostat. The wind tunnel pressure test is carried out the model of heliostats in the range of azimuth angles are between 0° to 180° and the range of elevation angles are between 0° to 90. The wind pressure time history of each measuring point on the mirror panel are obtained. On this basis, the mean wind pressure distribution of the mirror panel under typical working conditions is obtained, and then the maximum (minimum) value of the mean wind pressure under all working conditions and corresponding working conditions and measuring points are obtained. Then 10 representative measuring points are selected to study the variation law of wind pressure with wind direction angle and pitch angle respectively, and then the variation law of the mean wind pressure of 10 measuring points under all working conditions is obtained. Finally, the interference effect of the mean wind pressure of heliostats is studied, and the variation law of the interference effect of the mean wind pressure is obtained, and the maximum value, minimum value and corresponding working conditions of the interference effect are obtained. The results show that the maximum value of the mean wind pressure of heliostats under all working conditions is appeared at the measurement point of the lower edge of the mirror panel and on working condition 15-60 (wind direction angle - elevation angle), and the minimum value is appeared at the measurement point of the upper left corner of the mirror panel and on working condition 150-20. The variation law of the mean wind pressure of 10 measuring points under all working conditions is similar, and the position of measuring points has little effect on the variation law of the mean wind pressure under all working conditions. Only the working condition of the maximum value and minimum value are affected by the position of the measuring points. The mean wind pressure distribution under the most unfavorable working condition of heliostats is obtained, the maximum (minimum) value of the interference effect and corresponding working conditions are obtained. Which can be a reference for structural design and research.

Aeroacoustic testing on a full aircraft model at high Reynolds numbers in the European Transonic Windtunnel

This paper presents an end-to-end approach for the assessment of pressurized and cryogenic wind tunnel measurements of an EMBRAER scaled full model close to real-world Reynolds numbers. The choice of microphones, measurement parameters, the design of the array, and the selection of flow parameters are discussed. Different wind tunnel conditions are proposed which allow separating the influence of the Reynolds number from the Mach number, as well as the influence of slotted and closed test sections. The paper provides three-dimensional beamforming results with CLEAN-SC deconvolution, the selection of regions of interest, and the corresponding source spectra. The results suggest that slotted test sections have little influence on the beamforming results compared to closed test sections and that the Reynolds number has a profound, non-linear impact on the aeroacoustic emission that lessens with increasing Reynolds number. Further, sources show a non-linear Mach number dependency at constant Reynolds number but are self-similar in the observed Mach number range. The findings suggest that it is possible to study real-world phenomena on small-scale full models at real-world Reynolds numbers, which enable further investigations in the future such as the directivity of sources.

Influence of the wind tunnel model characteristics on the loading and response of cable-net hyperbolic paraboloid roofs

Aerodynamic modelling affects the prediction of wind loads if they are derived from wind tunnel tests. Depending on the structural type, difference in applied loads may induce larger or smaller differences in the predicted structural response. For low rise buildings, the roof roughness is a crucial parameter that affects the wind action distribution and magnitude, and its impact on the structural response. This paper discusses the results from wind tunnel pressure measurements on eight geometries of hyperbolic paraboloid roofs, coming from experimental campaigns in three different wind tunnels and using different models. The pressure distributions are then used to evaluate vertical displacements of cable nets tensile structures, which are also compared with each other. Results show that significant differences in the measured pressures are only slightly reduced when vertical displacements are compared, that is inaccuracy of the load is only slightly mitigated when propagated to the response.

Experimental investigation of wind effects on a 282-meter-high tower with complex aerodynamic shapes based on a rigid model and multi-degree-of-freedom aeroelastic model

Slender and flexible high-rise structures are very sensitive to large wind-induced vibration phenomena such as vortex-induced vibration and galloping under strong winds. However, pressure measurements on rigid models cannot consider coupling aeroelastic effects, and single-degree-of-freedom aeroelastic model wind tunnel tests can only consider the contribution of the first-order linear mode. For wind-sensitive structures with complex aerodynamic shapes, the effect of higher-order modes on the wind-induced response may not be ignored. In this study, a series of multi-degree-of-freedom (MDOF) aeroelastic model wind tunnel tests and pressure measurements of a rigid model were conducted to comparatively investigate the wind effects of a 282-meter-high tower with complex aerodynamic shapes. A detailed analysis of the aeroelastic effects on the high-rise tower is presented, and the effects of the structural damping ratio, wind speed, and wind direction are also discussed. The results show that the variation trends of the peak acceleration responses are generally consistent, while in those wind-sensitive directions (165-degree wind direction), the peak acceleration responses of the MDOF model are almost 1.5 times larger than those of the rigid model, indicating that the aeroelastic effects are remarkable. The corresponding response spectral peak values of the MDOF model are significantly larger than those of the rigid model by a factor of more than 3 and the correlations of responses in the two orthogonal directions also increase greatly by 43.5%. However, the “set-back” aerodynamic shape (180-degree wind direction) can considerably weaken aeroelastic effects and the peak acceleration responses are close to those of the rigid model. The generalized aerodynamic force spectrum also shows broadband features, implying its superior aerodynamic performance. The comfort assessments for different structural damping ratios are conducted based on various codes and criteria, suggesting that the structural damping ratio should be larger than 3%. The equivalent static wind loads on the upper floors are notably affected by aeroelastic effects while the lower floors are relatively insensitive. This study provides a detailed perspective of the aeroelastic effect for slender tower, and hence facilitates the wind-resistant design of flexible structures.

A New Research Scheme for Full-Scale/Model Test Comparisons to Validate the Traditional Wind Tunnel Pressure Measurement Technique

A new research scheme for a full-scale/model test comparison is proposed for effectively validating the wind tunnel pressure measurement technique in this article. With the new research scheme and using quantifiable data, future full-scale/model test comparisons are expected to reasonably disclose the main problem with the traditional atmospheric boundary layer wind tunnel pressure measurement technique with regard to the Reynolds number (Re) effects, the aero-elastic effects and the flow characteristic effects. Based on the engineering background of the Peng-cheng cooling tower, it was quantified by using the new research scheme that the average relative errors of the mean wind pressure coefficients are 52.39%, 1.87% and 35.91% for the Re effects, the aero-elastic effects and the flow characteristic effects, respectively. In view of the fluctuating wind pressure coefficients, the average relative errors are 97.58%, 21.14% and 20.20% for the Re effects, the aero-elastic effects and the flow characteristic effects, respectively. These suggest that Re effects are extremely significant for pressure measurement model tests of circular cylindrical structures, and flow characteristic effects are noticeable too. They should be mitigated using effective approaches, i.e., increasing the model surface roughness and placing the actively controlled devices at the beginning of the wind tunnel’s working section, respectively. Additionally, the key field measurement technique adopted (i.e., the calculation of the reference static pressure) and details of manufacturing the aero-elastic pressure measurement model for the present study are also expounded in the article for reference.

Numerical Simulation of the Flow in the ONERA F1 Wind Tunnel

This paper presents the outcome of numerical simulations of the flowfield inside the ONERA F1 wind tunnel, which is a large-scale pressurized low-speed wind tunnel mostly used to investigate the takeoff and landing performance of aircrafts in high-lift configuration. The simulations were carried out under Reynolds-averaged Navier–Stokes modeling assumptions. Results were compared to available experimental data characterizing the tunnel flowfield, especially in the test section. The overall flow physics is well captured by the simulations. However, when looking at the result with a more demanding level of accuracy, some important characteristics of the velocity distribution in the test section, such as flow upwash and total pressure distribution, are not replicated. Reasons are discussed in the paper, and some recommendations are derived for future similar simulations.

Wind‐Induced Response and Stow Position Analysis of the Flat Roof Parabolic Solar Collector

Under the action of wind load, the parabolic solar collector (PSC) is easily damaged. In order to ensure the stability and security of the flat roof parabolic solar collector (FRPSC), understanding the wind load effect on the FRPSC has always been an important research direction. This article studies the free vibration and wind-induced response characteristics of the FRPSC, and analyzes the optimal stow position of the FRPSC under strong wind. The modal analysis and wind-induced response calculation of the FRPSC are done through wind tunnel pressure experiment and finite element simulation. The changing laws of the FRPSC dynamic characteristic parameters, peak displacement response, and wind-induced vibration coefficient are obtained. The wind-induced response mechanism of the FRPSC under different working conditions is analyzed in detail. In addition, a comparison with the ground parabolic solar collector is made. Based on the research results, an optimal stow position is analyzed and proposed to minimize the impact of strong wind on the collector. This research work can provide a useful reference for the security design of the FRPSC.

Wind Pressure Field Reconstruction and Prediction of Large-Span Roof Structure with Folded-Plate Type Based on Proper Orthogonal Decomposition

The complex and diverse structural forms make it impossible to define universal shape coefficients for large-span roof structures, which usually need to be obtained by wind tunnel tests. However, the number of test measurement points is limited, which leads to obvious limitations in the study of wind loads on large-span roof structures. Taking a large-span folded-plate roof as an example, based on the wind tunnel pressure test results of the rigid model, the proper orthogonal decomposition (POD) method is used to reconstruct the wind pressure field of the roof using the first several eigenmodes. The wind pressure of several typical characteristic points is predicted based on four different interpolations methods, and the accuracy and feasibility of POD method in reconstruction and prediction of wind pressure field of large-span roof are analyzed and studied from multiple perspectives. The results show that the order of the selected structural eigenmodes has an impact on the reconstruction accuracy of the wind pressure field. The more orders are selected, the closer the wind pressure field reconstruction is to the true value. The reconstruction effect of the wind pressure field based on the POD method is related to the spatial position of the predicted point, and the reconstruction effect of the wind field based on the fluctuating wind pressure is obviously better than the that based on the mean wind pressure. When the POD method is used to predict the wind pressure of an unknown point, different interpolation methods can achieve ideal results. Among them, the bilinear interpolation method has the highest prediction accuracy, and the adjacent point interpolation method and Griddata V4 interpolation method only have certain errors in the low frequency region.

The axial fan design and commissioning test with nonuniform inlet flow

According to the two-dimensional flow theory of the axial fan rotor blades and the aerodynamic characteristics of the low speed wind tunnel, combined with the fan aerodynamic efficiency and wind tunnel pressure loss coefficient, a new equation which points out the inherent relationship of the fan blade setting angle, fan rotating speed and flow rate in wind tunnel circuit is derived. So a new method for fan rotor blade setting angle adjustment to satisfy the fan performance at off-design point by getting the test results of fan operating parameters but without the fan total pressure rise in the low speed wind tunnel is developed. Following the new method, the fan rotor blade setting angle adjusting value was provided directly only with the fan rotating speed and flow velocity in the wind tunnel test section, the adjusting target was achieved successfully by the new blade setting angle, the cost of the wind tunnel commissioning test were saved. The test results show that, after increasing the fan rotor blade setting angle by 4.5 degrees, when the flow velocity in the wind tunnel test section reaches 60m/s, the fan rotating speed is 570rpm, the deviation from the predicted fan rotating speed value of 575rpm is 0.9%. For the same test section flow velocity, the predicted value and the real value of the fan rotating speed are in good agreement, it proves that this method is reliable and accurate in practical application.

Flutter test of rudder with real servo actuator in continuous transonic wind tunnel

Flutter wind tunnel test is an important approach of investigation of transonic flutter characteristics of flight vehicle. Comparing with the blow-down wind tunnel, the long-running and low dynamic pressure capabilities of continuous transonic wind tunnel are very suitable for flutter test. The flutter safety protection and analysis of dynamic signals are developed. The safety protection control software, rapid reduction of Mach number and dynamic pressure, model debris catch screen are integrated, which can provide safety protection of test model and wind tunnel. During the test process, the flutter boundary can be achieved by interpolating the reciprocal of spectrum peak. The flutter tests of rudder are conduct through two methods of step and continuous varying dynamic pressure. It is illustrated that the error of flutter dynamic pressure is relatively small, less than 5% between the two methods. Meanwhile, the feedback effect of the real servo actuator on the flutter characteristics is hard to be obtained via numerical simulation. It is demonstrated that the flutter dynamic pressure has been increased by 10% due to the feedback effect.

Wind tunnel pressure data analysis for peak cladding load estimation on a high-rise building

A correct evaluation of wind loads on high-rise building cladding panels is essential to ensure safety while avoiding costly over-design. The estimation of peak design loads from wind tunnel tests requires post-processing pressure time histories to remove small-scale fluctuations that do not significantly affect the total load on cladding elements. This post-processing commonly employs a low pass filter with a time-scale that is linearly proportional to the ratio of a reference length scale and velocity. The objective of this study is to analyze the equivalence between the moving-average filter and the spatial averaging procedure, focusing on panels near the top corners and edges of a high-rise building. The real area-averaged pressure is calculated using high-resolution pressure measurements and compared to estimates obtained from moving-average filters with a range of time-scales. The error is within ±1Cp for most pressure tap locations and panels analyzed, although some locations near the top edge result in overestimates of the peak suction up to 3Cp. The optimal value of the proportionality coefficient defining the filter time-scale is shown to be dependent on both pressure tap location and panel size, suggesting that accurate estimates of area-averaged pressures based on single-point measurements require more advanced post-processing techniques.

Investigation of Reynolds Number Effects on Aerodynamic Characteristics of a Transport Aircraft

The scale difference between the real flight vehicle and the experimental model results in the Reynolds number effect, which makes it unreliable to predict the aerodynamic characteristics of flight vehicles by wind tunnel testing. To understand the mechanism of Reynolds number effects on the aerodynamic characteristics of the supercritical wing that is commonly used in transport aircraft in more detail, surface pressure wind tunnel tests of a transport aircraft reference model with a wing-body configuration were conducted in the European Transonic Windtunnel (ETW) at different Reynolds numbers. There are 495 pressure taps in total equipped on the surface of the test model with the Mach numbers ranging from 0.6 to 0.86 and Reynolds number varying from 3.3 × 106 to 35 × 106. In addition, an in-house developed CFD tool that has been validated by extensive experimental data was used to correct the wing deformation effect of the test model and achieve detailed flow structures. The results show that the Reynolds number has a significant impact on the boundary layer displacement thickness, surface pressure distribution, shock wave position, and overall aerodynamic force coefficients of the transport aircraft in the presence of shock wave and the induced boundary layer separation. The wind tunnel data combined with flow fields achieved from CFD show that the essence of the Reynolds number effect on the aerodynamic characteristics of transport aircraft is the difference of boundary layer development, shock wave/boundary layer interaction, and induced flow separation at different Reynolds numbers.

Wind-Induced Pressure Prediction on Tall Buildings Using Generative Adversarial Imputation Network.

Wind tunnel testing techniques are the main research tools for evaluating the wind loadings of buildings. They are significant in designing structurally safe and comfortable buildings. The wind tunnel pressure measurement technique using pressure sensors is significant for assessing the cladding pressures of buildings. However, some pressure sensors usually fail and cause loss of data, which are difficult to restore. In the literature, numerous techniques are implemented for imputing the single instance data values and data imputation for multiple instantaneous time intervals with accurate predictions needs to be addressed. Thus, the data imputation capacity of machine learning models is used to predict the missing wind pressure data for tall buildings in this study. A generative adversarial imputation network (GAIN) is proposed to predict the pressure coefficients at various instantaneous time intervals on tall buildings. The proposed model is validated by comparing the performance of GAIN with that of the K-nearest neighbor and multiple imputations by chained equation models. The experimental results show that the GAIN model provides the best fit, achieving more accurate predictions with the minimum average variance and minimum average standard deviation. The average mean-squared error for all four sides of the building was the minimum (0.016), and the average R-squared error was the maximum (0.961). The proposed model can ensure the health and prolonged existence of a structure based on wind environment.